AN OVERVIEW ON THE DRAFT OF THE EGYPTIAN CODE FOR MASONRY ANO A PROPOSED RESEARCH TO COVER THE

SHORTCOMINGS

Dr. Gouda Ghanern I and Dr. Arnr E. Salarna2

1. ABSTRACT

Masonry is one of the oldest fonns of construction, recently the design of masonry structures has been governed by codes and standards. These codes provides a means of establishing minimum standards for acceptance of design and construction by a legal!y appointed building official. In order to implement masonry structures as a cost-efficient building system in Egypt, national design code and standard specifications should be developed based on local materials, levei of quality control, and common construction practices. This require long­tenn research effort to provide an adequate data base for the development of design procedure. Great effort have been done to prepare the Egyptian code 1992 for masonry. Present state of this code indicates the need for more research to enable masonry structures to achieve its ful! potential. Areas needing further study are material properties such as axial compressive strength, modulus of elasticity, shear strength, splitting tensile strength, and behavior of elements such as walls under in-plane compression, in-plane shear, and out-of-plane loading, and wall with return for ali types of masonry (unreinforced, partially reinforced, and reinforced masonry). This research program will provide informations on strength and defonnation characteristics of masonry, design recommendations for wall element and empírical fonnulas for prediction of material properties and wall capacity.

2. INTRODUCTION

Although masonry is one of a man s oldest building material, it has probably remained the least understood of major construction materials. In the last 50 years, masonry has changed from just a role of thumb material to an engineered material, while in the last 20 years it has expanded its application from smal! buildings to a major high-rise structures especially in Europe and USA.

1 Assistant Professor, Helwan University, Cairo, Egypt 2 Professor, Helwan University, Cairo, Egypt

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The achievement of lateral stability by gravity places a practical economic limit on the size of the structure. This has led designers and engineers to the evolvement of plain masonry into reinforced masonry(4). A system which is buiIt mainly in regions of high seismicity. In areas where seismic or wind forces are not considered to be critical (as in Egypt and most of the Arab Countries) the use of reinforced masonry becomes uneconomical. The most cost-efficient system in such areas is masonry walls with partial (light) reinforcement to resist tensile and shear forces(3). This system offers an attractive building system with multifunctional characteristics, it save formwork, reduce the amount of reinforcement needed and eliminate expensive exterior plastering with the added advantages of speed of construction, simple erection techniques and dimensional tolerances(3).

In Egypt, the infilled reinforced concrete frame sttuctures are dominam in residential building consttuction. This system is becoming more expensive due to high cost of formwork, reinforcement, and plastering. There is an urgent need to use masonry as an engineered material and introduce a new system (partially reinforced masonry walls).

Lack of design information for unreinforced, partially reinforced, and fully reinforced masonry walls is restricting structural designers from evolving new uses for these systems. This can be overcomed by further research to develop formulas and recommendations for structural elements.

To develop a national design methodology for unreinforced, partially reinforced, and fully reinforced masonry, better understanding of the behavior of these walls is needed. The shear capacity, flexural capacity are necessary information for the development of a rational design methodology(S).

Like steel and reinforced concrete structures, the design of masonry structures has been governed by codes and standards to guide or regulate manufacturers, designers, and builders(6). For this reason the code should be adopted by government bodies having the police power to regulate building design and construction(l&2).

The building code states only the minimum requirements necessary to provide for public health and safety. Therefore the code should be based on this principle(l). For any structure, the owner or the structural designer may require the quality of materiaIs and construction to be higher than the minimum requirements necessary to protect the public as stated in the code. However lower standards are not permitted(l&6).The design code and standard specifications should be based on local material and enviouremental condition.

3. STATE OF THE ART

From the overview on the first draft of the Egyptian code for loadbearing masonry structures, there are some cases which are not covered it, and the general comments are: a- The list of the standards should include material specifications, sampling, test methods, detailing requirements, design procedures and classifications should be referenced whenever possible. b- The code is a collection of parts from different codes having different design philosophies and local conditions. c- Specifications should be included as part of the code, otherwise allowable stresses are not justified and be highly non-conservatiove.

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d- Specifications should include construction tolerances, quality control measures and execution. e- The Code is lacking information on deformation characteristics for masonry, for example coefficient of thermal expansion, creep, moisture expansion and shrinkage. f- Code specification should specify testing methods to determine material propenies required for designo . g- The code lacks design provisions for wall connections, anchor bolts and ties and their coating for corrosion resistance. h- The commentary directs attention to the other documents that provi de suggestion for carrying out the requirements and intent of the code, therefore the commentary should be included in the code.

