So Much for the No-Planers

A simulation put together by a Berkeley structural engineer shows that the buildings' skins should have offered very little resistance to the planes (as indeed they did, as the no-planers often state).

“The simulation model shows the plane slicing right through the outer walls of the as-built building like it was a thin soda can,” Astaneh-Asl explained to the spellbound crowd.

He described the issue in a nutshell: “Because of their unique design and the use of the so called “steel bearing wall” tube structural system, which as far as we know has never been used before or after its application in the WTC towers, the buildings essentially showed no resistance to the impact of a medium-sized plane flying into them at about 450miles per hour.”

Elaborating on the novelty of the design, he said that the notion of a ‘structural framing system’ simply didn’t apply in the case of the twin towers. “Rather than traditional columns and beams, the designers employed a steel bearing wall tube system for the perimeter and steel truss joists in the floors that connected the gravity load-carrying inner core columns to the outside perimeter steel bearing walls. The relatively thin steel bearing wall pre-fabricated units of the perimeter bearing tube were bolted together in a Lego-like fashion to expedite construction” he explained.

He also noted that designers chose to fabricate many of the building columns out of very high strength steel [90 ksi steel as opposed to the more typical 36-65 ksi steel]. “This is not allowed by the structural design codes then and is still notallowed in current codes,” he stressed. “But the World Trade Center did not need to obtain a permit from City Hall. Because of special status as Port Authority of New York and New Jersey, they could make such choices outside the prevailing codes.”

This choice, he argued, allowed builders to use less steel in the columns [two to three times thinner than typical columns] presumably to save cost.

But by using high strength steel and thin cross sections, he pointed out, on impact the plane was able to cut through the outside steel bearing wall and enter the building--delivering thousands of gallons of jet fuel to the interior. During the ensuing fire, he said, the thin outside columns of the steel bearing walls were quite vulnerable to the rapid rise of temperature in them and reduction of their strength as a result of rising temperature of the steel.