Creative Speculation

Closure to “Mechanics of Progressive
Collapse: Learning from World Trade
Center and Building Demolitions” by
Zdene˘k P. Bažant and Mathieu Verdure

Discussion by James R. Gourley

The interdisciplinary interests of Gourley, a chemical engineer with a doctorate in jurisprudence, are appreciated. Although none of the discusser’s criticisms is scientifically correct, his discussion provides a welcome opportunity to dispel doubts recently voiced by some in the community outside structural mechanics and engineering. It also provides an opportunity to rebut a previous similar discussion widely circulated on the Internet, co-authored by S. E. Jones, Associate Professor of Physics at Brigham Young University and a cold fusion specialist. For the sake of clarity, this closure is organized into the points listed subsequently and rebutted one by one.

1. Newton’s Third Law: The discusser is not correct in repeatedly claiming that Newton’s third law is violated in the paper and particularly in concluding that the “two-phase collapse scenario is scientifically implausible because it ignores Newton’s third law and the equal but opposite upward force dictated by it.” As explained at the outset in every course on mechanics of materials, this law is automatically satisfied, since all the calculations are based on the concept of stress or internal force, which consists of a pair of opposite forces of equal magnitude acting on the opposite surfaces of any imagined cut through the material or structure. This concept is so central to the discipline of structural mechanics and self-evident to structural engineers that Newton’s third law is never even mentioned in publications.

Closing Comments
Although everyone is certainly entitled to express his or her opinion on any issue of concern, interested critics should realize that, to help discern the truth about an engineering problem such as the WTC collapse, it is necessary to become acquainted with the relevant material from an appropriate textbook on structural mechanics. Otherwise critics run the risk of misleading and wrongly influencing the public with incorrect information.