ETA06-0138 Comment En

T HE NE W E TA - 06/0138

FOR KL H SOL ID WO OD SL A B S

A PPROVA L A ND COMMENT

M A D E F O R B U I L D I N GB U I L T F O R L I V I N G

© DI Johann Riebenbauer

Publisher: KLH Massivholz GmbH. Responsible for the content of the comment: DI J. Riebenbauer.Version: The new ETA-06/0138 for KLH solid wood slabs – Approval and Comment, Version 01/2013

The content of this brochure is the intellectual property of the company and is protected by copyright. Any information provided is intended only as a recommendation or proposal; any liability on the part of the publisher is not accepted. Any type of reproduction is strictly forbidden and only permitted after written approval from the publisher.

I M P R I N T

C O N T E N T

0 1

01 FOREWORD 02

02 ETA - 06/0138 – APPROVAL AND COMMENT BY J. R IEBENBAUER 04

03 ANNE X A : S IMPLIF IED PROCEDURE FOR DETERMINING MEMBER RESISTANCES IN CASE OF A F IRE 90

04 ANNE X B: DESIGN OF KLH STRUCTURES UNDER E ARTHQUAKE CONDIT IONS 97

05 ANNE X C: STRUCTUR AL MODELLING FOR LOAD -BE ARING STRUCTURES OF KLH MEMBERS 100

THIS BROCHURE INCLUDES THE COMPLETE ETA - 06/138 OF THE PRODUCT DESIGNATED AS KLH SOLID WOOD SLABS.

Additional explanations on the complex matter are provided on the right-hand side of the relevant background infor-

mation and recommendations. The production of an ETA is a long-term process. Therefore, more recent findings are

included in the form of recommendations for application. The comment on the approval was written by the experienced

civil engineer, DI Johann Riebenbauer, who was also in charge of the analyses of the tests and the drafting of the approval.

The Annexes A to C deal with a simplified method for structural fire design, with the design under earthquake conditions

as well as the structural modelling. They provide complementary information to the previous considerations.

THESE ARE THE MOST IMPORTANT ALTERATIONS TO THE PREVIOUS ETA:

• Consideration of shrinkage cracks (long-term behaviour of the slabs) by testing the slabs with layered boards with

reduced w : d relations of up to 2.3 : 1

• Consideration of partly cut layers (residual layer widths created during cutting-to-size)

• Increase of the maximum layer thickness to 45 mm; possibility of verification even with double cross layers up to

90 mm of overall thickness

• Structural fire design

• Extension and generalisation of structural design options

F O R E W O R D

0 2

THE NEWETA-06/0138

0 3

F O R E W O R D

REGARDING STRUCTURAL DESIGN, THE FOLLOWING ALTERATIONS HAVE BEEN MADE:

• Long-term behaviour – creep factors based on tests

• Verification for point-supported slabs – verifications of cross tension and shear in areas of supports

• Extended shear measurement in case of loading in plane (more precise data for G-modulus and strength values)

• Treatment of cross tension problems in general

• Extension for simplified measurement at contact surfaces and load introduction

• Treatment of individual loads perpendicular to the plane level – effect of shear deformation, even for multi-axial load-

bearing capacity

• Generalisation of slab measurement without the influence of key data on the system length

• Consideration of effects due to single loads in the mid-span area of slabs

Many previously unanswered questions on general “structural design situations” have now been clarified.

The many and varied possible applications have made it necessary to include relatively comprehensive information on

structural design in the ETA. This has not exactly made practical handling much easier. Due to this reason, computer

software has been created especially for the ETA, making it possible to identify the member resistance values depending

on the type of component and for all different types of stress. This way it is no longer necessary in everyday structural

design work to determine cross-sectional values and their relevant load-bearing values, etc. manually.

Especially the automated calculation of member resistance values in case of fire (including charring and the consideration

of different types of cladding) represents a massive advantage in the structural design of members.

The structural engineer of a building only has to determine the required sectional forces (which is possible with any cho-

sen software). The active forces identified this way can then be compared with the member resistance values in a very

simple way.

The structural fire design is currently regulated in very different ways. The method with d_0 according to EN 1995-1-2

(reduced cross-sectional values – verification with the characteristic tensions at normal temperatures) for full cross sec-

tions is generally accepted. The Annex to the EN 1995-1-2 provides another, “more precise” method, but the data of the

EN only allow a calculation with special software. Basically, what is missing is the information on the temperature curve

within the cross section at the different measuring times in order to be able and apply this more precise method even with

conventional structural engineering calculation methods.

For this reason, the company KLH offers a software tool (“KLHdesigner”) that allows a more precise determination of

member resistance values. The identification of member forces and moments can be carried out with any conventional

software (taking shear compliance into account), depending on what seems to be reasonable for the relevant system

(manual calculation, laminated or plate structure software). In the “KLHdesigner”, member resistance values are stated

for normal conditions (normal temperature) and in case of fire. Therefore, this tool can also be used for normal verifica-

tion purposes.

04

Original text ETA-06/0138 Validity 2012 to 2017

Authorisedand notified according

to Article 10 of the Council Directive 89/ 106/EEC of 21 December 1988 on the

approximation of laws, regulations and administrative provisions of Member States

relating to constructionproducts

Member of EOTA

Österreichisches Institut für Bautechnik Schenkenstrasse 4 | 1010 Vienna | AustriaT +43 1 533 65 50 | F +43 1 533 64 23 [email protected] | www.oib.or.at

European Organisation for Technical ApprovalsEuropäische Organisation für Technische ZulassungenOrganisation Européenne pour l’ Agrément Technique

European technical approval ETA-06/0138English translation, the original version is in German

Handelsbezeichnung KLH-Massivholzplatten Trade name KLH solid wood slabs

Zulassungsinhaber

Holder of approval

KLH Massivholz GmbH 8842 Katsch an der Mur 202 Österreich

Zulassungsgegenstand und Verwendungszweck

Massive plattenförmige Holzbauelemente für tragende Bauteile in Bauwerken

Generic type and use of construction product

Solid wood slab element to be used as structural elements in buildings

Geltungsdauer vom

Validity from

10.09.2012

bis zum

to

09.09.2017

Herstellwerk

Manufacturing plant

KLH Massivholz GmbH 8842 Katsch an der Mur 202Österreich

Diese Europäische technische Zulassung umfasst 43 Seiten einschließlich 7 Anhängen

This European technical approval contains 43 Pages including 7 Annexes

Diese Europäische Technische Zulassung ersetzt

ETA-06/0138 mit Geltungsdauer vom 01.07.2011 bis zum 30.06.2016

This European Technical Approval replaces ETA-06/0138 with validity from 01.07.2011 to 30.06.2016

THE NEW ETA-06/0138 – APPROVAL,COMMENT AND BACKGROUND INFORMATION

This brochure includes the complete ETA-06/138 of the product designated as KLH solid wood slabs.

Additional explanations on the complex matter are provided on the right-hand side of the relevant background information and recom-mendations. The production of an ETA is a long-term process. Therefore, more recent findings are included in the form of recommendations for application.

This ETA includes long-standing experience in the production and application of large-format plywood slabs. Over the last 15 years, we have made numerous positive and some negative experiences that always resulted in further improvements and developments.

These are the most important alterations to the previous ETA:

• Consideration of shrinkage cracks (long-term behaviour of the slabs) by testing the slabs with layered boards with reduced w : d relations up to 2.3 : 1

This also takes unfavourable effects into account, caused by shrinkage cracks. Experience has shown that such shrinkage cracks may appear at practically any area of a cross section (covering layer, internal layer) as well as with slabs glued on their edges. These cracks may have detrimental effects on the load-bearing capacity if they appear at unfavourable spots.The structural design work is generally possible without the use of crack factors, for example (such as those stated in the B 1995-1-1).Comparative tests have shown that shrinkage cracks may lead to reduced strength of 10-40% in a member, depending on the type of stress and the relevant position. These effects have been covered by the present test results. The unavoidable shrinkage has therefore been taken into account.

• Consideration of partly cut layers (residual layer widths created during cutting-to-size)The design can now be carried out without having to consider e.g. various narrow residual layers. It is no longer necessary to stick to minimum widths of individual boards, e.g. for the design regarding loads on slabs in plane.

• Increase of the maximum layer thickness to 45 mm; possibility of verification even with double cross layers up to 90 mm of overall thickness

Various cases of application have made this increase necessary. The application of the 45 mm thick layer will rather remain a special case, because these thick layers do not only have advantages.

• Structural fire designThe structural fire design is currently handled in very different ways. Verifications according to different standards or publications partly create very different results. This has caused the company KLH to investigate this topic in greater detail. To this end, comprehensive tests were carried out with fire exposure. Their results were summarised in the ETA (charring determination, distribution of temperatu-res along the cross section). As a result, it is now possible to make very precise designs for members. Even charring on both sides, with overlapping temperature influences (e.g. in case of thin members) can be investigated this way.

Extensions and generalisation of structural design options

The goal was to create a general basis for design that would allow exact calculations of slabs with the aid of FE models. Application rules were set up for simplified processes (beam-shaped calculation).

Regarding structural design, the following alterations have been made:

- Long-term behaviour – creep factors based on tests- Verification for point-supported slabs – verifications of cross tension and shear in areas of supports- Extended shear measurement in case of loading in plane (more precise data for G-modulus and strength values)- Treatment of cross tension problems in general- Extension for simplified measurement at contact surfaces and load introduction - Treatment of individual loads normal to the plane level – effect of shear deformation, even for multi-axial load-bearing capacity- Generalisation of slab measurement without the influence of key data on the system length- Consideration of negative effects due to single loads in the mid-span area of slabs

Comment on the ETA-06/0138 by J. Riebenbauer

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OIB-260-001/98-121

Table of contents

EUROPEAN TECHNICAL APPROVAL ETA-06/0138 ...................................................................................... 1TABLE OF CONTENTS .................................................................................................................................... 2I LEGAL BASES AND GENERAL CONDITIONS ........................................................................................... 4II SPECIFIC CONDITIONS OF THE EUROPEAN TECHNICAL APPROVAL......................................................... 51 DEFINITION OF PRODUCT AND INTENDED USE ....................................................................................... 51.1 Definition of product .......................................................................................................................... 5

1.1.1 Wood........................................................................................................................................ 5 1.1.2 Wood-based panels ................................................................................................................. 5

1.2 Intended use...................................................................................................................................... 5

2 CHARACTERISTICS OF PRODUCT AND METHODS OF VERIFICATION ......................................................... 62.1 Characteristics of product.................................................................................................................. 6

2.1.1 General .................................................................................................................................... 62.1.2 Boards, wood based panels..................................................................................................... 62.1.3 But joints .................................................................................................................................. 62.1.4 Adhesive .................................................................................................................................. 62.1.5 Hygiene, health and the environment ...................................................................................... 62.1.6 Identification............................................................................................................................. 6

2.2 Methods of verification ...................................................................................................................... 7

3 EVALUATION OF CONFORMITY AND CE MARKING .................................................................................. 73.1 System of conformity attestation ....................................................................................................... 73.2 Responsibilities ................................................................................................................................. 7

3.2.1 Tasks for the manufacturer; factory production control............................................................ 73.2.2 Tasks for the approved body.................................................................................................... 83.2.2.1 Initial type testing of the product .............................................................................................. 83.2.2.2 Initial inspection of factory and of factory production control ................................................... 83.2.2.3 Continuous surveillance........................................................................................................... 8

3.3 CE marking........................................................................................................................................ 8

4 ASSUMPTIONS UNDER WHICH THE FITNESS OF THE PRODUCT FOR THE INTENDED USE WAS FAVOURABLY ASSESSED...................................................................................................................... 9

4.1 Manufacturing.................................................................................................................................... 94.2 Installation ......................................................................................................................................... 9

4.2.1 Design of solid wood slab elements......................................................................................... 94.2.2 Installation of solid wood slab elements................................................................................... 9

5 RECOMMENDATIONS FOR THE MANUFACTURER .................................................................................... 95.1 General.............................................................................................................................................. 95.2 Recommendations on packaging, transport and storage................................................................ 105.3 Recommendations for use, maintenance and repair of the works .................................................. 10ANNEXES................................................................................................................................................... 11ANNEX 1 STRUCTURE OF THE SOLID WOOD SLAB..................................................................................... 11

ANNEX 2 CHARACTERISTIC DATA OF THE SOLID WOOD SLAB .................................................................... 13

ANNEX 3 PRODUCT CHARACTERISTICS OF THE SOLID WOOD SLAB............................................................ 14

ANNEX 4 DESIGN CONSIDERATIONS ........................................................................................................ 17


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DESIGN CONSIDERATIONS FOR KLH PLATE STRUCTURES............................................................................. 17

1 GENERAL DEFINITIONS AND TERMINOLOGY......................................................................................... 171.1 Mechanical actions perpendicular to the solid wood slab ...................................................... 171.2 Mechanical actions in plane of the solid wood slab ............................................................... 181.3 Normal stress and shear stress in the two main directions of the solid wood slab ................ 19

2 CALCULATION OF STIFFNESS PROPERTIES.......................................................................................... 192.1 Short-term deformation .......................................................................................................... 192.1.1 Bending stiffness.................................................................................................................... 192.1.2 Shear deformations................................................................................................................ 202.1.3 Longitudinal stiffness.............................................................................................................. 212.1.4 Shear stiffness in plane of the solid wood slab ...................................................................... 212.1.5 Bending stiffness for beams in plane of the solid wood slab.................................................. 212.1.6 Recommendations on Finite-Element-Analysis ..................................................................... 212.2 Long-term deformation........................................................................................................... 22

3 ULTIMATE LIMIT STATE DESIGN........................................................................................................... 233.1 General .................................................................................................................................. 233.2 Tension along the grain – actions in plane of the solid wood slab ......................................... 233.3 Tension perpendicular to the grain – actions perpendicular to the plane of the solid

wood slab............................................................................................................................... 233.4 Compression along the grain – action in plane of the solid wood slab .................................. 243.5 Contact compression along the grain – actions in plane of the solid wood slab .................... 243.6 Compression perpendicular to the grain ................................................................................ 263.7 Compression at an angle to the grain .................................................................................... 263.8 Bending perpendicular to the plane of the solid wood slab.................................................... 273.9 Bending in plane of the solid wood slab................................................................................. 273.10 Superposition of normal stresses........................................................................................... 273.11 Shear perpendicular to the plane of the solid wood slab ....................................................... 273.12 Shear perpendicular to the plane of the solid wood slab – Notches ...................................... 303.13 Shear perpendicular to the plane of the solid wood slab – Point supports ............................ 313.14 Shear in plane of the solid wood slab .................................................................................... 323.14.1 Slabs with general loading situation – verification of shear flow ............................................ 323.14.2 Solid wood slabs as beam – verification of shear stress........................................................ 333.14.3 Simplified verification for beams ............................................................................................ 343.15 Combined shear stresses ...................................................................................................... 35

ANNEX 5 STRUCTURAL FIRE DESIGN ....................................................................................................... 36

4 STRUCTURAL FIRE DESIGN................................................................................................................. 364.1 Performance R – load bearing capacity ................................................................................. 364.1.1 Parameters for structural fire design...................................................................................... 384.1.2 Local charring at corners, grooves, etc. ................................................................................. 394.1.3 Connections ........................................................................................................................... 404.2 Performances E and I – integrity and insulation..................................................................... 40

ANNEX 6 FASTENERS ............................................................................................................................. 41

ANNEX 7 REFERENCE DOCUMENTS......................................................................................................... 43



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I LEGAL BASES AND GENERAL CONDITIONS

1 This European technical approval is issued by Österreichisches Institut für Bautechnik in accordance with:

1. Council Directive 89/106/EEC of 21 December 1988 on the approximation of laws, regulations and administrative provisions of Member States relating to construction products1 – Construction Products Directive (CPD) –, amended by the Council Directive 93/68/EEC of 22 July 19932, and Regulation (EC) 1882/2003 of the European Parliament and of the Council of 29 September 20033;

2. dem Gesetz vom 20. März 2001 über das Inverkehrbringen und die Verwendbarkeit von Bauprodukten (Steiermärkisches Bauproduktegesetz 2000), LGBl. Nr. 50/2001, in der Fassung LGBl. Nr. 85/2005 und LGBl. Nr. 13/2010;

the law from 20 March 2001 concerning putting on the market and use of construction products (Styrian construction products law 2000), LGBl. � 50/2001, amended by LGBl. � 85/2005, and LGBl. � 13/2010;

3. Common Procedural Rules for Requesting, Preparing and the Granting of European technical approvals set out in the Annex of Commission Decision 94/23/EC4;

2 Österreichisches Institut für Bautechnik is authorised to check whether the provisions of this European technical approval are met. Checking may take place in the manufacturing plant. Nevertheless, the responsibility for the conformity of the products to the European technical approval and for their fitness for the intended use remains with the holder of the European technical approval.

3 This European technical approval is not to be transferred to manufacturers or agents of manufacturers other than those indicated on Page 1, or manufacturing plants other than those indicated on Page 1 of this European technical approval.

4 This European technical approval may be withdrawn by Österreichisches Institut für Bautechnik, in particular pursuant to information by the Commission according to Article 5 (1) of Council Directive 89/106/EEC.

5 Reproduction of this European technical approval including transmission by electronic means shall be in full. However, partial reproduction may be made with the written consent of Österreichisches Institut für Bautechnik. In this case partial reproduction has to be designated as such. Texts and drawings of advertising brochures shall not contradict or misuse the European technical approval.

6 The European technical approval is issued by the Approval Body in its official language. This version corresponds to the version circulated within EOTA. Translations into other languages have to be designated as such.

1 Official Journal of the European Communities � L 40, 11.02.1989, page 12 2 Official Journal of the European Communities � L 220, 30.08.1993, page 1 3 Official Journal of the European Union � L 284, 31.10.2003, page 1 4 Official Journal of the European Communities � L 17, 20.01.1994, page 34

Basic information on the European Technical Approval

In technical approvals, results from investigations on members are usually presented in a summarised form. The key data that is men-tioned is either based on basic data of other standards (such as e.g. strength values of the basic material) or on actual test results.

Plywood boards are complex construction materials that can be used in many different ways. On the other hand, a great amount of wood is used in this process (solid members). Wood as a construction material is valuable. Any work that involves wood should be sustainable and sparing.

It is therefore all the more important to design the product as precisely as possible in order to be able and make use of all possible functions and options.

The many and varied possible applications and the complexity of the product have made it necessary to include relatively compre-hensive information on structural design in the ETA. This has not exactly made practical handling much easier. Due to this, computer software has been created especially for the ETA, making it possible to identify the member resistance values depending on the type of component and for all different types of stress. This way it is no longer necessary in everyday structural design work to determine cross-sectional values and their relevant load-bearing values, etc. manually.Especially the automated calculation of member resistance values in case of fire (including charring and the consideration of different types of cladding) represents a massive advantage in the structural design of members.The structural engineer of a building only has to determine the required sectional forces (which is possible with any chosen software). The active forces identified this way can then be compared with the member resistance values in a very simple way.

On item 2: Through the use of the CE marking, the manufacturer confirms that the product was produced according to the same conditions that apply to tests in order to identify the relevant key data. The production conditions and the product quality have also been subject to internal quality assurance and external monitoring processes.

On item 3:In principle, an “initial test” of the product is required for every production facility. This test investigates whether the production condi-tions of the new production site actually comply with the applicable requirements. General approvals without such an initial test and subsequent external monitoring cannot be used to compare the performance of other manufacturing facilities.Since the new tests originate directly from the production site at Katsch a. d. Mur, no further initial test is required for KLH members.

On item 5: This is to ensure that not just favourable results get used, with less convenient results not being mentioned at all.The various different information in the ETA is interdependent and cannot be used to assess other members or products. Unilateral interpretations are not allowed, because external parties do not have the required background information available for a safe appraisal.In case of doubt, please contact our technical customer support.


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II SPECIFIC CONDITIONS OF THE EUROPEAN TECHNICAL APPROVAL

1 Definition of product and intended use 1.1 Definition of product

The European technical approval (ETA) applies to a product, the

KLH solid wood slabs,made of softwood boards, laminated boards or wood-based panels which are bonded together in order to form solid wood slab elements. Adjacent layers of the softwood boards are arranged perpendicular (angle of 90 °) to each other and cross sections of the solid wood slabs are symmetrically. The following extensions are considered.

� Single board layers, maximum 50 % of the cross section, may be replaced by one- and multilayer solid wood panels. The solid wood panels shall be suitable for structural use. Adjacent layers of solid wood panels are permissible.

� No load bearing function is assigned to wood-based panels other than solid wood panels. These are only used for providing the surfaces of the solid wood slabs.

� Multiple consecutive board layers may be arranged in the same direction if their overall thickness does not exceed 90 mm.

� For solid wood slabs with distinctive asymmetric cross sections the effects of asymmetry have to be considered.

The principle structure of the solid wood slab is shown in Annex 1, Figure 1 and Figure 2. Surfaces are planed.

The application of wood preservatives and flame retardants is not subject to the European technical approval.

1.1.1 Wood

Wood species is European spruce or equivalent softwood.

1.1.2 Wood-based panels

Wood-based panels are in accordance with EN 13986 or a European technical approval.

1.2 Intended use The solid wood slab is intended to be used as a structural or non structural element in buildings and timber structures.

The solid wood slab shall be subjected to static and quasi static actions only.

The solid wood slab is intended to be used in service classes 1 and 2 according to EN 1995-1-15. Members which are directly exposed to the weather shall be provided with an effective protection for the solid wood slab element in service.

The provisions made in the European technical approval are based on an assumed intended working life of the solid wood slab of 50 years. The indications given on the working life cannot be interpreted as a guarantee given by the manufacturer or the Approval Body, but are regarded only as a means for selecting the appropriate product in relation to the expected, economically reasonable working life of the construction works.

5 Reference documents are listed in Annex 6.

On item 1.1:A reasonable application of wood-based slabs is mainly possible for the production of visible surfaces. With regard to all other applica-tions, the slabs do not exhibit any advantages, or at least such advantages have not yet been verified. It is, however, foreseeable that the additional technical production efforts required would outweigh any possible advantages.What might also make sense would be large-scale plywood boards within the slabs, under the condition of absolute air-tightness (spe-cial cases). Shrinkage cracks can appear in every board-based or beam-based wooden material slab, which is why this represents no added value over normal, conventional board layers.

The regulation providing a maximum of 90 mm of layer thickness basically only refers to the internal layers (shear stress perpendicular to the grain), but it is also complied with for the layers at the edges. In case of thicker edge layers with connections on the surfaces and stresses perpendicular to the grain orientation, the principles of solid wood must be observed (cross tension, bearing stresses perpendicular to the grain, edge distances of connections, etc.).

The symmetrical structure is only significant with regard to slab stability (deformations due to changing moisture levels). If these de-formations, however, are not important (e.g. in case of fire), then it is irrelevant whether the structure is symmetrical or asymmetrical.Nevertheless, possible changes due to moisture fluctuations should be estimated. This is possible with simple FE software. Plywood board components may bend during uneven drying processes (which is always the case for exterior walls). This phenomenon is taken into consideration for data on pre-bending. Therefore, the formulas for the verification of deflections according to EN 1995-1-1 cannot be used unmodified. Solid wood and glued laminated timber have lower pre-bending values.

Only wood-based slabs are used that have secured product key values. This is possible through the use of CE-marked products, for example. In some special cases, like for the use as visual surfaces and only as cross layer (regarding production; slabs without butt-joints mainly under compressive stress), non-CE-marked wood-based slabs may be used in parts as well. This is, however, subject so special orders, and static clarifications must be made in advance.

On item 1.2:The intended use covers the entire area of structural engineering and also includes bridge constructions. Limitations only exist on the level of legal provisions.

Quasi-static effects also include low-cyclical alternating stresses due to vibrations induced by walking persons (e.g. ceilings, pedest-rian bridges), wind and earthquake stresses and (lower-frequency – note included by the author) heavy-goods traffic. The effect of the vibrations is mostly taken into account through a dynamic coefficient (see also EN 1990 item 5.1.3 (3)).With regard to the application for bridges, also refer to the relevant applicable standards (e.g. DIN 1074: Wooden Bridges; it also men-tions the issue of “plywood slabs”).“Real” vibration stresses caused by machines, etc. (wind power plants, engines) must be investigated separately.

In the usage classes 1 and 2, no directly weathered members are allowed. If so-called “sacrificed layers” are used on weathered sur-faces (e.g. “non-bearing” covering layer), then the effects on the deformation and load-bearing capacity of the residual cross section must be investigated. In addition, it must be ensured that the “static” load-bearing members will be absolutely safe from moisture (only in case of vertical members, at least 2 sacrificed layers, joint tightness through tongue and groove boards, etc.). Covering surfaces initially bonded on the edges do not represent any suitable long-term protection. Shrinkage cracks may appear at any spot. Therefore, narrow slab layers with tongue and groove boards provide much better protection.Members of this type should also be easily exchangeable and should not be used for any significant “static” functions! In any event, the use must be coordinated with the builder owner. Information on potential disadvantages must be given.


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2 Characteristics of product and methods of verification 2.1 Characteristics of product 2.1.1 General

The solid wood slabs and their boards correspond to the information given in the Annexes 1 to 3. The material characteristics, dimensions and tolerances of the solid wood slabs not indicated in these Annexes are given in the technical documentation6 of the European technical approval.

2.1.2 Boards, wood based panels

The specification of the boards is given in Annex 2, Table 2. Boards are visually or machine strength graded. Only technically dried wood shall be used.

If wood based panels are used, these shall conform to EN 13986 or a European technical approval.

Single board layers, maximum 50 % of the cross section, may be replaced by one- and multilayer solid wood panels. The solid wood panels shall be suitable for structural use.

Laminated boards are exclusively used in cross layers. They are supplied in supporting quality and CE-marked.

Wood-based panels other than solid wood panels are only used for providing the surfaces of the solid wood slabs without a load bearing function.

