STUDY
BLAMES BOLTS FOR WTC FALL
By AL GUART
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October 27, 2002 -- Single-bolt connections in the
framework of the World Trade Center's Twin Towers
contributed to their collapse in the Sept. 11
attacks, according to the findings of a team of
top engineers from the Massachusetts Institute of
Technology.
The researchers, who based their study on
blueprint plans of the buildings and an
examination of Ground Zero aftermath, say they
were surprised more bolts were not used to secure
the lightweight steel floor trusses to the
load-bearing steel columns that formed the
perimeter of each tower.
With its reliance on a solid core and a strong
exterior shell to support the building, the design
of the 110-story Twin Towers was regarded as
revolutionary. Standard high-rise construction
procedure is to distribute the weight of each
floor on a steel skeleton that crosshatches the
entire building.
In their 150-page study to be published shortly,
the MIT researchers conclude that the single-bolt
support of the floor trusses was the towers'
"Achilles' heel."
"It was not a faulty design, but it was a
weak design," said MIT professor Eduardo
Kausel, who worked on the study.
The study suggests the floor trusses at the point
of impact began to sag as the building burned,
causing the single bolts to be pulled toward the
center of the building.
Meanwhile, the columns lining the perimeter of the
building remained upright, and that caused the
bolts to shear, Kausel said.
As trusses began to fall, bolts popped in what
Kausel described as a "zipper effect"
that eventually led to floors collapsing on top of
each other.
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