Allien, that guy has to go back to school and learn some physics alright. It is enough that one main support beam partially reached 800 C to get the catastrophic collapse starting. By, the way, before the steel even lose its yield strength to 20% (at 800 C) of its room temperature yield strength, it starts and creep (deform), once creep starts, the load distribution is no longer along the axis of the beam, but part of the load is transversal, bending rather then breaking the steel. once one beam (partially bent) no longer bears the load of all the floors above, the other beams loading increases, and at one point a catastrophic (cascading) collapse is initiated, the load is no longer static, it becomes dynamic and thus even lower limits to the steel's strength (thus lower floors where the beams were not that hot also give way). Mind you, those building were planned with potential fire in mind (the steel beams had minimal thermal insulation), but the assumption was an office fire, which under very bad circumstances could bring the steel to maybe 400 C, not a pool of constantly feeding fuel (from fuel tanks). At a corner of a building, where the effect of mechanical breach by plane impact and subsequent explosion, an actual chimney effect soaking in air (and thus oxygen) actually can increase the local temperature well above 900 C. After all, any blacksmith wringing steel in his shop (by putting the steel in a little coal and a simple bellow blowing air on the coal from time to time), brings the temperature of the steel well above 800C (the "black body color of 800 C is a very dim red, at 1000 C it becomes more yellowing, and most steel is wrought around 900 C).
Zeev |