2.1.3 Butt joints within layers of solid wood panels

Butt joints within one layer of solid wood panels are to be statically regarded as a joint without transfer of tension or compression forces.

2.1.4 Adhesive

The adhesive for bonding the solid wood slabs and the finger joints of the individual boards is a PU adhesive and shall conform to EN 15425.

2.1.5 Hygiene, health and the environment

A manufacturer’s declaration to this effect has been submitted.

The product does not contain dangerous substances specified in EOTA TR 034, dated March 2012. A manufacturer’s declaration to this effect has been submitted.

In addition to the specific clauses relating to dangerous substances contained in the European technical approval, there may be other requirements applicable to the products falling within its scope (e.g. transposed European legislation and national laws, regulations and administrative provisions). In order to meet the provisions of the Construction Products Directive, these requirements need also to be complied with, when and where they apply.

2.1.6 Identification

The European technical approval for the solid wood slab is issued on the basis of agreed data, deposited with Österreichisches Institut für Bautechnik, which identifies the solid wood slab that has been assessed and judged. Changes of materials, of composition or characteristics, or to the production process, which could result in this deposited data being incorrect, should be immediately notified to Österreichisches Institut für Bautechnik before the changes are introduced. Österreichisches Institut für Bautechnik will decide whether or not such changes affect the European technical approval, and, if so, whether further assessment or alterations to the European technical approval are considered necessary.

6 The technical documentation of the European technical approval is deposited at Österreichisches Institut für Bautechnik and,

in so far as is relevant to the tasks of the approved body involved in the attestation of conformity procedure, is handed over to the approved body.

On item 2.1.2:For the key data of the KLH product, only boards of the C24 sorting category are relevant. Since it is practically unavoidable that lower quality material sometimes ends up in the production process or that C24 boards are also cut, this fact was taken into account by way of a reduction coefficient (k_sys). This reduction must be used for various application situations where a “worse” board might have unfavourable effects. In case of wider slab strips, the adjacent boards compensate for the layer with potentially lower load-bearing capacity.The old ETA (or other approvals for plywood boards) made no distinction in this respect, because it was obviously assumed that any responsible engineer would automatically make an assessment about when an individual, worse or partly cut board would become a significant factor or not.In this new ETA, the effect is taken into account in the relevant structural design processes by introducing the factor k_sys.

In principle, wood-based slabs only make sense if they are used as covering layers with requirements in terms of visual quality. For individual special cases it also makes sense to bond a veneering or OSB slab in a middle layer. This produces a 100% tight member, because any crack formations will be kept to an absolute minimum due to shrinkage. Moreover, sealing tapes may be positioned ex-actly at the edges of this layer.

On item 2.1.3:Due to production-technical reasons it is not possible to guarantee pressure contact for longitudinal butt-joints.Therefore, these joints must always be treated as member joints in terms of static considerations.If slab parts positioned on top consist of normal board layers, the residual cross section can be regarded as statically load-bearing. Nevertheless, caution is advised if this residual cross section is exposed to excessive stress. For wooden members, the possibility of elastic-plastic redistribution is limited. Any failure of the residual cross section will lead to the destruction of the entire cross section. The “internal” flow of forces partly creates cross tensions that must be taken into account.

On item 2.1.5: There are special investigation results on this issue that can be summarised as follows:

Isocyanate gas releases: No gas releases above the verified limits. Formaldehyde gas releases: < 0.02 ppm at 2 m2 surface per 1 m3 of space volume – corresponds to 0.017 mg/m3 (measured in a room cell with open slab fronts at doors and windows). The values basically correspond to the natural formaldehyde content of the wood. Warning: Class E1 partly allows considerably higher values. The relevant tests are carried out

with less layering and sealed edges (which does not correspond to normal usage). The fact that the test results for E1 are complied with is no guarantee that the contamination

inside a room is not above the limit value according to the test method for E1. In addition, various different organisations such as the WHO, etc. recommend significantly

lower limit values, especially for younger and older people (who are more sensitive to environ-mental influences).

Volatile organic compounds: Only wood-specific gas releases.


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2.2 Methods of verification The assessment of the fitness of the solid wood slab for the intended use in relation to the requirements for mechanical resistance and stability, for safety in case of fire, for hygiene, health and the environment, for protection against noise, for energy economy and heat retention, as well as for durability in the sense of the Essential Requirements 1, 2, 3, 5 and 6 of Council Directive 89/106/EEC has been made according to the CUAP for “Solid wood slab element to be used as a structural element in buildings”, Edition June 2005, ETA request � 03.04/06.

3 Evaluation of conformity and CE marking 3.1 System of conformity attestation

The system of conformity attestation applied to this product shall be that laid down in the Council Directive 89/106/EEC of 21 December 1988, Annex III (2) (i), referred to as System 1. This system provides for.

Certification of the conformity of the product by an approved certification body on the basis of

(a) Tasks for the manufacturer

(1) Factory production control;

(2) Further testing of samples taken at the factory by the manufacturer in accordance with a prescribed test plan7.

(b) Tasks for the approved body

(3) Initial type testing of the product;

(4) Initial inspection of the factory and of factory production control;

(5) Continuous surveillance, assessment and approval of factory production control.

3.2 Responsibilities 3.2.1 Tasks for the manufacturer; factory production control

At the manufacturing plant the manufacturer has implemented and continuously maintains a factory production control system. All the elements, requirements and provisions adopted by the manufacturer are documented in a systematic manner in the form of written policies and procedures. The factory production control system ensures that the product is in conformity with the European technical approval.

The manufacturer shall only use raw materials supplied with the relevant inspection documents as laid down in the prescribed test plan. The incoming raw materials shall be subject to controls and tests by the manufacturer before acceptance. Check of incoming materials shall include control of inspection documents presented by the manufacturer of the raw materials (comparison with nominal values) by verifying the dimensions and determining the material properties.

The frequency of controls and tests conducted during production and on the assembled solid wood slab is laid down in the prescribed test plan, taking account of the automated manufacturing process of the solid wood slab.

The results of factory production control are recorded and evaluated. The records include at least:

� Designation of the product, basic materials and components;

7 The prescribed test plan has been deposited at Österreichisches Institut für Bautechnik and is handed over only to the

approved body involved in the conformity attestation procedure. The prescribed test plan is also referred to as control plan.

On item 2.2:The CUAP (common understanding of assessment procedure) is a document that defines what material characteristics and key data must be identified for the planned usage of the slabs. The test method itself is not standardised. The tests were carried out on the basis of the tests for glued laminated timber.However, this was not possible for some types of stresses, and some product-specific characteristics were discovered that glued lami-nated timber does not have.Therefore it is not possible to perform a 100% comparison of the individual products from different manufacturers, because the key data could have been identified with different test settings.In addition, some of the effects were not even known at the time of some of the older approvals and therefore were not taken into account. The developments regarding this product have not yet been completed. If only very few test results were available for the assessment of the load-bearing behaviour, additional safety factors were provided for such results in order to ensure that a “sufficiently safe” struc-tural design concept can be made available for practical usage. The analysis of the tests was performed according to EN 1990 Appendix D (test-supported structural design).

On item 3.1:With the CE marking, the manufacturer guarantees the good quality of his product (compliance with key data).To this end, comprehensive quality assurance measures must be taken. Apart from internal quality assurance, the results of internal controls are checked and additional external tests are carried out.

If a product is produced in a new factory, it must be ensured that the production facility reaches the quality levels for the slabs present at the time of the tests resulting in the determination of the material key data for the ETA.For this purpose, an initial test by an accredited testing authority is required.The availability of an approval alone is no guarantee for the actual “usability of the product”.If there is any doubt, the latest test report of the external quality tests should always be requested. If no such report is available, or if such a report shows negative results, caution is advised!

In addition, every factory must have staff available who are aware of the complex problems of bonding load-bearing construction pro-ducts. These staff must attend a “bonding master course”.With these qualified staff and various required framework conditions in the production factory, a bonding approval for bonding these products will be granted. If there is any doubt, a currently valid bonding approval should be requested.The bonding approval also defines what products a production facility is allowed to bond. Very often this approval is limited to one single product. There are also general bonding approvals for general applications (= higher requirements for the members of staff).

In principle, this situation is similar to the EXC classes in steel construction. Not every steel construction company is allowed to perform welding work on complex steel structures without the necessary examinations and various quality assurance measures.

On item 3.2.1:It is defined exactly how often and what kind of tests a manufacturer must perform. In the event of errors, etc. the manufacturer must/can react immediately. The records on these in-house tests will be checked in the process of the ongoing external monitoring.


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� Type of control or testing;

� Date of manufacture of the product and date of testing of the product or basic materials or components;

� Results of control and testing and, if appropriate, comparison with requirements;

� Name and signature of person responsible for factory production control.

The records shall be kept at least for five years and they shall be presented to the approved body involved in continuous surveillance. On request they shall be presented to Österreichisches Institut für Bautechnik.

3.2.2 Tasks for the approved body

3.2.2.1 Initial type testing of the product

For initial type testing, the results of the tests performed as part of the assessment for the European technical approval may be used unless there are changes in the production line or plant. In the case of changes, the necessary initial type-testing shall be agreed between Österreichisches Institut für Bautechnik and the approved body involved.

3.2.2.2 Initial inspection of factory and of factory production control

The approved body shall ascertain that, in accordance with the prescribed test plan, the factory, in particular personnel and equipment, and the factory production control are suitable to ensure a continuous and orderly manufacturing of the solid wood slab according to the specifications mentioned in Section II as well as in the Annexes of the European technical approval.

3.2.2.3 Continuous surveillance

The approved body shall visit the factory at least once a year for routine inspection. It shall be verified that the system of factory production control and the specified manufacturing process are maintained, taking account of the prescribed test plan. On demand the results of continuous surveillance shall be made available by the approved body to Österreichisches Institut für Bautechnik. Where the provisions of the European technical approval and the prescribed test plan are no longer fulfilled, the certificate of conformity shall be withdrawn.

3.3 CE marking The CE marking shall be affixed on the accompanying commercial documents. The symbol “CE” shall be followed by the identification number of the certification body and shall be accompanied by the additional information:

� Name or identifying mark and address of the manufacturer;

� Number of the certificate of conformity;

� Last two digits of the year in which the CE marking was affixed;

� Number of the European technical approval;

� Species of wood used;

� Type of wood-based panels used including reference to the respective CE marking, if relevant;

� Number and orientation of layers;

� Number of layers of wood-based panels, if relevant;

� Nominal thickness of the solid wood slab.

On item 3.2.2:In principle, every change to the production process requires a review of the relevant effects. In cases of minor modifications, this can be performed by way of an expert statement by the monitoring body. In cases of significant modifications (e.g. change of compressive strength, changes to adhesive quantities), however, a complete series of tests may become necessary.

On item 3.3:Every KLH member must carry a CE marking – this can be checked at the construction site by the building inspection authority.


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4 Assumptions under which the fitness of the product for the intended use was favourably assessed

4.1 Manufacturing The solid wood slabs are manufactured in accordance with the provisions of the European technical approval using the automated manufacturing process as identified in the inspection of the plant by Österreichisches Institut für Bautechnik and laid down in the technical documentation.

Single and double layers of planed boards shall be bonded together to the required thickness of the solid wood slabs. Individual boards shall be joined in longitudinal direction by means of finger joints according to EN 385, there shall be no butt joints.

Adhesive shall be applied on one faces of each board. The edges of the boards need not to be bonded. Pressure shall be at or above 0,6 N/mm2.

4.2 Installation 4.2.1 Design of solid wood slab elements

The European technical approval only applies to the manufacture and use of the solid wood slab. Verification of stability of the works including application of loads on the solid wood slab are not subject of the European technical approval.

Fitness for the intended use of the solid wood slab is given under the following conditions:

� Design of the solid wood slab elements is carried under the responsibility of an engineer experienced in solid wood slab elements.

� Design of the works shall account for the protection of the solid wood slab elements in service.

� The solid wood slab elements are installed correctly.

Design of the solid wood slab elements may be according to EN 1995-1-1 and EN 1995-1-2, taking into account the Annexes 2 to 6 of the European technical approval. Standards and regulations in force at the place of use shall be considered.

4.2.2 Installation of solid wood slab elements

The manufacturer shall prepare installation instructions in which the product specific characteristics and the most important measures to be taken into consideration for installation are described. The installation instructions shall be available at every construction site and shall be deposited at Österreichisches Institut für Bautechnik.

Solid wood slab element installation shall be carried out by appropriately qualified personnel under the supervision of the person responsible for technical matters on site. An assembly plan shall be prepared for each structure, which contains the sequence in which the solid wood slab element shall be installed and the designation of the individual solid wood slab elements. The assembly plan shall be available at the construction site.

The safety-at-work and health protection regulations have to be observed.

5 Recommendations for the manufacturer 5.1 General

The manufacturer shall ensure that the requirements in accordance with the clauses 1, 2 and 4 as well as with the Annexes of the European technical approval are made known to those who are concerned during planning and execution of the works.

With the CE marking it can be checked whether the member complies with the static requirements for which it has been designed.Therefore, the approval number must be stated on the various plans (factory and installation plans).Alternatively, the product designation (e.g. KLH) must make a clear reference to the relevant approval.

Any deviations in the product can be noted by way of additional information.This may be the case with, for example, additionally applied layers or bonded ribs.An actual ribbed slab as such is not covered by this approval. If the rib and the slab each carry a CE marking, and if the manufacturer holds the licence to bond the slab with the rib (bonding appro-val, individual approval, expert report), then the combination of the CE-marked components is also allowed.

If glued laminated wooden ribs of higher quality are used (GL32, GL36), the CE marking should always be checked. The difference is impossible to tell with the naked eye. The material key data, however, is so different that damage might result from any kind of confu-sion (mostly higher deformation rates).As an additional means of control, requesting the delivery slips (at the same time as the member delivery) is also a reasonable mea-sure.It also allows a rough check of where the members come from and whether the quality information matches.Discrepancies with regard to quantities and dimensions might indicate that something is not quite right.

On item 4.1:If a CE marking is applied to the member, the manufacturer basically guarantees all technical production requirements for this approval.

The exact framework conditions of the production are kept on record at OIB and are not publicly available.This way, various special sorting efforts are carried out for the KLH product. Furthermore, the quantity of the adhesive has been optimised.A comparison of the slab key data merely on the basis of data that is publicly available (basic material, type of adhesive) is not possible and therefore not allowed, because persons who are not familiar with the internal processes of the company do not have the required background information available.For example, the quantity of the adhesive also influences the load-bearing behaviour as well as the behaviour in case of changes in the moisture levels. Thicker and slightly more compliant bonded joints are better at compensating tension perpendicular to the grain than thin, stiff joints. This has certain advantages, but it also has disadvantages.The behaviour in reaction to fire between the different bonding types (type, quality, quantity) is also different.

The company KLH has invested a great deal of time and effort in the further development and optimisation of the product. Therefore, only information that is absolutely necessary for structural design will be published, but no specific information on how slabs must be manufactured.

On item 4.2.1:Compared to conventional, beam-shaped wooden members, the KLH members are more versatile in use. This is because of the possi-bility of multi-axial load transfer and the use as slab and plane (surface with general load-bearing capacity).Not every engineer is familiar with the calculation of complex, even structures. Therefore, this “recommendation” should also be regar-ded as advice not to overestimate one’s own skills. The technical support of the company KLH will be happy to support you with advice and practical assistance. However, without a certain level of basic knowledge, this is very difficult.

For structural design purposes, the EN 1995 with various key data can be used as a basis. However, due care should be applied for verification. Not all rules and structural design provisions for glued laminated timber can be used for KLH members, because in part there are also entirely different failure mechanisms. Caution is also advised if general derivations of calculation methods are used for KLH members (layered FE models, etc.).The standard reference is always the information in this ETA, which, unfortunately, cannot be 100% complete. For special cases or in case of doubt, please contact the technical support of the company KLH.Never combine “generally” formulated expert reports and results from other approvals with the ETA. This could lead to very serious problems. For KLH members, only tests and expert reports are valid that were drafted specifically for KLH members.


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5.2 Recommendations on packaging, transport and storage The solid wood slab elements shall be protected during transport and storage against any damage and detrimental moisture effects. The manufacturer’s instruction for packaging, transport and storage shall be observed.

5.3 Recommendations for use, maintenance and repair of the works The assessment of the fitness for use is based on the assumption that maintenance is not required during the assumed intended working life. In case of a severe damage of a solid wood slab element immediate actions regarding the mechanical resistance and stability of the works shall be initiated.

On behalf of Österreichisches Institut für Bautechnik

The original document is signed by:

Rainer Mikulits

Managing Director

On item 4.2.2:Installations generally must be carried out according to the requirements of static and structural processing. Statics provides all data that must be complied with in the process of installation.This should also be noted in an installation plan, and the installation plan must be approved by the responsible structural designer.

The actual installation work may only be carried out by trained experts in the field or specially trained members of staff. Application itself, however, is very simple. The only essential rules to follow are the ones that apply to hoisting work with cranes and to securing measures to the building during construction work.In case of extreme situations, a special statics installation plan must be prepared.It makes sense to discuss the installation with the responsible structural designer.

The slabs are usually installed in large formats. Accordingly, the load suspended on cranes or stabilised with provisional bracing in the building are very heavy. This should always be kept in mind. Sudden gusts of wind should always be expected and taken into account.

On item 5:Everyone working with KLH members (planning, realisation) must be informed about the content of the approval, because s/he is responsible for the way the product is used. Only then is it possible for the responsible staff (structural designer, construction site inspection, etc.) to carry out checks.The check of the CE marking is only one part of all required measures.The CE marking alone does not guarantee that the right member with the right thickness and the right cover layer orientation gets to the right part of the building.Therefore, all different levels of control (approving factory plans, check on site, etc.) are essential for the quality of a building.

It is also essential that the members are protected from exposure to moisture during the entire time of transport, installation and as parts of the building shell. It should be mentioned again that the building is only approved for the usage classes 1 and 2.Experience shows, however, that short-term exposure to moisture usually does not lead to any long-term consequences.It must always be made sure that moisture which has soaked deeper into the slab (in case of slab connections, front areas, joint areas) is left to dry up completely.On the surface, the slabs usually dry up very quickly.

Due to this, it is recommended, especially for even or slightly inclined surfaces, to apply moisture protection directly after installation across the entire surface, or alternatively to keep the building parts to be installed small enough, so that several storeys can be ins-talled within a reasonable period of time. The top ceiling will then work as protection for lower building parts.

In case of open window cuts it must be ensured that rain and wind cannot transport too much water into the building.If this happens anyway, such “stagnant” water must be removed immediately before it can penetrate deeper levels of the wood.Especially in wall contact areas, the cross grain absorbs the moisture deeply into the slab.This must be kept in mind for connection areas to concrete construction parts. Concrete slabs usually have a higher level of inaccuracy. Therefore small water puddles may form. For this reason, the KLH walls on concrete slabs should always be placed on a small foot with a minimum height of 1-2 cm (e.g. mortar bed, insulation strip (XPS)).


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Figure 1: Principle structure of the solid wood slab

Figure 2: Typical examples of the structure of the solid wood slab

KLH solid wood slab

Structure of the solid wood slab

Annex 1 Page 1 of 2

of European technical approval

ETA-06/0138

90 °

The basic structure consists of board layers arranged in positions rotated by 90°.This results in the typical braced structure that accounts for many of the material key data.In case of multi-layer, parallel edge lamellas, various positive material characteristics are reduced. These areas can partly be regarded as solid wood areas again.

For special applications such as uniaxially strained ceilings or others, double the layers in the structural direction parallel to the span.This results in more economical slab thicknesses.

The double layers, however, also have disadvantages. If it is a double inner layer, then the shear-bearing behaviour perpendicular to this double layer is also changed. The new ETA, however, does provide structural design values for such cases.

In case of double cover layers, there is basically no shear stress perpendicular to the cover layer direction; at least not as a result of the slab load-bearing effect. Shear stress will, however, apply if you want to connect forces to this slab that are perpendicular to the cover layer direction (e.g. metal tangs with nails). Then the surface must not be treated in any way different from glued laminated timber. Higher loads might result in problems with reinforcements perpendicular to the grain. Even horizontal forces that are planned to be transmitted from bracing walls positioned on top through the ceiling and to the below walls can lead to problems with reinforcements perpendicular to the grain.

If you deal with the special characteristics of the product in the course of structural design (not only the structural design of members, but also the details), then such technical problems can usually be managed with simple means (fully threaded screws, etc.).


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Figure 3: Typical examples of the structure of the solid wood slab

Figure 4: Typical dimensions of cross section of KLH solid wood slab lamellas

Where

b ....................Width of a single board, solid wood or laminated board

bi....................Partial cross section of single board or single lamella of laminated boards

ti.....................Thickness of single layer

tq ....................Thickness of single or multiple layer in cross direction, tq � 90 mm

Laminated boards are bonded with an adhesive suitable for structural applications.

KLH solid wood slab

Structure of the solid wood slab

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The layer structure is basically irrelevant. The design regulations are formulated in such a general manner that all sorts of structures can be calculated. However, generally used formula systems might not work.

In the illustrations below, the boards are shown in slightly overlapping positions. This is more by chance than on purpose. The tests were carried out for extreme cases with joints directly positioned on top of each other, with the consequence that the position of the board joints (or shrinkage cracks) has no significant influence.

It is clearly recognisable that the board layers were tested with unfavourable joint arrangements. There is a relatively high probability that the joints correspond to appearing shrinkage cracks.

Caution is also advised if reduction factors are used for single loads near supports in order to determine the shear design. There is a certain amount of influence, but it is far from comparable to glued laminated timber.

Apart from normal boards, types of boards made of “laminated slabs” are also used. They are treated like normal boards made of solid wood.

The quality of the board strips made of laminated boards is checked internally.


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Table 1: Dimensions and specifications

Characteristic Dimension / Specification

Solid wood slab element

Thickness mm 57 to 300

Width m � 2.98

Length m � 16.50

Number of layers � 3 to 16

Maximum width of joints between boards within one layer: regions with fasteners to be applied elsewhere

mm mm

3 6

Board 1)

Surface � planed

Thickness, planed dimension mm 10 to 45

Width 1) mm 44 to 298

� 2.3 : 1 2) Ratio width to thickness �

� 4 : 1 3)

Boards shall be graded with suitable visual and/or machine procedures to be able to assign them to the strength classes according to EN 338.

� � 10 % C16 � 90 % C24 4)

Moisture of wood according to EN 13183-2 % 12 � 2

Finger joints � EN 385

1) Laminated boards with single lamellas bi and ti � 45 mm according to Figure 4, are considered

as boards. 2) Minimum ratio for layers oriented in cross direction (stressed on rolling shear). 3) In general 4) For the whole product as well as each single layer.

KLH solid wood slab

Characteristic data of the solid wood slab

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Slab thickness was determined with respect to the tested, most extreme slab dimensions.Based on experiences from the tests it can also be assumed that even thicker slabs can be calculated with the stated design pro-cesses. If very thick members are used for shorter spans, it must be ensured that the key data is checked with an FE analysis (if the technical bending theory of the beam is no longer admissible). However, this is also advisable for thinner slabs.

The width and length are technical framework conditions of production. (Context: favourable transport options)

The number of board layers results from technical aspects of production (open bonding time = time after which the compressive strength must be applied), but it is not relevant for the design or a general FE analysis.

The possible joints between the individual boards are not “standard”. They are exceptions. In the production process, individual board layers may slightly shift, which may lead to a small number of local joints.Joint widths of up to 3 mm were taken into account during tests with connections. If individual, wider joints appear, there is still time at the construction site to react. In case of sensitive connections, structural design should consider the possibility that the connection might have to be slightly shifted. This might sometimes even be useful in case of local defects on individual boards.

Bonding requires very precise planing of the board surfaces. Smaller, local defects are still possible, but they do not represent any problem in terms of statics.

The thickness of individual lamellas is stated with 10 to 45 mm. Currently, lamellas from 19 mm to 40 mm in strength are used most. 45 mm thick board layers are only used for special projects with larger quantities. For lamella thickness values of cover layers >34 mm, the production of visual surfaces is problematic. Visual quality for residential purposes is only offered up to a lamella thickness of 34 mm or with double, thinner lamellas.

The ratio 2.3 : 1 resulted from comparative calculations with shrinkage stress. Width-thickness ratios that are even below this limit only result in rather minor tension perpendicular to the grain in the board lamellas.This means that this relation must be expected in the final stage of a building. This exception has also been confirmed by over 15 years of experience with these members. Shrinkage cracks on slimmer boards are very rare.The more recent tests were performed with these relations. This means that the reference to the 4 : 1 ratio is actually redundant, because it means that these wider boards are certainly allowed for installation anyway. Nevertheless, the tests cover the effect of possible shrinkage cracks.

The board qualities are generally sorted for C24. In addition, internal quality requirements are amended.However, it cannot be absolutely avoided that even individual boards of lower quality may be used. Especially C24 lamellas of cut-to-size slabs are often partly cut in the process. In such cases, these boards do no longer have the original quality characteristics. This fact was taken into account during tests and analyses.Reduction factors were introduced in order to verify structural safety. This means that it plays no role for KLH members whether indivi-dual boards are partly cut or not. Minimum widths of board lamellas as stated in come approvals (e.g. for the design of shear in plane) are not relevant for KLH members.

In principle, for the determination of the load-bearing capacity, it is always the lowest quality that must be used as a reference for the design of a plywood board member if minor quantities of boards with lower quality are admissible, and if the lamellas are partly cut, and if the quantity of this material may become significant (e.g. small ceiling strips, ceiling edges, wall pillars between 2 windows).This applies in particular if the cross section is reduced even further – in case of fire exposure, for example.For the KLH members, this effect is taken into account in structural design by way of reduction factors. Therefore, the key data of C24 may generally be used as a basis. If there are deviations, they are noted.

