To Engineer Is Human Page 7
Through the very heart of this rocky mountain, a tunnel had been constructed of most admirable architecture, with a lofty arch and a spacious double track; so that, unless the earth and rocks should chance to crumble down, it will remain an eternal monument of the builder’s skill and enterprise. It is a great though incidental advantage that the materials from the heart of the Hill Difficulty have been employed in filling up the Valley of Humiliation, thus obviating the necessity of descending into that disagreeable and unwholesome hollow.
It was a “wonderful improvement, indeed.”
The ambivalence expressed by such writers as Wordsworth and Hawthorne was echoed in the popular press of the time. On the one hand, the fruits of the Industrial Revolution were plucked with anticipation and laid out graphically in all their succulence for the public to savor in such chronicles of the times as the Illustrated London News and Harper’s Weekly. On the other hand, Harper’s would report the accidents that occurred and Punch would satirize and parody the railroads. The railroads and their bridges had captured both the imagination and the fear of the public, just as airplanes would a century later. These technological advances were for Everyman and not just for kings and God, and their promise of a smoother route to the Celestial City presented benefits that made the risk of accidents along the way a risk worth taking. For all of Hawthorne’s ridicule, his first-person narrator does want to take a ride on the Celestial Railroad “to gratify a liberal curiosity.”
As the Oxford English Dictionary attests, the word engineer designated one who contrives, designs, or invents more than a century before it came to mean also one who manages an engine. The latter meaning dates from 1839, when the railroad was emerging as the great metaphor of the Industrial Revolution, and it is not surprising that there came to be a deliberate confusion of the contriver and the driver of the vehicle. The engineers of steam engines and iron bridges were in the driver’s seat. As these mechanical and structural pioneers were pushing the railroad further and further beyond the frontiers of technology, they were increasingly seen as controlling the speed and destination of the passengers on the Celestial Railroad. Although Hawthorne’s alter ego had some doubts about the railroad’s promise to fill in the Slough of Despond that had resisted efforts from time immemorial, Mr. Smooth-it-away pointed to a “convenient bridge” and explained:
We obtained a sufficient foundation for it by throwing into the Slough some editions of books of morality; volumes of French philosophy and German rationalism; tracts, sermons, and essays of modern clergymen; extracts from Plato, Confucius, and various Hindu sages, together with a few ingenious commentaries upon texts of Scriptures—all of which, by some scientific process, have been converted into a mass like granite. The whole bog might be filled up with similar matter.
Thus sometime around the middle of the nineteenth century the work of engineers was beginning to be seen even by the layman to involve “some scientific process” as it transformed classical thinking into hard calculations. As engineering began to apply the scientific method to structural problems, it moved away from purely aesthetic considerations and separated itself from architecture. The roots of the two cultures’ debate spread rhizoid-like in all directions throughout the Victorian era and periodically came to the surface here and there like dandelions in a spring lawn. Yet what is a weed and what a flower remains as difficult a problem of taxonomy as it was in Wordsworth’s time.
As engineering came to mean the application of the scientific method to railroad bridges and other ambitious structures, its practitioners had to address the question of structural failure and structural success more explicitly. The failures of pyramids and cathedrals were by and large failures during construction, not failures during use. The failure of a railroad bridge was more likely to involve the lives not only of construction workers engaged in a high-risk activity but of innocent people who had entrusted their safety to the engineers. Sudden and catastrophic bridge collapses were introduced into the daily way of life, and they had to be reckoned with not through the classical trial and error method, but with a newer and more abstract method that employed pencil and paper in lieu of chisel and stone. What the engineers of the nineteenth century developed and passed down to those of the twentieth was the trial and error of mind over matter. They learned how to calculate to obviate the failure of structural materials, but they did not learn how to calculate to obviate the failure of the mind.
No one wants to learn by mistakes, but we cannot learn enough from successes to go beyond the state of the art. Contrary to their popular characterization as intellectual conservatives, engineers are really among the avant-garde. They are constantly seeking to employ new concepts to reduce the weight and thus the cost of their structures, and they are constantly striving to do more with less so the resulting structure represents an efficient use of materials. The engineer always believes he is trying something without error, but the truth of the matter is that each new structure can be a new trial. In the meantime the layman, whose spokesman is often the poet or the writer, can be threatened by both the failures and the successes. Such is the nature not only of science and engineering, but of all human endeavors.
6
DESIGN IS GETTING FROM HERE TO THERE
Designing a bridge or any other large structure is not unlike planning a trip or a vacation. The end may be clear and simple: to go from here to there. But the means may be limited only by our imaginations.
