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 frères built 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 Whipp
le’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 enginee
rs 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.
Engineers of Dreams: Great Bridge Builders and the Spanning of America Page 2