Imagine a world without bridges. Imagine London, Paris, and Rome without dry paths across the Thames, the Seine, and the Tiber. Imagine Manhattan as an island with no hard crossings of the Hudson and East rivers. Imagine San Francisco without road communication across the gate to the north and the bay to the east. Imagine Pittsburgh wedged bridgeless between the Allegheny and the Monongahela rivers. Imagine Chicago without its massive lift- and drawbridges, or Amsterdam without its more modest canal crossings. Imagine Seattle without its long, low floating bridges, or St. Petersburg without its soaring cable-stayed structure arcing out over Tampa Bay.
Bridges and cities go together, in large part because so many of our greatest cities were founded where they are precisely because of the proximity of water. It is no mystery why so many settlements have grown up by rivers and bays, and it comes as no surprise that some of the oldest of them developed at important river crossings. Cambridge is one of the many English cities that date back to Roman times; a settlement was established there in A.D. 43. The location was that of a bridge over the navigable River Cam, on the road between Colchester and Lincoln. Oxford, another venerable English city, takes its name from its location as a crossing of the Thames. How many of our cities and towns have water words, like “port,” “bay,” and “haven,” as part of their names? How many of our states share the names of the rivers that bound or bisect them? Some towns, like Iron Bridge in England and Suspension Bridge at the Canadian border in New York, have even been named after the structures upon which they depended.
Water travel and commerce were highly developed long before there was the widespread erection of large bridges across navigable waters. Although today we transport so many products of manufacture and agriculture by railroad, truck, and airplane, we still “ship” the goods out and await new “shipments” of supplies. The priority of shipping and naval interests shaped the character of many of our port cities well into the twentieth century, until autobahns, autostradas, motorways, and interstate road networks focused attention elsewhere. But the water crossings of even the greatest roads still remain shaped by consideration for what happens in the water below.
Imagine Boston and Cambridge, Massachusetts, without bridges over the Charles and the early-morning rowers beneath them. Imagine Detroit without access to Windsor, its Canadian neighbor—by the oddity of local geography, to the south. Imagine Washington, D.C., without roads to Virginia across the Potomac and over its yachts. Imagine St. Louis—now with its arch, which is a bridge of sorts, bearing tourists to the sky—inaccessible across the Mississippi from Illinois. Imagine New Orleans, dry behind levees, but without a crossing of Lake Pontchartrain, or without the Huey P. Long Bridge across the lower Mississippi. Imagine Charleston without its serpentine Old Cooper River Bridge, known affectionately as Old Roller Coaster. Imagine Philadelphia isolated by the Delaware River because it had no Ben Franklin or Walt Whitman bridge. Imagine Portland, Oregon, with its beautiful hills but without its crossings of the Willamette River. Imagine Florence with its Uffizi and its Pitti Palace but without their connection across the Ponte Vecchio or Venice without its Ponte Rialto or its Bridge of Sighs, so called because the sounds of the prisoners who passed over it between the palace and prison could be heard on the canal below.
A view of Pittsburgh, circa 1969, showing many of its bridges (photo credit 1.1)
Bridges have become symbols and souls of cities, and each city’s bridges have been shaped by, and in turn shape, the character of that city. It is virtually impossible to go into a souvenir shop in San Francisco without being overwhelmed by images of the Golden Gate Bridge, on everything from T-shirts to spoons. The Sydney Harbour Bridge is as much a landmark of that city as is its famous harborside opera house. New York’s Brooklyn Bridge is legendary—as is London Bridge, even though its stones have been reassembled in Lake Havasu City, in western Arizona, and the now incongruous landmark stands as one of the strangest monuments to our sense of possession over purpose.
Imagine the Golden Gate spanned by anything but the Golden Gate Bridge. Is it possible? The bridge’s location, shape, proportions, scale, and color all seem so right for the site, and now it seems so for them. Is it possible even to imagine any other bridge between San Francisco and Marin County? Could, say, a copy of the Brooklyn Bridge, with taller towers and a longer span, have been cast across the gate? Or could a smaller version of the Golden Gate Bridge, color and all, have been erected between New York and New Jersey, where the George Washington Bridge now seems so naturally established? Yet this kind of questioning and imagining is precisely what engineers must do before any bridge exists. Some of the earliest proposals for bridges in New York and San Francisco looked nothing like what have since come to be such familiar features of those cities. Indeed, one nineteenth-century proposal for a crossing between New York and Brooklyn was a soaring arch, and an early idea for the Golden Gate Bridge was so ugly that it is a wonder any bridge there ever gained anyone’s support.
