So people like Kon133 can post 9-11 pics to their heart's content instead of on the THE MEGA WTC Picture Thread.
The floors were the weak points in the building. If you go back to earlier designs of skyscraper such as the ESB, the floors would have been heavy steel supported at regular intervals by a grid of columns over the whole plan area of the building.To be fair, Rizzato has a point. By undamaged beast i'm guessing you mean the acre in size floor and all of it's trusses which would in fact be a load bearing beast because they all worked together to cary the load. However, the moment the building started collapsing (before it's total collapse) the floors were collapsing unevenly, and some trusses were exposed to heavier loads than other trusses. Even the tower's total collapse occurred unevenly.
It would make sense that the tower could collapse in such a way. What i still don't understand to this day is the total disappearance of the core.
I have read that various building tenants would carry out work to the structure such as cutting staircases through where they occupied more than one floor. Interesting that they would need to reconstruct the floor to support all the loading. I find it odd though that they would need to beef up the core columns as the weight of your datacentre would be only a small part of all the loading that a core column would be designed to take.Thanks Martin, very illuminating, and answered my questions.
About cross-bracing, our datacentre was located on the eastern face of the 95th floor. If memory serves correctly, some of the core-columns, as well as the floor diaphragm, had to be reinforced because of the sheer weight of all the equipment that was in the datacentre; servers, networking hardware, cabling, UPS (battery backup) systems. I seem to also remember part of the concrete slab on that floor being re-poured to support the weight.
The 95th floor. The datacentre is the walled-off area on the eastern side of the floor.