Let us imagine that we are living in Chicago and that we have promised to take our children to see New York City during two weeks of summer vacation. One of our first decisions is how to get to New York and back, and we generally can quickly narrow down the ways to three or four. We can drive our own car or take a bus or a train or a plane. The possibilities of going by hot-air balloon or bicycling or even taking a boat through the Great Lakes and man-made seaways will probably not occur to the average family, though they might to those who are so devoted to ballooning or biking or boating that the means of transportation may be considered more important than the destination itself.
Most families will end up choosing between driving and flying to New York, and they will base their decision on economic considerations (driving will be cheaper for larger families), convenience (driving will enable them to make their own schedule and also give them transportation about New York), aesthetics (driving will enable them to enjoy the scenery along the interstate), emotions (driving makes them less anxious than flying), or even habit (they always drive). Another family may use the same criteria to choose flying over driving because airfares are cheaper than tolls and fuel for their gas-guzzler, because having a car in New York will be a pain, because they love to look at the clouds when flying, because they know it is statistically safer to fly than to drive, and because they always fly. It is clear that there is no best way to get to New York and back, for the right choice for one family might clearly be the wrong one for another.
Even when the major decision has been made, there remain countless other minor decisions. What time should they leave? If they are driving, what route should they take? Should they drive straight through or should they stop overnight en route? Where should they stop? What motel should they stay in? Where should they eat dinner? If they are flying, how should they get to the airport? What flight should they take? How should they get from the New York airport (which one?) to their hotel (which one?)?
Clearly the choices can appear endless. Most choices will not make much of a difference as far as the principal object of spending about two weeks in New York is concerned, and thus they are not worth dwelling upon for an inordinate amount of time. Other decisions, such as whether to look for an inexpensive motel in New Jersey and drive into the city each day or whether to stay in a midtown hotel and be within walking distance of what one wants to do in New York, may have a major impact on whether the vacation is indeed a vacation.
All of the decisions about how to have a vacation in New York can be seen as att
empts to maximize each family’s enjoyment of its own vacation. Instead of stating its choices as preferences of one choice over another, each family might also reach its decisions by stating what it will not or does not want to do. Thus the large family might reject flying as too expensive, leaving them without a car in New York, depriving them of the opportunity to enjoy the scenic drive, introducing unnecessary anxiety into their vacation, and keeping them from their summer ritual of driving somewhere. Indeed, such a family might further insure the success of their vacation by reminding themselves not to go to the restaurant that disappointed them last time, not to wait in those long lines in Times Square for theater tickets, and not to try to drive crosstown during the rush hour. In short, the family can improve the success of its vacation by anticipating what can go wrong to ruin it.
Engineering design is not much different. Many objects of design are no more exotic than spending two weeks in New York. Even if you and your own family have not done it before, there are plenty of people willing to give you advice about what to do and what to avoid. There are books on the general subject of New York and others on such specialized aspects as the city’s museums, restaurants, and shopping opportunities. Magazines and newspapers contain the experiences of the latest travelers to the Big Apple, telling you to be sure not to miss this or that attraction. And the availability and price of hotel rooms, theater tickets, and restaurants can be obtained over the telephone. In short, there is a wealth of experience and information out there for the asking. One can even find among his friends and neighbors experts on the negative aspects of visiting New York—crowds, the con men, the perverts, the muggers. Whether the small risk of encountering any of these detracts sufficiently from all the benefits of a visit is a subjective judgment that each family must make for itself.
The engineer designing a new highway bridge also has a wealth of experience available to him, as we all can imagine, having ourselves driven over and under tens of thousands of individual bridges on and off the interstate. We know there are still some covered wooden bridges out there, but today by and large we think in terms of concrete and steel. So many of the bridges resemble each other so closely that we soon pay no more attention to them than we do to the individual trees along the side of the road. But every now and then we come across a bridge that we can sense is special: a tall, curving arch spanning a deep ravine, a great suspension bridge across a wide bay, or a new cable-stayed bridge across a great river. Other bridges are special in ways that are not always obvious to the casual traveler, and sometimes these come to our attention only after their dramatic collapse. In some cases those colossal errors occurred because the bridge designer was doing what had not been done before, much as someone taking too exotic a holiday may not be able to arrange it through a conventional travel agent. To go through with exotic plans is clearly to be adventuresome, and one can ensure his safe and satisfied return by anticipating all that might go wrong. As the first trips of the astronauts to the moon demonstrated, travel to places without benefit of previous experience need not be doomed to failure.
