The claim made in your recent article, Steel on the ropes after the World Trade Center report (NCE 9 May) that tall buildings should be designed in reinforced concrete, displays worrying faith in a product about whose behaviour relatively little is known in these conditions.
This was demonstrated recently when a relatively small impact and fire at the Pirelli building in Milan led to extensive deflection and damage in a post-tensioned flat slab construction (NCE 2 May).
The understanding of the behaviour of concrete frames in fire is based on doubtful assumptions with limited data on whole building response.
Before it is possible to conclude that a concrete frame would perform better than steel in an event such as was experienced on 11 September, additional testing and analysis would be required.
Furthermore, when considering such extreme events in tall buildings, other issues come in to play such as ductility - which steel frames provide. Let us not forget that the ASCE/FEMA report emphasized that the buildings performed well in extraordinary circumstances and that was without the UK Building Regulations' design robustness requirements.
Dr. Derek Tordoff (F), director general, the British Constructional Steelwork Association, 4 Whitehall Court, Westminster, London SW1A 2ES