Fundamentals for Steel Constructions

Transcription

1 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 Alternatives to welding in cold-formed range Two examples 0 Broetje Automation GmbH

2 Change Status and Release Change Status: 05 Change Release Otholt, S. 19 Nov Change Release Otholt, S. 08 Oct Change Broetje logo Baumann Chap. 1.6: text amended; Chap. 5 added, Appendix 1 deleted. Lüder Wilken 29 Jun 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 serves as an additional source for company standards for External. 1 Broetje Automation GmbH

3 1. General design principles applicable to welded constructions 1.1 Keep welded joints at a minimum! Use rolled and cold-rolled sections pieces pieces 2 Broetje Automation GmbH

4 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. 3 Broetje Automation GmbH

5 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 Broetje Automation GmbH

6 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

7 5 * t t BN 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. 5 * t 1 2 max t mm min (r/t) , < 4 1 r Refer also to appendix 6 Broetje Automation GmbH

8 1.9 Edge Distances The edge distance should be e 2 x Slot Welding, slot width c Fillet welds in slots should provide for a slot width of c 3 x t. 7 Broetje Automation GmbH

9 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 a min 5mm 0,5 mm 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

10 1.12 Through Thickness Stress 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. 9 Broetje Automation GmbH

11 a. Design features to avoid lamellar fractures (best solution) Avoiding unnecessary weld volume: better Welding across the sheet metal thickness: 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

12 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: 11 Broetje Automation GmbH

13 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 Creative design of frames and frame corners 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 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

14 Design sample for low moment of area and shear force load Welds do not require additional verification if the following criteria are met: a F = 0,7 * t F a S = 0,7 * t S 13 Broetje Automation GmbH

15 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 transverse stiffeners Longitudinal stiffeners e.g. distributed load Transverse force distribution Bending moment distribution 14 Broetje Automation GmbH

16 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 15 Broetje Automation GmbH

17 bu ba BN 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: B A B C α 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 Figure 1 Figure 2 A 16 Broetje Automation GmbH

18 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 Figure 4 Figure 5 B B Area C Welds in acute angles may only be executed as fillet welds (fig. 6). 17 Broetje Automation GmbH

19 Rigid frame corners with rectangular hollow sections The design strength or load-bearing capacity is determined in accordance with DIN 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 b/t for flat-lying rectangular hollow sections h/b b/t Broetje Automation GmbH

20 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 cross-section design for tensile stress 19 Broetje Automation GmbH

21 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

22 4. Drafting All welds must be displayed and marked with the symbols pursuant to DIN EN 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

23 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

24 5. Common weld seams at Broetje-Automation 5.1 Fillet weld / fillet weld illustration 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 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 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

25 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. Explanatory illustration 24 Broetje Automation GmbH

26 t C C BN 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

27 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

28 2 Appendix Alternatives to welding in cold-formed range d12 (4) Common stiffening plate design at BA. Here, welding is done in cold-formed range. The table in chapt. 1.8 is applicable. R t min 1, 5 12mm 1,5 8mm allowed 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 27 Broetje Automation GmbH

29 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