The Pipers Row collapse has highlighted some serious deficiencies in the way we design, maintain, inspect and appraise the strength of all types of structure, particularly as decay develops.
The specific issue of the sensitivity of flat slabs to brittle failure and progressive collapse needs more attention than George Somerville's letter (NCE 8 January) suggests. Good detailing and quality control on site can enable robust flat slabs to be constructed.
However the vagueness of codes, particularly for innovative and unusual structural configurations, and the pressure for fast track construction will lead to fragile structures being adopted. This is a risk with all types of construction. When decay sets in, there are problems with the assessment of residual safety.
The concrete industry has supported the development of codes and design guidance which contain no margin for loss of strength from deterioration. Sensitivity of strength and robustness to deterioration varies widely with structural form and detailing.
This needs consideration in setting partial factors.
The development of whole life risk management, sustainability and the post Oklahoma and 9/11 requirements for improved robustness necessitate a radical review of codes and design practice to replace complacent inaction. The detailed analysis of Pipers Row will provide some useful input to that process.
Until improved guidance is available, engineers should review their design and appraisal procedures in the light of Report to the HSE on Pipers Row;
www. hse. gov. uk/research/misc/ pipersrow. htm).
Jonathan Wood, Structural Studies & Design, Chiddingfold, Surrey GU8 4UU