For calculations regarding deformation, however, these shares of lower-quality boards are insignificant.If should always be kept in mind that deformations in wood constructions are determined with the mean values of E and G moduli. The key data vary by about +/- 20%. This means that the actual deformation may also differ from the calculated values by approximately 20%. Therefore, in case of very sensitive constructions, the 5% fractile values of the E-modulus should be used.

The moisture of wood is checked prior to bonding. Despite that, certain differences might exist locally and between the individual layers. The distribution of moisture in wooden members is never 100% even. The manufacturer can only make an effort to keep these deviations as small as possible.The moisture differences between the individual layers may lead to warping of the slabs. Walls will bend outwards (they dry up inside or get wet outside). Cantilevers may bend upwards …


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Table 2: Product characteristics of the solid wood slab

ER Requirement Verification method Class / Use category / Numeric value

Mechanical resistance and stability

1. Mechanical actions perpendicular to the solid wood slab

Modulus of elasticity 3)

� parallel to the grain of the boards E0, mean Annex 4 CUAP 03.04/06, 4.1.1.1 12 000 MPa

� perpendicular to the grain of the boards E90, mean EN 338 370 MPa

Shear modulus 3)

� parallel to the grain of the boards G0,mean EN 338 690 MPa

� perpendicular to the grain of the boards, rolling shear modulus G90, mean CUAP 03.04/06, 4.1.1.1 50 MPa

Bending strength

� parallel to the grain of the boards fm, k Annex 4 CUAP 03.04/06, 4.1.1.1 24 MPa

Tensile strength

� perpendicular to the grain of the boards ft, 90, k EN 1194, reduced 0.12 MPa

Compressive strength

� perpendicular to the grain of the boards fc, 90, k EN 1194 2.7 MPa

Shear strength

� parallel to the grain of the boards fv, k EN 1194 2.7 MPa

� perpendicular to the grain of the boards(rolling shear strength) fv, R, k

Annex 4 CUAP 03.04/06, 4.1.1.3 0.8 to 1.2 MPa

2. Mechanical actions in plane of the solid wood slab

Modulus of elasticity 3)

� parallel to the grain of the boards E0, mean Anet, Inet, Annex 4 CUAP 03.04/06, 4.1.2.1 12 000 MPa

Shear modulus 3)

� parallel to the grain of the boards G0,mean 1) Anet, Annex 4

CUAP 03.04/06, 4.1.2.3 500 MPa 1)

Bending strength

1

� parallel to the grain of the boards fm, k Wnet, Annex 4 CUAP 03.04/06, 4.1.2.1 24 MPa

KLH solid wood slab

Product characteristics of the solid wood slab

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With regard to stress on the slab, we can distinguish between two main types of stress: “Slab effect” = internal forces due to loads perpendicular to the surface“Plane effect” = internal forces due to loads parallel to the surface

The E-modulus is higher than for the basic material C24. This is ensured through the special, company-internal sorting and is subject to continued checks.The mean values of the tests were at approximately 12,500 MPa. The design value is therefore on the safe side.However, please consider that the E-modulus may vary up to approximately 20% (or more in extreme cases). This means that you should rather use a reduced E-modulus in cases of members that are particularly sensitive to deformation.

Perpendicular to the grain slabs show the same characteristics as the basic material. There are no significant advantages due to the braced structure.

The shear modulus of 690 MPa is the value of the shear modulus of the individual board. It will become effective if the load-bearing capacity of 3-layer slabs is investigated perpendicular to the structural direction (only one single board layer). As soon as the structure has multiple layers, this key value is no longer significant.

The shear modulus of 50 MPa for stress perpendicular to the grain of a board shows a very good analogy between the calculations and the test results from over 200 tests that were performed.

As regards bending strength, the basic material is decisive. However, it is important to identify a realistic distribution of the bending stress.

The stress characteristics of the individual board perpendicular to the grain were reduced in this case, because it is not the board itself that becomes relevant, but the connection area of the board to the bonding joint or the overlapping of stresses perpendicular to the grain caused by the shrinkage process and the actual stresses. In order words, the “own stresses” due to the braced structure of the slab are included here. In general, stresses perpendicular to the grain should be avoided and completely covered by screw connections (reinforcements perpendicular to the grain, etc.).

As regards the pressure perpendicular to the grain, it is also the basic material that is decisive. Any positive effects are taken into account in the verification process by way of coefficients or provisions regulating the calculation process.

The shear strength of 2.7 MPa is only significant for 3-layer slabs where the direction perpendicular to the grain (only one individual board layer) is exposed to bending stress (otherwise it is always the shear stress in layers perpendicular to the grain that is decisive).This value may also become relevant for local design situations, such as slabs with double edge layers.

Rolling shear strength (shear perpendicular to the grain)A total thickness of the cross layer of up to 90 mm is now admissible for KLH members. This also leads to a categorisation of key valu-es. In addition, system-related reductions have resulted from this change.

E-modulus of stress in plane: See also E-modulus for the slab effect

The shear modulus was identified in tests with approximately 550 MPa. In order to cover uncertainties inherent to the model, the value for the ETA was slightly reduced. It is important to mention that this value applies to board layers that are not bonded to edges, because their individual boards have a w : d relation of up to 2.3 : 1 (long-term behaviour, shrinkage cracks).The earlier ETA contained a lower value. At the time, the key data was determined with a great deal of caution, and some of the effects were not even known.In this context it is important to mention that the shear modulus of the entire member also always depends on the relation between the thickness of plane layers and cross layers. The value of 550 MPa is therefore merely a basic value that is used to determine the shear strength of the entire member. This value must not be replaced by the G-modulus of the basic material (= 690 MPa). Not even if the boards are bonded on the edges (influence of stress perpendicular to the grain, caused by shrinkage processes).

As regards bending strength (as well as the compressive strength in the direction of the lamellas), the basic material is decisive.The same applies to low slabs that are calculated as beams/girders.


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2. Mechanical actions in plane of the solid wood slab

Tensile strength 2)

� parallel to the grain of the boards ft, 0, k EN 1194 16.5 MPa

Compressive strength

� parallel to the grain of the boards fc, 0, k EN 1194 24 MPa

� concentrated, parallel to the grain of the boards fc, 0, k CUAP 03.04/06, 4.1.2.2 kc,0 Annex 4, 2.4

Shear strength

� regardless of loading direction, per glue line fv,K,k Annex 4 – Shear flow 90 N/mm

� parallel to the grain of the boards fv, k Annex 4 – Shear stress 3.9 to 8.4 MPa

3. Other mechanical actions

Creep and duration of load EN 1995-1-1 Service class 1 and 2

Deformation factor kdef EN 1995-1-1 Equivalent to GLT

Modification factor kmod EN 1995-1-1 Equivalent to GLT

Dimensional stability

Moisture content during service shall not change to such an extend that adverse deformation will occur.

Fasteners Annex 5 Service class 1 and 2

Dimensional tolerance

� Shrinkage perpendicular to the plane of the solid wood slab 0.24 % in thickness per % moisture variation

1

� Shrinkage in plane of the solid wood slab 0.01 % in length per % moisture variation 1) This value is applicable for 2 dimensional structures, orthotropic plates. For a simplified beam

analysis, this value shall be reduced to 50 %. 2) In case of a non-uniform stress distribution, the characteristic bending strength may be applied. 3) For determination of the 5 %-fractile values of the stiffness properties the mean values may be

multiplied by 56.

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The tensile strength can only be used in case of real stresses in plane or if the tensile stress is constant across larger areas.

As regards compressive strength, the basic material is decisive.

As regards the local areas used for load introduction (no stability-critical areas), a positive effect of the braced slab structure has been verified. This effect, however, was only observed with lamellas that are directly connected to a crossed board layer, which means that these coefficients should not be used for double layers in the structural direction parallel to the span, or at least only used on certain condi tions (max. 45 mm).

The shear strength in plane has also been determined under unfavourable marginal conditions (boards with 2.3 : 1, without bonding on the edges).A dependency on the strength of the lamella and the type of stress was found.

For the most general, most unfavourable case, a shear flow was stated. Failure of the slabs under stress in plane will only happen in the area of the wooden parts adjacent to the bonded surfaces (vertical failure across the surface) – unlike solid wood or glued laminated wood in horizontal joints.The key data for shear stress is also coupled with a parabolic trend line. The proof of shear stress used for structural design purposes is only of a “theoretical” nature. The actual load-bearing behaviour is much more complex. The breakage cannot be assigned to any defined slab area. It is therefore important to strictly follow the verifica-tion procedure.It is not necessary to perform a separate verification of the cross layers for the proof with shear strength. With the shear proof of the layers in plane in the load-bearing direction, all effects are covered (the theoretical shear strength values of the cross layers are signi-ficantly higher and therefore not relevant here).In addition, the key data was not determined with general assumptions, but on the basis of tests. The different extreme board thick-ness conditions were taken into account (thick layers in plane, thin cross layers, etc.).

For the identification of long-term creep behaviour, a test was performed over the period of more than one year. No higher creep defor-mations were found compared to glued laminated timber.The k_def factors for glued laminated timber can therefore be taken from the EN 1995-1-1.

As regards dimensional stability, it has to be taken into account that even minor moisture differences in the individual board layers may already lead to bending. If slabs get moist on site (construction site, transport), deformations may happen as a result. It may even be enough to have an exposure to higher humidity levels.Measurements and an estimation of the shrinkage effects have resulted in values of up to H/400 parts. This is also the reason for the pre-bending of the slabs with regard to stability verification. Additional deformations may appear practically always and everywhere. Minor moisture differences cannot even be entirely excluded due to technical production conditions.

If exact straight slab lines are required for members (e.g. roof inclination for drainage), it cannot be achieved to 100% in many cases, especially in case of statically defined members. Therefore, as regards members sensitive to deformation, minimum inclinations for roof drainage should also always include a contingency reserve for the shrinkage behaviour of the members – a reserve that should never be undercut.

The data on shrinkage only refer to the total slab. The value in plane of the slab (0.01% per % of moisture change) only applies to board lamellas that are “not bonded on the edges”. The increased value of 0.02% defined in publications and standards includes the influence of intrinsic tensions (and therefore deformations) caused by the shrinkage of cross lamellas in longitudinal lamellas (see also comment on long-term deformations on page 47). Without bonding of the edge sides, this effect can be overlooked.

Locally, higher shrinkage deformations may be possible in the areas of joints, especially in plane of the slab. For the calculation of these local values, the shrinkage value for “shrinkage perpendicular to the slab grain” can be used per board. The easiest way to perform the calculation is by way of FE software. It can be used to even verify roof deformations due to entering moisture (e.g. in case of poorly secured covering).

On footnote 1): This reduction is a simplification for beams; in the chapter with the design values, a formula is quoted that can also be used to determine the realistic G-modulus for beam-shaped members.

On footnote 2): This refers to the tensile stress caused by bending effects. If the tensions are variable, higher values can be used (= bending effect).

On footnote 3): The conversion is necessary for stability calculations and for theory-II-order calculations. The test analyses (of a total of more than 400 tests) confirm this assumption.


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Reaction to fire

Solid wood panels excluding floorings(�mean = 420 kg/m³)

Euroclass D-s2, d0

Floorings of solid wood panels

Commission Decision 2003/43/EC

Euroclass DFL-s1

Resistance to fire

2

Charring rate EN 1995-1-2

Obtained test data according to Annex 5

Hygiene, health and environment 3

Vapour permeability, �, including joints within the layers EN ISO 10456 25 to 50

Protection against noise

Airborne sound insulation EN 12354-1

� Plain wall, thickness of 94 mm approximately 33 dB

� Plain wall, thickness of 145 mm approximately 37 dB

Impact sound insulation No performance determined

5

Sound absorption No performance determined

Energy economy and heat retention

Thermal conductivity, � EN ISO 10456 0.13 W/(m � K)

Air tightness No performance determined

6

Thermal inertia, specific heat, cp EN ISO 10456 1 600 J/(kg � K)

Durability

Durability of timber

�

Service classes EN 1995-1-1 1 and 2

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The designation D-s2, d0 only refers to the general reaction to fire, but not charring and the load-bearing capacity in case of a fire. This designation is used for various fire protection regulations.

With regard to the reaction to fire, comprehensive investigations were carried out on ceilings and walls, with and without cladding. Since the currently applicable design regulations in the EN 1995-1-2 in various publications and according to the approaches in various approvals yield very different results, the complete design process was verified with tests.Not only bending tests with tension at the fire-exposed side were carried out (conventional ceiling element), but also tests with pressure on the fire-exposed side (essential for the bending verification). All in all, 9 large fire tests were carried out, the analyses of which have helped to develop a fire protection design geared to KLH slabs.

As regards vapour permeability, conservative values should be assumed for problematic structures. In principle, the local joints between the members are most significant. The same applies to air tightness. The air tightness of the entire slab is achieved due to the considerably improved production quality for all types of slabs. Problems are rather caused by connections between slabs as well as between slabs and other members (concrete, window).

For sound protection, special documentation is available. The raw slabs achieved the listed values. The sound value inside the building, however, also strongly depends on the adjacent paths and roads.


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Design considerations for KLH plate structures

1 General definitions and terminology 1.1 Mechanical actions perpendicular to the solid wood slab

Along the two main directions of the solid wood slab, the two main structural directions are defined. See Figure 5 for mechanical actions perpendicular to the solid wood slab.

Figure 5: Main directions regarding mechanical actions perpendicular to the solid wood slab

Where

h ....................gross thickness of the solid wood slab

heff, x, heff, y ......effective height of the cross section in main structural direction x or y

x ....................direction parallel to the orientation of the cover layer

y ....................direction perpendicular to the orientation of the cover layer

KLH solid wood slab

Design considerations

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face

edges

edges

The KLH member tests were analysed by means of the design processes described underneath. Therefore, the verifications must also be carried out with the quoted sets of formulas.

Additional framework conditions and recommendations are used for a better general understanding of the issue. No own derivations, etc. based on these design processes may be carried out.

The slabs basically have two main load-bearing directions.The designation “in plane” and “cross” often partly refer to the stresses in practical application, but very often they also refer to the conditions of production.

Due to technical reasons of production, the KLH slabs are categorised in TL and TT slabs. “TL” means: “cover layer in plane” of the production direction; “TT” means: “perpendicular to the orientation of the cover layer” of production.The TT direction is always the smaller production width (max. 295 cm). The TL direction is always the longer dimension of the produced slab.

If we cut individual slabs out of the large produced complete slabs (called “mother slabs”), we may get slab parts that cannot be clearly assigned with regard to the produced slab direction anymore.Nevertheless, the categorisation into TT and TL slabs makes sense, because there are structures that can only be produced in a certain direction, and the static key data are partly different, even if the total strength is the same.Walls higher than 295 cm can therefore only consist of TL slabs that are placed upright adjacent to each other, and which also have to be connected accordingly. This must be taken into account for static and structural processing.Conversely, a ceiling with an approximate span of a maximum of 290 cm can also be built with TT slabs.

In order to avoid errors and misunderstandings, all slab views should be marked with arrows indicating the load-bearing direction of the cover layer – or the slabs are depicted “correctly” in the sections (end grain must be marked).

All slabs, irrespective of whether they are TT or TL, have these two main directions. The direction of the cover layer is always the x-direction; the weaker cross direction (only from a static point of view; this has nothing to do with “TL” or “TT”) is always the y-direction.

From a static point of view, the term “cross layer” or “cross direction” is used. This, in turn, only has to do with the direction of the stress. If we look at the load-bearing direction in TT (related to the produced slab), the lamellas in plane direction (the internal layers) are the cross layers, and vice versa.

The load-bearing effects in the two directions can be extremely different. Due to this it is very important that the orientation of the cover layer is always clearly pointed out on plans and static requirements. The definition of the slab type alone is no 100% guarantee for clear marking.

If there is a risk of confusion, a sketch should always be drafted, showing the wall and the cover layer.A check of the cover layer direction is essential, especially during checks of the cutting plans. These are usually the documents providing real clarity on whether the cover layer direction of the cut-to-size member is correct.

What is also essential is a check on site, if possible directly during or immediately after the installation, and the final acceptance of the building shell by the responsible structural engineer.If an error has happened, there is still time to perform rectifications of defects to the building.


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1.2 Mechanical actions in plane of the solid wood slab

Along the two main directions of the solid wood slab, the two main structural directions are defined. See Figure 6 for mechanical actions in plane of the solid wood slab.

Figure 6: Main directions regarding mechanical actions in plane of the solid wood slab

Where

Hx, Hy.............height of the cross section in the respective structural direction without consideration of joints between adjacent boards

ti, x, ti, y ............ thickness of the single layers in the respective structural direction

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ETA-06/0138

edgesface

edges

edges

For stresses in plane (load parallel to the level of the slab surface), the names of the axes are retained. The x-direction is always the direction of the cover layer.

On the difference between stress perpendicular to the plane of a slab and stress in plane of a slab:

Stress perpendicular to the plane results from stress in normal direction to the slab surface. This bends the slab and creates bending moments (in the two main directions) as well as cross forces.

The bending moments generate normal stress in the individual board layers.They must be superpositioned with the normal stresses due to potential structural behaviour in the plane.

Shear stress theoretically generates vertical and horizontal shear forces (duality of shear stress).In case of solid wood members under normal bending loads, members always tend to fail along the wood fibres (weaker direction). As regards plywood boards, the member fails only parallel to the slab surface as a consequence of shear stress.

The different breakage mechanisms show shear tension and shaving effects in the individual boards. In the area of an individual board they can also exhibit slanting or vertical breakage surfaces. Therefore reductions of shear stress shares are not possible for individual loads near supports (or only possible in certain conditions). The favourably acting shear pressure is not a “guaranteed” phenomenon.

The failure mechanisms described above are very complex and not predictable, because wood is very heterogeneous. However, these effects are all included in the shear verification. It is important to know that the shear failure of surfaces starts parallel to the slab level. Therefore it must be superpositioned with the shear stress verifications for loads in plane.

Stress in plane results from stress parallel to the slab surface, which expands the slab level. The lamellas in longitudinal and cross directions (x and y directions) will expand or contract.These expansions generate tensions along the direction of the grain that must be superpositioned with the normal stresses due to potential structural behaviour perpendicular to the plane. The most frequent type of this general stress in plane is the normal force stress, if the slab is used as a wall. The wall is the level variant of a support (= beam-shaped), only that the wall can also absorb other stresses (horizontal forces parallel to the wall level). However, supports usually only carry one load parallel to the axis (= normal force) – of course with any additional stresses resulting from bending effects acting as a beam.

In case of slabs there is the possibility to use them as girders at the same time (wall-shaped girders), or to use the residual cross section above door or window openings as “girders”.In such cases loads in plane create changing longitudinal tensions in both main directions.As soon as the longitudinal tension is variable, shear forces will appear. This in turn creates theoretical shear tensions (according to the general theories for the calculation of rod or plate structures).This applies theoretically, because with KLH members that work as planes, shear failure does not happen the same way as it does with solid wood, glued laminated timber or even KLH slabs under stress perpendicular to the plane. It is fundamentally different.

The failure mechanisms due to shear forces during loads applied in plane are very com-plex. One thing all different causes have in common is that the members fail along the bonded surfaces or in the connection area to the wooden parts. From a local aspect, the failure sketches seem similar to those of shear normal to the grain direction (shaving effects, shear stress failure).Failure due to shear forces no longer happens within an area that is normal to the “shear force” (left sketch – glued laminated timber), but within an area that is parallel to the shear force direction (right sketch – KLH member).

Therefore, no reduction of the shear force for loads near supports is possible for KLH members exposed to stress in plane.

As regards frame corners, the influences of both shear force directions must be superpositioned, because the transmission of the forces happens in the same joint areas.The longitudinal stresses at frame corners, however, do not have to be superpositioned, because the longitudinal stresses can be deflected through separate board layers that are available for both directions.

During the tests, different variations between layers in the structural direction and perpendicular to this direction were checked instead of a general estimation through theoretical approaches.The load-bearing behaviour mainly depends on the number of bonded joints between crossed board layers. It seems to have an influ-ence whether the observed board direction has variable normal stresses or not.


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1.3 Normal stress and shear stress in the two main directions of the solid wood slab

Normal stresses and shear stresses resulting from mechanical actions perpendicular to the solid wood slab and normal stresses resulting from mechanical actions in plane of the solid wood slab are shown in Figure 7.

Figure 7: Normal and shear stresses

2 Calculation of stiffness properties 2.1 Short-term deformation

The deformation behaviour of KLH-solid wood slab members can be considered by applying the following stiffnesses. Member forces and moments based on these stiffnesses shall be used for ultimate limit state design.

For actions perpendicular to the solid wood slab shear deformations of the layers perpendicular to the respective structural direction have to be considered.

Serviceability limit state design may be performed in accordance with EN 1995-1-1.

2.1.1 Bending stiffness

For calculation of the deformation due to pure bending, wnet, the net cross section, Inet, can be applied without shear deformations. I.e. layers oriented perpendicular to the considered main structural direction shall not be taken into account, i.e. E90, mean = 0 MPa and without shear deformation.

Where

Inet ..................moment of inertia of the net cross section for the structural direction concerned

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This illustration summarises the essential tension diagrams due to stress perpendicular to the slab (loads normal to the surface). The use of the net cross section data is always crucial.

In case of multiaxial stress, longitudinal tensions of individual board layers are also discharged by different board layers (similar to stress in plane). These tensions do not have to be superpositioned.

Tests have shown that tensions due to the “theoretical twisting moments” (resulting from calculations of plate structures) do not have to be taken into account.

The shear stresses resulting from shear forces on KLH members are only relevant in parallel to the slab surface. Of course, there are also theoretical shear stresses in levels perpendicular to the slab level (= necessary for the balance).This direction, however, is not decisive.

In case of 2-axial stresses, the shear stresses basically must be superpositioned, because theoretically the stresses act on the same levels.The analyses of the causes of failure and the test results show, however, that this is not the case.Failure happens mostly due to shear stress perpendicular to the grain of a cross layer. If the slabs are exposed to stress in two direc-tions, the cross layer of one direction does not correspond to the cross layer of the other direction. Therefore, separate slab areas are affected. The angle between the resulting shear stresses and the board fibres results in an increase of the shear strength.The resulting maximum theoretical shear stress is only 1.41 times the maximum “rolling shear stress” and is therefore below the shear strength of the wood in the direction of the grain.

The mere shear stress in one direction is always less favourable than a resulting shear stress that deviates from the grain direction by 90 degrees. Therefore we get a simplified verification for shear stress if the slabs are point-supported. Consequently, these tensions do not have to be superpositioned.There is no punching of slabs (as for example in concrete constructions). The failure is a mere shear failure or a failure due to shear stress of the cross layers close to the supported area.

On item 2:For the determination of the member forces and moments, it is necessary to make a calculation of deformations that is as realistic as possible.With these member forces and moments, the members can be designed. Therefore, the design of the members can only be as exact as the basis that has been determined for them (member forces and moments). This means that the determination of the stiffness is of special importance.The more inaccurate a member is treated with regard to the determination of the member forces and moments, the fewer key data may be used for the design of details.However, vice versa we can say: if the stresses are not used (such as in some ceiling and roof elements), the member forces and moments also do not have to be determined precisely.

The data below are intended for the calculation of the supporting system by way of IT solutions capable to take shear deformations into account.

Due to this, bending deformation alone is only calculated with the moment of inertia of the board lamellas in the direction of the struc-tural direction. No other effects are “included” in the calculation as it is the case with the γ-method (l_effective).In the γ-method (with I_effective, old ETA), the shear deformation is included in the calculation of the moment of inertia. This is only allowed in special cases. In many cases it is too inaccurate and partly even false. This method should no longer be used, because it produces inaccurate results, especially with individual loads (the reaction force at an internal support is an individual load), and if the theoretical solution is applied precisely, it results in wrong normal stresses.In the old KLH approval (old ETA), this unfavourable influence caused by individual loads was already taken into account with the formula for W_eff = 2 x l_eff / h_tot.If we analyse this formula more closely, it turns out to be wrong, because the reduction of the central stress with the γ-value is missing. Therefore, the calculated stresses are higher than the stresses determined with the theoretically correct formula.However, using this “wrong” formula for the analyses of member tests (for the old ETA) yielded a better correspondence with the test results. After all, every bending test was carried out with individual loads. Therefore, the effect of individual loads (higher normal stresses in the areas of individual loads or the internal support) was already taken into account.


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E0, mean............modulus of elasticity of the layers in the structural direction concerned

E90, mean ..........modulus of elasticity of the layers perpendicular to the concerned structural direction, normally E90, mean = 0 MPa

2.1.2 Shear deformations

The shear deformations of the perpendicular layers may be taken into account by application of a global shear modulus. This global shear modulus shall be determined for every cross section either by tests or by calculation. For calculation Annex B of

EN 1995-1-1 is employed, also referred to as �-method. Therein the expression si

ki shall be

substituted by tq

G90, mean · b .

Where

tq .................... thickness of the respective cross layers

b ....................width of the considered strip of the solid wood slab

G90, mean .......... rolling shear modulus

The shear deformation results from the equation

wv = weff - wnet

Where

wnet ................deformation due to bending by application of Inet, pure bending deformation

weff .................deformation due to bending by application of Ieff, bending- and shear deformation

wv .................. shear deformation, thus the global shear modulus can be calculated taking into account a shear deflection constant for the rectangular cross section of 1.2

The global shear modulus is determined with the effective cross section including cross layers according to Figure 7, i.e. Aeff, x = b · heff, x or Aeff, y = b · heff, y

NOTE For the structural direction perpendicular to the cover layers, the cover layers are disregarded for calculation of the effective cross section.

Where

Aeff, x, Aeff, y...... cross sectional area of the layers in the structural direction concerned, including cross layers

b ....................width of the considered strip of the solid wood slab

The global shear modulus, depending on the cross section and on the structural direction, accounting for shear deformation of the cross layers, can be taken to 60 MPa for all types of KLH solid wood slabs; this estimation is conservative.