Bridges define the approaches to cities, and passing over or under some of the world’s great spans is an unforgettable experience. Many travelers from the north have their first view of San Francisco framed in the tunnel approach to the Golden Gate Bridge. To sail into New York Harbor today is to watch the Verrazano-Narrows Bridge grow to mythic proportions even before the Statue of Liberty comes into view. The first glimpse of the tallness of New York when driving south down the Palisades Parkway is of one of the monumental steel towers of the George Washington Bridge looming over the trees. Once within cities, the structures of great bridges often serve as landmarks and beacons for the disoriented tourist. If you are walking or driving about the canyons of New York, it is often possible to catch sight of the tops of the Brooklyn, Manhattan, Williamsburg, and other great suspension bridges whose necessarily tall towers once totally dominated the city’s skyline.
Imagine traveling into, out of, or around a modern port city without bridges. Having known the speed of road communication that bridges make possible, we would have little patience with the reintroduction of long-since-displaced ferryboats. Tunnels, generally having a much lower traffic capacity than bridges, would need to be much more numerous than above-ground spans, and would burrow underwater every which way. But travel into or out of a city by tunnel is a much less dramatic, relaxing, or satisfying experience for the average driver or automobile passenger. Tunnels have dark connotations, and for many people the prospect of water rushing in is much more dreadful than that of a bridge falling into the water. There are of course some exceptional tunnel approaches, such as that which spirals down from atop the New Jersey Palisades into the Lincoln Tunnel under the Hudson River to New York, giving one of the best imaginable views of Manhattan’s skyline. But generally, tunnel approaches cannot rival bridge approaches for the panoramas of great cities that they make accessible.
Bridges not only provide a balcony from which to appreciate the architecture of a place; they may also inspire its subsequent architecture. Though now long eclipsed in height, the towers of the Brooklyn Bridge, with their twin Gothic arches, seem still to dictate an architectural mood to lower Manhattan, and it is not hard to imagine the bridge’s two stone towers having had something to do with the design of the twin steel towers of the World Trade Center. The arched Eads Bridge, constructed contemporaneously with the Brooklyn, might similarly be said to have influenced Eero Saarinen’s brilliant concept of the Gateway Arch as a monument to the westward expansion of America across the Mississippi River through St. Louis. And the increasingly large lift and bascule bridges that began to cross the Chicago River around the turn of the century may have inspired that city’s drive to build higher and higher skyscrapers in steel.
Nor is it only cities that rely on bridges. Imagine farm roads without culverts over which cows can pass from barn to field and back. Imagine mountain roads without suspension bridges only one person wide, to carry hikers and campers high and dry across a gaping gorge. Imagine backwoods roads without the narrow bridges that provide milestones in directions back to the main road. Imagine rural roads without the covered bridges that concealed so many lovers’ trysts over rushing streams. Imagine Madison County without its bridges.
The Mississippi River at St. Louis, on July 4, 1982, with the Eads Bridge visible behind the Gateway Arch, and with the fireworks recalling the opening of the bridge on July 4, 1874 (photo credit 1.2)
Though most of America’s more than half a million highway bridges are small and anonymous, they may not be any less important to the local traffic than the Golden Gate and Brooklyn bridges are to their hordes. The engineers of our greatest spans began by designing our smaller ones. The scale may be different, but the process is essentially the same, and so these bridges have proved to be the training grounds for dreams. Furthermore, every bridge, small or large, is also an aesthetic and environmental statement. Its lines are important beyond its span; every bridge must not only bear its burden, whether cows or coal trains, but must also be able to withstand the burden of proof that, in the final analysis, society is better served, tangibly and intangibly, by the bridge’s being there at all.
