AD 280: Structural Integrity of Light Gauge Steel Structures Building Regulations Approved Document A (2004)
The England and Wales Building Regulations and Approved Document A have been revised. The new revision came into force on 1 December 2004. Section A3 has been completely rewritten and should be studied. The main change is that the regulation now applies to all buildings, including those of less than five storeys. Now, all buildings have to be classified according to one of effectively four building classes, 1, 2A, 2B and 3. The forthcoming amendment to BS 5950‑1 will revise Section 2.4.5 to be compatible with the changes in Section A3 of Approved Document A – Structure (2004 Edition). However, proposals for the revision of BS 5950‑1 must first be issued for public comment before being accepted and this process may take some time.
BS 5950-1:2000 is the structural steelwork Standard referred to by Approved Document A, but this is not directly applicable to the design of the majority of light gauge steel structures. Recommendations for light gauge frames are available in:
1. BS 5950‑5:1998 Structural use of steelwork in building – Code of practice for design of cold formed thin gauge sections, in Clause 2.3.5 Structural Integrity
2. SCI publication P-301 Light Steel Framing in Residential Construction, in Section 2.1.5 Robustness of light steel frames.
P-301 was written to satisfy the England and Wales Building Regulations in force before the 2004 revision. It gives more extensive guidance than BS 5950‑5:1998, including design loads for splices in vertical members, removal of elements and the design of key elements. As interim guidance, the SCI recommends that designers use P‑301 to satisfy the 2004 regulations for light steel frame buildings, applying Section 2.1.5 as follows:
- Buildings of Classes 1 and 2A: only paragraphs (1) to (4) and (11) need be applied
- Buildings of Class 2B: paragraphs (1) to (11) should be applied
- Buildings of Class 3: paragraphs (1) to (11) should be applied as a minimum design requirement. In addition, Class 3 buildings should be designed to have a structural form that reflects the critical conditions that can reasonably be foreseen as possible during the life of the buildings, to the extent that collapse is not disproportionate to the cause. Approved Document A requires that these critical conditions be identified by a systematic risk analysis of normal and abnormal hazards
Designers choosing the “removal of columns” option in Section 2.1.5(8) should note that the 2004 Approved Document A necessitates a change from P-301. Clause 5.3 defines the length of external steel stud wall that must be considered to be removed as “the length measured between vertical lateral supports”. For internal steel stud walls, the length considered to be removed remains 2.25 times the storey height.
Where buildings combine both hot rolled and light gauge construction, designers are advised to use a logical combination of the recommendations of this AD and AD278.