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The E-modulus of the cross layers can be neglected for verification purposes, and the value of 0 MPa is assumed. In reality, cross layers can still generate resistance. This means it can happen that the slabs are stiffer in the direction perpendicular to the structural direction (cover layer perpendicular to the observed load-bearing direction) than the results from a calculation with l-net. This stiffness, however, will decline over time (shrinkage of cross layers), which is why it must not be taken into account.If we try to slightly bend the slabs during installation, we will notice that the cross layers create considerable resistance.Likewise, any humidity penetration of the cover layer may well lead to considerable deformations of the slab normal to the direction of the cover layer (sources) – depending on the basic stiffness of the slab.

On item 2.1.2:In addition to bending stiffness (l_net x E), the exact calculation of deformations is also significantly influenced by the shear strength. It is determined as G x A in the software programmes.The factor A (cross-sectional area) is a geometric value that is described through the cross-sectional data (slab thickness, etc.). There-fore, the G-modulus still has to be identified as a key value.Only certain parts of a KLH structure consist of cross layers. Therefore, a G-modulus that is assumed as a “joint” modulus (with refe-rence to the gross cross-sectional area of the load-bearing direction) is higher than the G-modulus of the cross layers alone.This means that the G-modulus depends on the structure of the cross section. This opens up a variety of options.We also have to distinguish between longitudinal direction and the direction perpendicular to the structural direction.

One way to determine the joint G-modulus is to make a reverse calculation according to the γ-method. This way a fictitious single-span girder exposed to an even load is calculated. For this static system with an even load, the theoretical solution of the γ-method is very accurate.If the bending deformation (with l_net) is calculated from this result, the “G-modulus” of the total cross section can be determined for this cross section. The l_effective still depends on the length, but no longer on the reverse-calculated G-modulus. This is the way it should be, because now the data can be used in general beam structure or plate structure programmes.

For more complex structures with more than 2 to 3 cross layers, we can also use a simplified FE simulation.

For the calculation of the “joint” G-modulus in dependence on the slab structure, the following formula can be used:

Gges

= 1.1 x (G90,i

+ ( 0.05 x tL x (60 – t

q)) – (10 / n

q) + (10 x t

L / t

q) x ((t

L,Mi / t

L)2 – n

q – 0.75)) in [N/mm2]

G

90,i shear modulus of the cross layer (load-bearing direction normal to the grain) = 50 N/mm2

tL thickness of the edge lamella in longitudinal direction in [mm]

tQ thickness of the cross layer in [mm]

nQ number of cross layers (1 cross layer for 3-layer slabs, 2 cross layers for 5-layer slabs, 2 cross layers for 7-layer slabs with

double longitudinal layers, etc.)t

L,Mi thickness of the longitudinal layer in the centre (= 0 for 3-layer slabs)

The formula is valid for a slab structure with constant thickness of the relevant layers in longitudinal direction or direction perpendicular to the structural direction. Minor deviations of up to approximately 15% of the thickness only have insignificant effects on the overall result. Longitudinal and cross layer thickness values can be varied discretionary (valid from 19 mm board thickness).

Basically, the Gges

-modulus for thicker cross layers will decrease, even if the longitudinal lamellas at the edges are thicker than the central longitudinal lamella (double edge lamellas).If the relation of the thickness values between the individual longitudinal layers and cross layers is equal, this also results in a more or less equal G-modulus.The G

ges-modulus varies between 60 und 220 N/mm2 with conventional member structures (e.g. with 40 mm cross layers). In many

cases, the exact determination of the Gges

-modulus will therefore lead to more economic results. Not only with regard to deformation, but also with respect to the load-bearing safety in case of individual loads/internal supports.

As an indication, the Gges

-modulus can also be determined with the following formula:

Gges

= G90,i

+ (tL/ t

q) x 50 in [N/mm2]

This formula applies for a maximum of 45 m thick cross layers and represents the lower limit (max. 5% undercut) of the G-modulus. The more exact calculation delivers results that can be significantly more accurate.

In a fire, the charring process will produce very thin edge lamellas. With the above formula, the Gges

-modulus can also be determined with sufficient accuracy. Sufficient, because in a fire, the shear modulus only plays an insignificant role. A higher level of accuracy in the determination of the G-modulus will not lead to any significant increase of load-bearing safety.


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2.1.3 Longitudinal stiffness

Longitudinal stiffness to determine deformations in plane of the solid wood slab shall be calculated with the net cross section of the layers in the considered structural direction, Anet, x, Anet, y. I.e. layers oriented perpendicular to the considered structural direction shall not be taken into account, E90, mean = 0 MPa.

Anet, x, Anet, y ....net cross sectional area of the layers in the structural direction concerned, without cross layers

2.1.4 Shear stiffness in plane of the solid wood slab

Shear stiffness to determine deformations in plane of the solid wood slab can be calculated with the net cross section of the layers in the considered structural direction, Anet, x, Anet, y.

In a simplified beam analysis, the shear modulus for the layers in the concerned structural direction shall be taken to GLL = 250 MPa for all configurations.

2.1.5 Bending stiffness for beams in plane of the solid wood slab

The bending stiffness for beams to determine deformations in plane of the solid wood slab

should be applied only for a ratio LH � 4

The bending stiffness in the considered structural direction, E · Inet, z, x, E · Inet, z, y can be calculated with the net cross section of the layers in the considered main structural direction. I.e. layers oriented perpendicular to the considered main structural direction shall not be taken into account, E90, mean = 0 MPa.

2.1.6 Recommendations on Finite-Element-Analysis

Finite-Element-Analysis is a suitable means for design of KLH solid wood slabs if the following items are considered.

Slabs loaded either perpendicular to the plane or in plane of the solid wood slab with a clearly separated structural behaviour, can be considered as orthotropic plate. However, the torsional stiffness shall be limited within the model to 50 % of the total torsional stiffness of the orthotropic plate. For members sensitive to deformations, e.g. cantilever slabs supported on two adjacent edges only, the torsional stiffness shall be reduced within the model to 40 %.

NOTE Suitable means for modelling of orthotropic plates are varying thicknesses or varying moduli of elasticity in the two main structural directions of the solid wood slab.

If combined structural behaviour, perpendicular to the plane and in the plane of the solid wood slab, is to be considered, care should be taken to adequately consider the stiffness according to the Clauses above.

In case the stiffness perpendicular to the structural direction is of unfavourable influence, this effect shall be considered. In all other cases floors and walls may be analysed as uniaxial plate strips.

NOTE Inclined edges above supports shall be carefully considered. Step shaped modelling according to Figure 8 is recommended.

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For this approximation (without claiming to produce 100% exact theoretical calculation results), a value of 60 MPa can be used to simplify the calculation. This way, the influence of shear deformation is taken into account as unfavourable.However, especially with respect to thinner cross layers, the G-modulus will be considerably higher!

On item 2.1.3:For the longitudinal stiffness, the board layers in the load-bearing direction are certainly the ones that are effective = net cross section area.

In reality, even tightly jointed cross layers or cross layers bonded on the edges show a certain amount of resistance. This resistance will, however, disappear over time (boards dry up = shrinkage).Vice versa, if moisture penetrates the slab, considerable deformations may appear, even perpendicular to the structural direction, if the cover layer expands in direction perpendicular to the structure (swelling).Very often, this is the cause of inexplicable deformations of slabs or wall areas.

On item 2.1.4:The shear strength of members regarding stresses in plane (stiffness in plane) is not only dependent on the boards of the observed load-bearing direction. However, the basis is formed by the two net cross-sectional areas/thicknesses of the main load-bearing direc-tions, longitudinal and perpendicular (longitudinal = load-bearing direction; does not automatically have to be the x-direction).In FE software, if KLH slabs are calculated as planes, it is usually possible to put in the thickness of every load-bearing direction (ortho-tropic slab). This software then calculates an internal “comparative shear strength” that applies to both load-bearing directions. The basis is the G-modulus according to table 2 (500 MPa).

For the simplified calculation of members with beam structure programmes, the shear modulus (GLL

) of board layers effective in load-bearing direction can be determined as follows:

G

0,mean Shear module of the boards in load-bearing direction (load-bearing effect in plane: 500 MPa)

tL Thickness of layers effective in load-bearing direction

tq Thickness of layers effective perpendicular to the load-bearing direction

This value may well be double the basis of the G-modulus. This is the case if, for example, the longitudinal layer of a wall is “supported” by two vertical (cross) layers. Exactly when a higher level of stiffness is actually needed.

On item 2.1.5:If the slabs are used as plane-type girders, the calculation results in the form of beam calculations are often merely rough approxima-tions. If the L/H relation is < 4, the slabs should be calculated by way of an FE analysis.The longitudinal stresses usually deviate too much from reality in the beam calculations. An estimation as a beam, without using 100 percent of the bending strength, is always reasonable.

The bending stiffness of plane-type girders for the observed load-bearing direction only depends on the stiffness of the lamellas in parallel to this load-bearing direction (net cross-sectional value).

On item 2.1.6:In principle, the KLH slabs are almost always plate structures. Therefore, an analysis as a beam is only accurate in special cases.This should always be kept in mind.To keep the efforts for the calculation at reasonable levels, a separation between the calculation as a plane or slab should be made. It would be possible to calculate both load-bearing effects together, but this should only be performed by persons who have the approp-riate theoretical background knowledge and who know how to handle the required software.

If the load-bearing effects for the determination of the member forces and moments are separated, even conventional FE software can yield relatively accurate results simply and quickly.The member forces and moments of the different load-bearing directions then have to be superpositioned during the design at the cross section, if required.

For calculations as slabs, the definition of torsional stiffness is also required. It can be assumed with 50%.The torsional moments themselves do not have to be verified separately.For cantilever slabs with high permanent loads (green roofs, etc.), torsional stiffness should be reduced to 40%.


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Figure 8: Modelling of an inclined edge by step shaped modelling

2.2 Long-term deformation

All long-term deformations, bending, axial force and shear shall be multiplied by the factors kdef given in Annex 3.

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H

dh dh

dh

dh

dh � 200 mm

Theoretical member edge for stress verification

The transmission of forces between the board layers in case of stress in plane is very complex, as has been pointed out above. Shear strength cannot be assigned to any defined horizontal joint (as is the case with glued laminated timber).

Therefore, in order to simulate slanted edges, a stepped form should always be chosen.Especially in areas where the verification of the shear force (in plane) can become decisive. For the case depicted in figure 8, for example, the verification of shear forces in plane may only be performed with the height H, even if the cross section at the front edge of the bearing surface is slightly higher.

This perspective (only the two main directions with cuts normal to the main load-bearing directions) is necessary for stress perpendi-cular to the slab as well as for stress in plane.

In case of ceiling edges with slanted edges, shear force problems also have to be taken into account (see also point-supported slab – edge perpendicular to the structure).Since the lowest longitudinal lamella will end at some point on the edge in case of a slanted cut (and if there is no support), the force transmission above to the cross layers on top will be exposed to shear forces.

On item 2.2:The tests have not shown any difference to glued laminated timber. Since the influence of shear deformation is relatively small, inac-curacies also have very insignificant impact.

Long-term deformations also include deformations created in the process of the shrinkage of cross layers, for example (as cover layer). Sometimes a slab is significantly stiffer at the time of installation than calculation results would suggest. As the cross layers dry up, this stiffness will be reduced over time. This means that in some cases deformations may increase significantly compared to the state at the time of installation.Similar to concrete construction, the shrinkage process (or the swelling in case of absorbed moisture) should not be underestimated, let alone ignored. Board layers bonded on the edges clearly react more sensitively than boards with joints, especially if the surfaces are very large.

Unfortunately, the opinion that technically dried wood is no longer subject to shrinkage has spread across the wood construction in-dustry in the last years, or that the effect would at least be negligible and would not appear at all on surfaces of braced bonded slabs (plywood boards). However, this is only the case if we look at the entire slab. This is where shrinkage deformation phenomena (as well as normal temperature-induced deformations) are negligible. Therefore no defined member joints (such as in concrete buildings) are required for KLH buildings.

From a local perspective and normal to the area, the shrinkage may also cause considerable deformations and even create stress within the member itself. In principle, these are “long-term stresses” due to the long-term deformation (shrinkage process).

The left graphic shows boards with a ratio of 2.3 : 1 – the right figure shows boards bonded on the edges.Both parts are exposed to “stress” due to changes in the moisture le-vels of 4%.At the boards bonded on the edges, the shear stress values are about 5 times higher than the limit values. The shear stress also results in high-er normal stress in the central layer.

With regard to board layers bonded on the edges, these normal stress values (in an order of magnitude of 40% of f_c,k across larger lengths) must be superpositioned with the other normal stresses, and their effects must be investigated. In case of narrow boards (edges not bonded), only about 12% of f_c,k work on short sections in case of changes of the moisture levels of 4%.


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3 Ultimate limit state design 3.1 General

Production related constraints, e.g. single boards cut longitudinal in cut outs for openings or the contribution of several layers to the load bearing capacity, should be considered by the system strength factor ksys. Strength characteristics shall be reduced for small members or if only a single layer is loaded in plane of the solid wood slab. They may be increased in case of a larger member or several layers contribute together to the load bearing capacity.

Table 3: System strength factor ksys for KLH solid wood slabs

Loading perpendicular to the solid wood slab

Loading in plane of the solid wood slab

Member width Number of layers System strength factor

b n ksys

b � 20 cm n = 1 0.90

20 cm < b � 100 cm 2 � n < 5 1.00

100 cm < b � 160 cm 5 � n < 8 1.05

b > 160 cm n � 8 1.10

n ....number of layers along the concerned structural direction – actions in plane of the solid wood slab

3.2 Tension along the grain – actions in plane of the solid wood slab

Only layers with a structural direction parallel to the stresses shall be considered. The following expression shall be satisfied:

�t, 0, d � ft, 0, d · ksys

�t, 0, d shall be determined with Anet, x or Anet, y.

For solid wood slabs loaded in plane and with varying tension stresses, the varying parts may be verified against the characteristic bending strength, fm, k.

3.3 Tension perpendicular to the grain – actions perpendicular to the plane of the solid wood slab

Tension perpendicular to the grain should be avoided and should be transferred with fasteners.

NOTE Tension perpendicular to the grain for actions in plane of the solid wood slab may be disregarded.

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On item 3.1:The KLH components are always produced in the form of large-scale slabs (max. 2.95 x 16.5 m). When they are cut to size, the indivi-dual parts are cut out of the large-scale slabs.In this process, it cannot be planned whether individual boards are partly cut or not.

If glued laminated timber (for example) is produced with a cross section of 24 x 60 cm, then the 24 cm wide boards are sorted out beforehand according to the assortment criteria.If the boards are now cut open, it can happen (and it is very likely) that a knot or other defective spots are located in the edge area of the board that is partly cut. This, however, means that the load-bearing capacity of the board will be dramatically reduced.In case of glued laminated timber, for example, a cross section that is produced as GL32 must not be used as GL32 quality as soon as it is cut open. The quality rating must be lowered by at least one category (GL32 cut open will become approx. GL28).

The situation with KLH members is quite similar.

This figure shows a slab section with a board that is cut on the edge.If this edge contains knots that are partly cut, the load-bearing capacity of the originally assorted board no longer applies.

Since, however, the boards can be positioned adjacent to each other, the “neighbouring” boards can support the weaker boards on the edges.There are other additional advantages created by the braced slab structure (cross layers) and other effects, so that slab strips with a width of ≤ 20 cm will not demand a higher reduction of their normal load-bearing capacity. A reduction to 90% of the original value will be sufficient.We find similar conditions if the slab is used as a plane. In this case, the width of the member is not the crucial figure, but the number of board layers in the same load-bearing direction. These reduction factors were identified on the basis of 300 tests. They also include a number of other effects (both favourable and unfa-vourable ones). It is therefore in no way advisable to transfer them to any other construction material or product!For KLH members, no other favourable effects may be taken into account, such as volume effects or height effects, etc.

On item 3.2:In case of mere tensile stress, the longitudinal layers are most exposed, especially if they are planes with narrow residual cross sections.If the residual cross sections are stressed on several axes, it is recommended to use the k_sys factor for every direction that is exposed to stress.Dealing with such highly stressed residual cross sections, it is also advisable to reinforce them with steel elements, even if it is not requi-red according to calculations, because wooden building components can easily be cut in two at construction sites by staff not familiar with the required expert knowledge in this field (fitters who need space for their installations, etc.).

In case of a varying tension curve, only the tension in the focus point must be verified with the lower tension value. The varying part can be verified with the design value for bending stresses.

On item 3.3:Due to the shrinkage process, relatively high shear forces perpendicular to the grain can form at bonded joints over time. Therefore, this tension form should not be fully exploited. If it is possible, it should even be avoided (and this is almost always possible).Self-drilling full-thread screws allow a transmission of forces in a simple way. Any joint action of wood and screws should, however, not be assumed.

As regards the determination of shear forces perpendicular to the grain (for wind and other short-term loads), the same procedure should be applied as for glued laminated timber. Three-dimensional load distributions may be taken into account.A 100% usage of shear force strength potentials is, however, not recommended.

Minor permanent loads (claddings, etc.) are certainly allowed, as long as they are evenly distributed. Higher local loads are more proble-matic, though.


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Only short term tension forces, e.g. wind loads, shall be applied perpendicular to the solid wood slab. The following expression shall be satisfied:

�t, 90, d � kvol · ft, 90, d

The volume factor kvol may be considered in analogy to glued laminated timber according to EN 1995-1-1, taking into account the penetration of the fasteners. Three dimensional effects, spreading of loads, may be taken into account for �t, 90, d.

3.4 Compression along the grain – action in plane of the solid wood slab

Only layers with structural direction parallel to the stresses shall be considered. The following expression shall be satisfied:

�c, 0, d � fc, 0, d · ksys

�c, 0, d shall be determined with Anet, x or Anet, y.

The stability of members may be accounted for with a second order linear elastic analysis. Shear deformation shall be taken into account. The analysis and verification shall be performed using the 5 %-fractile values of the stiffness properties E0.05 and G0.05. The value

for the initial deflection of a member shall be L

400 and covers long term deformations.

The stability of columns subjected to compression should be verified in accordance with EN 1995-1-1. Shear deformation shall be taken into account in the calculation of the slenderness ratio. The imperfection factor �c may be taken to 0.1 and the factor for redistribution of bending stresses km should be taken equal to unity.

The stability of at least 300 mm wide solid wood slabs loaded in plane with non-uniform compression stresses, may be verified with the stress value in a distance of 100 mm from the edge of the member. This takes into account the stabilising effect within plate structures.

In addition to stability for members with low slenderness ratio stresses shall be verified.

For members small in width, stability in plane of the solid wood slab shall be taken into consideration.

3.5 Contact compression along the grain – actions in plane of the solid wood slab

The following expression shall be satisfied for contact compression stresses:

�c, 0, d � fc, 0, d · kc, 0

�c, 0, d shall be determined with Anet, x or Anet, y. For layers of board or wood based panels, except OSB and LVL, the value for kc, 0 can be taken to

kc, 0 � 1.5........ for support or load introduction in a distance a � H2 or a � 500 mm (the

smaller value is decisive)

kc, 0 � 1.9........ for support or load introduction in a distance a > H2 or a > 500 mm (the

smaller value is decisive)

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On item 3.4:The longitudinal tensions in the direction of the grain must always be superpositioned with all other longitudinal tensions (e.g. bending pressure from slab effects).

In principle, almost all construction components of building constructions (with the exception of members under tensile stress) are ex-posed to some stability risks. Stability risks are created by compressive forces. Compression forces in walls and supports are created by vertical, permanent and varying loads.However, it must not be overlooked that buildings are also exposed to horizontal loads. This includes such forces as wind and earth-quake loads, but also stabilising forces created due to permanent loads.Even in case of fire (if only minor useful loads or usually no snow loads must be taken into account according to EN), normal forces always appear in the form of compression forces (due to the permanent loads and the share of the useful loads).Every wall that is assumed as supported by a hinge at the floor and ceiling areas will create horizontal force components in the level of the ceiling.These forces are partly minor and can sometimes even be neglected. In principle, however, it must not be assumed that these forces can always be neglected for plywood constructions.

The stability can be verified with the formula sets of the EN 1995-1-1 clause 6.3. For the E0,05

-value the value Eequiv.member

should be used (E

equiv.member = 0.95 x E

0,05 ; Eequiv.member = E-modulus for the equivalent member method).

The reason is that a verification with the equivalent member method and with the actual E0,05

-value according to table 2, footnote 3, will produce values that are too high compared to a more precise calculation according to the theory II order. Therefore I recommend not to use the method of the EN 1:1!The influence of the shear deformation, however, can be overlooked if the E

equiv.member value is used for the equivalent member method.

With this reduced E-modulus, such effects as creep and pre-deformation (unilateral shrinkage) of plywood members are all taken into account.Alternatively to the EN method (equivalent member method), the calculation can also be performed according to the theory II order.For this purpose, using the confirmed E

0,05-value is admissible.

The pre-deformation mentioned in the ETA is based on an examination of KLH constructions. Apart from influences from unequal drying processes and moisture level differences of the cover layers, creep influences are also significant factors.With the method according to the theory II order, even three-dimensional effects can be taken into account (bumps). It must be taken into account that an unfavourable deformation state is assumed by default. Usually there are several cases that have to be examined. The statement that the buckling analysis does not have to be carried out with the maximum value of the bending compression stress but with a reduced value (compression strength of 10 cm away from the edge) for slab strips with a minimum width of 30 cm is based on these three-dimensional reserves (buckling also takes three-dimensional effects into account and therefore allows slightly higher stress levels).This effect can certainly be even stronger, in which case, however, it has to be verified more precisely. The significant element is the stiffness of the slabs in both main directions. Shear deformation only plays a minor role. Torsional stiffness should be assumed with 10%.In case of members exposed to stability risks, the least favourable (most extreme) case must be assumed in any event.

On item 3.5:During the test analysis, a very positive effect was found for the KLH effect regarding structural behaviour in the plane. The compres-sive strength in the direction of the grain at the load introduction points was extremely high in parts – the multiple factor of f

c,0,k. This

effect was therefore more closely examined, because wood slabs loaded in plane usually are exposed to very high support forces that must be transferred to smaller areas.It was found that the cross layers have a stabilising effect that compensates most of the causes of failure at knots, slanted grain, etc. The tests showed mostly simple stress accumulation breakages.

It is important to note that these strength levels are directly related to the verification process for shear loads (failure due to shear stress), and that this hardening effect is exclusively observed with boards directly adjacent to the cross layer.The outer layers of double edge areas must not be loaded with increased compression strength levels.

The photographs show the accumulation breakage in the lower cross-sectional area. The shear force is transmitted from the lon-gitudinal layers to the vertical board layers, from where it is deflected across the contact surface. Layers in the structural direction have only limited effect in support areas.The load/deformation curves show pro-nounced elastic-plastic behaviour in the event of failure.


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Where

a ....................distance from the edge of a concentrated load to the closest end of the member in mm, see Figure 9

H....................member height in mm

kc, 0 greater than 1.3 is only applicable for end grain to steel contact. In slabs with more than one cover layers, a maximum thickness of 45 mm of the cover layer shall be considered in calculating Anet, x or Anet, y.

Figure 9: Geometry of load introduction

The capacity of the adjacent members (e.g. timber, concrete, or masonry) shall be verified. The distribution of stresses shall be determined taking into account the slab rotation and the compliance of the adjacent member.

The minimum bearing length LA shall be 50 mm. For determination of the contact areas only layers with end grain perpendicular to the contact areas shall be considered, tnormal according to Figure 10.

Figure 10: Bearing width and contact area

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In calculations, only the cross grain areas can be taken into account as contact areas. The load share of the horizontal layers in the structural direction (in this case) is relatively small, and due to the shrinkage process these layers lose contact with the support sur-face. After a certain period of time, the horizontal layers have no contact anymore. Therefore, only the vertical board layers with the grain direction normal to the contact area are effective (= calculated areas).The shrinkage process in local measurement situations is omnipresent. Only globally, with reference to the entire slab, can this effect be neglected.

The tensions in the contact area are very high. In case of concrete or wood contact areas, the thinner cell walls press into each other, resulting in slightly higher deformations.Therefore, higher loads can only be transmitted through steel plates.

The use of sheet steel is very reasonable, because with various different applications, wall elements are connected in normal position to each other. In this case, the contact area should also be as short as possible.Otherwise the connection detail will determine the wall strength. Details with e.g. additional members (e.g. screwed on steel angles) often generate excessively large eccentricities in the cross wall (additional bending moments, etc.). It is important to introduce high loads into the centre as much as possible!

The figures show a wall that is connected to the cross wall with a pin.For vertical loads, the connection will work in both directions. The cross wall can now be used as a wall plane, for example (above or below the connection opening the cross section is not weakened).

In addition, KLH walls do not have any shear force pro-blem with this type of load introduction, because the vertical layers in the cross wall act as “shear force re-inforcement” and will usually lead the loads to the top within the wall without any problems.

This figure shows a classic corner connection for canti-levered building parts.

Apart from the steel plates in the contact area, there are no other steel parts. Fire protection is optimal.

The connection can immediately be exposed to full loads. No extra supports are therefore required during installation of the cross wall.

In these cases, the board layer directions cross in the contact area. If no steel plates are used, only the contact areas of the end grains that have direct contact with each other can be exposed to loads. If an approximately 10 mm thick metal plate is used, however, the entire end grain area can be assumed as contact area. In cases of loads at an angle to the grain direction, the procedure according to EN 1995-1-1 (6.2.2 (2P)) can be followed. For pressure resistance in the direction of the grain, the increased local value (f

c,0,d x k

c,0 ) can be used.


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The contact areas of two KLH solid wood slabs in direct contact at their edges are the end grain to end grain contact areas only. If a rigid load distribution plate is placed between the two solid wood slabs, the full end grain contact areas of both solid wood slabs, i.e. Anet, x or Anet, y, can be taken.

