Report from ground zero

Engineer studies World Trade Center collapse for clues to failure By Robert Sanders, Public Affairs









This charred I-beam from the World Trade Center can help tell how the towers fell on Sept. 11.

Abolhassan Astaneh-Asl photo



03 October 2001 | As a structural engineer used to inspecting buildings and cities devastated by earthquakes, Abolhassan Astaneh is no stranger to disaster. Even so, he was apprehensive before flying to New York on Sept. 19 to conduct a two-week scientific reconnaissance of the collapsed World Trade Center towers. Astaneh typically visits after the dead have been removed. This time, he said in an e-mail message from New York last week, the site of “this horrible crime still has more than 5,000 of our fellow Americans, and others from all over the world, murdered and buried under that rubble.” For the first time, he consulted a psychiatrist about dealing with a disaster site, and about entering the area where thousands of victims are buried amidst rubble. The reality was sobering, but working 16-hour days out of his hotel a few blocks from ground zero, he was able to keep his mind off the carnage. Then, after a week on the job, the wind shifted, and for the first time, he smelled the burning, smoldering debris and the bodies. “It was a horrible — not like anything I had smelled before,” he said. Supported by funds from the National Science Foundation to investigate the collapse of the two 110-story towers, he spent his days and nights looking at twisted and burnt steel pulled from the wreckage, searching for clues to

the cause and collecting perishable data. “In just 10 days looking at the pieces that are coming out, I have learned so much important data about the collapse — it’s amazing,” he said. “We will be able to learn many valuable lessons from this tragedy to improve our structural design and construction and (to understand) the effects of fires on steel structures to avoid such a catastrophic and complete collapse and tragic loss of life.” By chance, while visiting the offices of The New York Times last week to chat with one of its science writers, he heard about plans to immediately recycle steel from the site, and launched a lobbying effort to convince the city to wait until the debris had been inspected by structural engineers. Thanks largely to a Saturday article by Kenneth Chang and James Glanz, the city has agreed to make the steel available to Astaneh and other engineers heading up an investigation for the American Society of Civil Engineers. They plan to draft a technical report to the National Research Council for forwarding to the federal government. Astaneh’s findings will be used in engineering studies to help improve the structural integrity of the nation’s buildings, utilities and other infrastructure during fires, earthquakes, explosions and other hazards. They will also be used to improve the nation’s response to such threats. For example, valuable information could come from analysis of the blackened steel from the floors engulfed in flame after the airplane collisions. Steel flanges had been reduced from an inch thick to paper thin, Astaneh said. He and others suspect that the buildings collapsed because the intense heat of the jet-fuel-fed fire softened the steel to the point that the columns no longer could support the weight of the floors above. As the top 10 or so stories fell, they collapsed the floors below in a cascade of pancaking concrete floor slabs. Despite the horror of the site, he said he wanted to be there to salvage something informative from the tragedy. As one of few, if any, Iranians or Muslims within the restricted area around the site, he recalled his own arrival to the United States in 1978 to embark on graduate studies. His first stop, accompanied by his wife and one-year old son, was New York City. His first picture: the unbelievably tall towers of the World Trade Center and the Statue of Liberty. Astaneh’s interest in the structural damage caused by bombs and how to prevent it dates from 1995 and the Oklahoma City bombing of the Alfred P. Murrah Federal Building. This earlier tragedy struck him personally, because in 1983, while a young assistant professor at the University of Oklahoma, it was the place where he started the process to become a naturalized citizen. That structure, built of non-ductile reinforced concrete, not steel, collapsed entirely, killing 168 people. In 1996 he began work on research on bomb-resistant designs. By 1998, after two years of intense study, he felt he was ready to start testing and studying specific technologies. The work led to a grant from the General Services Administration to analyze and test a new cable-based design that Berkeley emeritus professor of civil engineering Joe Penzien had suggested to the committee investigating the Oklahoma City collapse in 1996. The World Trade Center was far better constructed than the Murrah building, down to a pedigree for each steel beam and a welder’s signature on each weld. Berkeley alum Leslie Robertson was the lead structural engineer on the project more than 30 years ago, and his design included many innovations only now working their way into other buildings, Astaneh said. Designed to withstand a hit from a Boeing 707, both towers stood firmly after the Boeing 767s hit, the morning of Sept. 11. The columns, however, were not designed to withstand an intense fire from thousands of gallons of jet fuel, and both towers collapsed after about an hour. This was enough time, however, for many to flee. “The prudent decision by Les Robertson to design this building for a passenger plane hit saved the lives of more than 25,000 people who were in the buildings and were able to escape before the towers collapsed.” Ironically, Astaneh sought Robertson’s advice in his blast-resistant research, and he provided many valuable comments on how to can improve the test program and specimen. Astaneh will continue his research into protecting steel structures against terrorist attack, and has already tested an innovative design of his own involving bolting reinforced concrete plates to steel shear walls. Originally conceived for seismic applications with funds from NSF, he modified it to act as a composite shear wall to resist seismic forces, as well as withstand blast loads, better than steel or concrete walls alone. “Although I did not think of planes crashing into buildings when I was developing the system,” he said, “after seeing how easily the 767 entered the World Trade Center towers and delivered almost all of its jet fuel inside the building, I thought, ‘What would have happened if the exterior of the building was this composite system that we’ve developed?’” A plane hitting such a system would have a hard time penetrating the building intact, he said. Most likely it would “accordion,” keeping most of the plane and its fuel outside the building. He is eager to test it as a possible “plane stopper.” As he pursues bomb-resistant, anti-terrorist building designs, however, he will forever be left with images of the destruction at ground zero, such as the eyeglass lens he saw imbedded in a slab of concrete. “Human dignity has been brought down so much by this attack,” he said. “The depth of loss and sorrow is immeasurable.”