A suggested cause of the fire-induced collapse of the World Trade Towers

Abstract

An analysis is presented that calculates the temperature of the steel truss rods in the World Trade Center towers subject to a fire based on the building ventilation factor. The CIB correlation is used for the fire. Conduction analyses are made taking into account variable properties for the steel and the insulation. A structural failure model is described based on compression buckling of the truss rods due to a reduction in the Young's modulus. The computed times for the estimated failure or incipient collapse of the floors in both towers has been computed as 105±20 min for WTC 1 (north) and 51±9 min for WTC 2 (south), compared to the collapse times from the aircraft impact of 104 and 56 min, respectively. The insulation thickness and the difference of 19.1 mm ( 3 4 ″ ) and 38.1 mm ( 1 1 2 ″ ) between the two towers appear to have been the root cause of the collapses.