Today, we look at the Kansas City skywalk failure.
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.
Do you remember the failure
of the skywalk in a new Kansas City Hotel in the
Summer of 1981? A weekend crowd was dancing to
big-band music in the hotel atrium. Some were on
the floor. Others strolled on three crowded
skywalks above the atrium. Two of the skywalks
suddenly gave way. 114 people were killed, and 200
more were injured.
That sort of accident is so rare -- a seemingly
unprovoked building collapse. Twentieth-century
thinking being what it is, the first order of
business was fixing blame -- finding out who was
entitled to sue whom for what. The National Bureau
of Standards finally issued a 300-page report a
year later. It leads us on a fairly tortuous path
through a sequence of three minor complacencies on
the part of otherwise honorable people.
The walkways were hung from the ceiling on steel
rods. On one side of the atrium, one walkway was
suspended below another. In the original design
these two were both to have been mounted on the
same rods. Even at this stage of the design, two
errors had already been made. Neither of them would
have been fatal. The first was that the rod design
didn't meet the building code. While that made the
design illegal, a stress analysis showed that the
rods were still safe. And the whole concept was,
after all, so simple! The second problem seems to
be only a small detail. The designers didn't
clearly explain how the rods were supposed to grip
the upper walkway where they passed through it.
The contractor then unwittingly made the final
error of judgment. He solved the problem of
gripping the walkway. He simply ended one rod, and
started another next to it, in the skywalk's
cross-beam. The result was subtle but devastating.
This change doubled the stresses at one point in
the beam. I say the calculation is subtle. But it's
still within the grasp of our second-year
engineering students. Their applied-mechanics
professor now gives it to them as a homework
exercise.
So, under extreme loading, the upper walkway
failed, and both walkways fell away -- depositing
steel, concrete, and people upon the dancers below.
It was a terrible moment. But it never would have
occurred if the chain of blunders hadn't fit
together so perfectly. I'm chilled by the weight of
responsibility that vests in these little design
decisions. At the same time, I'm encouraged to see
that so much safety is inherent in our system of
design -- that so many dovetailing errors had to be
made before this dreadful accident could ever
happen.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
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