Heiwa, I know that one example that satisfies your challenge was brought to your attention once before, but in that case you dismissed it because it was a reinforced concrete building, whereas you were claiming in that thread that steel buildings were impervious to progressive vertical collapse. However, this challenge isn't arbitrarily restricted, so it's a fair example. The example was Skyline Towers, Baileys Crossroads, VA., in 1973 (
http://en.wikipedia.org/wiki/Skyline_Towers_collapse). The temporary wooden shoring was pulled from under the 23rd floor before it was fully cured. At the time, the 24th floor was being poured, and I don't know how far that had progressed, but go ahead and assume that it had been poured, so two floors fell onto the 22nd floor. That floor would have been poured two weeks earlier, so it was close to fully cured, and the 21st floor was three weeks earlier so it was fully cured. Nonetheless, the two falling floors took out everything below, down into the sub-basement (so it was really more than 22 floors destroyed), by destroying them one at a time. If you look at the picture, you will see that part of the building remained standing. But that doesn't save your indestructibility hypothesis because the collapse included everything up to an expansion joint. In a reinforced concrete building, expansion joints effectively create separate buildings so that thermal stresses don't crack the concrete, and the floor slabs on each side of the expansion joint would have been poured separately (probably on successive days in this case), so the collapse was everything in that independent section of the building. In fact, the collapse also triggered a progressive horizontal collapse in an attached parking garage, which was also destroyed.
So, what was the prize for meeting you challenge? I accept PayPal.
