Quite so and on the face of it with Built Up Plate members wieghing in at 1000lbs per foot, you'd think that would be good enough but as we all know - the thing fell down!
Let me add in my passing two penny worth upon our Mr Silversteins's comments about "redundancy" and the special qualities of WTC7 - take it with a pinch of salt. I don't think he has any more idea of what can be done with or to a building than my missus who is very fond of giving me blank looks if I bring my work home. He should leave all the technical stuff to others in his team but when pressed in interviews he has a habit of faux pas - which in the case of his infamous "pull it" has been jumped on by conspiracists.
No highrise building has ever been planned or built with a view to removing out whole floors - it's a fabulous undertaking ( if I'd have known about it back in 1989 I'd have come over and tried my damnest to get in on it!) I take my hat off to all those that made it work.
I hope everyone realises that the 3rd angle sketch of the stress frames and cantilevers is straight out of the NIST report and is their best opinion of how it was on 911 - an "as built" drawing as we say here - that would include all the 1989 refit.
Though the article I linked to mentioned 375 tons of extra steel - I'm sure that I've read of 300 odd tons coming OUT and 500 going back in during the refit ( notice it says the scrap was sold for 4c a pound but doesn't say how much?) This steelwork would have been for a whole rake of profiles - columns as well as beams ( please don't use the term "girder" - very non U!) commonsense dictates that you simply cannot take a floor out and just leave the old columns in place full of empty bolt holes where the connectors have been removed.
Here in the U.K. if you put a fuel tank inside an occupied office building - you'd be arrested! I think even the laxed N.Y. City Ordinances were modified for WTC to allow tanks full of diesel everywhere! That said, they were fed by double walled steel pipe - though I bow to anyone with specific knowledge of connections to the generator sets. Amazingly, the NIST reports seem to suggest that all or most of the fuel oil was accounted for in the recovery operations - I find this very hard to believe given the raging fires. To my mind, the supply line was severed by components of the North Tower crashing through it and the open end was interpreted by the control gear as demand - thus at least one fire was being fed by anything up to 75gals a minute.