Present state of this code indicate the need for more research to achieve full potential of masonry structures and to cover the shortcomings and comments of the following topics:

3.1 Axial Compression

a- Allowable Code values for deterrnining the characteristic strength of masonry by the two methods (prism strength or unit strength) should be based on local materials. b- Current code do not state specifications and dimensions of plate used in prism test. c- Code is lacking information on calculating or estimating the Young's modulus (E) of masonry, the code do not state which E . d- Allowable Code values for axial compression should include the effect of: - Correction factors for prisms built with full mortar bedding comparable to face-shell bedding. - Curing on the characteristics strength of masonry and also the effect of age on the masonry strength.

3.2 Shear Bond Strength

a- Current code for shear of unreinforced shear walls not based on material properties (not function of characteristics strength of masonry) but the code state absolute value for shear regardless the effect of masonry unit and mortar. The current code take the effect ofaxial load into consideration. b- The shear strength for reinforced masonry shear walls should be based on rectangularity ratio of the wall or the interaction between bending moments and shear force (M/V d ratio) and also the effect of characteristics strength of masonry. c- The current code as most of the other codes do not recognize the presence of vertical steel in the shear wall in preventing the propagation of diagonal tensile cracks across the wall. The presence of vertical steel acrually reduce the allowable shear stresses. d- Allowable Code values for shear strength do not take into account the effect of bonding type and grouting. e- Allowable Code values for shear strength do not reflect type of materials (brick, block and stone), wall geometry and construction details (hollow, solid and grouted). f- No provision was made for different mortar and unit strengths.

3.3 Tensile Stresses

a- Current code allows absolute values for tension stresses (0.7 kg!cm2 for tension normal to the bed joint and IA kg!crn 2 for tension paralJeJ to the bed joint) for running bond, no provisions were made for different types of mortar. b- Allowable Code values for splitting tension do not reflect type Df materials (brick, block

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and stone) and construction details (hollow, solid, grouted, and partially grouted).

3.4 Walls

a- Current code is lacking formulas for predicting the shear strength, flexural strength and nominal axial strength of unreinforced, fully reinforced and partially reinforced masonry walls subjected to in-plane lateralloads and axialloads b- The code is lacking information on partially reinforced masonry walls as a new system in Egypt and Arab Countries. c- The code is lacking infonnation on the behavior of unreinforced, fully reinforced and partially reinforced masonry walls under out-of-plane lateralloads. e- Empírical and analytical expressions should be developed to determine wall deflections, ductility, and capacity of such walls in terms of masonry strength, axialload, horizontal and vertical reinforcement and rectangularity ratio of the wall pane!.

4. RESEARCH PLAN

Present state of knowledge outlined above, indicates the need for more research to enable masonry to achieve its full potential(5) and topics needs further research are discussed later.

The proposed research program is divided into the following phases:

Phase 1 This phase is aimed at conducting structural performance tests to evaluate the important material properties of unreinforced, partially, and fully reinforced masonry. The results of this phase will enable specification of important material properties needed for structural use such as flexural tensile strength, compressive strength, modulus of elasticity, shear strength, and splitting tensile strength in different orientations. Further, development of analytical formulas will also be pursued to predict the above properties in terms of prism strengths of grouted and hollow block masonry.

Phase 2 This phase is aimed at conducting structural performance tests to study the behavior of wall elements. The results will enable development of design recommendations for walls (unreinforced, partially reinforced, and fully reinforced) under axial compression, in-plane loading and out-of-plane flexure. This phase is important for the development of design methodology. Further, the results will also enable to generate design information on walls with returns.

Phase 3 This phase is aimed at conducting analytical analysis using finite element method to study and analyze the behavior characteristics of partially reinforced masonry walls. This study is essential for the development of design methodology and building code requirements.

The proposed research program is expected to provide comprehensive design information on unreinforced, partially reinforced, and fully reinforced masonry, ready for inclusion in building codes, which will enable structural designers to utilize the fuII potential of this material. The final goal is envisaged to be the achievement of greater economy in concrete masonry structures by encouraging the judicious use of hollow block, partially reinforced or reinforced concrete masonry to satisfy optimally the requirements of any particular application.