3.6 Compression perpendicular to the grain

The following expression shall be satisfied:

�c, 90, d � fc, 90, d · kc, 90

�c, 90, d may be determined with Ac, 90 and kc, 90 should be taken to

kc, 90 = 2.2 ........ for support or load introduction at the end of the member

kc, 90 = 3.0 ........ for contact areas with very small rotations, e.g. internal supports of continuous slabs with constant spans

The determination of the contact areas Ac, 90 shall take into account:

Ac, 90 is the contact surface of KLH solid wood slab to timber, steel, or concrete. In the case of contact to the edge of a KLH solid wood slab, e.g. contact from wall to floor, Ac, 90 should be calculated with the effective width, beff, x or beff, y, to Aeff, x or Aeff, y, see Figure 11. For verification the complete contact area may be taken into account, assuming a uniform stress distribution. Rotations of the members at the contact area may be neglected.

Figure 11: Effective bearing width for determination of contact area

3.7 Compression at an angle to the grain

The design compressive strength fc, �, d at an angle � to the grain shall be determined in accordance with EN 1995-1-1.

The angle to the grain is to be considered in determining the contact areas. For a wide angle �, the cross layers may be taken into account. Thereby it shall be verified that the load can be uniformly transferred.

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In principle, the same applies to many other cases as well.At such contact areas, various tolerances must also be balanced. For this reason alone, metal plates (load distribution and tolerance compensation) are reasonable.

On item 3.6:With the grain, KLH boards react similar to solid wood or glued laminated timber.The KLH constructional design also has some special characteristics that are included into the calculation through the coefficient k

c,90.

These coefficients still must not be transferred to solid wood or glued laminated timber in any event.

In general, pressure forms between KLH members only directly through the end grains and through the cross layer areas surrounded by end grain areas and located in between.

For verification, the entire area can be used if an equal distribution of stress can be assumed. Uneven distribution of stress does not have to be assumed.This, however, only applies to supports of ceilings on KLH walls or slim supports (which is mostly the case).

If the members (ceilings, roof slabs) are placed on stiff members such as concrete ceilings, concrete walls, etc., a verification of com-pression normal to the grain with variable stress distribution is necessary.

In figure 11 – to the right – a situation is depicted where a ceiling rests on a wall with horizontal cover layers. Due to the shrinkage of the boards it can happen that the contact between the horizontal cover layers of the wall and the ceiling element gets lost at some point in time.This also happens with the horizontal layer inside the wall slab. There, however, the fact comes to bear that the local compression directly in the contact area can be slightly higher for very small contact areas (if only the net area of the vertical board layers is taken into account) if the compression can subsequently be distributed over a larger area.

If the horizontal inside layer, however, has a thickness of more than 45 mm, this simplified verification should be adjusted. The horizon-tal board layer (or double layer) can only be taken into account with a maximum of 45 mm of thickness.

On item 3.7:In principle, it is possible to proceed in the same way as for solid wood or glued laminated timber.In case of a load introduction of single loads (e.g. individual supports) at an angle to the slab level, it must be ensured that the right areas and stresses are used for the verification against “shear” forces.It must be assumed at any point that there are joint gaps between the boards. This means we must always assume shear areas that are parallel to the slab plane level.Furthermore, the further transmission of the shear forces to the next cross layer must be examined as well.

In most cases this means that – for these types of connections (e.g. identification of the required wood protrusion length in case of load introduction at an angle) – the shear stress normal to the grain (rolling shear) is decisive.


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3.8 Bending perpendicular to the plane of the solid wood slab

Shear deformation shall be considered in determining bending stresses. The following expression shall be satisfied:

�m, d � fm, d · ksys

In a simplified stress analysis for members with a slenderness ratio Lh > 10, and by

neglecting shear deformations, the design stresses shall not exceed a percentage �M of the design strength.

�M � 90 % ........ within in the span

�M � 70 % ........ close to supports and concentrated loads

More accurate methods for the determination of stresses take into account the shear deformation and are e.g.: Finite-Element-Analysis, the shear-analogy-method, or other specific correction methods.

Superposition of bending stresses resulting from bending in both structural directions is not required, since in both structural directions different layers are stressed. Twisting moments, mxy, resulting from two-dimensional analysis need not to be verified.

3.9 Bending in plane of the solid wood slab

The technical bending theory may be applied to beams with a slenderness ratio of Lh � 4.


�m,d � fm,d · ksys

�m,d may be determined by application of Wnet, z, x or Wnet, z, y.

Wnet, z, x, Wnet, z, y .........section modulus of the layers in the structural direction parallel to the span

Superposition of bending stresses resulting from bending in both structural directions is not required, since in both structural directions different layers are stressed.

3.10 Superposition of normal stresses

Normal stresses in the same layer and of the same structural direction resulting from different actions shall be added for verification, see Figure 7.

3.11 Shear perpendicular to the plane of the solid wood slab

The crack factor kcr according to EN 1995-1-1 is to be taken equal to unity. The following expression shall be satisfied:

�v, d � fv, R, d · kv

fv, R, d...............design rolling shear strength, characteristic values according to Table 4

kv ................... factor taking into account notches or areas with similar failure modes, see Annex 4, Clause 3.12

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On item 3.8:In case of loads perpendicular to the slab level, shear deformations form in addition to bending deformations. These and other effects generate additional stress in the structural direction of the layers that become significant in edge areas.These additional stresses due to shear deformation can be neglected if the conditions of the practical construction situation is simple (e.g. single span girder under even load).If thick slabs are used on short spans, the stress levels will be higher, but the loads relevant to practical construction work (maximum surface loads of 10 kN/m2) are not significant. Therefore, verification with the net cross section will be sufficient in 99% of all cases.The situation is slightly different with single loads, and any intermediate support of a continuous girder is also regarded as a “single load”. Along the shear deformation line, “theoretical buckles” appear for single loads. These buckles are impossible in nature. Such irregularities, however, are the main reason for the local increase of stress along the normal stresses due to the additional bending of the layers in the structural direction.In normal cases, these additional stresses are not significant, because ceilings are usually not used to a high degree. It is mostly the deformations that are significant. Therefore, the percentages of the design strength are quoted here, up to which the effect of the additional stress due to individual loads (interim supports) will not be significant.

The effect can, however, also be determined more precisely. The most precise method would be an FE model (the longitudinal slab section is simulated as a plane) that also includes a precise registration of the conditions of storage and the load introduction (above non-linear springs), in order to identify additional bending strength due to shear deformation fairly exact. The problem is that this me-thod is rather complex.

A useful approximation – to be on the safe side – can be seen in the formula below. The additional stress can be determined for each direction and every edge lamella (which is why this is suitable for FE results), depending on the thickness of the layer in the structural direction, the number of cross layers and the strength of the single force or the force on the support:

[in N/mm2] ………… additional normal stress at line loads or single loads for b = 100 cm due to shear deformations

Warning: The formula includes various KLH-specific key data and system-related characteristics and is therefore not “generic” in terms of its units. This applies not only to the influence of the shear deformations of cross layers. In the KLHdesigner, these additional edge stresses are calculated with a more precise method, and the results are more accurate in some cases.

t ra

Thickness of the edge lamella or total thickness of e.g. double edge lamellas in load-bearing direction in [mm]n

q Number of cross layers

G q Shear module of cross layers in [N/mm2]

F Single load or force on the support in [kN]

This way calculations can be performed with net cross-sectional values (deformations and stresses). They do not depend on the length. The influence of single loads (shear deformations and other effects) can be verified locally with the mentioned formula. Basically, this formula can also be used for point supports or point loads, and the force F must be split up into 2 components. The force F basically equals the value of the “shear force leap” in the shear force trend. In case of a beam-type view, this is the value of the individual load or the force on the support. As regards point loads, the shear force trends should be determined with an FE calculation (calculation as orthotropic slab).

Note on alternative calculation methods:The shear analogy method or the calculation with layered FE models is only more precise under certain conditions and only for specific framework conditions. These framework conditions, however, are not known exactly and have not been determined for KLH members.

On item 3.9:The most precise results can be gained with an FE modelling as an orthotropic slab. Nevertheless, the results still have to be interpre-ted by an engineer, which requires a certain level of experience and background knowledge. At local points, FE calculations can often yield extreme stress peaks that do not happen in this form in reality. It is always a question of how precisely the model was formed.

Most of the time, residual cross sections are designed as beam-shaped members over windows and doors. Then we get the usual moment depictions and stress distributions. In any event, it must always be kept in mind that the storage conditions (the degree of restraint in the full wall areas) must be recorded accurately. Alternatively, the calculation can be regarded as a rough estimate, which is acceptable if the intention is to not use the stress levels to the fullest extent. It is also always a question of how precisely the model was formed.


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Table 4: Characteristic values of rolling shear strength

Thickness of the cross layer Ratio

width of boardthickness of board

characteristic rolling shear strength

tq fv ,R, k

mm �

MPa

� 4 : 1 tq � 45 mm

� 2.3 : 1 1.2

tq > 45 mm � 2.3 : 1 0.8

�Figure 12: Shear stresses resulting from actions perpendicular to the plane of the solid wood slab

Figure 13: Effective height for calculation of shear stresses �

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On item 3.10:The normal stresses in both main load-bearing directions do not have to be superpositioned, because different board layers are stressed. Normal stresses in one of the main directions from different loading situations (slab and plane loads), however, must be superpositioned.Likewise, intrinsic stresses due to long-term behaviour – the shrinkage of board layers – must also be superpositioned. As regards board layers that are not bonded on the edges, these stresses are locally limited and very small, which is why they can be neglected.

On item 3.11:The wording “shear normal to the slab level” is a bit confusing: what is actually meant is the shear stress due to a load that works normal to the slab level.After all, shear stresses do not only form normal to the slab level, but also parallel to the slab level.

For the shear verification, the verification procedure of the old ETA was modified.In the old ETA, the full cross section (A_eff in load-bearing direction) was always used for shear verification. Therefore, the tests were also analysed with this cross-sectional value, which resulted in the characteristic strength value of 1.5 N/mm2.

The verification process for bending stresses, normal stresses, etc. should, however, always be performed with the net cross-sectional values. Therefore, the net cross-sectional values are now taken even for shear verification. In terms of the calculation, this yields slight-ly reduced shear strength values.

The values were determined for the extreme b/t ratio of 2.3 : 1 (from tests). Furthermore, also for thicker cross layers up to a total strength of 90 mm. This thickness may also be produced with 3 layers of 30 mm each.The position of joints (= possible shrinkage cracks) is irrelevant here. The most unfavourable conditions were tested (see also figure on page 27).

Since the characteristic shear strength values normal to the grain are smaller than those in the direction of the grain, the cross layer that is closest to the centre of gravity is always decisive. It does not always have to be a layer in the middle of the cross section.If we were to place double layers in the structural direction inside the cross section on purpose, this could yield an advantage.

Single loads close to supports:The verification procedure must not include any reduction for single loads in areas close to supports.Stress due to shear forces only results in “theoretical” shear stresses used as verification basis for practical building design purposes. In reality, the breakage is induced by shear stress or shear effects in cross layers. In these processes we sometimes observe breakage points that are almost vertical, i.e. it is possible that higher shear pressure does not lead to higher loads in horizontal joints.

The tests have shown a slight increase in the “theoretical” shear stresses, but not to the same extent as we see it in solid wood or glued laminated timber.For the sake of simplicity, the ETA only states one single shear strength value for cross layers or a reduced value for cross layer thick-ness of > 45 mm (= total thickness of the boards in the same load-bearing direction).In reality, the load-bearing resistance in case of shear force stress (verification in the form of “theoretical shear stresses”) not only depends on the position of the load introduction, but also on the thickness of the cross layers.If higher shear strength values should result in a more economic design for special applications, then an approval for such individual cases or an expert report on the basis of test results can be issued for relevant specific projects.

As an orientational value, 1.4 N/mm2 can be used for 19 mm thick cross layers (no double cross layers).Interim values can be interpolated linearly.For an expert report to verify an individual case, a concrete project is required or the course of action must be clarified with the respon-sible stakeholders (inspector, authorities, structural engineer).

The decisive areas for verification are of course only the slab areas in the structure that are enclosed by the outer layers in structural load-bearing direction.This results in a lower load-bearing member thickness (“effective height”) for the weaker main load-bearing direction (the y-direction).


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Shear stresses can be determined by application of Inet and Snet, not taking into account shear deformation. In general, layers with orientation perpendicular to the structural direction concerned, rolling shear strength fv, R, are governing.

NOTE If the effective cross section, heff, comprises only one layer, the shear strength fv according to Table 2 is applicable.

The design shear stress is calculated with

�v, d = Vd � Snet

Inet � b

Where

Snet................. static moment of the respective part of the net cross section

Inet ..................moment of inertia of the net cross section

Snet and Inet are calculated by disregarding the layers perpendicular to the structural direction concerned, i.e. E90, mean = 0 MPa

The characteristic value of rolling shear strength in a single or a multiple span slab shall be reduced to 0.8 MPa for the proportions of the shear force resulting from a concentrated load acting in the central third of the span. Interim values may be calculated by linear interpolation according to Figure 14.

Superposition of shear stresses resulting from both structural directions is not required, since in both structural directions different layers are stressed.

Figure 14: Characteristic values for rolling shear strength for shear forces resulting from

concentrated load close to mid-span

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concentrated load

uniformly distributed load

load arrangement:

fv,R,k = 1.2 MPa fv,R,k = 0.8 MPa

span L

L/6 L/3L/6 L/6 L/6

The shear deformation itself has no influence on this verification process. The unfavourable influence of high single loads is subject to separate consideration.

Unfortunately there is also one negative effect that was observed during tests: single loads in the central third of the field have shown partly lower shear load-bearing capacities.These are unfortunately not “statistical exceptions” – the effect was observed in various different test series.

In practical work, this can become significant for continuous girders or in cases where the deformation is not the decisive design criterion.The reduction is approximately 33% (from 1.2 to 0.8 N/mm2), which means that even with a maximum usage of the shear verification, there is no need for action. The effect needs no closer consideration.

The causes of this effect are the larger member lengths combined with higher shear force stress. This increases the likelihood that there will be a weak point along this length, and there can be no redistribution to cross layers before or after the area with high shear forces.A certain influence can also be observed due to the single load itself (stresses due to the influence of the shear deformation directly in the area of load introduction). However, breakages at the end of the slab (far away from the single load) were also observed.

The depiction in the ETA unfortunately does not show all possible practical building scenarios.The following description is probably more accurate: in principle, we can speak of a sort of “shear force saturation” if there are areas with higher and relatively constant shear force acting over a length of 12 x the slab thickness. In this case, the reduced value of the characteristic shear strength normal to the grain should be used in this area.With this determination, other areas than the system depicted in figure 14 can also be assessed.


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3.12 Shear perpendicular to the plane of the solid wood slab – Notches

To take account for notches or support details similar to notches, e.g. edges subjected to shear forces at a partly unsupported edge, the effective cross section heff, red shall be determined according to Figure 15 and Figure 16. The notch factor kv shall be determined according to EN 1995-1-1, with kn = 4.7 for KLH solid wood slabs. The notch inclination i shall be taken to zero in any case.

Figure 15: Reduced height, heff, to account for notches

Examples of typical notches, including notches from connections with fasteners, are given in Figure 15. In connections with wood screws, the width of the cross section shall be taken as the centre spacing of the screws, however not large than heff, i, red.

Edges which are supported only in part shall be considered by a notch.

Figure 16: Left – partly supported edge – edge perpendicular to the cover layers

Right – partly supported edge – edge parallel to the cover layers

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On item 3.12:The wording “shear normal to the slab level” is not ideal. What is meant is the shear stresses due to loads acting normal to the slab level (slab structural behaviour).

It happens frequently that slab edges are produced with rebates. Especially the connection of the slabs can be made in an optimal form with regard to the plane structural behaviour (force transmission in longitudinal direction of the joint).

Furthermore, a failure mechanism was observed with point-supported slabs. It must be covered with a verification as a support with notches.This contradicts the information under point 3.3 (shear stress), according to which shear stress should be avoided.

Shear stresses build up at every notched support, but they are included in the verification and are therefore covered.

However, it is not feasible to reinforce these member situations with full-threaded screws all the time and in all cases. An estimate of the consequences of a possible local shear stress breakage may be helpful.

Due to uneven loads in case of failure, the shear stress perpendicular to the grain at a step joint will normally only lead to a load redis-tribution.The local failure of a linear support will also not lead to total failure.As regards the support situations according to figure 15 – at the upper two drawings – I would still recommend a 100% shear force protection by way of full-threaded screws for the situation on the right-hand side.For the situation on the left, I would recommend the same if the usage of the notch is high. I would not make this recommendation if the usage is low. The other figures also have to be interpreted in this respect.

The verification should also be used to provide engineers with a calculated tool that can handle a large number of practical cases.The recommendation to realise a shear stress protection for sensitive members (even if it is not required according to the calculation) still stands!

As regards slab edges without any direct support, where the lowest lamella acting in the load-bearing direction is also the lowest cover layer (see figure 16, left image), the shear force is transmitted into the lamellas of the other load-bearing direction positioned on top.In principle, this leads to a notched support and subsequently even to one more shear stress load for the weaker load-bearing direction.

This situation occurs with all slab edges cut at an angle, at point-supported slabs or even with ceiling slabs that merely rest against the wall edges.

The verification is performed similar to solid wood or glued laminated timber. The k_n factor for the verification is quoted.

In addition to the information stated in the ETA, the following must be taken into consideration: if the formula according to EN 1995-1-1, point 6.5.2, is used, unrealistic k_v values will result if x = 0 (according to figure 16) is used for extreme conditions (= low residual cross sections). If, however, a minimum value of x = 20 mm is assumed for x in general, then there will be additional safety compared to the tests as well as realistic reduction factors (k_v) for extreme “notches” (e.g. with 3-layer slabs). For residual cross sections (h_ef), a value of 1.5 MPa can be used for the “full cross section (w x h_ef) in general – this also takes the k_cr factor into account if only one lamella (= solid wood) is left for h_ef (which of course only applies to cross layer thickness values of < 45 mm).In this context I repeat my recommendation to choose a residual height (h_ef) that shall be no smaller than 25% of the total height. If it is still smaller, shear force protection should be mandatory (full-threaded screws).

These two images show the failure mechanism during tests at point-supported slabs.The breakage starts from areas directly adjacent to the support. Since the bending resistance grows to a maximum towards the support, this area will absorb most of the stress

Kommentar zur ETA-06/0138 von J. Riebenbauer

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Shear forces of unsupported edges close to point supports may be determined in a distance e, see Annex 3, Clause 3.13, away from the support.

In reinforcements perpendicular to the grain, e.g. by fully threaded self tapping screws, the total shear force is to be covered by the reinforcement elements. The screws shall extend down to layers below heff, red, with a minimum pointside penetration in the layer of 2 � d. The part of the cross section between the point of the screw and the surface of the solid wood slab shall be verified as a notch.

Where

d ....................nominal diameter of the wood screw

3.13 Shear perpendicular to the plane of the solid wood slab – Point supports

For solid wood slabs stressed in both structural directions, different stiffness for these two directions shall be considered.

Point supports and linear supports may be modelled as points and lines. This inherent gives close to that point or line distorted results. For shear stress verification the stresses in a distance of e = 0,5 � h away from the edge of the supporting member may be applied, see Figure 17. A uniform distribution of shear stresses may be assumed in each cross section. The total reaction force at the support may be distributed proportional to the shear areas in the two structural directions, see Figure 18.

Reductions in the cross sectional area, e.g. holes, or drill holes, shall be taken into account if they are within the distance e, see Figure 17.

Figure 17: Relevant cross section for calculation of shear stresses close to point supports or concentrated loads

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The tests were cross-checked with FE software calculations (orthotropic slab). For the analysis, the shear force line in a cut adjacent to the support (with a distance of e according to fig. 17) was determined. Subsequently the k_n value for the design was extrapolated from it.

Therefore, the cuts also have to be made adjacent to the support for the mathematical verification.

Shear force lines directly through the point support (in FE programmes, slabs are almost always point-supported) are often not very informative, because there is no real “point” in nature.

On item 3.13:The possibility to realise point-supported slabs, or slabs that only rest partly on wall edges, is a great advantage of KLH slabs.Therefore, tests regarding the design of these areas were also performed.

An important verification part is the proof of the “notched support” as described in the previous chapter.

Shear force protection is not necessary for point-supported slabs, even if the degree of usage is high, because the forces can redistri-bute. Despite local shear force failure in one point, the slabs can continue to bear loads.

For verification, the areas depicted in figures 17 and 18 can be used.The verification can be carried out at a distance e from the support edge.Cross-sectional weaknesses in this area (between the support edge and a distance of (2 x e) to the support edge) must be subtracted from the verification areas.

Due to the different stiffness values of the slabs in the two main load-bearing directions, the shear stresses in the individual load-bearing directions are not easy to estimate.

The following procedure is recommended:Calculation of the slab share with an FE programme (orthotropic slab) with point supports.This will achieve the force required.

If cuts are subsequently made through the point support – in the direction of the two main load-bearing directions – the maximum shear forces (in kN/m) per load-bearing direction and per side (for edge supports this results in 3 shear forces and 3 connection areas; with inside supports 4 shear forces and 4 connection areas) can be determined.These shear force lines vary even perpendicular to the cutting line. Due to inaccurate modelling (point as support) they do not depict reality.

The force at the support can, however, be split up in the relation of these “maximum” shear forces (per connection area).

This yields the shear force per connection area that is decisive (and realistic) for verification.The effect of different stiffness levels in the two main load-bearing directions is included relatively precisely. And this is what it is about.Because a calculation with factors, as is common with concrete constructions, will not produce relevant results. In addition, failure does not mean punching (as in concrete constructions), but it is a mere shear failure.

This picture shows a failure situation after the breakage. The tests show that the force at the support splits up in shear forces per connection area according to the distribution of the stiffness in the main load-bearing directions. However, the stiffness conditions cannot be determined sufficiently accurate with the slab key data. It always requires the inclusion of the system effects.Therefore simplified formulas for shear verification – with factors for the position within the building, such as in concrete construction – are not possible.


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Figure 18: Relevant cross sections for shear stress verification – example of a point support at a

corner

3.14 Shear in plane of the solid wood slab

Shear forces in plane of the solid wood slab are to be transferred to a large extent in the contact areas between the crosswise arranged layers. These glue lines are parallel to the direction of the force and hence a reduction of the shear force is not to be applied, i.e. the full shear force has to be taken for verification.

3.14.1 Slabs with general loading situation – verification of shear flow

For in plane shear forces without distinctive loading direction the following expression shall be satisfied:

tv, d � fv, K, d

The design shear flow tv, d may be determined by application of LK.

tv, d = nxy, d � 1

LK

LK................... total glue line length between adjacent, crosswise arranged layers, where LK = nK · H

H....................design-relevant member height in mm

nxy, d ...............design shear force per unit of length resulting from e.g. an Finite-Element-Analysis

nK...................number of gluelines between adjacent, crosswise arranged layers in the respective cross section

Normally H is to be taken to unity and tv, d = nxy, d

nK applies.

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Figure 18 shows the two “connection areas” for shear verification.

With the FE model, only the corresponding shear force components (= share in the total force at the support) must be determined.

On item 3.14:In “conventional” wood construction (beam-shaped members), shear forces are mainly transmitted through areas normal to the shear force. This is the case, because such joints in grain direction become decisive in case of failure (left figure).

The left figure shows a glued laminated timber part with the probab-le failure joint (horizontal, normal to the shear force).

The right figure shows a KLH member exposed to a plane structural behaviour.The decisive failure area is vertical and is located in the area of the bonding joints of crossed board layers.

With plywood constructions, the situation is entirely different in principle. The decisive cause of failure is found in a vertical area run-ning parallel to the plane area or parallel to the shear force.There is also a direct connection to the compression of the end grain (pressure in grain direction) at the point of load introduction.

Since the load introduction on smaller areas is crucial for slabs loaded in plane, only very slim support areas were used in the tests (see also point 3.5).Therefore, if the support areas are larger, the loads may be higher for various slab types.

Since the failure area is positioned vertically, the reductions for single loads close to the support must not be applied.

The following can be said about the test results:A clear linear connection between the shear force and the cross section height was found. However, no direct connection to the stress line – that varies with height – was found. The breakage cannot be assigned to any member area (regarding its height). The maximum stress is not necessarily found at half the height.The tests have shown a dependency on the number of bonded joints between crossed board layers.

The verification of shear flow – instead of shear stress – is likely to be the more reasonable option.

Therefore the verification – as general “basic verification” – is performed as shear flow. The shear forces can be taken from FE calcula-tions (orthotropic slabs) and verified across the entire length of the bonded joints of crossed board layers.This verification is independent of the shear force direction and can therefore be used as conservative value for general FE analyses for verification purposes.

It can, however, not be used to determine the potential loads for special stress situations (they are higher than the results from the shear flow verification). Therefore, there is another option, which is a verification based on “theoretical shear stresses”.

It is called theoretical because the load-bearing behaviour in case of a breakage is very complex. It should more accurately be referred to as “shear force verification” than “shear stress verification”.However, the shear stress verification is generally accepted, and many software programmes perform this verification automatically. Therefore this method was selected.


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Figure 19: Verification of shear forces in plane of the solid wood slab – shear flow

NOTE Design shear forces, as a result of a Finite-Element-Analysis, are related to a

specific unit of length, e.g. kN/m, so H shall be in relation to this length.

3.14.2 Solid wood slabs as beam – verification of shear stress

Members or parts of members with a distinctive loading direction, even for LH < 4, may be

verified by shear stress analysis. A distinctive loading direction can be assumed, if the layers perpendicular to this direction are nearly unloaded or if their main purpose is the coupling of the adjacent layers. This is applicable for most beam like members, e.g. lintels above doors and windows, or columns between windows.


��v, d � fv, d

The design shear stress �v, d may be determined by application of Anet, x or Anet, y.

