Henry Petroski. American Scientist. Volume 84, Issue 3. May 1996.
America has more than half a million bridges, ranging from nondescript highway overpasses to monumental works of structural art, but only a few of them are known by name. Although just about everyone has heard of the Brooklyn Bridge and the Golden Gate Bridge and can tell you where they stand, only local residents, attentive tourists or bridge aficionados are likely to know where to look for such structural jewels as Caveman Bridge or the McCullough Memorial Bridge. Of those who can locate these bridges on a map, only a small fraction are likely to low that Conde McCullough is the name of the engineer and not of a local politician. But whether or not they or their engineers are well known, masterpieces of bridge engineering are everywhere, a legacy of their designers’ structural artwork that is as much a part of the American scene as are the red barns and white churches of the countryside or the tall buildings and chasm-like streets of cities.
From Maine to California, from Washington to Florida, there are bridges of note, and to each belongs a story that is at once unique and typical. Most bridges are truly one-of-a-kind construction projects, and local constraints of topography, geology, traffic, politics and economics always make complications commonplace. Across America over the past century, local idiosyncrasies have led to the design and construction of bridges as odd and individual as many of their engineers. For example, the Bailey Island Bridge, which carries traffic a thousand or so feet between the island and the coast of Maine, is supported over most of its length on a crib of large and heavy stone that allows the tides to move freely in and out of Casco Bay. By designing a masonry structure, the state bridge engineer, Llewellyn N. Edwards, obviated the problems of rot and corrosion that plague timber and steel bridges. Today, the almost 70-year-old Bailey Island Bridge structure stands as solid as ever, a monument to the foresight of its engineer, who in his later years also looked backwards to write a valuable history of early American bridges.
In a park near Kansas City, a modest span of 100 feet peaks 40 feet in the air, thus serving as a beacon for pedestrians looking to cross Rush Creek to the picnic area. The bridge was originally built in 1898 to carry a line of the Quincy, Omaha & Kansas City Railroad, until it was abandoned in 1930. The bridge then stood unused for some years, but after the Second World War it was converted to local highway traffic use. With the filling of nearby Smithfield Dam threatening to submerge the bridge, it was disassembled in 1982 and its parts stored by the Army Corps of Engineers. The reconstruction of the bridge five years later was spearheaded by George Hauck, a professor of civil engineering at the University of Missouri, who sought to preserve it as a monument to its engineer, J. A. L. Waddell, who patented the A-frame truss in 1894 and built scores of such bridges in the Midwest and Japan.
The Canadian-born Waddell received his civil engineering degree in 1875 from Rensselaer Polytechnic Institute, the premier engineering school in America at the time. After gaining experience with bridge-building companies and further study at McGill University, in 1882 Waddell accepted a faculty position at the Imperial University in Tokyo, which enabled him to revisit the Orient, to which he had traveled for his health as a sickly youth. After a few years in Japan, Waddell returned to America and soon started a consulting practice in Kansas City, which was to evolve over time to be known successively as Waddell & Hedrick, Waddell & Harrington, Waddell & Son and Waddell & Hardesty, and lives on to is day as Hardesty & Hanover.
From building modest A-frame trusses, Waddell’s practice grew to the point where he was designing major bridges of many kinds. One of his firm’s most unusual projects still spans the Missouri River in Kansas City. As originally designed, it carried railroad trains on a lower deck and highway traffic above. Because the bridge was built close to the water, it incorporated a lift mechanism to raise a section of the railroad tracks by retracting into the upper structure so that the flow of highway traffic could continue uninterrupted. The lift mechanism for the bridge does not tower above the upper deck the way it generally does in vertical-lift bridges, and this Kansas City bridge is believed to be the only one of its kind extant. The structure is known today as the ASB, or Annour, Swift, Burlington, Bridge, after the meat-packing and railroad companies that once controlled it. Like many an old highway bridge, it had narrow lanes, and so was closed to vehicle traffic when the modern, higher and wider Heart of America Bridge was completed nearby in 1986.
