Whether the regulations require it or not any structure should be designed to avoid disproportionate collapse. All it means is that there should be some redundancy in the system. E.g. if one column collapses the whole building should not fall down because the next one falls down and so on.

Carl Bauer
www.bauerconsultbotswana.com

To answer pie's question - yes, the whole of a five-storey building needs to be designed against progressive collapse to comply with British Building Regs.  This means that if you were thinking of loadbearing masonry carrying ordinary prestressed concrete planks, that probably won't do.  You would need continuity in the floor plate to bridge a missing wall (by catenery or diaphragm action), or some complicated system of secondary beams and posts to do a similar job.  Much better to have a framed structure

On Carl's wider point, where should we be drawing the line?  Most people would agree there's no need to consider progressive collapse for a two or three storey domestic building, and at the moment British Regs require it for five or more storeys.  Progressive collapse got a lot of press in the wake of September 11, but I'm not convinced it was a real issue.  After all, the towers DID stand up for quite a while after the attack.

Richard

WTC did stand up maybe even more than what would have been forecasted given the fire protection embedded.

I agree that the structure should be checked for disproportionate collapse as per the regulations.  However, even though some may argue that this is actually a four storey structure, the designer should really consider the use of the building and the likely effect on the occupants of a partial collapse (whether 5 storeys or not).  If there are likely to be large numbers of people in the structure then this check may be prudent on structures with fewer than 5 floors

Andy Machon