BN10.060 Fundamentals for Steel Constructions (english)

BN 10.060

0 © Broetje Automation GmbH

Fundamentals for Steel Constructions

1. General design principles applicable to welded constructions

2. Frames, girders, etc.

3. Sheet metal construction, box girder

Appendices

4. Drafting

Appendix Alternatives to welding in cold-formed range Two examples

5. Common welds at Broetje-Automation

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Change Status and Release

Change Status:

05 Change Release Otholt, S. 19 Nov. 14

04 Change Release Otholt, S. 08 Oct. 14

03 Change Broetje logo Baumann 09.08.12

02 Chap. 1.6: text amended; Chap. 5 added, Appendix 1

deleted. Lüder Wilken 29 Jun. 09

01 Original Version 1 Lüder Wilken 28 May 09

Index Description Name Date

Release:

This company standard is valid and released only on the intranet of Broetje-automation. Prints and

copies are stored locally to test. They are not subject to the amendment service. The website

www.broetje-automation.de serves as an additional source for company standards for External .

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1. General design principles applicable to welded constructions

1.1 Keep welded joints at a minimum! Use rolled and cold-rolled sections. 1 2 3 4

5 6

6 pieces

1 2 3

4

4 pieces

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1.2 Pay attention to consistent force flow!

Every diversion of the force flow will lead to stress peaks (notch effect); the greater the diversion, the stronger

the notch effect. In case of static stress, stress peaks resulting from notches can be relieved through the

formability of the material. This is, however, not possible for dynamic stress. The notch may cause fatigue

fractures. Butt welds are preferable. Fillet welds on the T-joint should be carried out as double V-welds. Drastic

changes in cross-sections should be avoided.

Unfavorable force flow more favorable force flow (1:4 or less)

1.3 Arrange welded joints symmetrically when possible!

Unilateral distortion and warping is avoided, thus minimizing necessary straightening.

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1.4 Concentrations of weld seams and weld intersections are to be avoided!

Shrinkage stress may otherwise lead to multiaxial stresses which, in turn, impede deformation and cause fissuring.

1.5 Cut-outs

Re-entrant corners and cut-outs are to be rounded with a radius of at least 8 mm

1.6 JointPreparation

Joint preparation must be in accordance with DIN EN ISO 9692.

better

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1.7 Girder Reinforcement

The economic utilization of materials requires the use of thin web plates for beams. The associated risk of buckling is eliminated

by the arrangement of reinforcements.

Reinforcement and web plates require sufficient cut outs. Circular cut outs are preferable to straight cuts as circular cut outs are

easier to weld around and are more favorable in terms of stress.

mmR 35

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1.8 Welding in Cold-Formed Areas

When welding in cold-formed areas, including the adjacent areas with a width of 5*t, the limit values min (r/t) specified in the

table below must be adhered to. Linear interpolation of the values in lines 1 to 5 is allowed.

The deformation degree values indicated in the table below must not be observed when cold-formed parts are stress-relieved

prior to welding.

1 2

max t mm min (r/t)

1 50 10

2 24 3

3 12 2

4 8 1,5

5 4 1

6 < 4 1

5 * t

5 *

t

r t

Refer also to appendix

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1.9 Edge Distances

The edge distance should be e ≥ 2 x.

1.10 Slot Welding, slot width c

Fillet welds in slots should provide for a slot width of

c ≥ 3 x t.

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1.11 Fillet Weld Thickness, Throat Thickness Limit

The throat thickness of fillet welds should be taken from the static calculation and be specified in the technical

documentation (drawings).

The following limit values must be observed:

Min. throat thickness – a min mma 2min

5,0maxmin ta

mma 5min

mm

minimum throat thickness (DIN 18800; DIN 15018)

for t ≤ 30 mm

for t > 30 mm

Max. throat thickness – a max

It should be observed that the throat of fillet welds should be sized according to the calculated necessary thickness and are

not be based on the limit value “a max”.

Multilayer welds are requried for a > 4.0 mm. Pay attention to accessibility!

minmax *7,0 ta

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1.12.1 Stress in through thickness direction, lamellar fractures

1.12 Through Thickness Stress

If rolled products are stressed in through thickness direction, the formability in longitudinal and transverse direction is often

impeded. This is caused by the layered arrangement of non-metallic inclusion parallel to the surface as a result of the rolling

process. These inclusions react differently than the metal matrix when being formed which subsequently leads to a risk of fractures

parallel to the surface with rolled products.