Imagine how a bridge can ruin a setting of natural beauty, whether the tranquillity of the countryside or the skyline of a city. Imagine what the wrong bridge across the Golden Gate might have done to that unique site. This is why place so often influences bridge design—for, contrary to the popular misconception, engineers are not insensitive to setting and aesthetics. The Rainbow arch bridge across the river gorge north of Niagara Falls was an appropriate form to mirror the rainbows ever present in the mist about the falls. Arch bridges can actually open up great spaces, as Navajo Bridge did over the Colorado gorge upriver from the Grand Canyon, providing to crossers views of Marble Canyon uninterrupted by any significant human artifact for as far as the eye can see. A second crossing, its steel structure again below the bridge deck, will also intrude only minimally on the natural beauty of the site. In Switzerland, the bridges of Robert Maillart and Christian Menn harmonize with the Alps in a different, yet totally compatible and successful way. In Tampa Bay, the replacement bridge for one that was rammed by a tanker is a soaring design whose pattern of towers and cables evokes the masts and sails of pleasure boats crisscrossing the bay. Though not a natural setting, the Tower of London so dominated the section of the Thames where a crossing was to be erected in the late nineteenth century that Tower Bridge was designed in consonance with the historic site, even at the risk of offending some structural purists with its stone-encased steel. Earlier in that century, Thomas Telford similarly respected the prior claim of Conwy Castle to the location of the river mouth in Wales for which he designed his suspension bridge with crenellated towers.
That there were bridges long before there were engineers does not diminish the achievement or the value of either. The earliest bridges were modest, instinctive, and imitative of nature; the latest are models of what we can achieve with experience and tools of which no primitive bridge builder may ever have dreamed. We can get some idea of the nature of the earliest bridge building by thinking of what is embedded in our own tradition, lore, and store of commonplace experiences. As infants, we have the grasping instinct, clutching at the air for something to take us over the void of separateness. We reach from mother to father and back as they take turns holding and bouncing us in their arms, swing bridges transporting us between them. As we grow, we learn that our own arms are bridges to everything. And so are our legs, as we crawl over obstacles between here and there, and then walk and run and skip and jump over space and time more in the joy of doing than in the joy of getting anywhere. We learn to walk along the sidewalk, avoiding cracks to save our mothers’ backs—bridges all—and taking joy in counting how many great canyons in the concrete we have conquered without a fall. We learn from legends and lore how the gallant gentleman, if he did not carry his fair maiden across, threw his cape over the puddle, that the maiden might step dry to her destination. Even after we stop reciting nursery rhymes and we forget gallantry, we and our companions make a bridge fleeting in time when we step or jump across the water in the gutter in our way.
Long before there were fairy tales, at least as we know them today, nature provided models for bridges in the form of stepping-stones, arching branches, hanging vines, and fallen logs across streams. These found bridges were used by animals as well as men and women and their children, and eventually people learned to make their own bridges deliberately, placing stones step by step in streams, bending branches to a purpose, stringing vines in patterns of determination, and felling logs that did not fall by themselves. This was the work of the first bridge builders, and as their bridges grew and multiplied, so did the dreams and ambitions of the more reflective among the builders. Dreams became necessary when natural gaps became deeper than stones could fill and wider than vines and trees could reach. To bridge such gaps took more than imitating nature, it took the imagination and ingenuity that are the hallmarks and roots of engineering.
Almost three millennia ago, Homer wrote of bridges as commonplace achievements, mentioning in particular how armies crossed water on pontoon bridges. The Persian kings Cyrus, Darius, and Xerxes employed such structures about twenty-five centuries ago, as did Alexander the Great a century or two later. Among the earliest recorded specific bridges is one over the Euphrates at Babylon described by Herodotus, writing almost twenty-five hundred years ago. It was made of timber beams resting on stone piers. Engineering and technology have always advanced whether or not their achievements were recorded in words, and Greek and Roman bridge building, not to mention that of non-Western civilizations, long ago reached well beyond the limitations of the log as girder. The origins of the cantilevered or corbeled arch, which children who play with blocks still construct instinctively today; of the true arch, which we still admire in nature and in art; and of the suspension bridge, which is believed to have its roots in such diverse locations as China, northern India, central Africa, and South America, are lost to history.
Though some Roman bridges still stand after two thousand years—most notably the wonderful aqueducts, such as the one that dwarfs the marketplace in Segovia, Spain, and the magnificent Pont du Gard near Nîmes in southern France—many other ancient bridges have been lost to use and the elements. All bridges have always suffered a degree of wear and tear, of course; by the Middle Ages, there was widespread deterioration of the infrastructure of bridges whose materials or initial construction were not so fortunately chosen or carefully crafted as the most hardy of the Roman arches. One reason the aqueducts were less threatened by time was that they generally carried the constant load and laminar flow of water, rather than an ever-increasing and sometimes turbulent burden of people, animals, and vehicles. In the Middle Ages, as the conventional history has it, there appeared brotherhoods of bridge builders, in the form of congregations of clergy who had established themselves in remote monasteries in the hills to escape the barbarians. As some of them remain to do today, such congregations came to toil manually in their fields and vineyards to sustain themselves physically so they could continue to pray in their chapels and sustain themselves spiritually.
