Terri-Jane Yuzda

The Evidence at Ground Zero

'War Zone' Reveals That Steel Weakened But Did Not Melt

Dr. Venkatesh Kodur, P.Eng., was the sole Canadian on the Building Performance Assessment Team. Organized by APEGGA, the Canadian Society for Civil Engineering and the Edmonton Society of Structural Engineers, Dr. Kodur's visit was sponsored by the City of Calgary and Alberta Economic Development.


He went as a scientist, with aloof calculations, data collecting, causes and effects on his agenda. But for Dr. Venkatesh Kodur, P.Eng., the sole Canadian on a team of experts charged with finding out why the Twin Towers of the World Trade Centre collapsed, professional objectivity could not shroud the human side of Ground Zero and its sheer, unspeakable magnitude.

"It was just like a war zone," said Dr. Kodur, who spoke to APEGGA members and others in Calgary and Edmonton in May. The structural engineer with the National Research Council in Ottawa said the scope and size of the Sept. 11 terrorist attack, which killed more than 3,000 people and decimated New York City's financial district, went far beyond what television cameras captured. Damages affected buildings for two to three kilometres. Ten major buildings at least partially collapsed. Weeks later, visitors still needed masks to breathe because of the airborne particles.

To a large extent, however, this was a mess that Dr. Kodur and his colleagues were able to sort through. The Queens University PhD and master's graduate, who spent six days in New York in October as the only non-American on the Building Performance Assessment Team, is an expert in the effects of fire on building materials. His speeches here - before about 300 people in Calgary and another 200 in Edmonton -- were organized by APEGGA, in cooperation with the Canadian Society for Civil Engineering and the Edmonton Society of Structural Engineers.
When the two commercial jet airlines hit the 110-storey towers, falling debris caused extensive collateral damage and started new fires, some of which caused further collapses of other buildings. But it was weakened structure, not melting steel as media reports hypothesized, which brought down the towers. Much of the jet fuel aboard the hijacked planes actually burned off in fireballs outside the building. The fuel ignited other combustible materials over several floors, however, which eventually weakened the steel. It would take 1,600 C temperatures to melt steel - but the actual peak temperatures were more like 1,100 C.

When the steel weakened, particularly between columns and beams, the buildings shifted and progressively collapsed. Although the collapse astonished the engineering community, an executive summary of the team's findings says that the buildings held up well considering the load factors they were subjected to in the attacks.

"The structural damage sustained by each of the two buildings as a result of the terrorist attacks was massive," says the summary. "The fact that the structures were able to sustain this level of damage and remain standing for an extended period of time is remarkable and is the reason that most building occupants were able to evacuate safely. Events of this type, resulting in such substantial damage, are generally not considered in building design, and the ability of these structures to successfully withstand such damage is noteworthy."

It's impossible to design for every conceivable load factor that a terrorist attack can place on a building. But Dr. Kodur says there's a lesson in how the spreading of the fire was central to the collapse. Buildings are designed to allow people to react to fire - but more thought should be put into designing to prevent the spread of fire in the first place, he said. Also, the disaster raises the question of how high buildings need to go.

"Tall buildings, we can live without them. They are not critical for commerce and trade. When I go to hotels, I used to ask for a room in the highest floor. Now, I ask for a room in the basement."


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