To Engineer Is Human Read online

  Recent studies of the condition of our infrastructure—the water supply and sewer systems, and the networks of highways and bridges that we by and large take for granted—conclude that it has been so sorely neglected in many areas of the country that it would take billions upon billions of dollars to put things back in shape. (Some estimates put the total bill as high as $3 trillion.) This condition resulted in part from maintenance being put off to save money during years when energy and personnel costs were taking ever-larger slices of municipal budget pies. Some water pipes in large cities like New York are one hundred or more years old, and they were neither designed nor expected to last forever. Ideally, such pipes should be replaced on an ongoing basis to keep the whole water supply system in a reasonably sound condition, so that sudden water main breaks occur very infrequently. Such breaks can have staggering consequences, as when a main installed in 1915 broke in 1983 in midtown Manhattan and flooded an underground power station, causing a fire. The failure of six transformers interrupted electrical service for several days. These happened to be the same days of the year that ten thousand buyers from across the country visited New York’s garment district to purchase the next season’s lines. The area covered by the blackout just happened to be the blocks containing the showrooms of the clothing industry, so that there was mayhem where there would ordinarily have been only madness. Financial losses due to disrupted business were put in the millions.

  In order to understand how engineers endeavor to insure against such structural, mechanical, and systems failures, and thereby also to understand how mistakes can be made and accidents with far-reaching consequences can occur, it is necessary to understand, at least partly, the nature of engineering design. It is the process of design, in which diverse parts of the “given-world” of the scientist and the “made-world” of the engineer are reformed and assembled into something the likes of which Nature had not dreamed, that divorces engineering from science and marries it to art. While the practice of engineering may involve as much technical experience as the poet brings to the blank page, the painter to the empty canvas, or the composer to the silent keyboard, the understanding and appreciation of the process and products of engineering are no less accessible than a poem, a painting, or a piece of music. Indeed, just as we all have experienced the rudiments of artistic creativity in the childhood masterpieces our parents were so proud of, so we have all experienced the essence of structural engineering in our learning to balance first our bodies and later our blocks in ever more ambitious positions. We have learned to endure the most boring of cocktail parties without the social accident of either our bodies or our glasses succumbing to the force of gravity, having long ago learned to crawl, sit up, and toddle among our tottering towers of blocks. If we could remember those early efforts of ours to raise ourselves up among the towers of legs of our parents and their friends, then we can begin to appreciate the task and the achievements of engineers, whether they be called builders in Babylon or scientists in Los Alamos. For all of their efforts are to one end: to make something stand that has not stood before, to reassemble Nature into something new, and above all to obviate failure in the effort.

  Because man is fallible, so are his constructions, however. Thus the history of structural engineering, indeed the history of engineering in general, may be told in its failures as well as in its triumphs. Success may be grand, but disappointment can often teach us more. It is for this reason that hardly a history can be written that does not include the classic blunders, which more often than not signal new beginnings and new triumphs. The Code of Hammurabi may have encouraged sound construction of reproducible dwellings, but it could not have encouraged the evolution of the house, not to mention the skyscraper and the bridge, for what builder would have found incentive in the code to build what he believed to be a better but untried house? This is not to say that engineers should be given license to experiment with abandon, but rather to recognize that human nature appears to want to go beyond the past, in building as in art, and that engineering is a human endeavor.

  When I was a student of engineering I came to fear the responsibility that I imagined might befall me after graduation. How, I wondered, could I ever be perfectly sure that something I might design would not break or collapse and kill a number of people? I knew my understanding of my textbooks was less than total, my homework was seldom without some sort of error, and my grades were not straight As. This disturbed me for some time, and I wondered why my classmates, both the A and C students, were not immobilized by the same phobia. The topic never came to the surface of our conversations, however, and I avoided confronting the issue by going to graduate school instead of taking an engineering job right away. Since then I have come to realize that my concern was not unique among engineering students, and indeed many if not all students have experienced self-doubts about success and fears of failure. The medical student worries about losing a patient, the lawyer about losing a crucial case. But if we all were to retreat with our phobias from our respective jobs and professions, we could cause exactly what we wish to avoid. It is thus that we practice whatever we do with as much assiduousness as we can command, and we hope for the best. The rarity of structural failures attests to the fact that engineering at least, even at its most daring, is not inclined to take undue risks.

  The question, then, should not only be why do structural accidents occur but also why not more of them? Statistics show the headline-grabbing failure to be as rare as its newsworthiness suggests it to be, but to understand why the risk of structural failure is not absolutely zero, we must understand the unique engineering problem of designing what has not existed before. By understanding this we will come to appreciate not only why the probability of failure is so low but also how difficult it might be to make it lower. While it is theoretically possible to make the number representing risk as close to zero as desired, human nature in its collective and individual manifestations seems to work against achieving such a risk-free society.