Among the monastic groups was the Altopascio Order, located near Lucca, Italy, on the ancient road between Tuscany and Rome. Members of the Altopascio wore embroidered on their robes an insignia resembling the Greek letter τ (tau), whose arms “were nicked or pointed in such a way that the vertical shaft may have represented an auger and the crossbar a hammer or ax,” thus indicating a proficiency in carpentry. Since the order’s Hospice of St. James was not far off the busy road in wild and dangerous country, travelers and pilgrims frequently sought refuge there. To serve these travelers, the Holy Roman Emperor Frederick II decreed in 1244 that the Altopascio “build and maintain upon the public pilgrim’s highway” a bridge, thus prompting the name Fratres Pontifices. After the Fall of Rome, the Pope himself was known, of course, as Pontifex Maximus, the supreme bridge builder.
The fame of the Italian Brotherhood of Bridgebuilders spread, and in France a group of Benedictine monks established the Frères Pontiffes. According to tradition, their first settlement was on the River Durance, in southeastern France, at a treacherous ford called Maupas. After the frèresbuilt their bridge at this location, it became such a safe crossing of the Durance that the place name was changed from Maupas to Bonpas. As the work of bridge brotherhoods spread, so did the evolution of bridge types and construction techniques; eventually, the endeavor became a secular and moneymaking activity, as lotteries were held to raise funds for construction or tolls were charged to repay and reward investors, as well as to maintain the capital investment itself. The arch bridge, first in stone but later in iron, became the most common form by far, but that was to change with the development of engineering as a subject of study in its own right, and thus as a profession.
The familiar triangular roof truss—which, like all roofs, is really a bridge between walls and over house and home, barn and manger—has long been painted matter-of-factly in scenes both social and domestic, both rustic and religious. The wooden truss came in for attention as a true bridge with its discussion by Palladio in the sixteenth century. It was taken to new lengths in the eighteenth century in the hybrid arch-truss forms of the Swiss brothers Grubenmann, and it began to flourish in the nineteenth century, especially in America, where it was patented and thereby named by scores of inventors making use of ubiquitous timber, abundant iron, and fertile imaginations. These inventors and their trusses were among the last of the mechanic-builders; as spans of increasing length and strength were required for the advancing heavy railroads of the mid-nineteenth century, it took a sense of and a capacity for calculation before construction to achieve success in an increasingly competitive environment, for bridge building and everything else.
Squire Whipple, who was born in 1804 to the farming and mill-owning family of James and Electa Johnson Whipple in Hardwick, Massachusetts, has been called the “father of American bridge building” and the “father of iron bridges.” Young Squire (his name, not a title) attended Hardwick Academy and the Academy at Fairfield, Connecticut, before going to Union College, in Schenectady, New York, where he earned his bachelor-of-arts degree in 1830. Whipple’s education at Union actually predated its formal creation of an engineering course, which was announced in 1845 by President Eliphalet Nott, who had been serving simultaneously as president of the Rensselaer Institute, across the Hudson River in Troy. Since Rensselaer had been offering a program in civil engineering for a decade, Nott found he had a conflict of interest and resigned from the other school to serve Union for what would be a sixty-year tenure.
Union was a natural choice for Whipple’s higher education. When he was a young teenager, his family had moved to Otsego County, New York, in which Cooper’stown is located, and where young Squire farmed in the summer and taught school in the winter. Even though he attended Union before it offered a formal program in engineering, Whipple would have been expected to take a course in the elements of the science of mechanics, just as his contemporaries at Harvard would on their way to an A.B., and so he was as prepared as any of his time to see a truss not only as a bridge to be constructed but also as the object of study and calculation. After a decade of experience working on railroads and canals, Whipple patented a combination arch-truss bridge, and in 1847 published the first edition of his seminal Work on Bridge Building, which evolved into his definitive Elementary and Practical Treatise on Bridge Building. It was this work—which explicated his method of determining the distribution of forces in the various members of a truss, thereby making it possible to determine the most economical sizes of the parts to manufacture and ship to the location where they would be assembled—that earned him his appellations. In the association of bridge building with drawing and calculation and written argument before any construction was started, a new era was begun. From then on, the grandest dreams could be articulated and tested on paper, and thereby communicated to those who would have to approve, support, finance, and assist in designing a project that could eventually take years, if not decades, of planning and construction.