�v, d =

��

nxy, d � 1Anet, x

ornxy, d � 1Anet, y

Where

Anet, x, Anet, y .... cross sectional area of the layers parallel to the concerned structural direction, without cross layers

fv, d..................design value of shear strength parallel to the concerned structural direction, depending on the thickness of the layer

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During the tests, unfavourable board width conditions were tested. In such cases, the joints between the boards take the shrinkage cracks (long-term behaviour) into account.Comparative tests between elements with board areas without joints and with joints (shrinkage cracks) have theoretical crack factors from 0.95 to 0.65 (depending on board thickness, slab structure, etc.). This means that the shrinkage cracks will have a clear effect.During the KLH tests, these shrinkage cracks were already taken into account during the examinations. The same applies to partly cut boards. Therefore, minimum board widths do not have to be taken into account, as it is the case with some approvals of other plywood products.

The functioning mechanism of force transmission is very complex. Since the breakage takes place inside the slab, assigning it to a place and pointing out the first breaking parts is very difficult.The forces acting at crossing points can be described roughly in a simplified manner as follows:

A torsional moment and a generally orientated force are effective. Both these forces generate theoretically modified, directed shear stresses in the plane.It is not known exactly how these stresses are distributed. The breakage ima-ges have not shown any clear failure pattern.On torsional shear stress: Often the torsional shear stress extrapolated from tests was much higher than stated in various approvals and publications. In addition, not only the shear stresses due to torsion work, but there is always a joint action with general shear stresses that reach a maximum due to the load introduction in the support area (transmission of the “shear force” from the vertical position to the horizontal layers in the structural direction).

The verification by way of these “forces” in the crossing points does not seem very practical to me, because the board widths always have to be known. In addition, it often results in extreme stresses at partly cut boards (slim, longitudinal contact areas), and if minimum board widths have to be taken into account, low girders cannot be verified anymore. (For example, a 25 cm high residual cross section over a window cannot be verified if the minimum board width is 15 cm. It can happen that a slab cross section only contains 2 x 12.5 cm wide boards if the originally 15 cm wide boards have been partly cut.)

Due to merely practical reasons, verification by way of the shear flow or by way of shear stresses seems to be the more reasonable option. This verification is generally known, and the shear forces are also issued as results of general FE calculations.However, it is important to know that the verification of the shear flow or the shear stresses used to verify the shear force load-bearing capacity is only of a theoretical nature. It does not reflect the real structural behaviour. The same applied to the verification of cross layers in case of shear due to the load-bearing effect of slabs in plane.

On item 3.14.2:For the most part, KLH slabs are calculated under structural behaviour as girders in the form of beam support structures.However, this is only sufficiently accurate with low girders.

At the formulas for the determination of stresses it says that Anet,x

or Anet,y

has to be used.The “OR” is very significant in this context.The test analysis always covered both directions. It was found that the “cross layers” are not decisive, even with an unfavourable arrangement of the boards.The theoretical shear stresses were so high (up to 22 N/mm2) that stating this value would potentially lead to wrong applications. Therefore, these values are not used in detail for design purposes.

The theoretical shear stresses can be used for the design of all members, on the condition that the normal layers (edge or middle positions) are stressed with variable normal stresses, and that the cross layers are mostly used to couple the normal layers, i.e. the cross layers are exposed to theoretical shear stress, but only very minor stress in the direction of the grain of the cross layers. The load introduction points are exceptions as well as the stresses that form at the distribution of the support or single loads.

This allows a simple verification of a girder with the full cross section of the normal layers – without taking the board joints or the thickness of the cross layers into account.

This is the case with all girders with L/H < 4, and certainly also with the residual cross sections above doors and windows as well as narrow wall pillars.


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Table 5: Characteristic values of shear strength – shear in plane of the slab

Thickness of layer t mm 19 2) 34 45

Characteristic value of shear strength fv, k1) MPa 8.4 2) 5.5 3.9

1) Interim values may be calculated by linear interpolation. 2) Shear strength values > 8.4 MPa are not applicable, e.g. for laminations with

t < 19 mm

The characteristic values of shear strength according to Table 5 may be increased by 25 % for inner layers. When cover layers and inner layers are stressed simultaneously, 25 % higher shear forces shall be assigned to the inner layers. In cover layers with a thickness greater than 45 mm, a maximum thickness of 45 mm shall be taken for stress calculation.

Figure 20: Verification of shear in plane of the slab – shear stress

3.14.3 Simplified verification for beams

Members or parts of members with a distinctive loading direction and with LH � 4 and a

depth of H � 800 mm may be verified by applying the technical beam theory. The cross section may be calculated with the layers parallel to this direction, disregarding the joints between the single boards and longitudinal cut boards. In the case of a rectangular cross section, the shear stresses may be calculated according to the following equation.

�v, d =

��1.5 � Vd

Anet, x

or1.5 � Vd

Anet, y

Where

Vd...................design shear force

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The structural design process of the ETA is based on comprehensive examinations. The different variations of normal and cross layers, the single loads close to supports, frame-type members (slabs with openings) and continuous girders are tested. The effects of shrin-kage cracks (narrow board strips) and partly cut boards are also included.

From this data, the stress for the structural design was extrapolated. The formula for the extrapolation was 1.5 x V / A LL

.This yielded the highest design values.

Therefore, the verifications are also bound to this formula and the underlying theoreti-cal distribution of the shear stresses. An example: In the test, a characteristic load-bearing level was identified. It was used to calculate the design value of the shear stress. The result for the illustrated example was 14.6 N/mm2.If we verified this member with an even distribution of shear stresses, a stress of 9.7 N/mm2 would be the outcome, even though the force is the same. This means that the load-bearing capacity of the member would be massively overestimated!

Therefore, the shear strength values in table 5 are only admissible for a parabolic, theoretical shear stress distribution.If the shear stresses received by way of an FE calculation are not parabolic, then the characteristic values according to table 5 must be reduced.

For the example illustrated in the figure this means that – assuming an even stress distribution – the values of table 5 would have to be divided by a factor of 1.5 (reduction).

The shear in the “cross layers” (= perpendicular to the structural behaviour) was also extrapolated. However, the values of the normal layers are most significant.The situation with glued laminated timber or solid wood is similar: the shear load-bearing capacity depends on the weaker direction (shear parallel to the grain). Nobody would get the idea to assume or verify shear failure normal to the grain.This was already the case in the old ETA – the direction perpendicular to the grain did not have to be verified (although some did it and even called this formula in the old ETA a “mistake”).

The tests also showed a slight increase of the theoretical shear stresses for board layers located “inside” – but no doubling compared to edge layers, as we might assume.The stated 25% increase is a conservative assumption. This effect has not yet been fully examined.If the shear forces are distributed to different layers in the relation of the stiffness of these board layers, inner layers would not receive any higher stresses as these are only theoretical shear stresses. Therefore, these additional 25% – share of the stress can be assigned to the inner layers.With 3 x 34 mm thick normal layers (2 x edge position, 1 x middle position), the outside board layers would not deflect 1/3 of the shear force, but slightly less.In a simpler way, it can be determined as total load-bearing capacity – related to the characteristic shear strength of the edge layers. This way, the effective width would not be 3 x 3.4 = 10.2 cm but 2 x 3.4 + 1 x (1.25 x 3.4) = 11.1 cm.

What is also important is how double lamellas are dealt with in edge areas: the key data in table 5 are based on the tests that were carried out. At the time, however, no double normal layers were tested, which is why there is this limitation to a maximum of 45 mm thick normal layers as edge layers. If the edge layers are thicker, then a maximum of 45 mm can be taken into account.More recent tests have shown some extra potential (not very much) for thicker edge layers. This way, the approach is also on the safe side.

On item 3.14.3:This verification actually precisely represents the process during the test analysis. The theoretical shear stresses are calculated with the formula for a parabolic shear stress distribution for rectangular cross sections.

Note the term “OR” between the two verifications of the main load-bearing directions. We must always only look at the stress of the cross section in load-bearing direction.

In principle, the shear verification is rather a verification of the shear force load-bearing capacity. On the occasion of the next review or after further testing, this calculation process may again change and be adjusted to the actual situation.


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Anet, x, Anet, y .... cross sectional area of the layers parallel to the concerned structural direction, without cross layers

3.15 Combined shear stresses

Shear stresses resulting from actions in plane of the solid wood panel and perpendicular to the solid wood slab shall be combined by linear superposition, as these stresses are effective in the glue lines between the layers.

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On item 3.15:The shear load for the normal structural behaviour is verified through the theoretical shear stress of the lamella in load-bearing direc-tion, but in reality the shear stress is used to assess the stresses in the areas of the bonded joints.

In case of loads on the slab (load normal to the slab), “shear stresses” also work on the same areas.

Therefore, these two effects have to be superpositioned. The total usage of the two structural behaviours must remain ≤ 1.

These superpositions, however, are only significant in extreme situations in the building.

The tests also examined the frame-like members. The analysis showed that the “shear force load-bearing capacity” slightly decreases. This indicates a superposition of effects of both load-bearing directions in the area of the frame corner.

Depending on the stiffness distribu-tion, there is a vertical and a horizon-tal shear force in the frame corner.

The illustration shows the shear force distribution in a wall perspec-tive. The frame corner itself only has very little shear forces. Only in the areas between the load and the inner corners of the opening, the calculated shear forces apply.

These shear force distributions, however, are only of a theoretical nature.The force transmission from the horizontal to the vertical board layers takes place in the frame corner. In this place, in the contact areas, the relevant stresses are effective.

In concrete construction, the shear force distribution wood look similar. The distribution of forces in the frame corner itself cannot be determined with such an FE model. This should always be kept in mind, even in wood construction.

For the verification of these frame corners, the following procedure is recommended:

The shear force distributions in the two “transition areas” to the frame corner are determined through FE models. On this basis, the shear forces (= resulting force of the shear forces per metre) can be determined.

If the shear force distribution (result from FE calculation) is nearly parabolic, then the values can be taken over directly.

Subsequently, both directions are verified separately (through the shear stresses).

Since the stresses of both shear forces in the same contact areas are transmitted between the boards in the corner area, the total usage must remain ≤ 1.

This procedure is on the safe side with regard to the test results.

If openings are cut out of KLH slabs, the remaining rectangular cross sections must be calculated as exactly as possible. To this end, a framework calculation is required. The assumption of hinged corners or connections (e.g. door overlay on slim wall pillar, lower residual cross section above window openings) neglects the effects of forced deformations. These deformations, however, generate additional bending moments, and wood construction knows no pronounced elastic-plastic behaviour such as steel or concrete (in case of tensile loads basically by the armouring), only for compression stresses.


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4 Structural fire design 4.1 Performance R – load bearing capacity

Structural fire design of KLH solid wood slabs shall be by applying the charring depth and the reduced strength and stiffness parameters for the part of the cross section which is influenced by elevated temperatures. For verification, a method with reduced cross sections considering the structure of the KLH solid wood slab shall be applied according to EN 1995-1-2. Strength and stiffness parameters for the part of the cross section which is influenced by elevated temperatures can be either taken from Annex B of EN 1995-1-2, by application of test results or by analogy to e.g. glued laminated timber.

The temperature profiles, 300 °C isotherm, and depths of elevated temperatures within the cross section are given in Table 4.

NOTE For members or parts of members subjected to compression, a non-linear relationship, elastic-plastic, may be applied. It can be assumed, that tensile stresses in sections with a temperature > 200 °C lead to local failure and the stresses are redistributed to sections with temperatures � 200 °C.

Where

dchar................ charring depth; distance between the outer surface of the original member and the 300 °C isotherm

� i ................... charring rate of the considered layer i in mm/min

dStart ............... initial value for the determination of the 300 °C isotherm, char line

TStart ............... time corresponding to dStart

Ti.................... time of fire exposure of the considered layer

Tges ................ total time of fire exposure

� .................... inclination of the member with respect to the horizontal, 0 ° � � � 90 °

Tges = TStart + � Ti

dchar = dStart + � (Ti � �i)

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The structural fire design is currently regulated in very different ways. The method with d_0 according to EN 1995-1-2 (reduced cross-sectional values – verification with the characteristic tensions at normal temperatures) for full cross sections is generally accepted.

The method with the reduced characteristics (point 4.2.3 of the EN 1995-1-2) is not allowed in Austria. Apparently it overestimates load-bearing capacities.

The Annex to the EN 1995-1-2 provides another, “more precise” method, but the data of the EN only allow a calculation with special software. Basically, what is missing is the information on the temperature curve within the cross section at the different measuring times in order to be able and apply this more precise method even with conventional structural engineering calculation methods.It is a moot point whether temperature curves determined by calculations only are actually meaningful. Personally, I cannot see how coal layers, etc. could be simulated precisely. It would again take tests to calibrate the results. This makes it a method that is again only usable for “specialists”.

The KLH tests have shown that the temperature curves are relatively uneven, just like the wood itself.The bottom line is that we still get theoretical curves (adjusted to the tests) that can be used to describe temperature trends sufficiently accurately.

Comparative calculations have also shown that methods based on d_0 values that are constant per slab structure and stress exposu-re, lead to results that under- or overestimate the load-bearing capacity of the member quite clearly. In part they also deliver very unscientific results (see also the explanations in the Annex).

The method with d_0 values also has other disadvantages.If the temperature areas in case of charring on both sides (interior walls) are partly superpositioned, the d_0 values determined for one-sided charring are not accurate anymore.See also SIA 165, point 4.5.2.4: There is says that members for an R 60 verification must at least be 14 cm thick if one intends to use the d_0 method for charring on both sides.After 60 minutes the residual cross section will have a thickness of approximately 6 cm. This means that internally the temperatures are already slightly superpositioned. As regards residual cross sections with thickness values below 6 cm, we already see a clear super-position of temperature lines with the appropriate effects. There is practically no area of the member left that would not be influenced by the temperature.

Charring on both sides, however, is no exception for KLH buildings. It is rather the normal case (load-bearing inner walls).

Therefore, this method (d_0 value) is not used for KLH members. Even the orientational values of the EN 1995-1-2 were only used for rough calculations. Separate tests were carried out to identify the required key data (stiffness and strength).

In the Annex to this comment you find a simplified and relatively easy calculation method that can be used to calculate the effects of the reductions in the areas exposed to temperature influence. This method can also be programmed fairly easily with a spreadsheet calculation programme. The process can also be implemented very easily in software programmes.The key data, for example, only apply to KLH members, however. The comparative calculations were carried out with KLH key data. Any transfer to other products is not possible without the knowledge of the exact background.

A really precise consideration of all thermal effects (own stresses and deformations due to high temperatures, elastic-plastic redistri-butions, positive and negative system behaviour, etc.) is very complex.The calculation is also relatively complicated if all different combinations of member structures and cladding types should be taken into account with both one-sided charring and charring on both sides.A depiction in tables or in the form of diagrams is not meaningful due to the large number of possible combinations.In addition, not all relevant data could be entered, which would potentially lead to errors.

Therefore, the company KLH offers a software tool (“KLHdesigner”) that allows a more precise determination of construction compo-nent resistance values.The identification of member forces and moments can be carried out with any conventional software (taking shear compliance into ac-count), depending on what seems to be reasonable for the relevant system (manual calculation, laminated or plate structure software).In the “KLHdesigner”, construction component resistance values are stated for normal conditions (normal temperature) and in the event of fire. Therefore, this tool can also be used for normal verification purposes.


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�

Figure 21: Charring behaviour with and without cladding

Figure 22: Temperature profiles for non cladded and cladded KLH solid wood slabs

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On item 4.1:The criterion R regards the load-bearing capacity of the residual cross section.

The reduction factors for the stiffness and load-bearing capacity were determined in reference to the EN 1995-1-2 and on the basis of tests. The calculations of load-bearing capacities are, however, not suitable for manual calculating. The software tool “KLHdesigner” identifies the required key data. For an estimate and cross-check, a simplified method (see Annex) is stated. The load-bearing capaci-ties it determines are, however, lower (conservative, on the safe side) than the more precisely calculated member resistance values.

On the comment regarding “tensile stresses in temperature areas > 200 degrees”: This is about the fact that calculations may show that slabs areas might fail above a certain temperature, while the residual cross section shows sufficient load-bearing capacity. This is not always the case at normal temperatures, because a failure due to tensile stress would normally cause a series of subsequent breakages. This way the possibility of redistributions to other board layers should be allowed in case of fire, because this is about areas with low E-modulus, meaning that effects do not appear at normal temperatures.

On figure 21:Here the calculation process of charring is stated.

Charring behaviour of KLH slabs without cladding (lower red line):On the surface, the charring starts with a defined charring speed (β1). Starting from the first bonded joint, a delaminating effect (partial flaking of the coal layer in front of/below the bonded joint) will cause a slightly higher charring rate (β2). If the charring continues within a lamella and if this lamella is thicker than 25 mm, then the full coal layer will again work as a protective layer from these 25 mm, and the charring rate will again correspond to the basic value (β1).At the next bonded joint, the same process will be repeated. These processes are calibrated by the measurement of temperatures at approximately 40 measuring points.

Charring behaviour of KLH slabs with cladding (upper red line):For KLH slabs, different fireproof gypsum board claddings were tested. They were designed according to special application directives. The comparison to a calculation according to EN 1995-1-2 has shown favourable effects.Due to this fact, the layer of the 300 degree line (that is required for further charring calculations or for the precise calculation of the stiffness or strength) is stated as fixed value.This makes the application easier. It is also necessary for calculatory verification if the theoretical 300 degree line lies within the fireproof gypsum board layer.

For these mentioned cladding types, no values must be calculated for t char

and t failure

according to EN 1995-1-2.

The fire tests have shown that there is a difference between horizontal and vertical members. The reason for this fact is that the delaminating effect and the flaking of the fireproof gypsum board layer also depends on gravity. Nearly vertical surfaces show a slightly more favourable behaviour than horizontal ones.

On figure 22:This figure shows the temperature curve required for further, exact verification purposes.This curve is relatively irregular during exposure to fire, because the charring rate also varies.

In case of fireproof gypsum board claddings, the heat has a bit more time to pervade the inner areas of the member. Therefore, the d100

and d

20 values directly behind the fireproof gypsum board claddings are also higher than in case of normal charring.

Vice versa, these values will become smaller if the charring rate is higher.In order not to make the verification process even more complicated than it already is, a bi-linear trend was assumed for the tem-perature curve, and the d

100 distance (distance between the 300 degree line and the 100 degree line) was assumed rather high

(= unfavourable) compared to some publications.The temperature curves were determined on the basis of the data of more than 40 measuring points (with 4-5 temperature sensors each in a row).

Due to the bi-linear curve, the temperature areas near 100 degrees are depicted relatively precisely (essential areas). The temperature areas between 20 and 50 degrees are depicted rather unfavourably, meaning that superpositions of temperatures create a conser-vative effect.


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4.1.1 Parameters for structural fire design

Table 6 is applicable for fire exposure up of 120 minutes for cladded KLH solid wood slabs. For non cladded KLH solid wood slabs the time of fire exposure may exceed 120 minutes.

Table 6: Charring rates and depth of elevated temperatures for KLH solid wood slabs

dStart 1) �1 2), 1) �2

3), 1) d100 d20 TStart Time of exposure Inclination �

Cladding System KLH mm mm/min mm/min mm mm min min

� > 75 ° none 0 0.55 / 0.65 0.80 / 0.90 15 25 0 T > 0

-12 -6 - - 25 25 30 T = 30 � > 75 ° 1 � 15 FGB 4)

11 16 0.55 / 0.65 0.80 / 0.90 15 25 60 T � 60

-35 -25 - - 25 35 30 T = 30

-15 -10 - - 25 35 60 T = 60

0 5 - - 25 35 90 T = 90 � > 75 ° 2 � 15 FGB 4)

8 13 - - 25 35 120 T = 120

-30 -25 - - 25 35 30 T = 30

-20 -15 - - 25 35 60 T = 60

-10 -5 - - 25 35 90 T = 90 � > 75 ° 2 � 18 FGB 4)

10 5 - - 25 35 120 T = 120

� � 75 ° none 0 0.65 / 0.75 1.00 / 1.10 15 25 0 T > 0

-12 -6 - - 25 25 30 T = 30 � � 75 ° 1 � 15 FGB 4)

30 34 0.65 / 0.75 5) 1.00 / 1.10 15 25 60 T � 60

1) 1st value = global, mean value – 2nd value = local, increased value for a solid wood slabs with width b < 300 mm

2) regular charring rate within one single layer

3) increased charring rate after the failure / drop off of one layer 4) Fireproof Gypsum Board 5) Following the initial value T0 the charring rate a2 shall be applied until the next glue line is reached

For KLH solid wood slabs with fire exposure on both sides, the temperature profiles may be determined independently for each side. The temperatures shall be added where temperature profiles are overlapping with temperatures above 20 °C.

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On item 4.1.1:The charring processes and the temperatures in the residual cross section can be identified according to table 6, using the figures 21 and 22.

In areas where the temperature curves are superpositioned from 2 sides, the temperatures above 20 degrees can simply be added up.

If this key data is used for fireproof gypsum board claddings, it is important that these fireproof gypsum board layers are carried out according to the application directives of the company KLH.For other claddings or deviations from the application directives, the 300 degree lines according to EN and B 1995-1-2 must be deter-mined.

This key data is used as the basis to identify the member stiffness values and member strength values.In the Annex to this comment, there is a simplified method to determine the stiffness and subsequently to perform stress verifications (using the stresses at normal temperature).

Be careful when using the reduction factors from the EN 1995-1-2, Annex B: they are not compatible with the KLH members. The re-duction factors were extrapolated from tests. The temperature curves might have been determined with FE models. If only about 10 mm was used for the d_100 values, this will yield more favourable reductions. This will in turn lead to unfavourable (= unscientific) results if used for KLH members with the d_100 values in table 6.


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Figure 23: Definition of regions for application of regular and increased charring rates

4.1.2 Local charring at corners, grooves, etc.

The depth of the 300 °C isotherme may be assumed according to Figure 24. Grooves with a cross section � (20 / 20) mm may be disregarded. Grooves smaller than 80 mm shall be considered as shown in Figure 24.

To account for the increased charring at edges, the charring rate at the edges of solid wood slabs shall be taken to 1,5 times the rate at the face.

Figure 24: Charring at a groove and at an edge of a wall

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On figure 23:This illustration shows in which design situations the higher local charring rate can become significant. In reality, there is of course no abrupt transition between narrow and wide strips (there will not be such an excessive increase of the load-bearing capacity for a 31 cm wide strip compared to a 30 cm wide strip).It should be noted here, however, that the analysis for the narrow strip was based on approximately 20 cm wide parts.Therefore, the value of the global, mean charring rate can safely be assumed for strips with a width of > 30 cm (in exceptional cases and with borderline verifications, this minimum width of 30 cm can also be slightly undercut, e.g. for 28 cm wide strips; this method, however, must be coordinated with inspectors and authorities).

In addition to the higher charring rates, narrow strips also require the use of the k_sys values (reductions in order to take partly cut boards and local weaknesses into account).

On item 4.1.2:During the examinations, a number of specific ordinary locations (sockets, millings, wall ends, corner formations, etc.) were also exa-mined.The results can be gathered from the figures 24 and 25.The charring rate at the narrow sides was assumed slightly higher in order to cover effects such as an increased charring at the corners, etc.

In case of charring in the direction of the slab (wall ends, lintel areas), the d_0 value of 7 mm (as for solid wood and glued laminated tim-ber) can also be used to determine the cross-sectional values. This facilitates the calculation of the residual cross section in case of fire exposure on several sides (wall pillars, window lintels). The effects not included in d_0 are covered by the slightly higher charring rate.

This is admissible because the load-bearing board layers in the direction of the wall form a full cross section (in case of charring normal to the wall we have a weakening of the cross section through the cross layers).

The factor 1.5 x d char

is a conservative assumption. In principle, this value can also be determined through a more precise calculation (such as for glued laminated timber). Then, however, effects such as round corner, etc. must also be taken into account.


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Figure 25: Charring behaviour in the vincinity of a step-joint or an inside corner

4.1.3 Connections

The capacity of connections may be assumed as unchanged if the complete fastener is exposed to temperatures < 200 °C. Edge distances are measured from the char line if the forces are parallel to the char line. Forces perpendicular to the char line relate to the 200 °C isotherm as the edge of the member.

4.2 Performances E and I – integrity and insulation

The performances E and I, penetration of hot gases through the member and limited temperatures on the unexposed side, may be regarded as acceptable under the following conditions:

� The residual cross section comprises at least one cover layer and one glue line and

� the distance between glue line and 300 °C isotherm is greater than 15 mm.

The use of sealing tapes is not required if the following is fulfilled:

� The surface temperature on the unexposed side is determined with the above given temperature profiles and does not exceed 120 °C.

� This is also applicable to butt-joints in corners of two solid wood slabs, if the maximum centre spacing of the screws does not exceed 250 mm.

� The temperature in the contact surface of step joints, with the contact surfaces parallel to the face of the solid wood slab, shall be not exceed 150 °C. The step joint shall be connected with wood screws with a maximum centre spacing not exceeding 250 mm.

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On figure 25:For inner corners and supports of ceilings on walls, this charring process can be assumed.This is important for ceiling supports, because the eccentric load introduction (from ceiling to wall) can be determined.For the contact area, an edge compression of approximately the double to triple value of the characteristic value for compression normal to the grain can be assumed. This way the distance of the resulting force to the centre of gravity (of the reduced cross section) can be determined.

On item 4.1.3:Due to the fact that the temperature curve inside the slab can be calculated fairly accurately, we also gain an advantage in verifying the means of connection.A means of connection that is used to transfer forces must be fully located in areas where temperatures are lower than 200 degrees.In addition, the edge distances must be maintained (to the charring line for loads parallel to the charring area, to the 200 degree line for loads normal to the charring area). This will automatically create a situation in temperature areas of < 100 degrees for a means of connection with high load-bearing capacity (screws, nails, etc.). At a temperature exposure of < 100 degrees, the strength of wood is already so high that the load-bearing capacity of the screw (accor-ding to EN 1995-1-1) can be calculated with a reduction of the bearing stress strength by 50% (in temperature areas < 100 degrees, the load-bearing capacity of wood is > 50% of the load-bearing capacity at normal temperature).

