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The Fire Next Time 

Tony Fitzpatrick, an S.F.-based engineer and world-renowned authority on tall buildings, says the most reasonable response to the World Trade Center disaster is also one of the simplest: improved fire codes for skyscrapers

Wednesday, Sep 25 2002
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Of all the acts of ostentatious frippery accompanying Great Britain's bid to lay exclusive claim to Jan. 1, 2000, the Millennium Bridge over the River Thames was perhaps the most humiliating.

Not to say there weren't others. The $1.1 billion Millennium Dome was a complete financial failure. The giant London Eye Ferris wheel wasn't ready in time for millennium festivities. And the "river of fire" fireworks display hailing the millennium simply failed to light.

But the bridge was the saddest, perhaps because in some ways it was the boldest. The bridge was built as a singular symbiosis of architecture, art, and engineering, the result of a collaboration among Britain's most esteemed architect, Norman Foster, modernist sculptor Sir Anthony Caro, and renowned bridge and tall-buildings engineer Tony Fitzpatrick. In conception, it would be the slimmest suspension bridge in the world, a "blade of light" connecting St. Paul's Cathedral on the north bank of the Thames and the Tate Modern Gallery on the south, and the first such new crossing in more than a century.

When it opened in June 2000, a thin ribbon of stainless steel and aluminum floated, 36 feet above the water, on two Y-shaped pylons. Eight steel cables, four on each side, were draped between the pylons and tied back to the riverbanks; a pedestrian walkway rested on steel transverse arms hanging from the cables. The effect was spare, dramatic, and ultimately for those who crossed it, terrifying.

On the day of the bridge's opening, some 150,000 walkers set out across the span, and, as is normal with moving crowds, each settled into a gait roughly matching adjacent walkers, until everyone on the bridge was more or less in step. The resulting synchronized motion set off a massive horizontal vibration at one cycle per second, a frequency perfect for throwing the unique structure into a writhing, side-to-side wobble.

The bridge was quickly closed. British newspapers reverberated with puns: "Winds of Change," "Shaken But Not Stirred," and "A Bridge Too Far."

Lead engineer Fitzpatrick told reporters he was embarrassed and then set to work constructing computer models, running vibration tests, and ultimately correcting the problem with a series of shock-absorbing bumpers. This February the bridge reopened, sans shimmy. Fitzpatrick was quoted as saying that fixing the vibrations "was the toughest thing I've ever done."


Tony Fitzpatrick is a wiry, self-possessed man who speaks in the snappy sentences of a person accustomed to exposing architects, sculptors, and developers to the brutal realities of the world. Fitzpatrick last year moved to San Francisco to run the American operations of the London engineering firm Ove Arup & Partners, of which he is a director. An avid cyclist and half Italian by parentage, Fitzpatrick travels the world attending to various Arup projects during the week, then spends weekends on bike rides with a club in Marin County. Afterward he's fond of sitting on his deck with a plate of pasta, enjoying the sensation of fatigue.

This morning, a couple of days before the one-year anniversary of the terrorist airliner hijackings, Fitzpatrick is in his Market Street office trying to explain to me how, in engineering as elsewhere, the world's most complex-seeming questions can become simple ones. In London, one question -- How could an architectural-engineering dream team create a bridge that wobbles? -- became another: How do people behave while walking in large groups?

In New York, where Fitzpatrick has become a leading expert on the collapse of the World Trade Center towers, the question of how to apply technology to make tall buildings safer from terrorist attack also begat another: What are we truly afraid of?

Fitzpatrick has been a world authority on the mechanics of tall buildings since 1985, when he engineered the 47-story Hong Kong and Shanghai Bank building in Hong Kong; the structure's system of massive steel masts and two-story suspension trusses made it one of the world's more spectacularly modernistic buildings. This year the bank opened a new Fitzpatrick-engineered London world headquarters, the United Kingdom's second largest building.

So it was only natural that, during the days after the Sept. 11 disaster, Fitzpatrick would gather Arup engineers from all over the world to determine what owners and managers of $50 billion worth of Arup-designed structures around the world might do in an age of global terror. The result was an "extreme events mitigation task force" that attempted to figure out what to do with the hundreds of buildings that might become terrorist targets.

"We have clients who are building owners and clients who are building occupiers. And, quite rightly, they said to us, "Advise me. What should we do?'" Fitzpatrick says.

Fitzpatrick and his colleagues conducted some of the most sophisticated analysis imaginable, obtaining planning documents from Airbus airplanes, then developing one-of-a-kind computer-modeling software to emulate what happens when the most massive part of an airplane, an engine, slams into an edifice. Fitzpatrick revisited his firm's work in constructing terrorist-bomb-proof containers for transporting nuclear waste. Arup engineers collaborated with investigators who were analyzing the precise engineering reasons for the World Trade Center collapse.

In the end, Arup engineers de-emphasized the idea of reinforcing buildings to withstand an airplane impact -- though their analysis provided them with the tools to do so.

"It's not a question of ability, but it's a question of cost and risk and how much you are willing to pay," Fitzpatrick says. "What you're asking is, '"What is your worry about at the end of the day? Do you care if you lose a building, if you can get everyone out?' We found, frankly, our clients are quite happy to let it burn down if they can get the people out."

He also found that people who work in tall buildings, especially ones near the World Trade Center, are most worried about the buried-alive nightmare of being stuck at the top of a blazing building with no way out. As with the Millennium Bridge, determining the best engineering response to a terrorist threat required, first, that someone figure out which questions to ask.

About The Author

Matt Smith

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