Today, a bridge collapses, and we ask why. The
University of Houston's College of Engineering
presents this series about the machines that make
our civilization run, and the people whose
ingenuity created them.
I'm looking at two
photographs, both taken in late August, 1907. In
one, a great cantilever structure extends almost
900 feet from its pier -- half a huge bridge over
the St. Lawrence River -- 40 million pounds of
structural steel reaching toward Quebec. The second
photograph is not so pretty. It shows 40 million
pounds of what looks like wet spaghetti, splashed
across the ground, leading away from the pier and
off into the water.
For eight years the Quebec bridge project had been
under the direction of an American engineer. He was
Theodore Cooper, the biggest name in bridge
building. Cooper had never produced a true
superlative, and his first move was to extend the
span from 1600 to 1800 feet. That got the piers out
of the water and on to dry land. But it also made
this the largest cantilever span ever attempted.
The contract was let to the Phoenix Bridge Company.
And soon many factors were gnawing at the design's
integrity. The Company lacked funds for preliminary
design and testing. Cooper's health was poor, and
he limited his travel to the site. But maybe the
largest problem was that he was just too highly
regarded.
The Phoenix Company increased the span without
recalculating stresses. They accepted the change on
Cooper's reputation. And Cooper was inattentive to
this lack of care. When the Canadians finally
raised money to start construction, they suggested
that stresses should be checked independently. But
they backed down when Cooper angrily said, "We've
lost enough time already!"
So work began. By 1906 it was clear that loads
would be a lot higher than people had thought. By
then everyone was overcommitted, and Cooper opined
that the structure could take it. In 1907 some
buckling was reported to Cooper, and now he began
to worry. On August 27th, he finally sent a wire:
"Add no more load to the bridge!" The Phoenix
Company shrugged and went on working. The
structural members must have been bent when they
were installed, they said. They worked the next day
without incident.
Then, at quitting time on August 29th, two
compression members caved in and the rest of the
bridge followed them. Eighty-four men were still on
the bridge; eleven lived to tell about it.
Blame for the Quebec bridge failure diffuses out
among a lot of people, all of whom were distracted
from the job itself. And we see parallels in many
modern disasters. Good technology has to be
personal and self-expressive. This first Quebec
bridge was to have been the great masterpiece of
cantilever construction, yet no one really poured
his soul into it. It collapsed because it wasn't
buoyed up by the human spirit.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
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