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better

a. Design features to avoid lamellar fractures (best solution)

Avoiding unnecessary weld volume:

better

Welding across the sheet metal thickness:

Increasing the base of the weld seam:

better

better

b. Material-related features to avoid lamellar fractures (expensive & not certain)

Material-related features are aimed at increasing the formability upon stress in through thickness direction. Steels with low

contraction in area in through thickness direction are particularly susceptible to lamellar fractures.

e.g.: S355 J2 + N Z35

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1.12.2 Stress in through thickness direction, lamination

Sheet metals and wide flat steels in main support elements of class E (not predominantly statically stressed) which are subject

to tensile stress in thickness direction must undergo ultrasonic testing starting at nominal thickness of 10 mm.

Example1 : U180 stair stringer with

intermediate plates

Example 2:

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2. Frames and Frame Structures

Frames comprise the following components:

- Horizontal or angled girders = waler or binder.

- Vertical girders with simply supported bases = post or column.

- Joint between waler and column = frame corner.

Column and waler are beams and subject to normal, transverse and bending forces. Frame corners are rigid connections

which prevent any distortion of column and waler ends. Frame corners are executed as full welds or partial welds with

screwed connections.

Frames and their components require a static design (dimensioning) which are not further detailed at this point.

.

2.1 Creative design of frames and frame corners

2.1.1 Design of open cross-sections (predominant static stress).

Advantages:

- joints can be designed and produced easily

- empty cavities can be used for installations

- it is often possible to use standard rolled profiles (e.g. DIN 1025-1 to 4)

Disadvantages:

- low moment of inertia of area and moment of resistance, respectively, in one direction

- conservation is more complex

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aF = 0,7 * t

F

aS = 0,7 * t

S

Design sample for low moment of area and shear force load

Welds do not require additional

verification if the following criteria

are met:

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Arrangement of stiffeners (also refer to 1.7).

Transverse stiffeners must be positioned in areas of strong shear forces and strong force applications.

Longitudinal stiffeners must be positioned with large root face beams and in areas with high bending

moments.

e.g. distributed load

Transverse force distribution

Bending moment distribution

Example of a reinforced bending beam with distributed load

transverse stiffeners Longitudinal stiffeners

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2.1.2 Closed cross-section, tubular structure

Welded constructions must always be executed with hot-finished hollow sections (DIN EN 10210).

Advantages:

- nearly identical moment of inertia of area and moment of resistance in both directions

- conservation less complex

Disadvantages:

- design and execution of joints are complex

- high material costs (twice as much as rolled sections)

Design Details

Joints around the circumference should be executed as butt welds, as fillet welds or a combination of both weld

types.

The throat thickness of mounted hollow sections with a sections thickness of ta ≤ 3 mm must be at least equal the mounted

section: a = ta

The throat thickness of mounted hollow sections with a section thickness > 3 mm must be at least equal the section thickness

of the mounted section: a ≥ ta; it may, however, not be less than 3 mm

A broader throat thickness may be required for design reasons.

Applicability:

pipe diameter: d ≤ 500 mm

dimensions of hollow section:

b ≤ 400 mm / h ≤ 400 mm

0.5 ≤ h/b ≤ 2.0

t ≥ 1.5 mm (for S355)

t ≤ 25 mm (for S355)

d/t ≤ 67 (for S355)

b/t ≤ 36 (for S355)

Mounted hollow

section

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Design of welded seams

Joints between hollow sections are categorized into 3 areas: A, B and C. The following requirements apply

for joints between rectangular hollow sections:

A C B

B

α

Area A

The weld should be executed as HV seam for lug angles α < 45° (fig. 1).

Fillet welds are possible as well when α ≥ 45° (fig. 2).

bu

ba

Width ratio γ

bu

ba

A A

Figure 1 Figure 2

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Area B

For γ ≤ 0.8: the welded joints may be executed at fillet welds (fig. 3).

For γ > 0.8: welding may not always be possible due to the flanging radii (fig. 4) and should

therefore be avoided. Full penetration welding cannot be ensured with smaller flanging radii.

The welds must be executed as V-seams (fig. 5).

B B B

Figure 3 Figure 4 Figure 5

Area C

Welds in acute angles may only be executed as fillet welds (fig. 6).

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Rigid frame corners with rectangular hollow sections

Applicability:

b ≤ 300 mm

h ≤ 300 mm

0.33 ≤ h/b ≤ 3.5

t ≥ 2.5 mm

t ≤ 25 mm (for S355)

d/t ≤ 67 (for S355)

b/t ≤ 36 (for S355)

Weld testing is not required if the following applies:

for upright rectangular hollow sections

for flat-lying rectangular hollow sections

The design strength or load-bearing capacity is

determined in accordance with DIN 18808.

h/b b/t

1 ≥ 15

1.2 ≥ 15.5

1.4 ≥ 16.5

1.6 ≥ 17.5

1.8 ≥ 19

2 ≥ 21.5

h/b b/t

1 ≥ 15

1.2 ≥ 14.5

1.4 ≥ 14

1.6 ≥ 14.5

1.8 ≥ 15

2 ≥ 15.5

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3. Sheet metal construction, box girder

Whenever large component thicknesses are needed, it is recommended to use box or cellular constructions so that the

cross-sections of the individual metal sheets can be reduced.