The stories of modern bridges are stories of engineers at their best, dreaming grand dreams of tremendous potential benefit to mankind and then realizing those dreams in ways consonant with the environment, both natural and previously built. Though there also have been misdirected schemes and pork-barrel projects and political corruption and disruption of neighborhoods associated with bridge building, the stories of the overwhelming majority of our grandest bridges are about technological daring and adventure and creative competition for the common good. Great bridges are conceived by great engineers; since there are often more than enough of these to go around at a given time in history, there are more often than not a plethora of proposals for bridges where there were not bridges before, frequently because the physical and intellectual challenges of the problem had been thought to be beyond the reach or means of the times.
Drawings from a patent issued to Squire Whipple in 1841, one of many truss-bridge designs patented in the middle of the nineteenth century (photo credit 1.3)
Engineers are also people, of course, and so rivalries have developed among them for commissions to build the greatest bridges, but by and large the bridge engineers of a particular era have formed a kind of fraternity and an interlocking directorate of experts who work more in concert than in discord. Where one may have been the chief engineer, others will have served on a board of consultants. In another project, some of their roles will have been reversed. Thus the bridges of an era will often share certain characteristics, reflecting the collective wisdom and prejudices of the leading practitioners, while at the same time bearing the stamp of individuality of the leader of each particular project.
The generally acknowledged dean of American bridge engineers of the late nineteenth and early twentieth centuries was the Moravian-born Gustav Lindenthal. His masterpiece, Hell Gate Bridge in New York, built to carry a connecting railroad through New York City and thus between New England and the rest of the continent, was a training ground of sorts for the young engineers Othmar Ammann, born in Switzerland, and David Steinman, born on the Lower East Side of Manhattan in the shadow of the Brooklyn Bridge. Their stories, and those of American bridge engineers like Leffert Buck, Theodore Cooper, James Eads, Ralph Modjeski, Leon Moisseiff, the Roeblings, Joseph Strauss, John Waddell, and a host of others, reveal the way in which bridges are conceived and built and, in the process, tell the story of the flowering of engineering as a profession in America.
Telling the story of engineering through its engineers and their works was the method of Samuel Smiles, whose five-volume Lives of the Engineers was popular reading in Victorian times. He described his work as a history of inland communication, chronicling as it did the draining and reclamation of swampland, the development of harbors, the digging of canals, the pushing through of roads, and, finally, the building of the railroads and their concomitant bridge and tunnel structures. Mundane and pedestrian as the subject matter might otherwise have seemed, Smiles brought the adventure and altruism of British engineering alive and raised the status of the profession while at the same time inspiring new generations to creative lives of service to humankind. The stories of the American engineers have no less potential for bringing them alive as heroes of technology and culture, and no less potential for illuminating the process of engineering as an indispensable ingredient of civilization.
Try to imagine a world without engineers. In such a world, an absence of bridges would be among the least of inconveniences. Would there be a ready supply of food, for are farmers not soil and water engineers, and is agriculture not crop engineering? Would food be distributed very far beyond where it was grown, for how far could it go without roads or canals or ships or even containers in which to carry it—all such artifacts being the products of some kind of engineering, informal as it may be? Would food be refrigerated for shipment in summer or put away for the winter, for how long would it last without some form of preservation that involved engineering of a kind? And what of shelter? And what of human pride and pleasure and purpose in the construction of cathedrals and temples and monuments? Are any of these things imaginable without the ingredient of engineering, albeit rudimentary or informal?
To understand the works of engineers and engineering is to understand the material manifestations and progress of civilization. The monuments of ancient Egypt, Greece, and Rome, in turn, illuminate the nature of engineering in those cultures, which was in many fundamental ways the same as the nature of engineering today. To conceive and execute the pyramids, the Parthenon, or the Colosseum required the same kind of conceptual design and analytical mental projection that it takes to conceive and realize a grand stadium, skyscraper, or bridge today. Even if the scientific understanding and mathematical and computational tools of engineering have advanced beyond what must have been the wildest imaginings of the ancients, the basic ways in which engineers conceive of new designs and think about bringing them to fruition is essentially the same today as it has always been. And although science and mathematics and computers are likely to continue to develop beyond our most extreme prognostications, the conceptual and methodological aspects of engineering in the thirtieth century are likely to be little different from those we know today. This is why the history of engineering will always be relevant.
