On 21/09/18 20:00, juan wrote:
On Mon, 17 Sep 2018 22:20:19 +0100 Peter Fairbrother <peter@tsto.co.uk> wrote:
WTC was rated for 3 hours major fire resistance.
Put that another way - *it was rated so that it _would_ collapse after 3 (or so) hours of major conflagration*.
It's in the design docs.
Where's your evidence for that claim Peter? WHERE are those 'design docs' ?
Most steel-framed buildings are still built with either a 3 or 4 hour structural steel fire rating for columns - for other steel like girders, spandrels and trusses the ratings are less. Can't be bothered to look up any original references, and they need a lawyer to interpret anyway, but it's in the International Building Code, which the NYC building codes are based on. Class 1A requires a 4 hour rating for columns, Class 1B 3 hours. Parts of the WTC 1+2 columns were protected to Class 1A, but mostly they were Class 1B. Nowadays a building the size of WTC1+2 would have to have a 4 hour rating, but it wasn't a requirement in the 60's. Incidentally, the floor trusses were not even up to 1B Class standard (2 hours for trusses), needing 38mm of SFRM rather than the 13mm they had (the Port Authority overruled the NYC building code and specified 13mm). The significance of this discrepancy wasn't entirely realised at the time they were built, and they were refurbishing the truss SFRM on an off-and-on basis when the buildings collapsed, but had only done 19 floors. WTC7 was built to class 1B. It wasn't a tube-framed building, so it didn't pancake from the top like WTC 1+2. The WTC7 collapse looks much more like a building implosion, but there are no explosions to be seen or heard, and some details are wrong. -- Peter Fairbrother