|
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.
|
|
BY GEORGE LEE
The PEGG
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."
|
