AD399 - Codes & Standards

NSCJuly2016digi

Advisory Desk and Codes & Standards AD 399: Design of partial penetration butt welds in accordance with BS EN 1993-1-8 Partial penetration butt welds are covered by Clause 4.7.2, which directs the designer to ‘use the method for a deep penetration fillet weld” given in clause 4.5.2(3). Clause 4.5.2(3) really concerns only the definition of the throat, and leaves the designer unsure of how the design resistance is to be calculated. Partial penetration welds are considered to be less ductile than full penetration welds and therefore many design Standards require that they are to be treated in the same way as fillet welds. This is the principle behind the advice in clause 4.7.2. Unless rotation is suitably restrained, eccentricity must be taken into account when calculating the stress in the weld. Examples of details where eccentricity is introduced in partial penetration butt welds are shown in Figure 4.9 of BS EN 1993-1-8. Eccentricity need not be considered if the weld is used as part of a weld group around the perimeter of a structural hollow section (clause 4.12(3)). It is reasonable to assume that there is no eccenticity if the welded element is part of a member which itself cannot rotate at the joint – for example if a partial penetration weld is used to connect the flange of a beam to an end plate. In the numerical example which follows, it is assumed that rotation cannot take place. Throat The throat of a partial penetration butt weld is the distance from the root to the external face of the weld, as described in clause 4.5.2(1). Examples are shown in figure 1. a 33° (a) (b) (c) Figure 1: Throat (a) of partial penetration welds Common practice is to either (a) assume the penetration (and hence the BRITISH STANDARDS BS 5427:2016 Code of practice for the use of profiled sheet for roof and wall cladding on buildings Supersedes BS 5427-1:1996 BS EN PUBLICATIONS BS EN ISO 12707:2016 Non-destructive testing. Magnetic particle testing. Vocabulary Supersedes BS EN 1330-7:2005 30 NSC July/Aug 16 a a BRITISH STANDARDS WITHDRAWN BS 5427-1:1996 Code of practice for the use of profiled sheet for roof and wall cladding on buildings. Design Superseded by BS 5427:2016 BS EN 1330-7:2005 Non-destructive testing. Terminology. Terms used in magnetic particle testing Superseded by BS EN ISO 12707:2016 design throat) is less than the preparation, or (b) to conduct weld procedure trials to demonstrate what penetration can consistently be achieved. The first approach was encouraged by the 1990 version of BS 5950, where clause 6.6.6.2 specified a reduction of 3 mm for V and bevel welds. Clause 6.9.2 of the 2000 version of BS 5950 specifies no reduction but refers to the depth of penetration, which may be more or less than the preparation. Design resistance It is recommended the the directional method of clause 4.5.3.2(6) is used when calculating the resistance of a partial penetration butt weld. Assuming there is no longitudinal stress, the direct stress must be resolved into a perpendicular stress on the throat, σ⊥ and a shear stress on the throat, τ⊥. Expression 4.1 of BS EN 1993-1-8 requires that the combination of perpendicular stresses are verified and also limits the perpendicular stress. With no longitudinal stress on the weld throat, the verifications become: (⊥2 + 3⊥2)0.5 fu WM2 and NEW WORK STARTED EN ISO 14713-2 Zinc coatings. Guidelines and recommendations for the protection against corrosion of iron and steel in structures. Hot dip galvanizing Will supersede BS EN ISO 14713-2:2009 ISO 5173 Destructive tests on welds in metallic materials. Bend tests Will supersede BS EN ISO 5173:2010+A1:2011 ISO 11666 Non-destructive testing of welds. Ultrasonic testing. Acceptance levels Will supersede BS EN ISO 11666:2010 New and revised codes & standards From BSI Updates June 2016 ⊥ 0.9fu M2 In case (b) of figure 1, assuming the applied force is 2000 N/mm, and the throat is 9 mm, the components of force become: σ⊥ = 2000 Cos(33)/9 = 186 N/mm2 and τ⊥ = 2000 Sin(33)/9 = 121 N/mm2 The combined check of shear and perpendicular stress, with βw = 0.9 for S355 (taken from Table 4.1) becomes: (1862 + 3(121)2)0.5 = 280 N/mm2. The limit is 470 0.9 × 1.25 = 418 N/mm2 The perpendicular stress σ⊥ is 186 N/mm2; the limit is 0.9 × 470 1.25 = 338 N/mm2 Of course, if a standard fillet weld is verified by the same process, using an angle to the throat of 45°, it can be demonstrated that the resistances are those quoted in the Blue Book1 for a transverse weld. Reference 1 Steel building design: Design data. In accordance with Eurocodes and UK National Annexes (P363). SCI, Reprinted 2015. Contact: Abdul Malik Tel: 01344636525 Email: advisory@steel-sci.com


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