As Mr. Astaneh-Asl examined the construction documents, however, he was horrified by aspects of the design. He says the structure essentially threw out the rule book on skyscraper construction. "This building was so strange, and so many violations of practice and code were introduced," he says.
The design contains at least 10 unusual elements, he says. For example, rather than using a traditional skeletal framework of vertical and horizontal columns, the twin towers relied partly on a "bearing wall" system in which the floors and walls worked together to support each other, says Mr. Astaneh-Asl. That system allowed designers to use thinner steel in the buildings' columns and exterior than would be used in a traditional design, he says, adding that in some places the steel in columns was only one-quarter of an inch thick. And he says the designers used stronger steel (measured in what is known as "yield strength") in some columns than is allowed by any U.S. building codes, and that such steel is less flexible — and therefore more brittle — than the type traditionally used in such buildings.
As a result of such design elements, he argues, when the two airliners smashed into the upper floors of the towers, both planes plunged all the way in, wings and all. Airliners carry much of their fuel in their wings. His model clearly shows that in the initial fight between the plane and the building's exterior, the plane won, easily breaching the structure.
"It's like a soda can hit with a pencil," says Mr. Astaneh-Asl. "It was so easy that the plane went in without any damage and took the thousands of gallons of jet fuel in."