AD 316: BS 5950-1: 2000, Amendment No 1

Design engineers should be aware that Amendment No 1 (BSI reference Amendment No 17137) to BS 5950-1: 2000 has been issued, dated 31st August 2007. The new amendment has been incorporated directly into the Standard by BSI and therefore the Standard is still referred to as BS 5950-1: 2000 although the copyright is now BSI 2007. This makes it easy to tell if the right version of the Standard is being used because the copyright symbol (© BSI 2007) appears in the footer of each page. In addition, the start and finish of text introduced or altered (including deletions) by Amendment No 1 is indicated in the text by A1 tags. It is therefore easy to tell what has been altered.

The Standard should be studied because there are numerous small changes, modified notes and clarifications in the amended document. These range from the addition of a word or two in a sentence in several instances to the inclusion of a new Clause. Clause 4.2.1.4 on the curtailment of flange plates is an example of the latter. The addition of ‘or welded’ extends the range of application of Clause 3.5.3 to welded sections where it previously only applied to rolled sections. Design equations in Clauses 4.8.3.3.3, 5.7.3.2 and G.4.3 have also been amended and Section 2.4.2.7 on ‘Sway-sensitive’ frames has been rewritten, with the inclusion of new clauses (although, this is essentially a rewrite tomake it clearer and not a technical change).

Clause 6.8.7.2 in the amended Standard will appeal to many designers as it restores the rule concerning symmetrical fillet welds provided the connected elements are grade S355 or lower and appropriate electrodes are used. Symmetrically disposed fillet welds deliver the capacity of the connected part, as long as the sum of the throats is greater than the thickness of the part joined.

Two sections of the Standard have been heavily revised and these revisions affect interim guidance previously issued by the SCI in the form of Advisory Desk Notes. The Sections are Brittle Fracture (2.4.4) and Structural Integrity (2.4.5). Comment on each is given below.

Brittle Fracture
Following the issue of Amendment No1, the SCI’s Advisory Desk Note 279 is withdrawn and should not be used for design.

The limiting thickness values in AD 279 were recommended for interim use and were taken from the draft for public comment which was issued prior to Amendment No1. As a result of the comments received on the draft for public comment and further work by the code committee, not all the values in AD 279 appear in the amended Standard and the AD is thus withdrawn. In fact, the thickness values t1 in Table 4 of the amended Standard for external and lower temperatures are greater than the comparable values in AD 279; this allows wider use of the steel grades they relate to. Tables 3, 4 and 5 and / or the design equations in Section 2.4.4 of the amended Standard should be used for design.

As well as Tables 4 and 5, Tables 3 and 6 and the equations in Section 2.4.4 have been amended. Some of these changes have been necessary to keep this section in the Standard up to date with recent changes to various product standards for steel. However, the amendments to Table 3 relate to design issues and mostly result from questions received by The Advisory Desk over the years.

Structural Integrity
Advisory Desk Note 278 has also been withdrawn, following the issue of Amendment No1 and thus should not be used for design.

AD 278 was issued as interim guidance following the revision of Section A3 (Disproportionate collapse) of Approved Document A – Structure (2004 Edition) to the Building Regulations (England and Wales). The main change in the revision of Section A3 is that it applies to all buildings, which have now to be classified according to one of effectively four building classes, 1, 2A, 2B and 3. AD 278 related these building classes to the clauses in Section 2.4.5 of BS 5950-1: 2000 prior to Amendment No 1.

In Amendment No 1 to
BS 5950-1: 2000 Section 2.4.5 has been rewritten to incorporate the revisions to section A3 of Approved Document A. This now includes the building classes and their descriptions as well as directions to which clauses are to be used for the design of a particular building class for steel framed buildings. Although the technical content of AD 278 is correct, it now relates to a previous version of the Standard with different headings etc and the continued use of AD 278 would most likely only lead to confusion.

Section 2.4.5 of the amended Standard should be studied in detail because it also contains technical amendments including the restoration of transfer structures as key elements under certain circumstances. In addition, a factor related to the number of storeys in a structure has been introduced into the tying equations in Clause 2.4.5.3 a), which reduces the magnitude of the new tying forces for certain structures of less than 5 storeys.

Contact: Thomas Cosgrove
Tel: 01344 636525
Email: t.cosgrove@steel-sci.com