  2

  FALLING DOWN IS PART OF GROWING UP

  We are all engineers of sorts, for we all have the principles of machines and structures in our bones. We have learned to hold our bodies against the forces of nature as surely as we have learned to walk. We calculate the paths of our arms and legs with the computer of our brain, and we catch baseballs and footballs with more dependability than the most advanced weapons systems intercept missiles. We may wonder if human evolution may not have been the greatest engineering feat of all time. And though many of us forget how much we once knew about the principles and practice of engineering, the nursery rhymes and fairy tales of our youth preserve the evidence that we did know quite a bit.

  We are born into a world swathed in trust and risk. And we become accustomed from the instant of birth to living with the simultaneous possibilities that there will be and that there will not be catastrophic structural failure. The doctor who delivers us and the nurses who carry us about the delivery room are cavalier human cranes and forklifts who have moved myriad babies from delivery to holding upside down to showing to mother to cleansing to footprinting to wristbanding to holding right-side up to showing to father to taking to the nursery. I watched with my heart in my mouth as my own children were so moved and rearranged, and the experience exhausted me. Surely sometime, somewhere, a baby has been dropped, surely a doctor has had butterfingers or a nurse a lapse of attention. But we as infants and we as parents cannot and do not and should not dwell on those remotely possible, hideous scenarios, or we might immobilize the human race in the delivery room. Instead, our nursery rhymes help us think about the unthinkable in terms of serenity.

  Rock-a-bye baby

  In the tree top.

  When the wind blows,

  The cradle will rock.

  When the bough breaks,

  The cradle will fall.

  And down will come baby,

  Cradle and all.

  Home from the hospital, we are in the hands of ou
r parents and friends and relatives—and structurally weak siblings. We are held up helpless over deep pile carpets and hard terrazzo floors alike, and we ride before we walk, risking the sudden collapse of an uncle’s trick knee. We are transported across impromptu bridges of arms thrown up without plans or blueprints between mother and aunt, between neighbor and father, between brother and sister—none of whom is a registered structural engineer. We come to Mama and to Papa eventually to forget our scare reflex and we learn to trust the beams and girders and columns of their arms and our cribs. We become one with the world and nap in the lap of gravity. Our minds dream weightlessly, but our ears come to hear the sounds of waking up. We listen to the warm whispers giving structure to the world of silence, and we learn from the bridges of lullabyes and play that not only we but also the infrastructure needs attention.

  London Bridge is falling down,

  Falling down, falling down.

  London Bridge is falling down,

  My fair lady.

  Build it up with wood and stone,

  Wood and stone, wood and stone.

  Build it up with wood and stone,

  My fair lady.

  The parts of our bodies learn to function as levers, beams, columns, and even structures like derricks and bridges as we learn to turn over in our cribs, to sit up, to crawl, to walk, and generally to support the weight of our own bodies as well as what we lift and carry. At first we do these things clumsily, but we learn from our mistakes. Each time the bridge of our body falls down, we build it up again. We pile back on hands and knees to crawl over the river meandering beneath us. We come to master crawling, and we come to elaborate upon it, moving faster and freer and with less and less concern for collapsing all loose in the beams and columns of our back and limbs. We extend our infant theory of structures and hypothesize that we can walk erect, cantilevering our semicircular canals in the stratosphere. We think these words in the Esperanto of babble, and with the arrogance of youth we reach for the stars. With each tottering attempt to walk, our bodies learn from the falls what not to do next time. In time we walk without thinking and think without falling, but it is not so much that we have learned how to walk as we have learned not to fall. Sometimes we have accidents and we break our arms and legs. We have them fixed and we go on as before. Barring disease, we walk erect and correctly throughout our lives until our structure deteriorates with old age and we need to be propped up with canes or the like. For the majority of our lives walking generally becomes as dependable as one can imagine it to be, but if we choose to load the structure of our bodies beyond the familiar limits of walking, say by jogging or marathoning, then we run the risk of structural failure in the form of muscle pulls and bone fractures. But our sense of pain stops most of us from overexerting ourselves and from coming loose at our connections as we go round and round, hand in hand, day in and day out.

  Ring around the rosie,

  A pocket full of posies,

  Ashes, ashes,

  We all fall down.

