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Collapse and Crash

The Tacoma Narrows Bridge in Washington State, which collapsed in high winds shortly after it was built, November 1940

Throughout my adult life, I’ve crossed the Crown Point Bridge connecting Vermont with the Adirondacks across Lake Champlain. Built in 1929, it was one of the first continuous truss road bridges constructed in the US. Then governor Franklin Roosevelt addressed the celebration, which drew 50,000 farmers and their families from both sides of the lake; the new span heralded a “wedding after more than 150 years” between the two states, he said, and added that he was sure there “would be no divorce.” Airplanes crisscrossed the sky overhead, and according to the New York Times correspondent, one pilot “risked his neck in a sudden swoop beneath the arched roadway of the bridge, with less than a 100 feet headroom.” But the grand celebration was marred by at least one small failure:

A specially constructed ferryboat …was scheduled to be destroyed by dynamiting to symbolize the passing of an era, but something went wrong with the charge and the boat continued to float arrogantly when the throngs started homeward along roads choked with traffic.

Henry Petroski would not be startled by that small failure, nor by the larger failure of the entire bridge after eighty years. Indeed, he briefly describes in his engaging book the October 2009 inspection that discovered that the Crown Point Bridge was badly cracked—so badly that a few weeks later it was closed forever, and then demolished with high explosives to make sure it wouldn’t fall on passing boaters. In fact, I think it’s fair to say that no failure surprises Petroski. His classic first book, To Engineer Is Human (1985), whose title sets up twenty-seven years later this book’s pun, also dealt with failure, as do many of his columns in The American Scientist. “A single failure…is a source of knowledge we might not have gained in any other way.” They reveal “weaknesses in reasoning, knowledge, and performance that all the successful designs may not even hint at.” “The best way of achieving lasting success is by more fully understanding failure.”

It’s also the best way of entertaining an audience not necessarily gripped by engineering as a topic. Dams and bridges have their beauty—but collapsed dams and fallen bridges can be more fun to describe, albeit ghoulish fun. Reading these pages reminds us of how many spectacular failures have occupied the news pages for a week or two in our lifetimes: the Aloha Airlines flight where part of the fuselage peeled away, the collapsed cranes in midtown Manhattan, even the wreck of the Edmund Fitzgerald. (In recent weeks, of course, it has been the horrific collapse of a Bangladesh garment factory that has captured global attention, though that seems less a story of engineering stupidity than human cupidity—indeed, the day before the collapse, an engineer, noting a large crack in the structure, urged its evacuation.)

But it’s bridges above all that preoccupy Petroski: pedestrian bridges that have to be closed when the rhythm of foot traffic causes them to sway alarmingly; bridge cables that corrode, wire by wire, steadily lessening the “safety factor” of the span; bridges that collapse while under construction like the 1907 tragedy at the Quebec Bridge across the St. Lawrence1; or now-forgotten disasters like the 1967 collapse of the Silver Bridge connecting Point Pleasant, West Virginia, to Gallipolis, Ohio. That bridge, in use for half a century, went down ten days before Christmas, killing forty-six and severing US Route 35; LBJ immediately established a President’s Task Force on Bridge Safety, which went to work collecting eyewitness testimony and investigating the remains as they were dredged from the waters of the Ohio.

These forensic inquiries are rarely easy and straightforward—popular explanations talked of sonic booms. As Petroski writes, more likely possibilities included the fact that cars and trucks had tripled in weight since the road was built, adding big new stresses. As the months wore on, investigators closed in on their target, establishing that the suspension chain on the upstream side had failed first, and eventually establishing exactly what had failed. Attention became focused on the “eyebars,” the metal bars with a hole or “eye” at each end that could be linked together like a chain to hold up the bridge:

The Safety Board finds that the cause of the bridge collapse was the cleavage fracture in the lower limb of the eye of eyebar 330 at joint C13N of the north eyebar suspension chain.

The bridge was built in such a way that these metal rods were susceptible to corrosion and fatigue cracking, and couldn’t really be inspected; a bridge of the same design ninety miles upstream was dismantled as a precaution, and eyebars fell out of favor for suspension bridges as engineers returned to wire cables.

If you’re like Petroski (or me) you find that kind of specificity (“eyebar 330 at joint C13N”) reassuring; in fact, the rational language of the engineer is one of the great American vernaculars, and perhaps the best part of To Forgive Design is Petroski’s account of one of the founts of that sort of analysis, the engineering departments of the nation’s great land-grant colleges. Petroski arrived in the 1960s at the University of Illinois, where his desk as a graduate student was in the Talbot Laboratory of the Department of Theoretical and Applied Mechanics. Academic offices occupied part of the building, but its huge atrium, the “crane bay,” was dominated by a three-million-pound capacity testing machine, essentially designed to put stress on metal or stone or any other material until it broke. Alarms would sound when testing was about to begin, alerting occupants of the lab

that something was about to fracture—releasing enormous amounts of energy in the form of an explosive noise accompanied by a recoil of the megamachine that made the entire building shudder.

The great testing machine—really, a failure machine—was the symbolic as well as the literal center of the enterprise,

always at the ready to apply real forces to confirm or contradict theoretical predictions of strength. It was the final arbiter between competing theories and contradictory predictions…. Failure was the incontrovertible counterexample to putative success.

If you want to understand what made postwar America the greatest design and engineering and manufacturing powerhouse the world has ever known, that hulking machine standing in a brick building on the edge of the prairie and attended by postdoc acolytes with slide rules at the ready seems like a reasonable symbol. Forget the virtual, the postmodern, the digital and pixelated; here’s a monster crushing concrete columns, figuring out the ways things work in the realest of worlds.

It was not an easy time to be a brush-cut engineer, however, even in the American heartland. Vietnam protesters, among many other targets, assailed their fellow students who aimed to work at companies tied to defense industries. Partly in response, engineers organized a new order for the profession, and began holding ceremonies where graduates took an oath to

practice integrity and fair dealing, tolerance and respect, and to uphold devotion to the standards and the dignity of my profession, conscious always that my skill carries with it the obligation to serve humanity by making the best use of Earth’s precious wealth.

Petroski applauds the effort, but then explains that it followed an older and humbler Canadian tradition, designed to instill in young engineers a strong sense that failure was always stalking their work. Not many years after the 1907 collapse of the Quebec Bridge, engineers in Canada aimed to improve the standards of their profession, and came up with not just an oath, but a ring ceremony—at first, in fact, the pinkie rings awarded the new engineers may actually have been cast from the bridge’s fallen iron girders. An anvil would be struck seven times, representing the driving home of a rivet, and then a Kipling poem, “Hymn of Breaking Strain,” would be read. It begins:

The careful text-books measure
(Let all who build beware!)
The load, the shock, the pressure
Material can bear.
So, when the buckled girder
Lets down the grinding span,
The blame of loss, or murder,
Is laid upon the man.

Not on the stuff—the man!

Petroski remains a son of the twentieth century, confident that the creed of the engineer is unchanged and sufficient. You could prevent failure, he writes, but only if you could “freeze technology at its present stage. Everything made subsequently would have to be designed and produced exactly like what had already been demonstrated to have been successful.” Instead, “endless improvement is what engineering is all about,” even if that inevitably leads to some failures (from which we then hope to learn). And in this enduring chain of progress, “good war stories are never obsolete.”

  1. 1

    A collapse that also had great cultural impact, at least on the Mohawk ironworkers who went on to build many of New York’s high-rises. See Joseph Mitchell’s classic account of their lives, “The Mohawks in High Steel,” The New Yorker, September 17, 1949. 

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