A City of Bridges
Portland, Oregon, is a veritable open-air museum of bridges designed by some of the most productive and influential engineers of the late 19th and early 20th centuries. Bridge historian Sharon Wood conducts fascinating tours of these structures and is a valuable source of information about Portland’s bridges and their engineers. There are two bridges built by Waddell & Harrington: the Hawthorne and the Steel. The former is a conventional lift bridge, with tall towers on either side of the movable span that serve as cranes to lift it out of the way of shipping passing up and down the Willamette River. Completed in 1910, it is believed to be the oldest vertical-lift bridge still in full operation. The Steel Bridge, completed in 1912 has the telescoping feature of Kansas City’s ASB Bridge, but it also has the conventional lift towers, allowing the entire movable span to be raised even higher out of the way of the larger vessels that use the Willamette. The name of the Portland structure dates from an earlier railroad bridge near the same location, which was built in 1888 when steel was displacing wrought iron as the railroad-bridge material of choice.
Other bridges in downtown Portland are associated with the names of some of the most innovative and prolific American engineers, designers who flourished during the period that reached from the heyday of the railroads through the ascendancy of the automobile. Among these engineers is Gustav Lindenthal, who began his career in Pittsburgh, where his Smithfield Street Bridge, completed in 1883, remains one of the outstanding examples employing a lenticular truss, whose lens-shaped profile makes the bridge easy to recognize. From Pittsburgh, Lindenthal moved to New York, where for almost 50 years he promoted unsuccessfully his designs for a monumental bridge across the Hudson River. Lindenthal did, however, succeed in designing and building New York’s massive Hell Gate Bridge, which served as a model for the landmark Sydney Harbor Bridge in New South Wales.
In Portland, Lindenthal left his mark on three bridges: the Sellwood, the Ross Island and the Burnside, all completed in the mid-1920s. This last is a double-leaf bascule (from the French for seesaw), with an opening mechanism designed by the firm of Joseph Strauss, who at the time was expending much of his energy in and around San Francisco promoting the design and construction of the Golden Gate Bridge. In Portland, another double-leaf bascule, the Broadway Bridge, was designed by Strauss’s contemporary, Ralph Modjeski, whose accomplishments ranged from modest-span movable bridges in Chicago to the Delaware River (now the Ben Franklin) Bridge in Philadelphia, the longest suspension bridge in the world when it was completed in 1926.
Perhaps the most striking Portland structure is the St. Johns Bridge, a major suspension bridge distinguished for its Gothic towers and “verde-green” paint, both choices of David Steinman, who began his bridge-building career working under Lindenthal on the Hell Gate. Unlike most large suspension bridges, whose steel cables are spun in place strand by strand, those of the St. Johns were assembled out of fully formed lengths made at the John A. Roebling’s Sons plant in Trenton, New Jersey. Steinman was responsible for bridges around the world but like many a prolific engineer, he did not realize all of his dreams. His proposal for a monumental “Liberty Bridge” across the entrance to New York Harbor was passed over in favor of that of the Verrazano-Narrows Bridge. That bridge was the design of Othmar Ammann, who had also worked under Lindenthal on the Hell Gate project, and whose 1931 George Washington Bridge across the Hudson realized the dream that eluded his mentor.
Bridging the Oregon Coast
Though many an American city can claim, like Portland, to be a city of bridges, few areas of the country can rival the Oregon coast in sheer numbers of beautiful and unusual bridges. What distinguishes these bridges as a group is the genius of their chief engineer, Conde B. McCullough, who was born in 1887 in South Dakota, studied engineering at Iowa State, worked for the Iowa highway department for a few years, moved to Oregon in 1916 to teach and soon became the state’s bridge engineer. In Oregon, he also studied law, wrote of economic and legal matters in addition to bridge design, and left a legacy of graceful bridges built in the 1930s to complete the Oregon Coast Highway. Although no two of McCullough’s major bridges are exactly alike, they virtually all contain his signature elements: concrete arches and Art Deco entrance pylons.
Driving north from California on U.S. Highway 101, the first McCullough bridge encountered is also one of the grandest—the Rogue River Bridge at Cold Beach. The seven 230-foot reinforced concrete arches, the first in America built employing the then-new method of prestressing developed by the French engineer Eugene Freyssinet, leap gracefully across the estuary. About 75 miles north, at the much wider Coos Bay, 13 concrete arches flank a steel cantilever of major proportions and complement it nicely. After the engineer’s death in 1946, this bridge was renamed the Conde B. McCullouh Memorial Bridge.
