In 1978, William J. LeMessurier, one of the nation's leading
structural engineers, received a phone call from an
engineering
student in
New Jersey. The young man was tasked with writing a paper about the unique design of the Citicorp tower in
New York. The building's dramatic design was necessitated by the placement of a
church. Rather than tear down the church, the designers, Hugh Stubbins and Bill LeMessurier, set their fifty-nine-story tower on four massive, nine-story-high
stilts, and positioned them at the
center of each side rather than at each
corner. This daring scheme allowed the designers to
cantalever the building's four corners, allowing room for the church beneath the northwest side. (see the pictures, listed below)
Thanks to the prodding of the student (whose name was lost in the swirl of subsequent events), LeMessurier discovered a subtle conceptual
error in the design of the building's wind
braces; they were unusually sensitive to certain kinds of winds known as
quartering winds. This alone wasn't cause for worry, as the wind braces would absorb the extra load under normal circumstances. But the circumstances were not normal. Apparently, there had been a crucial change during their
manufacture (the braces were fastened together with
bolts instead of
welds, as welds are generally considered to be stronger than necessary and overly expensive; furthermore the contractors had interpreted the New York
building code in such a way as to exempt many of the tower's
diagonal braces from loadbearing calculations, so they had used far too few bolts.) which multiplied the strain produced by quartering winds. Statistically, the possibility of a storm severe enough to tear the joint apart was
once every sixteen years (what meteorologists call a sixteen year storm). This was alarmingly frequent. To further complicate matters,
hurricane season was fast approaching.
The potential for a complete
catastrophic failure was there, and because the building was located in
Manhattan, the danger applied to nearly the entire city. The fall of the Citicorp building would likely cause a
domino effect, wreaking a devestating toll of destruction in New York.
The story of this oversight, though amazing, is dwarfed by the series of events that led to the building's eventual
structural integrity. To avert disaster, LeMessurier quickly and bravely
blew the whistle - on himself. LeMessurier and other experts immediately drew up a plan in which workers would
reinforce the joints by welding heavy steel plates over them.
Astonishingly, just after Citicorp issued a bland and uninformative
press release, all of the major newspapers in New York went on
strike. This fortuitous turn of events allowed Citicorp to
save face and avoid any potential
embarrassment. Construction began immediately, with builders and welders working from 5 p.m. until 4 a.m. to apply the steel "
band-aids" to the ailing joints. They built plywood boxes around the joints, so as not to disturb the tenants, who remained largely oblivious to the seriousness of the problem.
"Instead of
lawsuits and public
panic, the Citicorp crisis was met with efficient
teamwork and a swift solution. In the end, LeMessurier's reputation was enhanced for his courageous honesty, and the story of Citicorp's building is now a
textbook example of how to respond to a high-profile, potentially disastrous problem."
Pictures of the unique Citicorp tower:
http://www.bluffton.edu/~sullivanm/stubbins/citicorp.html
http://www.bluffton.edu/~sullivanm/stubbins/ccshaft.jpg
http://www.lehigh.edu/~inctbuh/bom_citi_graphics/citicorp_montage.jpg
Thanks to
mkb for making me find new pics to replace the old ones!
Sources:
Most of this information came from a
New Yorker article by Joe Morgenstern (published May 29, 1995). This article also appears to have inspired these webpages: http://onlineethics.org/moral/LeMessurier/lem.html and http://www.pbs.org/wgbh/nova/pisa/moncit.html