Today, an ominous tale of three designers and three
bridges. 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.
The 46-mile rail trip from
Edinburgh to Dundee took half a day in 1870. You
had to ride the ferry over two wide fjords that
slice into Scotland -- the Firth of Tay and Firth
of Forth. Henry Petroski tells how an English
engineer, Thomas Bouch, sold backers on building
bridges over those inlets.
The first was an immense two-mile bridge over the
Firth of Tay. When its 85 spans were finished in
1877, they made up the longest bridge in the world.
And Queen Victoria knighted Bouch.
Then, disaster! The Tay Bridge collapsed in 1879,
killing seventy-five people including Bouch's
son-in-law. Cost-cutting had yielded a bridge that
couldn't stand up to the wind forces. Bouch died in
humiliation four months later.
By 1881 the Tay Bridge was rebuilt with heavy
unbeautiful trusses, and attention turned to the
Firth of Forth. It was a mile wide, with only one
shallow spot for a central pier. It would require
two huge half-mile spans. How to proceed?
An engineer named Benjamin Baker rallied public
support for a new kind of bridge: triangular
structures reaching out from opposite sides to hold
central spans in the middle. That cantilever
construction was still radical in 1881. And Baker's
Firth of Forth design was a striking array of
massive tubular steel members.
While Bouch and Baker struggled to link Edinburgh
and Dundee, a young American bridge builder,
Theodore Cooper, watched and learned. When the
first Tay Bridge fell he was 40 -- a seasoned
designer just opening a consulting office in New
York. Cooper was known for hands-on care in his
work. He knew not to be careless the way Bouch had
been. He knew to stay on top of the work.
In 1887, as Baker's Firth of Forth Bridge was going
up, the Canadian Government set out to bridge the
St. Lawrence River at Quebec -- another wide inlet,
splitting southern Canada!
Like Baker, Cooper designed a cantilever bridge.
But years of success had buoyed his belief in
saving money on material. His Quebec bridge was
light and buoyant, and it was to be the longest
cantilever structure ever made. By 1907, its
delicate girders reached, unsupported, 900 feet
over the water.
But Cooper was now 68 and America's leading bridge
designer. He'd grown content to sit in New York
directing the work by telegram. When a wire warned
that beams were buckling, he didn't react in time.
The arm collapsed, and 73 workers fell to their
deaths.
And so history repeated itself. Success following
failure, and failure following success. That's a
cycle we forget at our peril. Today, all three
inlets have their bridges. But, of the three, the
Firth of Forth Bridge, built in disaster's wake,
was the one that did not have to suffer a collapse.
It was the only one built in the right phase -- of
that murderous cycle.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
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