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Pbase 1

Objectives

The primary objective of this phase of the study is to cover the cases not eovered in the existing code and to determine the most influential material properties of masonry. The material properties considered are eompressive strength, modulus of elasticity, shear strength, splitting tensile strength and flexural tensile strength. The secondary objectives of this phase is: - To develop formulas, empirieal or analytieal, to prediet the material properties in terms of prism strengths of hollow, partially and fo1ly grouted eoncrete masonry assemblages.

Scope

The following are the parameters and corresponding leveIs to be eonsidered for eaeh material properties.

Axial Compression and Modulus of Elasticity

Parameters - Grouting - Block and Brick strengths - Mortar bedding area (fo1l bedding, face-shell bedding) - Slenderness ratio h/t = 1,2,3,4,5 for briek

h/t = 2,3,4,5,6 for block - Joint reinforeement

Figure 1. Specimens For Prism Test

Shear Stren~th

Parameters - Grouting - Mortar bedding area - Axial stresses - Type of mortar

Figure 2. Specimen For Bed Joint Shear Test

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Splittin~ Tensile Stren~th

a) Parallel Tensile Strength parameters

- Block strength and brick strength

b) Nonnal Tensile Strength Parameters

- Mortar bedding area - Grout strength - Grout spacing - Type of mOltar

c) Diagonal Tensile Strength Parameters

- Block strength - Grout strength - Grout spacing - Type of mortar

Flexural Tensile Stren&th

Parameters - Grout Spacing - Grout Strength - Block Strength - Type of mortar - Mortar bedding area - Reinforcement

Figure 3. Specimens For Splitting Tensile Test

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Figure 4. Specimens For Flexural Test

The above parameters cover a wide practical spectrum of construction details of unreinforced,partially, and fully reinforced masonry walls.

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Present Status

The studies on material components, flexural tensile strength, in-plane shear, and splitting tensile strength are currently in progress at the structural laboratory (Mataria), Helwan University.

Pbase 2

Objectives

The primary objective of this phase of the study is to focus on the structural behavior of unreinforced, partially reinforced and fully reinforced masonry wall elements and to develop rational design methodology of such walls. Wall e\ements are subjected to axial compression, in-plane loading, and out-of-plane flexure to cover the critical modes of loading likely in actual applications . Some tests on behavior of walls with returns are also envisaged. The secondary objectives are: - To study the relative influence of main parameters on structmal behavior of wall elements under the above modes of loading, - To develop design recommendations to enable structural design of unreinforced, partial, and fuJly reinforced masonry walls - To generate design information on waIls with retmns

Scope

The foIlowing parameters and corresponding leveIs, which cover most practical applications, are considered for walls under axial compression:

- Grout spacing - Grout strength - Block and brick strength - Slenderness ratio of the wall - Percentage and distribution of vertical steel - Percentage and distribution of horizontal steel - Walls with retums - Openings

Figure 5. Walls For In-Plane Loading (Axial Compression)

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The following parameters and corresponding leveIs, which cover most practical applications, are considered for walls under in-plane loacling:

- Grout spacing - Grout strength - Block and brick strength - Aspect ratio (height/length) - Percentage and distribution of venical steel - Percentage and clistribution of horizontal steel - Precompression stresses - Walls with returns - Openings

Figure 6. WalI For In-Plane Loading (Lateral Load)

The following parameters and corresponding leveis, which cover most practical applications, are considered for walls under out-of-plane flexure

- Grout spacing - Grout strength - Percentage and clistribution

of vertical steel - Precompression Stresses - Walls with returns

Figure 7. Wall For Out-Of-Plane Loading

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Present Status

The experimental studies on partially reinforced concrete walls under in-plane loading (Monotonic and Cyclic) were completed by the authors, except the effect of openings.

Phase 3

Objectives

The primary objective of this phase of study is to analyze the behavior of unreinforced, partially, and fully reinforced masonry walls analytically using the finite element method. and to develop analytical formulas to predict the strength, deflection and ductility of such walls. The experimental results will be used to check the accuracy of the computer mode!. The secondary objectives are: - To deve10p analytical model which provide an easy tool to conduct parametric study on the effect of different parameters on the deformation and strength of partially reinforced masonry walls. - Discussion of potential design methodology of unreinforced, partially, and fully reinforced masonry walls.