The evolution of bridges can be traced back to primitive man felling a log across a brook, and the proud history includes the Roman aqueducts. But modern bridges are made neither of available logs nor of piles of stones. They are deliberate designs in concrete and steel arranged to suit the functional, aesthetic, and economic demands of our complex society. Because new demands are constantly being made—for a larger, more attractive, or less expensive bridge—it is not always possible, even if desirable, for the designer merely to copy what has been done successfully before. Copying may work for an ordinary highway bridge, but it clearly will not do when the highway is to cross a wider bay or a deeper ravine than ever spanned before. Then there are no examples to copy; there is no proven experience to follow. Thus the history of modern bridges is also the history of the development of a more scientific approach to designing large engineering structures than the pyramids and cathedrals or even the Roman aqueducts.
In 1779 the first iron bridge was erected in England at Coal-brookdale near the foundries that cast its iron arches with details that mimicked then-familiar (and successful) stone-and-timber construction. Ironbridge spanned a hundred feet across the Severn River and is still used by pedestrians today. At the time of its making, Ironbridge represented a bold experiment with a new material for bridge building, and it worked because the stone arch bridges on which its structural details were based had worked. But once iron had proven itself as a viable new construction material at Coalbrookdale, it was to be called upon to bridge ever wider gaps not only in space but also in knowledge. Because the new material could resist being pulled apart in ways that stone construction never could, new bridge designs sought to exploit iron in new ways. This combination of newly tried elements should have been a sure signal that the accumulated experience of centuries of stone would not be able to play a guiding role in the development of iron bridges, and it is not surprising that iron bridge makers would have to go through a period of trial and error to learn from their own and others’ experiences.
The development and expansion of the railroads in the nineteenth century required bridges, and timber provided the material of many of the early railroad bridges. It was a familiar material and one that was usually available near the construction site. However, timber bridges required maintenance to be sure they did not rot away, and they were susceptible to the very fire that the iron horses carried in their bellies. It was inevitable that iron was to become a natural replacement for wood in bridges, but the conversion took a good part of the nineteenth century, in large part because iron bridges seemed not only new but also unpredictable. They collapsed in numbers that are still debated today.
In 1847 Queen Victoria appointed a commission to look into the use of iron in bridges, charging its members to “endeavor to ascertain such principles and form such rules as may enable the Engineer and Mechanic, in their respective spheres, to apply the Metal with confidence, and shall illustrate by theory and experiment the action which takes place under varying circumstances in Iron Railway Bridges which have been constructed.” What was happening was that the bridges were experiencing what we know today to be fatigue failures, collapsing without warning under a passing train. The commission’s report, published in 1849, promulgated a misguided idea about the fatigue of metals, theorizing that “crystallization” occurred under vibratory action, and this misconception was to persist well into the twentieth century. Nevertheless, the report did lead the English Board of Trade to formulate some requirements regarding stresses in bridge construction and thus had a beneficial effect on safety, even if it provided an inaccurate explanation of fatigue.
A considerable number of all-metal bridges were likewise built in America in the 1840s, but, in 1850, when a bridge in Pennsylvania broke under a train, all the metal structures on the New York and Erie Railroad were ordered replaced with wooden bridges. Not surprisingly, however, the development of the new technology persisted, with competing bridge designers and builders promising advantages in performance and price, and new iron bridges continued to be built. Despite the apparent risks, they came to be regarded as superior to wooden structures in the second half of the nineteenth century, in part because of the increasing availability of iron at decreasing cost, thus making it competitive with timber, which in some places was becoming more scarce and thus more costly.
No history of bridges is complete without at least an acknowledgement that many ambitious designs did fail. The famous ones, such as the Tay Bridge in 1879, the first Quebec Bridge failure in 1907, and the Tacoma Narrows collapse in 1940, are always mentioned, but the numerous failures of unnamed railroad bridges during the nineteenth century are generally grouped together as statistics. The casual mention in a recent book review that at one time iron truss bridges were failing at the rate of one in four elicited a series of letters to Technology and Culture, the international quarterly journal of the Society for the History
of Technology, disputing the claim and offering various references and statistics of their own. The argument seemed especially curious because it pitted several humanists against one another in a debate over numbers. To an engineer, exactly how many railway bridges failed during the nineteenth century is not so important as the fact that failures did occur. The collapse of a single bridge made from a relatively new material or design should have been enough to make engineers of that era and their customers, the railroads, reflect on the new technology. The repeated collapses of iron railway bridges could only have cast suspicion on the adequacy of technological understanding and raised doubts among insiders and the public at large about the developing railroad industry. And doubts were raised.
One incident, the collapse of a bridge at Dixon, Illinois, prompted the American Society of Civil Engineers to create a committee to determine the most practicable means of averting such accidents. Though the committee was divided in its opinion, its report in 1875 made recommendations not only for railroad but also for highway bridge construction. Another specific incident, the collapse of the 157-foot-long truss bridge at Ashtabula, Ohio, in 1876, which killed almost a hundred people, prompted Harper’s Weekly to ask, “Is there no method of making iron bridges of assured safety?”