For decades, industry professionals have debated the performance characteristics and benefits between steel frame structures and concrete frame structures in mid- and high-rise buildings. Until the tragic events of September 11, 2001, specifically those involving the terrorist attack on the World Trade Center, such debates had revolved primarily around theories. As terrible and tragic as the destruction of the WTC is, we, as industry professionals, have the responsibility of looking deeply into the performance of our building structures to reasonably and responsively prevent such immediate destruction and catastrophic failure from happening in the future. The following discussion is not intended to capitalize on this tragedy but to analyze several key factors surrounding the structural failure of the WTC and consider whether a concrete frame would have performed differently.

This discussion is between Bill Klorman, president of W.M. Klorman Construction Corp., El Monte, Calif., and Ken Bondy, a consulting structural engineer in West Hills, Calif. Both Klorman and Bondy are members of the ACI Responsibility Committee, Klorman its chairman. Bondy is one of the country's leading designers and authorities on post-tensioned concrete structures.