We can learn a great deal about ancient, modern, and future engineering by looking closely at virtually any artifact, from a safety pin to a jet airplane, but some made things are inherently more interesting than others, the stories about them more charged with human drama. Bridges are in this latter category, and there is no purer form of engineering than bridge building. Daring and distinctive suspension spans like the Verrazano-Narrows Bridge or the Golden Gate Bridge, which are so familiar to so many, have the shapes and proportions they do, not because of some architectural golden section or some abstract theory of space and mass. Rather, the greatest bridges look the way they do because physical constraints, engineering inspiration, and judgment have led to calculations concerning the relative strength and cost of foundations and towers and cables and anchorages and roadways and rights of way. That is not to say, however, that aesthetic and political questions do not also inform the calculations of the engineer, for they most certainly do, as we shall see.
Whereas some of the greatest skyscrapers, like Chicago’s Sears Tower and John Hancock Center, are the result of close collaboration between architect and structural engineer, this is not generally the case. Large buildings and monumental structures are often sketched first by an architect, with an eye toward the visual, and engineers may be asked afterward to develop a structural skeleton to support the façade. This was the case with the Statue of Liberty. It was first suggested as a symbol of friendship between France and the United States at a dinner party in 1865 by the French historian and politician Edouard-René de Laboulaye, and another dinner guest, the sculptor Frédéric-Auguste Bartholdi, embraced the idea. On a trip to America in 1871, he identified the present site in New York Harbor, then, back in France, began to make models. In the meantime, money for the statue was raised in France through lotteries and dinner parties, while that for the stone pedestal upon which Liberty would stand was raised in America with the support of Joseph Pulitzer, the influential newspaper publisher.
Bartholdi, realizing that it would be impractical to ship a bronze or stone statue across the ocean, designed one to be made up of beaten sheets of copper that could be mounted on an iron framework. The design of this latter, hidden part of the statue was to be done by Eugène-Emmanuel Viollet-le-Duc, the French architectural critic whose practical bent had led him to write, among more theoretical works, a very basic book on how to build a house. But Viollet-le-Duc died in 1879 without completing the iron frame. Bartholdi then turned to Gustave Eiffel, whose engineering firm was, at the time, the designer and builder of some of France’s most daring bridges. In the end, it was the bridge-building experience of Eiffel and his engineers that enabled the Statue of Liberty to be erected in New York Harbor, and to withstand the elements for over a century, as his tower has in Paris. The refurbishment of the statue for her centennial revealed that structural weaknesses that had plagued the monument and had closed Liberty’s arm to tourists for so many years were due not to any structural miscalculation on Eiffel’s part but, rather, to some alterations made during construction and to an electrochemical reaction between the dissimilar metals used for the statue’s skin and skeleton. Much effort involved in restoring the one-hundred-year-old symbol went to addressing this problem.
A Currier & Ives print, circa 1886, showing the Brooklyn Bridge across the East River and the Statue of Liberty in New York Harbor (photo credit 1.4)
Bridge designs cannot evolve the way the Statue of Liberty or glass-faced high-rise buildings do, from the artistic outside in. A great bridge is an engineering structure first, and only when its structural integrity has been established on the drawing board and through elaborate engineering calculations can architectural embellishments be considered. This is not to say that architects have no role in bridge design, for bridge engineers have a strong tradition of involving architects as consultants. Many of the distinctive visual features of the Golden Gate Bridge, including its sculpted towers and color, are owing to the involvement of the consulting architect, Irving F. Morrow.
The George Washington Bridge, when it was conceived in the 1920s, was to be twice as large as any existing suspension span, and so the towers had to be as tall as skyscrapers. Such massive structures demanded some special treatment, it was felt, and no less an architect than Cass Gilbert, designer of New York’s Gothic-style Woolworth Building, was involved in the design of their façade. The full story of the George Washington Bridge will be told later in this book, but it is not giving away too much to say that the architectural stone façade was never applied to the towers, whose bare steel forms stand today as one of the masterpieces of modern bridge engineering. Imagine what the George Washington Bridge would look like with stone applied, and imagine what might have been its influence on later suspension bridges, almost all of which have been built with steel towers. Each great bridge influences each later one, and that is why it is necessary to understand the history of bridges and their engineers in order to understand present and future spans and perhaps something of their builders.
