BN 10.060
Fundamentals for Steel Constructions
1. General design principles applicable to welded constructions
2. Frames, girders, etc.
3. Sheet metal construction, box girder
4. Drafting
5. Common welds at Broetje-Automation
Appendices
Appendix
0
© Broetje Automation GmbH
Alternatives to welding in cold-formed range
Two examples
BN 10.060
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
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 .
1
© Broetje Automation GmbH
Date
BN 10.060
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
5
6 pieces
2
© Broetje Automation GmbH
1
4
6
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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© Broetje Automation GmbH
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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.
better
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.
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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.
R  35mm
5
© Broetje Automation GmbH
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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
3
4
5
6
Refer also to appendix
6
© Broetje Automation GmbH
2
min (r/t)
10
3
2
1,5
1
1
r
5*t
1
max t mm
50
24
12
8
4
<4
t
5*t
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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.
7
© Broetje Automation GmbH
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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
a min  2mm
a min  t max  0,5
mm
a min  5mm
minimum throat thickness (DIN 18800; DIN 15018)
for t ≤ 30 mm
for t > 30 mm
Max. throat thickness – a max
a max  0,7 * t min
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!
8
© Broetje Automation GmbH
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1.12 Through Thickness Stress
1.12.1 Stress in through thickness direction, lamellar fractures
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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© Broetje Automation GmbH
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a. Design features to avoid lamellar fractures (best solution)
Avoiding unnecessary weld volume:
Welding across the sheet metal thickness:
better
better
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
10 © Broetje Automation GmbH
BN 10.060
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
11 © Broetje Automation GmbH
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
12 © Broetje Automation GmbH
BN 10.060
Design sample for low moment of area and shear force load
Welds do not require additional
verification if the following criteria
are met:
aF
=
0,7
*
tF
aS
=
0,7
*
tS
13 © Broetje Automation GmbH
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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.
Example of a reinforced bending beam with distributed load
e.g. distributed load
transverse stiffeners
Longitudinal stiffeners
Transverse force distribution
Bending moment distribution
14 © Broetje Automation GmbH
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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)
15 © Broetje Automation GmbH
Mounted hollow
section
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Design of welded seams
A
B
bu
B
C
α
ba
Joints between hollow sections are categorized into 3 areas: A, B and C. The following requirements apply
for joints between rectangular hollow sections:
Width ratio γ
 
ba
bu
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).
A
A
Figure 1
16 © Broetje Automation GmbH
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
Figure 3
B
Figure 4
Area C
Welds in acute angles may only be executed as fillet welds (fig. 6).
17 © Broetje Automation GmbH
B
Figure 5
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Rigid frame corners with rectangular hollow sections
The design strength or load-bearing capacity is
determined in accordance with DIN 18808.
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
h/b
1
1.2
1.4
1.6
1.8
2
b/t
≥ 15
≥ 15.5
≥ 16.5
≥ 17.5
≥ 19
≥ 21.5
for flat-lying rectangular hollow sections
h/b
1
1.2
1.4
1.6
1.8
2
18 © Broetje Automation GmbH
b/t
≥ 15
≥ 14.5
≥ 14
≥ 14.5
≥ 15
≥ 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
19 © Broetje Automation GmbH
More favorable
cross-section design for
tensile stress
BN 10.060
Unfavorable
cross-section design for
bending stress
More favorable
cross-section design for
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.
20 © Broetje Automation GmbH
BN 10.060
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.
21 © Broetje Automation GmbH
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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
22 © Broetje Automation GmbH
BN 10.060
5. Common weld seams at Broetje-Automation
5.1 Fillet weld / fillet weld illustration
Example double fillet weld
a-min
a-max
allowable fillet
weld sizes at BA
2 mm
15 mm
(consult
SFI)
Preferred range
at BA
3 mm
8 mm
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 multilayered (cost).
Example multi-layered fillet weld a = 10 mm, number of layers approx.
between 4 and 5.
Explanatory illustration
23 © Broetje Automation GmbH
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5.2 V-weld / V-weld illustration
Einzelteil 02
Example half V-weld
Example V-weld
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.
Explanatory illustration
24 © Broetje Automation GmbH
BN 10.060
t
C
C
5.3 Y-weld / Y-weld illustration
Example half Y-weld
Example Y-weld
Single part 02
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.
5.4 I-weld / I-weld illustration
No weld preparation. For sheet thickness up to 3 mm.
Example I-weld
25 © Broetje Automation GmbH
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5.5 Offset, intermittent welds
On the example of fillet welds
Symbol
Explanatory illustration
The seam to be welded must be divided (see
explanatory illustration) and the symbol must be
completed accordingly. The ends must be welded
around.
Example
26 © Broetje Automation GmbH
BN 10.060
2 Appendix
Alternatives to welding in cold-formed range
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
Common stiffening plate design at BA. Here,
welding is done in cold-formed range. The table in
chapt. 1.8 is applicable.
R 
 ÷min 1,5
t 
 12mm 

  1,5
 8mm 
27 © Broetje Automation GmbH
allowed
- production of single parts is less complex
Disadvantages:
- assembly more complex
- greater exposure to heat (distortion)
- more parts
BN 10.060
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
28 © Broetje Automation GmbH