Advantages:

• less throat thickness, i.e. reduction of weld material

• the workpiece is exposed to less heat during welding, i.e. less distortion

• cost reduction due to the elimination of thickness surcharges by using metal sheets with a thickness up to t=25mm.

• risk of brittle fractures due to multi-axial stress with large sheet metal cross-sections is counteracted

• reduction of weight

Unfavorable

cross-section design for

tensile stress

More favorable


tensile stress

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Unfavorable


bending stress

More favorable


bending stress

Note:

In many cases, designs at Broetje-Automation are based on the principle of allowable distortion rather than on the

principle of allowable stress, i.e. the allowable load. This requires a high dimensional stability/rigidity which is

achieved through large cross-section surfaces and a high moment of inertia, respectively.

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4. Drafting

All welds must be displayed and marked with the symbols pursuant to DIN EN 22553. Drawings must be properly

dimensioned and suitable for production. The weight of the weld piece must be indicated on the drawing. Single part drawings

must illustrate the weld preparation.

Dimensions must be rounded to the full millimeter where possible; for reasons of utilizing symmetries and the like,

dimensions are rounded to 1/10 millimeter.

Unlike in mechanical engineering, it is frequent practice to enter (closed) dimensional chains. Reference dimensioning in structural

steel engineering is often not very suitable for production.

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For curved parts, it is often useful to enter the radian. The radius of curvature related to the radian or radian dimensional

chain must be entered in parenthesis after the radian or radian dimensional chain.

View of a curved beam (rolled section) with attachments

suitably dimensioned for production

View of a curved beam (rolled section) with

attachments not suitably dimensioned for production

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5. Common weld seams at Broetje-Automation

Example double fillet weld Example peripheral fillet weld

No weld preparation; a-dimensions between 2 and 15 mm allowed; preferred dimensions between 3 and 8 mm. Choice depends on

sheet metal thickness and static analysis. Peripheral fillet welds are preferred. Refer also to chapt. 1.11.

Attention: Fillet welds with an a-dimension of more than 4 mm are multi-

layered (cost).

Example multi-layered fillet weld a = 10 mm, number of layers approx.

between 4 and 5.

a-min a-max

allowable fillet

weld sizes at BA 2 mm

15 mm

(consult

SFI)

Preferred range

at BA 3 mm 8 mm

5.1 Fillet weld / fillet weld illustration

Explanatory illustration

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5.2 V-weld / V-weld illustration

Example half V-weld Example V-weld

Einzelteil 02

α = 50° to 60 °; a = 45° possible for smaller wall thickness

c = 1 to 2 mm

for sheet metal thickness between 3 and 20 mm.

Attention: V-welds are multi-layered for sheet metals with greater

thickness (cost). Example sheet thickness t = 15 mm, number of

layers approx. between 5 and 6.


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5.3 Y-weld / Y-weld illustration

Example half Y-weld Example Y-weld

C = seam depth. The C-value is entered as a numerical value (in mm) in front of the Y-symbol. α = 60°; α = 45° allowed for

smaller C-value. C value depends solely on static requirements.

C

t

C

Single part 02

5.4 I-weld / I-weld illustration

No weld preparation. For sheet thickness up to 3 mm.

Example I-weld

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5.5 Offset, intermittent welds


Symbol

Example

The seam to be welded must be divided (see

explanatory illustration) and the symbol must be

completed accordingly. The ends must be welded

around.

On the example of fillet welds

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Common stiffening plate design at BA. Here,

welding is done in cold-formed range. The table in

chapt. 1.8 is applicable.

d12

(4)

Possible alternative 1:

Weld stiffening plate with flat steel. Subsequently weld flat

steel with wall plate.

Advantages:

- problem with welding in cold-formed range is eliminated

- production of single parts is less complex

Disadvantages:

- assembly more complex

- greater exposure to heat (distortion)

- more parts

2 Appendix Alternatives to welding in cold-formed range

5,18

12

mm

mmallowed

5 , 1 min ÷

t

R

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Possible alternative 2:

Design single parts to be “pluggable”

Advantages:

- problem with welding in cold-formed range is eliminated

- production of parts is complex

Disadvantages:

- assembly is more complex

- greater exposure to heat (distortion)

- protrusions on the wall plate

BN10.060 Fundamentals for Steel Constructions (english)

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