When the proportions of ancient bridges, having been arrived at by trial and error, were codified in stone according to rules that such architects as Vitruvius and Palladio prescribed for buildings, then bridges could be designed as architectural edifices. Even the great Roman aqueducts, such as the Pont du Gard in southern France, could be built with little calculation of the kind required for designing a modern bridge, for each of the individual semicircular arches could be supported by the massive piers on either side of it, and construction was more or less a matter of piling arches like blocks one beside and one upon another until the valley was filled with bridge to the desired level. Though superficially analogous processes can be said to suffice for bridge building today, now each step in the construction must be weighed so that the incomplete structure is as able to support itself as the completed bridge. Because this simple fact was overlooked, the Quebec Bridge over the St. Lawrence River, planned to be the largest of its kind, spontaneously collapsed while under construction in 1907. Great suspension bridges can be constructed without falling only because elaborate engineering calculations determine the precise order in which the parts, which individually might weigh as much as a large locomotive, will be assembled.
The modern bridge-building era began in the late eighteenth century, with the daringly shallow stone arches built over the Seine by the French engineer Jean-Rodolphe Perronet, and with the revolutionary use of iron in British bridge building. What is generally considered the first iron bridge was built in 1779 across the River Severn at Coalbrookdale, where increasingly larger iron castings had been made by the Darby family of founders. The first iron bridge mimicked a stone arch, with connection details that suggested timber construction. When wrought iron became available in larger quantities and pieces, these were formed and assembled into chains to support a bridge that worked not on an arch but on a suspension principle. The increasing use of iron in bridges of ever-greater span led to increasingly innovative and daring designs, which more than once over the course of the nineteenth century culminated in a colossal failure. However, as the Victorian era was drawing to a close, advances in engineering, mathematics, and science had given bridge engineers a perspective and a collective set of tools that enabled them to tackle with confidence and success problems of bridging that had once been thought impossible.
This book is about how the late-nineteenth- and early-twentieth-century engineers did what they did to leave us a legacy of bridges that define our material environment, shape our cities, suburbs, and rural areas, and ordain our routes of communication over distance and time. That period of great bridge building, especially in America, coincided with the rise of the engineering profession, and so the story of bridges provides an excellent vehicle also for understanding the development of the engineer and engineering generally. How the engineer interacted with society in the process of conceiving, promoting, financing, designing, and building bridges serves as a paradigm for appreciating the nature of engineering endeavors, and thus provides a basis for understanding how technology and society interact today and can be expected to interact in the future. No bridge is an island, entire of itself, and the story of any bridge is the story of every bridge in that it involves a plethora of characters and circumstances. By considering the stories of a few of the most significant, though not necessarily the best-known, engineers and the bridges that they conceived and built over the last century or so, we can come to understand more fully the nature of the interaction of the engineer with the rest of society, of the relationship between technology and the rest of the stuff and ideas of the world.
From another viewpoint, fully understanding how bridges have been conceived, financed, and built requires a fully integrated view of technology, society, and culture. The financial link is often the crucial metaphorical span between the dream and reality of an actual bridge. Many a wonderful concept, beautifully drawn by an inspired structural artist, has never risen off the paper because its cost could not be justified. Most of the great bridges of the nineteenth century, which served to define bridge building and other technological achievements for the twentieth century, were financed by private enterprise, often led by the expanding railroads. Engineers acting as entrepreneurs frequently put together the prospectuses, and in some cases almost single-handedly promoted their dreams to the realists. In the early twentieth century, in larger cities like New York, there were needs for bridges to move citizens, increasingly in automobiles, from homes to workplaces and back, across rivers and bays that were becoming choked with ferryboats and other water traffic and sometimes ice, and so local and state governments began to get more and more involved in the building of great bridges. Debates over how to pay for them were common. When the Delaware River Bridge, now known as the Ben Franklin Bridge, was under construction in the mid-1920s, an argument between Philadelphia, which wanted a free bridge, and Camden, New Jersey, which wanted to collect tolls, brought progress on the structure to a standstill.
