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BY HENRY PETROSKI

Visiting an Engineering Icon

75 years later, Hoover Dam still inspires awe.

Photo: HENRY PETROSKI - The bypass bridge is a magnificent addition.As I wrote here last October, Hoover Dam turned 75 years old that month. In conjunction with the anniversary, the History and Heritage Committee of the American Society of Civil Engineers sponsored a symposium on the project’s planning, design, and construction. It was held in Las Vegas, which is just 35 miles from the dam and is a beneficiary of the water impounded and the electricity generated at the site.

There was a special tour of Hoover Dam on the day before the symposium began, and busloads of civil engineers journeyed from the fabled Las Vegas Strip to the Visitor’s Center at the dam. It had been years since my wife and I were last there, and remarkable changes had been made to the iconic complex in the interim.

The talk of the town was the new bypass bridge, carrying traffic on a much-improved highway that eliminated the need for vehicles to navigate the narrow switchback roads that led down to the dam’s crest, over which just two lanes of traffic crept between Nevada and Arizona. Whether by coincidence or by design, the new bridge opened to traffic on the day of the engineers’ visit.

Hoover Dam

The bypass bridge is a soaring concrete-arch structure, which came into view as we drove down the old road toward the canyon. The bridge is in itself a magnificent engineering achievement, carrying as it does four lanes of traffic almost 900 feet above the riverbed on a 1,060-foot concrete arch, the longest-spanning one in the Western hemisphere. Engineers and laypersons alike craned their necks from buses and automobiles carrying them on their pilgrimage to this virtually hallowed site of engineering, infrastructure, and art.

Hoover Dam is a massive concrete structure, but it is also a graceful one. The dam proper, which exploits a combination of arch and gravity principles, has an apparent monolithic face that curves in two orthogonal directions. But it is the details of the generator buildings and appurtenances that show the true attention to detail that went into the overall design. The concrete work surrounding the outlets for the water that has spent its energy in the turbine generators shows thoughtful texturing and sculpting that resulted from the creative use of the wooden formwork employed during construction. The impressions left in the concrete are complemented with grooves and other accents that make what might otherwise have been an unrelieved hard surface into an aesthetic statement.

I do not know whether the crowds I saw swarming over the approach road, the visitor center, and the dam crest came to view these artistic details or simply to marvel at the sheer immensity and sense of power of the complex — and the labor that created it — which now includes the bypass bridge. But I doubt that they were all engineers, or spouses or relatives or acquaintances of engineers. I feel sure that some of them were simply drawn to this outstanding achievement that ASCE has designated not only as a National Historic Civil Engineering Landmark but also one of just 10 “Monuments of the Millennium.”

Engineers have been known to complain that their accomplishments are not appreciated by the general public. Visiting Hoover Dam easily dispels that impression. All one has to do is observe the anticipation on visitors’ faces and eavesdrop upon their conversations as they queue up to descend into the depths of the dam and stand in awe within the cavernous generator bays that are dwarfed by the concrete monolith towering above. This dam is an icon of engineering not because engineers say it is, but because people from all walks of life do.


Henry Petroski, the Aleksandar S. Vesic Professor of Civil Engineering and a professor of history at Duke University, chairs ASCE’s History and Heritage Committee. His latest book is The Essential Engineer: Why Science Alone Will Not Solve Our Global Problems.

 



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