Means of connection directly exposed to fire must be examined separately. The effect of the temperature conductivity inside the means of connection must also be examined.This procedure is the same as for glued laminated timber or solid wood.

On item 4.2: The E criterion refers to the room tightness. “Tight” in the conventional sense, however, does not always apply to members. Smoke that might permeate through joints has cooled off to a degree that no ignition is possible on the side that is not exposed to the fire.

If 100 percent smoke tightness is required, at least 2 bonded joints should be in temperature areas below 200 degrees.For the I criterion, a maximum surface temperature on the side facing away from the fire is stated in the standards. It is higher than the criterion of 120 degrees that is mentioned here. This provides additional safety, and the criterion is also complied with in most practical and relevant building cases.

The member tests were always carried out with step joints, partly with and partly without the use of sealant strips – this also affects corner formations and ceiling supports. In principle, no sealant strips are necessary.

If, however, joints appear in practical usage due to constructional inaccuracies, compensation must be provided by way of suitable measures. Or the detailed design allows a full-area compression of a joint area (like with step joints). This will also guarantee tightness. However, it is not possible always and everywhere.


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FastenersThe determination of the load bearing capacities of the fasteners in KLH solid wood slabs shall be carried out according to EN 1995-1-1 and/or the European technical approval which has been granted for the relevant fastener for softwood and/or for glued laminated timber or the wood based panel used.

Only wood screws and split ring connectors may be employed as load bearing fasteners in the edges of the solid wood slabs.

To all fasteners apply

� Only nails, wood screws, bolts, dowels and connectors according to EN 1995-1-1 and/or a European technical approval may be used as fasteners, observing the following particularities.

� The edge of the solid wood slab is the edge of the member. As long as the maximum joint width according to Annex 2 is not exceeded individual joints need not to be considered.

Nails

� Nails shall have a diameter of at least 4 mm.

� The load bearing capacity of nails shall be determined according to EN 1995-1-1. Minimum spacing and distances shall be determined following the direction of grain of the surface layer.

� Smooth nails shall not be employed for axially loading. For axially loaded nails the recommendations of the ETA holder shall be observed.

Wood screws

� Laterally loaded screws shall have a nominal diameter of minimum 4 mm and a nominal diameter of minimum 8 mm if driven in the edges of the solid wood slab.

� The load bearing capacity of laterally loaded screws shall be determined according to EN 1995-1-1. The embedment strength shall be determined according to the direction of grain of the surface layer. If driven in cross grain, the embedment strength shall be reduced by 50 %. Minimum spacing and distances shall be determined according to the direction of grain of the surface layer.

� Axially loaded screws shall have a minimum diameter of 4 mm. Axially loaded screws driven in cross grain shall have a minimum diameter of 8 mm.

� The load bearing capacity of axially loaded screws shall be determined according to EN 1995-1-1. The load bearing capacity of screws driven in cross grain shall be reduced by 25 %.

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As regards the means of connection, the data of the individual technical approvals or the EN 1995-1-1 can be used.

Only a few special characteristics of the KLH slabs must be taken into consideration.

In case of connection on the end grain of the edges, reductions must be made with regard to the bearing stress strength.In most cases this is unproblematic, because the members are rather thick and the screws themselves are decisive (screw bending), not the wood.

Tensile force connections in the end grain should be avoided, even if some approvals allow them. At least a part of the thread should be placed in the diagonal wood. This way, any appearing shrinkage cracks in the area of the screws will be less problematic (because the screws weaken the wood, which is why shrinkage cracks are very likely exactly in the areas around screws).

Screws and nails must have a certain minimum diameter, so they can still function in areas of possible joints and shrinkage cracks and maintain their long-term load-bearing capacity.Maintaining a minimum diameter, however, is not necessary if the purposeful arrangement (positioning) of the screw can guarantee that no joints are hit (e.g. screws in longitudinal wood of an edge side).Or if one single failure or a reduction of the load-bearing capacity due to joints will not represent a problem (reduce the degree of usage, position more screws than required according to calculations).

In case of pin-shaped means of connection, the slab edge can always be regarded as the member edge – without any consideration of possible joints.

In case of very highly loaded connections, however, the possibility of joints should always be taken into account, meaning that classic pin bolt connections are not the ideal choice.It would be better to have connections with grooved metal plates and self-drilling bolts. This leaves some leeway to react on site with regard to the positions of the pin bolts. It is possible to avoid larger joints.This must, however, already have been considered during static measurement – the reduction of distances (lever arm) may lead to higher loads. Therefore, a mutual coordination between the installer on site and the responsible structural engineer is necessary. It must also be possible to shift the means of connection by approximately 3 cm, which must have been planned in advance.

Still, it is better to make an unfavourable assumption on the measurement of joints in structural design in order to adjust the type of connection to the relevant product.


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Bolts and dowels

� Bolts and dowels shall have a diameter of at least 10 mm.

� The load bearing capacity of bolts and dowels shall be determined according to EN 1995-1-1. The embedment strength shall be determined following the direction of grain of the surface layer. Minimum spacing and distances for dowels and bolts are

� 5 � d from the loaded edge and between each other and

� 3 � d from the unloaded edge.

This applies regardless to the angle between the direction of force and the direction of grain.

� Self-tapping dowels shall be used only in the face of KLH solid wood slabs. The minimum nominal diameter should be 5 mm. The requirements of the European technical approval for the fastener shall be observed.

� For connections with steel plates as the central member the direction of the nearby layers shall be taken into account.

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The edge is always the slab edge, independent of the joints between the board layers. Therefore, the minimum diameter is stated with 10 mm.

Independent of this, it should still be verified on site whether there is any larger board joint directly at the pin bolt. This circumstance can already be taken into account for structural design by not using the connection to 100 percent.

As regards the bearing stress, the grain direction of the wood directly in the area of the transmission of forces is decisive, e.g. in case of a force transmission from wood to a steel member.If only very thin residual wood layers with unfavourable grain directions remain, the nearest adjacent board layer (in the direction of the grain) can be used. This must, however, be subject to separate examination in each individual case, and the additional bending of the dowels must also be taken into account.


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Reference documents CUAP (Common Understanding of Assessment Procedure), ETA request � 03.04/06, Version June 2005: Solid wood slab element to be used as a structural element in buildings

EN 301, 06.2006, Adhesives, phenolic and aminoplastic, for load-bearing timber structures - Classification and performance requirements

EN 338, 10.2009, Structural timber - Strength classes

EN 385, 10.2001, Finger jointed structural timber - Performance requirements and minimum production requirements

EN 1194, 04.1999, Timber structures - Glued laminated timber - Strength classes and determination of characteristic values

EN 1995-1-1, 11.2004, EN 1995-1-1/AC, 06.2006, EN 1995-1-1/A1, 06.2008, Eurocode 5 - Design of timber structures - Part 1-1: General - Common rules and rules for buildings

EN 1995-1-2, 11.2004, EN 1995-1-2/AC, 03.2009, Eurocode 5 - Design of timber structures – Part 1-2: General - Structural fire design

EN 12354-1, 04.2000, Building acoustics - Estimation of acoustic performance of buildings from the performance of elements - Part 1: Airborne sound insulation between rooms

EN 13183-2, 04.2002, 13183-2/AC, 09.2003, Moisture content of a piece of sawn timber – Part 2: Estimation by electrical resistance method

EN 13986, 10.2004, Wood-based panels for use in construction - Characteristics, evaluation of conformity and marking

EN 15425, 02.2008, Adhesives - One component polyurethane for load bearing timber structures - Classification and performance requirements

EN ISO 10456, 12.2007, EN ISO 10456/AC, 12.2009, Building materials and products - Hygrothermal properties - Tabulated design values and procedures for determining declared and design thermal values

ETAG 011 (2002-01): Light Composite Wood-based Beams and Columns

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Reference documents

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In the reference documents, various standards are listed that are connected to this ETA.

However, the procedure for examinations, test analyses, etc. is not yet standardised. This means that calculation methods stated in this ETA are not necessarily compatible with the key data from test series of other producers.

Nevertheless, the ETA as such is consistent. The application of the EN 1995-1-1 and EN 1995-1-2 in the listed references is admissible, but not vice versa.

As regards plywood members, the breakage mechanisms are essential and decisive with regard to shear (slab or plane) for the struc-tural design. The test configurations for this are not yet standardised, neither are the analyses of the tests.

The design, however, is directly connected to the analyses of tests. Therefore, all essential effects and framework conditions must be taken into account.

This is especially important for the calculation types for beam or plane-type members. The verifications as a beam are only theoreti-cally more exact compared to more precise results from FE calculations, but they do not necessarily translate into reality. Everything depends on how the comparative values (= design values) from the tests are determined.

In the chapter on shear due to loads in plane, a relevant example is quoted.


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ANNEX A:SIMPLIFIED PROCEDURE FOR DETERMININGMEMBER RESISTANCES IN CASE OF A FIRE

For this procedure, various simplifications were made, so that a “manual” calculation and “comprehensibility” of the actual load-bearing behaviour could be made possible.In comparison to more exact determinations of member resistances, the results lie on the safe side and provide security for the tests.In this simplified procedure, many thermal effects are taken into account, any favourable effects (e.g. elastic-plastic behaviour as a result of compressive stress, etc.) must therefore not be taken into account if these are not specified in these instructions.

For consideration of reduced material properties in the areas under influence of temperature, an area is defined as h_temp, which can be calculated using the formula h_temp = d

100 + 0.6 x d20 (= 30 to 40 mm). In this area, the reduction of the E-modulus from 100% to

0% can be carried out.The calculation results in reduced cross-sectional widths. This reduction remains independent of the supporting direction.

Note: in reality the influence of the temperature is effective in the whole area d100

+ d20

(= bigger than h_temp).This simplification only affects temperature ranges < 50 degrees, the effects are negligibly small.

To take into account the influence of the reduction in resistance in the area h_temp, the proof of changeable tensions (as a result of M or due to (M + N)) must only be conducted up to the limit of detection_fi. The area underneath only has to be proven in residual lamella thicknesses < d

klh_fi, then the determined tensions have to be multiplied with the correction factor t

rest / d

klh_fi.

Annex A to the comment on the ETA-06/0138 by J. Riebenbauer

Y

Z

X

For further evidence, the characteristic material data at normal temperature can be used, or can be increased according to EN 1995-1-2 (20% fractile values). This applies for normal and shear stress, for planes and plates.

This figure shows the effects of this E-modulus reduction, which in principle results in a reduction of the cross-sectional widths.The area h_temp always begins directly above the charring line (300 degree line).

For this cross section with reduced widths, for each supporting direction the relative cross-sectional values can be determined (net cross-sectional values).

Due to the reduction in width, for further calculations the G- and E-modulus at room temperature can be used.

Reduction in width in the area influenced by temperature

Load-bearing residual cross section with reduced width

Charring/temperatures > 300°C)

Y

Z

X

Charring on the narrow edge

dchar

dchar dchares_fi

dklh_fi

er_fi

er

d0 =7mmReduction E-modulus

Stress distribution on cross section with reduced width

Limit of detection_fi

100%

h_temp

0%Charring on the side

To determine the bending tension, the distance e r_fi

should always be estimated as smaller than e s_fi

- d klh_fi

. d

klh_fi correction value for proof in area h_temp, this figure can be assumed as 0.5 x d

100.

e r_fi

distance of the edge fibre to determine maximum edge tension (< e s_fi

- d klh_fi

)e

s_fi distance of charring line (300 degree line) from the centroid axis of the cross section with reduced width

For the other main supporting direction, in principle the process is the same, with the only difference that only the lamellas that are relevant for this supporting direction are used for determination of the cross-sectional values.

In 2-sided charring a somewhat adapted process of reduction factors results.

The only difference is that the reduction and the proof with d_klh_fi must be carried out on both sides.If the temperature areas overlap (areas with reduction), then the total reduction can be calculated by multiplying the reduction (for each grain) of each charred side.The rest of the procedure remains as already described.

The majority can be thus verified. Shear verification for slab stress is not decisive. There is an automatic reduction with the reduction of the cross-sectional key values.The verification under action in plane of the slab can also be carried out with these cross-sectional key values. The bending tension as a plane is calculated somewhat conservatively, but that is usually not relevant.For the shear verification under action in plane of the slab, a mean thickness can be calculated for the cross-sectional area in the h_temp area.

Increase in areas of tensile stressThe member resistances (strength and stiffness), in which the tensile stress due to bending in areas of temperature influence are influential, can be multiplied (increased) by factor 1.2.

These two illustrations show the procedure in case of double-sided charring.

If the areas with temperature in-fluence do not overlap, the proce-dure can be the same as for one-sided charring.


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2-sided charring without mutual influence

2-sided charring with mutual influence

dchar

dchar

dchar

dchar

100%

10

0%

h_temp

h_temp

h_temp

h_temp

Effective reduction

0% 0%

Charring on the narrow edge

dchar

dchar dchar

es_fidklh_fi

er_fi

er

d0 =7mm

Limit of detection_fi

100%

h_temp

0%Charring on the side

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For the verification of load bearing systems, the following effects are to be taken into account with plywood constructions:

To determine the member forces and moments, a realistic supporting system must be used as a basis. That means that all influencing factors must be sufficiently exactly considered.


Because the ceiling deformation could take on up to L/100 part in a fire, extreme twisting is the result in the supporting areas on the walls. Only with two-span ceiling systems with approximately identical spans would the twisting above the middle wall be a bit less extreme. Unequal charring in both rooms could in turn cause more extreme twisting.

Basically, the thermal effects are to be considered as unfavourable: due to the increased temperatures, residual stress and also defor-mations result. With the simplified procedure for KLH members, these thermal effects are already included. The effects determined by the system can only be taken into account by the engineer responsible in the course of static tests.

In a fire, the properties of wooden building components change sometimes in an ext-reme way from a static point of view. This applies mainly to deformation. Due to the reduction of the cross sections, much more deformation results than at normal temperatures. This means that assump-tions that applied to normal measure-ments, no longer apply in case of a fire.

This is especially important with walls and stability-vulnerable members. With these members, additional eccentricities can occur due to deformation of neighbouring components (e.g. bending of ceiling com-ponents) – in addition to the displacement of centres of gravity, which arise from the reduction in cross sections.

Wall load from above works against twisting, but cannot fully compensate!

Eccentricity due to cross section reduction

Wall

Wall

Ceiling deformation up to L/100 part possible)

Between ceiling and wall a local contact area develops on the front wall edge

Load on wall

Member dimension in case of fire

Charring

Centroid axis of original cross section

Eccentricity of load on centroid axis of reduced cross section

Background on measuring with a d_0-value:

In the EN 1995-1-2, point 4.2.2, it says that for the area d_0 it is assumed that there is no load-bearing capacity and no stiffness. Based on this information, you could think that with KLH members (no full cross section from a static point of view, the cross layers cause reductions compared to a full rectangular cross section) the procedure would be similar. For this reason, the procedure with the EN d_0-value was adopted in the old ETA .That the stiffness and resistance are not in the d_0 area, is only half the truth – in reality it is more complex.

In a fire, the temperature penetrates the cross section, after 30 minutes approx. 30 to 40 mm of the cross section behind the charring line are warmer than before the fire. The charring line can be taken as 300 degrees (280 degrees more than before the fire). The temperature then decreases (within the layer thickness of approx. 30 to 40 mm).

In various publications you can find curves showing these temperature fluctuations, but the information varies considerably. It is possible that these curves were only determined by FE analysis.In the reduction curves of the material key values according to the EN (Annex B), at approx. 100 degrees a more extensive reduction in values occurs. Therefore in the following, this 100 degree point is used as a reference value.

In the publications a value of 10 to 15 mm was specified for difference between 300 and 100 degrees, between 100 and 20 degrees a value of approx. 20 to 40 mm.

The following illustrations explain the effects:

The left illustration shows the idealised temperature curve, both middle illustrations show the reduction of the E-modulus and the resistance for this area under temperature influence. The illustration on the right shows the stress curve that results. In areas with temperatures > 20 degrees, stress distribution changes due to decrease of the E-modulus (orange line). The characteristic resistance for verification also changes according to temperature.

As a result, the cross section for verification is reduced somewhat. The “load-bearing capacity” of the cut off section (red area, height d_0) compensates here in principle for the missing “load-bearing capacities” of the areas above (blue area).

The illustration shows the “theoreti-cal” procedure for determining the d_0 value.A distance from the bottom edge is determined (d_0), at which the load-bearing capacity of the residual cross section at normal temperature (red stress distribution) corresponds to the load-bearing capacity of the cross section under temperature influence (black line).


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%

%

Temperature curve

20 degrees base temperature

E-modulus

100 100%

25mm

15mm

100 degrees

300 degrees

50 to 90% at 100 degrees

Resistance Actual stress distribution

Limit stress at normal temperature

Limit stress, reduced in areas influenced by temperature

Stress distribution due to M/N load stress

Reduction in material key values Dependent on type of load stress

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If that is transferred to KLH members, it results in the following illustrations:

There is also another extreme case – when the 300 degree line resides transversely:


Essentially, with plywood board members the theoretical d_0 value during a fire constantly changes (depending on the height of the members).

This course of action is therefore not really advisable for KLH members. Either the components are measured very uneconomically, or a relatively high degree of effort is needed for the calculation of the d_0 values.

In diverse publications – and also in some approvals (France) – already for plywood building components d_0 values (and s_0 values) are specified, graded by type of load, whether with or without fireproof gypsum board cladding, and dependent on the number of board layers.

There are also cases where the use of the d_0 value results in a line which coincides with the lower edge of the supporting lamella next to it.

The load-bearing capacities in such situations are in part massively overvalued (on the uncertain side).And for that again, extra rules would have to be specified. That makes the measuring more complex and less clear.

These measuring situations are no exception. If members are optimised according to the d_0 values, then inevitably rather multi-layered slabs with thinner lamella thicknesses are the result. And exactly this is when these situations, as described, come about, in which the load-bearing capacities are overestimated.

For this reason, this measuring procedure (d_0) is not used for KLH members.

It is recognisable that this “compensati-on” of the load-bearing capacities cannot be adopted 1 : 1. The load-bearing cross-sectional parts (green area) are partly mis-sing inside the members, so that for that reason the d_0 for plywood boards must be differentiated from the d_0 for glued laminated timber or solid wood.

Here, in principle, the d_0 also includes the non-load-bearing cross layer. As a “compensation”, the load-bearing capacity for the part of the cut off cross layer area is missing.

The d_0 would then be very large or very small – according to how it is viewed.

According to the basic principle of the d_0 procedure, the residual cross section can be calculated using the material key values at room temperature (red tension illustration).In reality, the stiffness and strength are less (black line).

The d_0 values in the publications vary between approx. 12 and 20 mm. It can thus happen that after deducting 12 mm (as d_0 value) in the supporting lamella, there can still be temperatures of approx. 100 degrees – and according to An-nex B of EN 1995-1-2, only 25% of the compressive strength would be existent with compression??? There seems to be a “system error” here!Or the d_0 values should always be measured only from the supporting layers onwards.

Component tests with KLH slabs for determination of diverse characteristic data:

9 large fire tests were carried out, with different lamella grading, with and without fireproof gypsum board cladding, as ceiling and wall, and also with pressure loads on the burning side (important for calculating stability-endangered members = walls). This covers most of the possible measuring situations.

Wall members with and without fireproof gypsum board cladding, with milled/drilled holes for sockets, ceiling connections, etc.

Warning: test loads in individual fire tests on wall elements under stress have no direct significance concerning the bearing capacity. Therefore, the test values can never be used as a designed load. This must always be mathematically calculated. And for that, the necessary characteristic data are needed.When test loads of this kind are used for a measurement, then the marginal conditions of the building for the trial have to be exactly kept to (1 : 1) – and that is practically not possible. The E-modulus would have to be the same, the pre-deformations would have to stay the same over the whole service life of the member (the wall could, however, over time bend a little due to shrinkage), the storage conditions would have to be the same (distortion of the ceiling cannot really be simulated for the test), etc.That is “realistically” not possible in practice. Thus in the tests, only possible characteristic data for mathematical verification can be determined, not the “permissible” stress in case of a fire, however.

In principle, it is the same with ceilings, although the possible negative effects are considerably more serious with walls.

As the fire tests are very expensive, mostly only 1 or 2 tests per load, etc. can be carried out. The test load can in no way be adopted 1 : 1 for the assessment of load-bearing capacities. For that, the characteristic values of the wood vary too much.

From more than 40 KLH test series it is known that there is a difference of between 95% and 5% in fractile values. It could therefore be assumed for the test analysis that the material properties of the test objects corresponded to 95% fractile values, and thus it was possible to calculate backwards to the 5% fractile values. In principle, this corresponds to the EN 1990, Annex D (test-supported mea-surements).


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Ceiling members with pull or pressure on the burning side, with and without fireproof gypsum board cladding, step joints, etc.

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In general, the following values were determined with the tests:

Charring lines:

Charring is relatively irregular. With regard to wider wall and ceiling elements that is unproblematic, because the cross layers distribute the load to the parts of the slabs that are less charred.With narrow strips of slab that is not possible, which is why 2 different values were specified for the characteristic data: on the one hand, local charring rates for areas with slab strips with widths < 30 cm; on the other hand, global values for wider strips.The data for slab strips with widths < 30 cm are in principle the most extreme charring rates measured. The data for wider strips are mean values of the charring lines.This makes it possible for narrow slab strips to be measured, where normally a number of tests (supports, girders) would have been necessary.

In the charring lines, all effects are included that concern the material. This also includes the delaminating effect (falling off of coal layers).In individual tests, smaller charring rates also resulted, but for the ETA only the most unfavourable charring rates were listed. These more favourable charring rates can probably be accredited to an optimisation of the amount of glue used in the previous fire tests.

The delaminating effect (and thus also the charring rates) depend in principle on the method of gluing (type of glue, amount, etc.). This makes a transferral of the charring rates and thus also the temperature penetration depths to other plywood products at 1 : 1 impossible.In the tests, KLH standard slabs in non-visible quality were used, which is why all possible effects of the joints between the slab layers were taken into account.

For verification with fireproof gypsum board cladding, theoretical 300 degree lines were specified, so that the general calculation mo-del (see Annex) is also possible with cladding. With other kinds of cladding, the 300 degree lines could be worked out according to EN 1995-1-2.The data for the quoted cladding are only permitted in connection with the processing guidelines of the company KLH. This is why other screws or types of fireproof gypsum boards are not permissible. With deviations, calculations must be made according to EN 1995-1-2.

Temperature profiles:

These are independent of the charring speed, and also of the cladding. If the cladding stays on the slabs longer, then the temperature has more time to penetrate to the inside. This is why the penetration depths of the temperature are somewhat higher directly behind fireproof gypsum board cladding.In comparison to temperature profiles in some publications, these values are on the safe side.

Strength:

The structural behaviour and the thermal influences and effects are too complex to be able to describe them in a short paper. In this Annex, a simplified procedure is cited, the results are calibrated with the tests and lie on the safe side. More exact verification is not suitable for “manual” calculation processes.The essential characteristic data are not available to the general public, so that competitors cannot adopt them for their products.

Load-bearing capacities of the glued layers in the range of 20 to 300 degrees:

In the tests no failure was observed with the glued joints and also no weakness in glued joints at high temperatures. The load-bearing capacity of the glue used is thus proven.The forces to be transferred in areas influenced by temperature are minimal due to the reduction in material properties. The higher the temperatures in the glue layer, the lower the forces that need to be transferred.

Structural behaviour after the fire:

Even after the fire is extinguished, the temperature continues to be distributed in the cross section. This goes on so long until room temperature is reached again. This temperature flow takes place in all directions. The time of charring is therefore not necessarily the time of the highest temperature influence.That is especially important with wall elements if further change of the material key values can lead to a sudden loss of stability. These effects are taken into account with member properties (simplified procedure and also with detailed verification).


Annex B to the comment on the ETA-06/0138 by J. Riebenbauer

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ANNEX B:DESIGN OF KLH STRUCTURES UNDER EARTHQUAKE CONDITIONS

In almost all buildings, it is necessary to consider the threats and loads posed by an earthquake.Depending on the location, ground plan, height, etc. of the building, the load of an earthquake may not be serious, but in these cases it must always be possible to verify that the stresses posed by an earthquake are insubstantial.

A simple estimate or generalisation is not possible. If we look at the example of wind, an elongate building has only the end walls at risk from wind – a comparatively small area. With an earthquake, a great deal of the building is at risk because of the large ceiling mass. That means that the wind may be more of a threat in one direction, but in the other longitudinal direction, an earthquake would be a risk.

The decisive parameters for the effect of an earthquake on a building (next to location-specific factors like fault lines and ground com-position) are its vibration behaviour and the building weighting factor.

The earthquake load can be simply projected according to this formula:

FEb

= m x S x ag x 2.5 / q

m weight of the member (permanent stress of the ceilings, walls and including a part of the superimposed load)S ground parameters – describes the influence of the subsoil (max. approx. 1.4)a

g vibration acceleration depending on the earthquake area (e.g. in Austria, approx. 0.2 to 1.2, according to ÖNORM B 1998-1)

2.5 constantq building weighting factor (between 2.0 and 2.5 depending on the construction method)

Other parameters also have an influence on the design – see EN 1998-1 (significance category, for example). Reaction of a building to vibration influences the extent of earthquake damage, in that very weak supporting structures hold out for longer when vibrating, and thus alter the spectrum of plausible possibilities. However, that only applies to taller and narrower buildings. In most practical cases, the maximum value applies (value S in table 3.2, or point 3.2 in EN 1998-1). This lies somewhere between 1.0 and 1.8, depending on the ground. Rocky, hard ground will give results under this value, and the results for soft ground will be higher. This value or subsoil classification is normally available in ground surveys; but should this not be the case, then the values should be assumed to be poor.

