> > burn through the insulation around the steel beams and cause them to
> melt<
>
> From what I remember of my BSc education stuff on materials, you don't
> need to melt steel, or anything like it, to cause a loaded structure to
> fail. Heating for a time (dunno what time but not as long as one would
> think) will lead to a loss of strength and increased elasticity. Once
> structural members in one place have distorted sufficiently for, say, a
> floor section to drop out onto the one below - also weakened and even less
> likely to take the increased weight, much less the impact force of an
> accelerating load - the whole pack of cards comes down. As we saw :-(
>
> I suspect there will be a lot of work done to assess the structural
> capabilities of large buildings to sustained heating. And also impacts of
> large aircraft. It seems people thought about the impact of a large
> aircraft - the building withstood this - but perhaps didn't think enough
> about the impact of very large quantities of fuel burning (and potentially
> detonating from vapour traps in the structure?). As always with
> engineering disasters, the thing that gets you is the thing that one
> hadn't thought of before...
>