Reply #21: What about the weight of the towers?

[Kevin Fenton]

Several people have suggested that this weight was contained in the above-ground portions of the Twin Towers, i.e. each tower weighed 500,000 tons, of which steel accounted for 100,000 tons and concrete 400,000 (or a bit less if some of it were lighweight concrete). Do you agree with them or with NIST (which says each tower weighed 250,000 tons)?

If there were 800,000 tons of concrete in the towers and 200,000 tons of steel, then that would give us a steel: concrete ratio of 1:4, meaning that the towers were really heavy concrete structures, not lightweight steel ones. Even if we reduce the weight of some of the concrete (as Make7 suggests above), then we're not going to get a steel:concrete ratio below 1:3.

Vincent Dunn says, "The ratio of concrete to steel in the WTC is 40/60." (http://vincentdunn.com/wtc.html) That's just an estimate, but he was a Deputy Fire Chief in NY and seems to know quite a lot about the WTC and other NY buildings.
Also, every single other source describes the WTC as lightweight buildings, for example Wikipedia says the buildings had a "very light, economical structure". (http://en.wikipedia.org/wiki/World_Trade_Center)

As far as the basement goes, we should be able to get some ballpark figures using averages. The bathtub wall is 1,000 + 500 + 1,000 + 500 feet long, 3 feet thick and 70 feet high, that's not a difficult calculation, even for me. How thick do you think the various basement floors were? What about vertical (load-bearing) walls in the basement below the plaza?