As a further consequence, the resistance to earthquake is significantly influenced by building weighting factor q. This factor takes the absorbing effect (the ability to dissipate energy) of the building into account. Rigid constructions have rather low q values, whilst more elastic constructions with flexible connections have a higher q value. The behaviour of the building is classified according to ductility (DCL – low; DCM – medium; DCH – high ability to dissipate energy). Wooden framework walls (where OSB panels are nailed or stapled to the beams) have a q value of between 3 and 5 (DCH). Rigid KLH board constructions have a rather low q value if other steps are not taken to correct this.

Shear walls are the most important factor in energy dissipation, whereas roof diaphragms contribute little. However, the latter are important, of course, for transferring horizontal stress to the wall braces. With the walls, it is important that energy dissipation can only be applied to vertical wall joints and tension anchors – that means the parts of the building that can be fixed with flexible connections. The flexibility of the cross layers in the board itself, and of weaker parts of the wall with openings cut in the board is irrelevant in this respect. These distortions are more relevant to the vibration period of the building (natural frequency).

Horizontal joints are rarely flexible, because the frictional forces are mostly too high in these joints. This friction should not be assessed in a normal design, as it cannot be certain that it will be present. In the event of an earthquake, possible frictional forces cause a higher level of rigidity of the building, and higher stress levels as a result. For this reason, this effect has to be calculated as negative (so no flexibility in horizontal joints).

Nevertheless, frictional forces must not be considered in the transfer of earthquake loads, because it is not certain that these will be present. Earthquakes challenge buildings not just horizontally, but also vertically (even if this factor is not assessed). This can lead to a tipping point in a critical situation, where the frictional force is neutralised by a vertical vibration.

When all this is taken into account, KLH buildings can be assumed to have very low q values – unless areas with energy dissipation behaviour have been expressly added to. A q value of 1.5 is stated in the standards, which can be used for all buildings, even the more rigid ones. KLH structures, though, do show a certain difference when compared to standard, rigid concrete structures, so a q value of between 2.0 and 2.5 seems fair. That meets the specifications of EN 1998-1, Table 8.1, where a q value of 2.0 is given for a building with use of glued shear walls and glued shear fields. If a building needs anchoring due to tension, then the anchor points act as absorbers, and a value of 2.5 can be taken. The responsibility for choosing a q value always lies with the assigned engineer, and should always be cleared with the authorities or surveyors. In principle, one could easily try to divide the shear walls and use smaller board strips, to make the building more flexible and raise its q value. One should, however, always remember that a q value of 4 to 5 in framework walls means the destruction of such a wall in the event of a seismic event – in all probability a total write-off. Additionally, although a higher q value reduces the stress on a framework wall, the load-bearing capacity of the wall is also reduced.

That is especially true when partitioning plywood shear walls. The q value is raised a little (in a test in Japan, a reverse calculation was made for the q value, from approx. 3.0 to 3.5, with a large number of wall joints and flexible anchors), but the joints severely compromi-se the load-bearing capacity. As with the framework walls, the building will probably be useless after an earthquake, as the nails and screws will no longer support any weight.

In general terms, a building in an earthquake zone should be designed to withstand strong earthquakes, which means that a planner should get in touch with an experienced structural engineer at an early stage. Along with various other coefficients, the most significant contributor to the stress of an earthquake is the weight of the flooring and roofing. Weight per se need not be a disadvantage if used in the right places in reinforcing structures. The right amount of weight can also help to reduce stress on bracings. However, when there is no longer any tension to anchor, the q value is reduced – it is a rather complicated relationship.

A low q value (in buildings without anchors, or with only a few), however, means that if the shear walls have been designed correctly, it is highly likely that the load-bearing frame will still be fully useable after an earthquake. Buildings which collapse into stiff “blocks”, but which have flexible attachments to the foundations are also ideal. In the event of an earthquake, the energy is released in smaller blocks. A collapse of the building (structural stability) is very unlikely, because a horizontal impulse from a given direction is always followed by another from another direction, and the building would need some time to collapse. The exceptions, of course, are buildings with very high or narrow bracing systems (towers or reinforcement cores).

If the KLH building method has been followed correctly, with “whole” shear walls (with cut out openings), low q values are not an obstac-le to much higher load bearings. This can result in a building with high dissipative properties being financially disadvantageous (harder to build), in addition to the disadvantage that the building would probably be a write-off after an earthquake.

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In the left bearing structure, there are much higher abutment loads at all wall ends (and with them, higher stress on the walls). The stresses on the divided structure are nearly three times as high. Additionally, there is high tension at all wall ends, not just at the bridge with the concrete, but on all floors (in spite of the extra burden of the ceilings). On the structure depicted on the right, on the other hand, there is only a little tension at the outer wall ends, which is probably even compensated by the adjoining wall in the other direction.

With regard to the q value, this means that despite a potentially higher q value in the divided house, the advantages of the “whole” shear walls cannot be compensated. This does not even reflect the advantage of the much simpler construction with fewer anchor points (also between floors). The disadvantage of the higher level of wooden off-cuts (in the window area) can normally be compensated by the possibility of using thinner boards.

The graphic shows the reinforcing ground floor walls of an 8-storey building. In the construction on the left, the walls are divided up near the windows (with laminated lintels). In the building on the right, the window openings are made out of solid boards. In both buildings, the stress is the same.

ANNEX C:STRUCTURAL MODELLING FORLOAD-BEARING STRUCTURES OF KLH MEMBERS

Calculating KLH structures requires forming a sufficiently precise model. Exact calculations of a member are only possible in very rare cases, let alone if the construction material is wood.Only homogenous materials such as steel can be calculated exactly. Therefore, the γm value = 1 can be applied in such cases.In case of wooden members, the γm value is 1.25 (for glued laminated timber). This value contains a number of uncertainties with regard to modelling. The level of precision in calculating cross-laminated timber (KLH) is similar. KLH-specific inaccuracies are included in the calculations stated in the ETA.

Nevertheless, any structural calculation of a load-bearing system must be based on a simulation that should be as precise as possible.The higher the level of usage of the material key data, the higher the precision of the simulation must be. In individual cases, the responsible engineer must make an educated estimate on this issue. These estimates are still necessary, because there is still no software for an assessment of the load-bearing behaviour of KLH slabs that would be sufficiently comprehensive.

The calculation can be structured in 2 areas. On the one hand, it is about the determination of section forces. In principle, these are the impacts on the member in different positions of the load-bearing structure. On the other hand, the member resistance values must be determined.The impact values must be smaller than the resistance values.

In order to determine the member resistance values, the ETA contains comprehensive data in order to be able and assess the material cross-laminated timber from an economic perspective. Since the scope of application of the slabs has become very diverse, so has the set of data, especially because fire verifications also have to be made in addition to the standard measurements.Therefore, an IT software has been developed (the “KLHdesigner”) in order to identify the member resistance values based on the ETA.In this software, the member resistance values are stated with regard to load-bearing safety (for normal cases and fire events).In addition, information is given on the member resistance values regarding stiffness. With this information, the section forces and the impacts on the members can be calculated with conventional computer programmes or even by manual calculations.

In principle, the types of load-bearing systems are very diverse. The calculation of the section forces is not material-dependant and must be carried out by an educated expert (structural engineer). Software that would cover all measurements regarding the members would certainly be desirable, but no such solution is in sight yet. Still, to facilitate this task, the KLHdesigner has been developed. It makes verifications for KLH structures a whole lot easier.

The input parameters for the different IT solutions for deformation and section forces calculations are used in this programme. Every software solution has certain characteristics. They will be explained in the following.

The below remarks should be used as to assist in the estimation of the effects of various calculation models.

Exact simulation as general 3-dimensional plate structures (combined structural behaviour of planes and slabs)

This simulation is hardly ever really required. In most cases, a structural system can be divided in the two main stress types. In the course of verification at the cross section, the stresses must, however, be superpositioned if this is essential.Some FE programmes provide access to the individual parameters of the coefficient matrix. These parameters are usually determined automatically. However, there is no software yet that would carry this out on the basis of the KLH ETA. This would be welcome, but is not the case yet. A “manual” input of the individual parameters of the coefficient matrix is often still possible, or the input can be saved and retrieved again later.With this data, the deformation behaviour of a 3-dimensionally stressed slab section can be calculated relatively precisely. Since the deformations are close to reality, the section forces will also be relatively precise (they are extrapolated from expansion and bending values). This is, however, on the condition that the support conditions and coupling to other members are recorded precisely (with non-linear fields).The local effects for single loads (point support, additional bending stress, load introduction for planes, etc.) can, however, not be taken into account this way. These effects can only be taken into account by way of “manual” verifications.

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Annex C to the comment on the ETA-06/0138 by J. Riebenbauer


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In addition, there are most often “discontinued” areas at local load introduction points, where the stated section forces are not neces-sarily in line with reality. Such FE models should only be prepared and assessed by well-trained persons with the appropriate background knowledge. Not eve-rything developed by an FE programme is actually relevant!Advantage: Relatively exact determination of deformations and section forces. Disadvantage of this option: High input effort, expert knowledge required for the interpretation of results.

Calculation for stresses normal to the surface – structural behaviour of slabs

In most cases, the calculation is performed in strip form. Area calculations are only required for special problem settings.The difference between area calculation and line calculation as slab strips only regards the consideration of the structural behaviour of both main load-bearing directions – the process of determining the stiffness values in the relevant load-bearing direction is the same. The torsional stiffness required for area calculations only has minor effects (and the torsional stiffness is only relevant for special framework conditions such as two-axis cantilever slabs, etc.).

The essential difference to other materials refers to shear deformation. It can be taken into account in different ways:

Net cross sections and “blurred” G-modulus This process is recommended for KLH members. The ETA is adjusted to it.The most simple and generally valid way is the separation of the two stiffness shares. The bending stiffness is calculated with the net cross section. The shear stiffness is calculated with the full cross section in load-bearing direction and with a blurred shear modulus. The shear modulus depends on the structure of the slab: the larger the number of cross layers and the thicker the cross layers, the lower the G-modulus will be. There are also dependencies regarding the relation of the thickness value of normal and cross layers.This method also makes sense for area calculations (orthotropic slab), but it can only be used to define the right G-modulus for one direction. This inaccuracy, however, is not relevant.FE programmes mostly allow the input of a reduced member thickness (orthotropic slab) in both main load-bearing directions for such cases in order to determine the bending and shear stiffness values (internally). This means that the G-modulus actually also has to be recalculated to this reduced member thickness. The effort for determination must not be exaggerated, though, since the shear deformation is only about 10 to 15% of the total defor-mation (in conventional building cases). Accordingly, the influence of this deformation is also minor. The effects of any inaccuracies can simply be estimated and taken into account with conservative values.Advantage: Strip-shaped members and area-shaped members are easily calculated. The deformations and there-

fore the section forces are relatively accurate. Even vibration analyses are relatively exact – on the con-dition that the simulation of the framework conditions (support conditions, slab joints, etc.) are correct.

Disadvantage of this option: The calculation of stresses by means of currently available IT programmes is most often inaccurate. The member verifications must be completed “manually”. With the assistance of the KLH-designer (design tool), however, this effort is minimised.

-methodIn the γ-method, an I_effective is determined. In this cross-sectional value, the shear deformation share is included. This, however, makes this value dependent on length. For various member situations, this method leads to very uneconomic solutions. For situations with interim supports and single loads, the results are also not correct – some of the stress values are calculated too low, others too high. This makes the method uncertain. It is necessary to know exactly when and what case applies.For an area calculation, the method is also unsuitable, because for many practical situations, the “relevant length” is not so easily determined. As a consequence, conservative estimates must be made, which in turn result in uneconomic design results.

Advantage: Generally known calculation method; shear deformation for single-span girders under even load can be calculated relatively exactly with software programmes that do not have to take shear deformations into account (older programmes and simpler girder solutions).

Disadvantage of this option: Only relatively precise solutions for FE girders, otherwise very inaccurate and partly wrong (uncertain results); wrong solutions for single loads and interim supports; very inaccurate for FE.

Shear analogy methodThis method calculates 2 separated girders that are coupled at certain points. By way of the allocation of the “Steiner share” of the net cross section and the blurred shear model to one girder and the total of the intrinsic inertia moments of the longitudinal lamellas to the other girder, the additional stresses due to shear deformations can be determined for the individual lamellas.This method can also be used for plane members. There are also solutions that have been developed for compound glass, for example. In principle, this is the same problem setting (flexible intermediate layers).

Advantage: Registration of the shear deformation effect and resulting additional stresses, even for stress due to support loads in case of interim supports and due to single loads.

Disadvantage of this option: The results depend on the distribution of the coupling points. Another unfavourable factor is that the results become too unfavourable if the distribution is narrow, and that the results will be wrong (not within the safe side margin) if the distribution is too wide. If it is not possible to adjust the distribution or if this distribution is not determined by production-specific conditions, then this method is not much more accurate than the γ-method. Close attention must be paid to how the mathematical solution of the recalculation from the bending and expansion values to the stress values is performed, and what key data the results are compared to. The KLH key data are not adjusted to this method.

Calculation with conventional beam structure programmesIn principle, only the correct stiffness must be taken into account for section force calculations.This can be achieved by converting the net inertia moment in a member with the width w = 100 cm and the relevant thickness (as required for orthotropic slabs), or by conversion into a rectangular cross section with the member thickness of the KLH cross section with the relevant width.This way, good results can be achieved, even in case of “manual” pre-design, and conventional software programmes can be used.In such cases, the best material to use is GL 24. This way, the E-modulus is slightly lower than admissible for KLH members. This diffe-rence often takes a large share of the shear deformation into account already.After all, the stresses are mostly not decisive, and they can be verified with the KLHdesigner and the calculation of the member resistance values. Only the decisive section forces are calculated, and then the KLH slab type is selected that has a higher member resistance than is necessary.Advantage: Use of general beam and girder programmes, simple and fast manual calculations for pre-design pos-

sible, exact verification of the member possible by comparing resistance values.Disadvantage of this option: The correct reading of the results requires some experience.

Calculations for stresses parallel to the plane – structural behaviour of planes

In most cases, the calculation is carried out in the form of girders, i.e. the residual cross section above windows and doors is calculated as girder fixed on one side or on two sides. In many cases this will be sufficient. The verification, however, will be inaccurate and it is necessary to know exactly where the limits of this verification method are.For more general cases, such as planes under horizontal loads (load parallel to the wall plane), a calculation by way of FE programmes should still be carried out. If we want to make a manual estimate of the section forces, we already need a fair amount of experience in the calculation of such members.

Calculation as beam/girderThe stiffness values can always be calculated with the full cross section of the lamellas acting in load-bearing direction. The shear modulus for the relevant lamella combination is issued by the KLHdesigner.The calculation still requires a girder programme that is capable of taking shear deformation into account. The share of the shear deformation is no longer as minor for this application (as plane or plane-like girder) as it was for slab stress situations. It is absolutely imperative to take shear deformations into account more precisely here, because it is often even higher than the bending deformation.Advantage: The determination of the section forces and deformations and the comparison with member resistance

values is possible fairly quickly. Even manual estimates are fairly accurate and easily performed.Disadvantage of this option: In cases of higher degrees of usage, various structural behaviours cannot be covered sufficiently pre-

cisely (e.g. support on thin wall pillars). In case of shear walls with openings, this method is possible in order to calculate a load-bearing framework structure, but the shear deformation values must be taken into account by the programme. Manual estimates for framework-type members (slabs with cut-out openings) are only admissible with a great deal of experience.

Calculation as FE modelDue to the fact that many FE programmes have simple graphic input methods available, calculations as FE models are no more time-consuming than framework calculations. The calculation with FE as orthotropic slab mirrors the section forces very precisely if the data of the ETA are used. This is what recalculations of various tests have shown (frames, walls with openings, continuous girders, etc.) In addition, by varying the support conditions (non-linear springs), considerably more economic member dimensions can be calculated. The KLHdesigner for the member resistance is useful here for providing input data and for comparing section forces with member resistance values (design/verification).Advantage: Can be used to make very precise calculations for many practical building cases, thus allowing economic

solutions. The concurrence with tests is very high.Disadvantage of this option: The section forces must be “manually” compared with the member resistance values; slightly higher

input effort. Software with graphic input environment and the possibility to calculate orthotropic slabs, taking shear deformation into account, must be available.

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Model formation in detail

In every calculation of structural load-bearing systems, there are certain detail areas that cannot be covered with the general mathe-matical models for beam or plane structures.The mathematical models often use a number of simplifications that might lead to partly serious deviations from reality in case of special applications and on a more detailed level.This is no specific characteristic of wood construction. It also applies to steel construction, especially concrete-steel construction, and must be taken into consideration accordingly.Detailed points where simplified mathematical models do not apply are called discontinuity areas (D areas) or detailed areas, or, easier to remember: double check areas (areas that require additional efforts). We can also call such areas “disturbed areas”, because this is where mathematical standard models for beam or plane structures do not deliver realistic results.

In the below depiction, some of these D areas that may become relevant for KLH members, are shown:

D areas in structural slab behaviour

This procedure has taken into account the effect of single loads in a simplified way. For normal cases, the calculated stresses were too high.

Since comparisons with competing products often include comparisons of member resistance values (equality), the KLH products gave worse results in some cases.Therefore, the new ETA states a method that basically provides a calculation of the slab with the net cross-sectional values and “blur-red” shear moduli. The normal stresses can be determined for standard cases (uniformly distributed loads, etc.) with the resistance moment of the net cross section. In case of single loads, the additional normal stresses can be taken into account with a correction value.

One advantage of this method is that the determination of the stresses no longer depends on length (as is the case with theγ-method). This way, even plane members can be calculated relatively realistically.The correction value of the normal stress due to the influence of single loads at point loads or point supports can be calculated for the cross section width that is also used for shear verification.The verification can be performed for both load-bearing directions.

Comparative calculations with realistic FE models (slab strips as plane) show a good analogy with the tests. In case of direct compari-son with the results of the γ-method, however, certain applications yield relatively high errors (too favourable stress figures).

1 KLH slabs have a certain share of shear defor-mation that influences the normal stresses if expo-sed to slab stress (load normal to the surface). In case of evenly distributed loads (uniformly distri-buted loads, trapezoidal loads), this influence is so small that it can be ignored, i.e. a single-span girder under a uniformly distributed load can be calculated relatively accurately with the γ-method.However, if single loads are applied on the structure or if the slabs rest on an interim support (acting like a single load), there will be a buckle in the theoreti-cal shear deformation line. This creates additional normal stresses that may be decisive.With the γ-method (l_effective), these effects can-not be taken into account correctly. The results part-ly show errors of up to 25%, which is actually too much. In the old KLH ETA, an adapted γ-method was used: I_effective was calculated according to the theore-tical approaches. The calculation of the resistance moment – and therefore the stresses – was, howe-ver, adapted.

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The influence of shear deformation on shear stress is minimal. In addition, the tests were analysed with the cross-sectional values of the net cross section. It is important that the calculations fit the analysis of the tests. This still takes all effects into account that are possible and not directly taken.For tests, for example for the old KLH ETA, the shear stresses were analysed with the full cross section, and in the ETA, the full cross section was also stated for verification.In principle, this procedure yielded a higher characteristic shear deformation (1.5 N/mm2).In the process of the test analyses for the new ETA, the older tests were analysed once again with the net cross-sectional values, be-cause all the other calculations are also based on the net cross-sectional values.This has now yielded a slightly lower characteristic shear stress level (0.8 to 1.2 N/mm2). This does not mean that the material has got worse or that the data in the old ETA would have been wrong. It simply depends on how the tests are analysed.Nevertheless, one effect has resulted from the analysis of the shear tests with regard to the influence of cross layers: in cases of single loads in the central third of a span, the characteristic shear strength goes down. It is likely that this is to do with the fact that the normal layers are coupled through cross layers (transfer of shear forces), and in cases of greater lengths under high theoretical shear stress, there will be an unfavourable statistic effect.Individual weak points can then become decisive more often than normal. If lengths are shorter and shear forces are high, the forces can be transferred to cross layers in front of or behind these areas.This is another detailed problem that cannot be solved with mathematical standard models for beam structures or plane structures (= D area).

3 In case of point-supported slabs or single loads, special shear veri-fications have to be made. The results from FE calculations partly result in very high local shear forces. Tests, however, have shown that shear forces may transfer to a larger width in case of slabs, i.e. verification with the maximum shear forces from the FE model leads to uneconomic results.In addition, the support points and load introduction points for single loads are most often taken into account as “points”. These create even more extreme (and unrealistic) local section forces.Even if the support points are simulated more precisely as plane contact areas with springs, results will show local maximum values for shear forces. Calculations that are really exact can only be carried out with a volume model that also takes elastic-plastic transfers into account. This effort, however, would be disproportionately high for the calcula-tion. It would be like taking a sledgehammer to crack a nut. Therefore, verification according to the simplified standard FE calculation is the best choice.

4 In principle, every load introduction area is a D area. The loads are only transferred into the direction of the board layers parallel to the loads. The intensity of the stress depends on the location of the load. The “evenness” of the compression is also relevant. The breakage beha-viour shows elastic-plastic behaviour, but caution is advised with regard to such influential areas, because there is an interplay with the theoreti-cal shear stresses due to stresses acting in plane.

Linear supports also have to be measured in detail. It has to be taken into account whether the support viewed in the cross section is even or not. If e.g. wall elements are not supported centred on concrete bases, this might result in eccentric support conditions and load introductions (e.g. eccentricities in case of thinner wall members).

2 Support points (with compression normal to the grain) can, of course, also not be identified directly with a beam structure programme. Such verification also has to be carried out “manually”.

D areas in structural plane behaviour


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5 As regards framework corners, FE calculations in the corner areas most often yield minor shear forces. This seems conclusive if we are aware of the underlying mathematical model.In the corner area, however, an important load transfer takes place. The normal stresses of the horizontal layers are transferred to the vertical layers through the contact surfaces. The stresses in the contact surfaces are complex. At present, a precise calculation is neither possible nor useful, because the required effort would be way too high.It is essential for the verification process that the verification of the shear forces (resulting force = shear force) at every section regards the vertical contact surfaces between the board layers. Therefore, a framework corner also requires a superposition of verifications of both load-bearing directions. If we view the section force image from the FE calculation, this is not something we would automatically assume.

6 In the inner corners of openings, there are also always local shear forces. These forces, however, are only to be attributed to the calculation model. The calculation results at these inner corners do not correspond to reality and can most often be ignored. It must be assumed in general that a joint (= shrinkage crack) appears exactly in the corner. This way, the shear force is not transferred directly through the individual board layer, but again through the crossed contact surfaces.In case of stresses in plane, shear forces are only to be regarded as theoretical. It is obvious that the total shear forces per section (resulting force = shear force as in a beam structure) must be transferred at the relevant sections.

Verification at the cross section with the influence of temperature

The distribution of the temperature in the cross section was determined with charring tests. In the EN 1995-1-2, the area at about 100 degrees is stated as significant with regard to stiffness and load-bearing capacity. Therefore, this area was used for the analysis of the KLH tests. The temperature curve was depicted with a bi-linear curve. The depths of elevated temperature stated in the new KLH ETA have yielded the greatest analogy with the tests.

The depiction shows the cross section of a 5-layer, 95 mm thick KLH slab with a 15 mm thick fireproof gypsum board cladding – after 60 minutes of fire exposure.The full lines represent the measured temperatures. The interrup-ted lines represent the mathematical model, which – in this case – follows the test curve very closely.In the model, the distance between 280 and 80 degrees is assu-med with 15 mm. The distance between 80 and 0 degrees is assu-med with 25 mm.The temperature data refers to the “excess temperatures”, i.e. “280 degrees” actually mean a measured temperature of 300 degrees including room temperature. The blue lines represent the mean values; the red lines are the measured maximum values.

This depiction shows the test after 30 minutes of fire exposure. The temperature in the wood is still below 200 degrees, i.e. there is still no charring. This case cannot be calculated with conventional models, because these models only start from the charring line.The model will yield additional safety compared to the measured data.

Due to the special design of the fireproof gypsum boards (material and fixing), the failure time is longer, and the insulation effect is higher compared to the data in the EN 1995-1-2, which – as far as I know – is based on tests with framework structures.The depiction also shows that the temperature curve here is flatter. This means, due to the protective effect of the fireproof gypsum board, the temperature has more time to intrude the inner part of the member.Accordingly, the d_100 and the d_20 values are higher (25 + 25 mm – see also ETA).

‐100

0

100

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300

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‐15 ‐5 5 15 25 35 45 55 65 75 85 95

‐100.0‐100

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‐15 5 25 45 65 85

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In some publications, these temperature curves are stated with very low d_100 values of about 10 mm. These curves were probably calculated with computer simulations, otherwise the curves would not be so regular. Whether and how the coal layers and the instatio-nary heat flow can really be simulated exactly is something I doubt. For any normal design process, this is certainly not usable.

It is important to note that these calculated temperature curves are used for the determination of the d_0 values of some products. This has direct influence on the load-bearing capacity. If the d_100 value is only 10 mm, then this results in a lower reduction of the load-bearing capacity than with a d_100 value of 15 mm (as is used for KLH).Therefore, the results cannot automatically be compared. Generally stated stiffness and strength reductions may not be used for the calculation of KLH structures (for KLH members, these reduction factors were extrapolated from tests; if only the calculated distance of 10 mm was used for other products, then these values are not usable for KLH members).

The reduction curves of the EN 1995-1-2 were therefore only a means of orientation for calculating the reduction factors to design the KLH slabs.

The procedure for the determination of the load-bearing capacities and the reduction factors as well as the analyses for simplified design methods (e.g. d_0 method) for fire events is not standardised. And if the exact background information is not known, then only results can be compared, which would be the structural member resistance value itself. It is not permissible to perform any extrapo-lations or to mix different data.

N O T E S

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