The stories of the building of great long-span bridges coincide with the rise of the steel industry. Beginning with the Eads Bridge, whose requirements for steel were almost too demanding for the fledgling industry and its up-and-coming barons, like Andrew Carnegie, the desire for stronger and stronger materials to make ever larger and relatively lighter structures drove research and development among competitive suppliers. Later, the introduction of concrete, first reinforced and subsequently prestressed, as an alternative to steel in some structures, provided a new element of competition that remains to this day. Whether a bridge should be steel or concrete in some cases can be a toss-up financially, and the decision becomes one of aesthetics, maintenance, or technological preference.
Though it is true that no individual engineer, no matter how great, can single-handedly do everything—from detailed calculations to supervision of construction—required to bring a major span to fruition, great bridges do appear to have had masterminds behind them, albeit masterminds with many helper minds. Indeed, the stories of the great bridges built in the half-century or so between the 1870s and the 1930s, the era when length records were set that remain unsurpassed or just barely surpassed today, are stories of recurring characters, both major and minor, who seem to have played a role in almost every bridge of any significance that was constructed during the period in which they flourished. There was also a necessarily large cast of supporting engineers, of course, and their roles in the realizations of dreams will be seen to be no less significant. However, the main action shows that a few handfuls of leading engineer-entrepreneurs, by the force of their personalities, talents, ambitions, and dreams, rose to or seized the leadership roles during the era of great bridge building. Yet these great engineers were also as much a product of the opportunities and circumstances of their times, which they often influenced themselves, as of their dreams and talents.
If the stories of bridges begin in dreams, they often reach a climax, at least formally, in celebration. The completion of a great bridge, especially one linking what theretofore had been so close to the eye and yet so far from the body, has traditionally been cause for celebration. The formal opening of the Eads Bridge on July 4, 1874, which began with a huge parade in the morning and closed with a grand display of fireworks in the evening, set the standard for subsequent American bridge openings. The opening of the Brooklyn Bridge in 1883 was the subject of many a lithograph, and its spectacular fireworks show was recalled by an equally spectacular one on the occasion of its centennial in 1983. Great suspension bridges and celebrations seem especially to go together, and the clearly distinct stages of construction provide various opportunities to acknowledge progress and achievement. Discrete ceremonies often mark the topping out of towers, the completion of foot-walks for cable spinning, the finishing of the cables, and the placement of the final segment in the roadway.
A special rivet was put in place by the Prince of Wales when the Firth of Forth cantilever bridge was opened in 1890. Though the engineers, bankers, and politicians are often joined only by the press on such occasions, the opening ceremonies of a bridge can also be a veritable test of the bridge itself. Pedestrians have traditionally had the run of bridges on their first day, and re-created walks across them have marked their anniversaries. Throughout the course of its opening day, May 27, 1937, which was designated Pedestrian Day, about two hundred thousand people had the Golden Gate Bridge all to themselves, and they walked leisurely between San Francisco and Marin County. To celebrate the fiftieth anniversary of the bridge, another Pedestrian Day was held in 1987, and of the half-million or so people who showed up all at once, only a couple hundred thousand could get onto the bridge’s main span at one time. It turned out to be the heaviest load the bridge had ever experienced, and the structure was visibly strained under the weight.
The Golden Gate Bridge, on the occasion of Pedestrian Day in 1987, marking the structure’s fiftieth anniversary (photo credit 1.5)
Unfortunately, our thoughts about bridges often end the day after such celebrations, and we tend to take these structures, once thought impossible to finance or build, for granted. Yet bridges are affected by their environment no less than people are, and the wear and tear of traffic, pollution, abuse, neglect, and just plain old age take their toll. It is implicit, and often made quite explicit, in the design of every product of engineering that there are limits to its health and strength, and therefore limits to what it can be subjected to. A recognition of those limits and regular checkups and inspections of the artifact are required, as is a certain amount of preventive maintenance and repair. To neglect this common sense is to find ourselves in the position in which we now are in America, with roughly one out of every five of our bridges said to be structurally deficient. A familiarity with the stories of our bridges not only can bring a fuller appreciation of their rich history and significance, along with an appreciation and understanding of the humanity of engineers and of engineering generally, but also can promote a greater enjoyment and pride in the contribution of bridges to our physical and cultural infrastructure, and a sense of obligation to maintain them. Imagine what our lives would be without bridges.