Scope

The same parameters as mentioned before and corresponding leveIs, which cover most practical applications are considered for walls under axial compression, in-plane loading, and out-of-plane flexure.

Present Status

Empirical and analytical formulas for predicting the shear strength, axial strength and flexural strength of partially reinforced concrete walls under in-plane loading tak.ing into consideration alI the factors mentioned above were completed by the author.

5. ANTICIPATED RESULTS

Phase 1

The following are the test results that will be measured, observed, and documented during the course of the proposed testing program: - Cracking load and crack pattem - Ultimate load - Failure mode - Load deformation curve - Maximum masonry strain - Control test data such as masonry prism strength, mortar cube strength, block strength, and grout strength

The above measurements and observations for different structural performance tests are expected to provide a data base to cover the shortcorning in the existing draft code and to give a thorough understanding of the material properties of unreinforced, partially, and fully reinforced masonry walls, their magnitudes and how they are influenced by grouting, and block and brick strength. The results will also give an insight into how major parameters can be varied to attain the required characteristics for specific applications of unreinforced,

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partially, and fully reinforced masonry walls. Test results will also provide a data base for developing and assessing formulae for prediction of material properties.

Pbase 2

The following are the test results that wiU be measured, observed, and documented during the course of the proposed experimental program: - Cracking load and crack pattem, - Yielding and ultimate load, - Failure Mode, - Load deformation curve, - Ductility and energy dissipation capability of these walls, - Maximum masonry strain and maximum strain in reinforcement - Control test data such as masonry prism strength, mortar cube strength, block strength, grout strength, and steel properties - Shear stiffness and flexural stiffness of masonry walls

Pbase 3

The following are the results that will be observed and documented during the course of the proposed analytical program: - Provide a national design methodology for unreinforced, partially, and fully reinforced masonry walls, and - Develop analytical formulas to predict the strength and capacity of unreinforced, partially, and fully reinforced masonry walIs.

Several significant indicators can be read from load deformation curves such as initial and subsequent slopes, cracking load, yield point of the wall, ultimate capacity and the ductility ratio. These indicators will help to determine the wall response, wall parameters can be varied to improve wall response, and relative suitability for various applications.

Sirni1arly, several significant indicators can be read from the graphs of the load-deflection such as peak ultimate loads, working ultimate loads, ductility ratios and stiffness degradation coefficients. These indicators will help in determining wall response and resistance.

Ultimate ductility factors are required to determine ultimate collapse conditions using inelastic response spectra. Ultimate ductility is also essential to apply more sophisticated failure analysis methods such as a [mite element time-history computation.

Past-yield envelopes will be established from the hysteretic curves. The characteristics of these envelopes are essential to determine the applicability of standard analysis methods such as the inelastic yield spectra and energy balance technique to unreinforced, partially, and fully reinforced masonry walIs.

FinalIy, the results will adjust the code allowable to fit the local condition and to cover ali the shortcomings, the analysis of the above results is expected to produce design recommendations for walls under in-plane compression, in-plane shear, out-of-plane flexure, and design information on walls with returns. It is also expected that limits within which unreinforced, partialIy, and fully reinforced rnasonry walls can be used optimalIy, for various applications can be identified during this phase of the study.

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REFERENCES

ACI 530-88 / ASCE 5-88 "Building Code Requirement for Masonry Structures" American Concrete Institute, Detroit 1988.

2 American Society for Testing and Materials, ASTM C-447, "Standard Test Methods for Compressive Strength of Masonry Prisms", Annual Book of Standards, VoI. 4.07, Philadelphia, PA, 1985.

3 Chandrakeerthy, S. and Hamid, A.A., "Partially Reinforced Concrete Masonry as an Alternative Building Material in Deve10ping Countries", Proc. the 3m International Masonry Serninar for Developing Countries (Mauritiues, July 1990.

4 Ghanem, G.M. "Behavioral Characteristics of Partially Reinforced Loadbearing Masonry Walls", Ph. D., Thesis, Helwan University, Cairo, Egypt, 1992.

5 Hamid, A.A. and Ghanem, G.M. "Behavior of Partially Reinforced Masonry Walls", Proc. 9lh International Brick/Block Masonry Conference (Burlin , Germany, October 1991)

6 Uniform Building Code, 1988 Edition, Intemational Conference of Building Officials, "Masonry Codes and Specifications", CA, May 1988.

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