Seventy-five miles north of Coos Bay, approaching Waldport, Oregon, one gets a spectacular view of Alsea Bay and the multiple-arch bridge crossing it. Today, however, one sees not an original McCullough bridge but a modem one that replaced it in 1991, because the original structure was so damaged by the corrosive effects of salt water on reinforced concrete. The original bridge, with its three arches above the road nicely providing a visual focus along the curving line of 32 150-foot-span under-deck arches, was considered so significant a historic structure that the weakened and narrow bridge was allowed to be demolished and replaced only under special conditions. These included erecting a museum, known as the Alsea Bay Bridge Interpretative Center, beside the northbound bridge approach. Beside the southbound approach, a viewpoint for the new bridge is located in a pleasant park, into whose landscaping and design are incorporated some of the original bridge’s concrete pylons and part of its railings.
Many a bridge has a pleasant park in its shadow, often providing a fresh perspective on the scale of the structure. The Tacoma Narrows Bridge, rebuilt in 1954 with more attention to the aerodynamic forces that twisted the original structure apart in 1940, straddles War Memorial Park, in which visitors can stroll among artifacts of battle and conflict. It is from such a park that the true scale of a great suspension bridge can often be best appreciated, especially when one stands beside the massive anchorages, the size of which is dictated by the dead weight needed just to counteract the pull of the cables.
Other bridgeside parks provide more insight into the history of bridges than of battles. On the Kentucky side of the Ohio River near the suspension bridge to Cincinnati, sometimes said to have served as a model for the Brooklyn Bridge, a plaque describes the bridge and a statue depicts its builder, John Roebling, after whom the bridge is now named. Near the toll plaza of the Golden Gate Bridge, there is a pleasant flower-filled park and a statue of the bridge’s chief engineer, Joseph Strauss. Beside it a section of cable shows how it is made up of individual wires, a display that attracts more attention than Strauss’s statue. Tourists seem pulled to the cable to touch it, as they are to a section of the cables of the George Washington Bridge that stands near the Connecticut Avenue entrance to the Smithsonian Institution’s National Museum of American History in Washington.
Walking across bridges is another pleasurable way of appreciating their scale and the accomplishment they represent. A leisurely stroll across a bridge like the Golden Gate or the George Washington can take a good hour. Another hour for the return trip to where one’s car is parked offers a reminder of the importance of a bridge’s long approaches, which raise its roadway a couple of hundred feet above the water. A walk across a great bridge can also provide a perspective on the size and height of its towers, which are akin to skyscrapers. Indeed, when the towers of the Brooklyn Bridge, at 276 feet above mean high water, were under construction in the 1870s, they were among the tallest structures in New York. Today, the 690-foot-high steel towers of the Verrazano-Narrows Bridge, completed in 1964, remain taller than all but a couple dozen New York skyscrapers, and the curvature of the earth coupled with the 460 feet between the towers makes them more than an inch farther apart at their tops than at their bottoms. In San Francisco, the 746-foot height of the towers of the Golden Gate Bridge makes them the city’s third tallest structures, just short of the Transamerica Pyramid and the Bank of America Building.
Many recently built highway bridges do not allow for pedestrians. Such a practice feeds self-fulfilling prophesies that people today prefer to drive rather than walk, thus justifying the elimination of “unnecessary” sidewalks on economic grounds. It is also sometimes said that the intent is to discourage suicides, but nothing has kept cars from being abandoned by truly desperate drivers near midspan railings. The Coronado Bridge in San Diego, which has no pedestrian access but does have suicide hotline numbers posted on its approaches, arcs both vertically and horizontally in a long and graceful curve across the bay in order to achieve a considerable height over the main channel, allowing huge Navy ships to pass beneath. This plan not only enables the bridge to match the existing different street alignments of both the mainland and Coronado Island but also eliminates the need for approach viaducts on the island itself, thus maintaining its residential character and low silhouette in southern California sunsets. It is a shame the sunset is not readily available for viewing from the bridge by pedestrians.
Every city has its distinctive bridges, whether they be oddly configured to satisfy local geology and politics or curiously named to commemorate engineers whose accomplishments have been long forgotten by the users of the bridges. In any case, knowing the story of any bridge and its builders invariably reveals a rich and rewarding chapter in the history of a place, its people and their dreams.