User Profile

Consulting civil/structural engineer with over 22 years in private practice (39 years total). Experience ranges from custom residential to heavy industrial structures. Some major project involvements include: Lead civil/structural engineer on a $700 million project for the US Air Force; structural design engineer for a 41,000 sq. ft. Pulp Machine Building; and Resident Engineer on a 550 MW Natural-gas fired power plant.

Idaho PE, 1980
Idaho SE, 1990
California PE, 1987
BSCE, 1976, University of Colorado, Denver/Boulder, CO

Professional Affiliations:
Member, American Concrete Institute (ACI)
Member, American Society of Civil Engineers (ASCE)
Charter member, Structural Engineering Instititute (SEI)
Professional member, American Institute of Steel Construction (AISC)
et al.

I began having doubts about, so called, official explanations for the collapse of the WTC towers soon after the explanations surfaced. The gnawing question that lingers in my mind is: How did the structures collapse in near symmetrical fashion when the apparent precipitating causes were asymmetrical loading? The collapses defy common logic from an elementary structural engineering perspective. “If” you accept the argument that fire protection covering was damaged to such an extent that structural members in the vicinity of the aircraft impacts were exposed to abnormally high temperatures, and “if” you accept the argument that the temperatures were high enough to weaken the structural framing, that still does not explain the relatively concentric nature of the failures.

Neither of the official precipitating sources for the collapses, namely the burning aircraft, were centered within the floor plan of either tower; both aircraft were off-center when they finally came to rest within the respective buildings. This means that, given the foregoing assumptions, heating and weakening of the structural framing would have been constrained to the immediate vicinity of the burning aircraft. Heat transmission (diffusion) through the steel members would have been irregular owing to differing sizes of the individual members; and, the temperature in the members would have dropped off precipitously the further away the steel was from the flames—just as the handle on a frying pan doesn’t get hot at the same rate as the pan on the burner of the stove. These factors would have resulted in the structural framing furthest from the flames remaining intact and possessing its full structural integrity, i.e., strength and stiffness.

Structural steel is highly ductile, when subjected to compression and bending it buckles and bends long before reaching its tensile or shear capacity. Under the given assumptions, “if” the structure in the vicinity of either burning aircraft started to weaken, the superstructure above would begin to lean in the direction of the burning side. The opposite, intact, side of the building would resist toppling until the ultimate capacity of the structure was reached, at which point, a weak-link failure would undoubtedly occur. Nevertheless, the ultimate failure mode would have been a toppling of the upper floors to one side—much like the topping of a tall redwood tree—not a concentric, vertical collapse.

For this reason alone, I rejected the official explanation for the collapse of the WTC towers out of hand. Subsequent evidence supporting controlled, explosive demolition of the two buildings are more in keeping with the observed collapse modalities and only serve to validate my initial misgivings as to the causes for the structural failures.