  If ontogeny recapitulates phylogeny, if all that has come to be human races before the fetus floating in its own prehistory, then the child playing relives the evolution of structural engineering in its blocks. And the blocks will be as stone and will endure as monuments to childhood, as Erector Sets and Tinker Toys and Legos will not. Those modern optimizations will long have folded and snapped in the frames and bridges of experiment, though not before the child will have learned from them the limitations of metal and wood and plastic. These lessons will be carried in the tool box of the mind to serve the carpenter in all of us in time.

  Step on a crack

  And break your mother’s back.

  The child will play with mud and clay, making cakes and bricks in the wonderful oven of the sun. The child will learn that concrete cracks a mother’s back but that children’s backs are as resilient as springs and pliant as saplings. The child will watch the erection of flowers on columns of green but break them for the smiles of its parents. Summer will roof houses in the bushes, vault cathedrals in the trees. The child will learn the meaning of time, and watch the structures fall into winter and become skeletons of shelters that will be built again out of the dark in the ground and the light in the sky. The child angry and victimized by other children angry will learn the meanings of vandalism and sabotage, of demolition and destruction, of collapse and decline, of the lifetime of structures—and the structure of life.

  The Sphinx asked, “What walks on four legs in the morning, two legs in the afternoon, and three legs in the evening?”

  The child learns that the arms and legs of dolls and soldiers break, the wheels of wagons and tricycles turn against their purpose, and the bats and balls of games do not last forever. No child articulates it, but everyone learns that toys are mean. They teach us not the vocabulary but the reality of structural failure and product liability. They teach us that as we grow, the toys that we could not carry soon cannot carry us. They are as bridges built for the traffic of a lighter age, and their makers are as blameless as the builders of a lighter bridge. We learn that not everything can be fixed.

  Humpty Dumpty sat on a wall;

  Humpty Dumpty had a great fall.

  All the King’s horses and all the King’s men

  Couldn’t put Humpty together again.

  The adolescent learns that bones can break. The arms counter-balancing the legs locomoting are as fragile as the steel and iron railroad bridges under the reciprocating blows of the behemoths rushing through the nineteenth century. The cast of thousands of childhoods reminds the arms and legs, while they have grown stronger but brittler, that they have also grown taller and wiser. They fall less and less. They grow into the arms and legs of young adults making babies fly between them, wheeeee, up in the air unafraid of the gravity parents can throw away. But the weight of responsibility and bills and growing babies brings the parents down to earth and they begin to think of things besides their bridges of muscles and columns of bones. They think of jobs and joys of a different kind, perhaps even if they are engineers.

  Jack and Jill went up the hill

  To fetch a pail of water,

  Jack fell down and broke his crown

  And Jill came tumbling after.

  The natural fragileness of things comes to be forgotten, for we have learned to take it easy on the man-made world. We do not pile too high or reach too far. We make our pencil points sharper, but we do not press as hard. We learn to write without snap, and the story of our life goes smoothly, but quickly becomes dull. (Everyone wishes secretly to be the writer pushing the pencil to its breaking point.) We feel it in our bones as we grow old and then we remember how brittle but exhilarating life can be. And we extend ourselves beyond our years and break our bones again, thinking what the hell. We have wisdom and we understand the odds and probabilities. We know that nothing is forever.

  Three wise men of Gotham

  Went to sea in a bowl:

  If the vessel had been stronger,

  My song would be longer.

  As if it were not enough that the behavior of our very bodies accustoms us to the limitations of engineering structures, our language itself is ambiguous about the daily trials to which life and limb are subjected. Both human beings and inhuman beams are said to be under stress and strain that may lead to fatigue if not downright collapse. Breakdowns of man and machine can occur if they are called upon to carry more than they can bear. The anthropomorphic language of engineering is perhaps no accident since man is not only the archetypal machine but also the Ur-structure.

  Furniture is among the oldest of inanimate engineering structures designed to carry a rather well-defined load under rather well-defined circumstances. We are not surprised that furniture used beyond its intended purpose is broken, and we readily blame the child who abuses the furniture rather than the designer of the furniture or the furniture itself when it is abused. Thus a chair must support a person in a sitting position, but it might not be
expected to survive a brawl in a saloon. A bed might be expected to support a recumbent child, a small rocking chair only a toddler. But the child’s bed would not necessarily be considered badly designed if it collapsed under the child’s wild use of it as a trampoline, and a child’s chair cannot be faulted for breaking under the weight of a heavier child using it as a springboard. The arms and legs of chairs, the heads and feet of beds, just like those of the people whom they serve, cannot be expected to be strong without limit.

  Mother Goose is as full of structural failures as human history. The nursery rhymes acknowledge the limitations of the strength of the objects man builds as readily as fairy tales recognize the frailties of human nature. The story of Goldilocks and the Three Bears teaches us how we can unwittingly proceed from engineering success to failure. Papa Bear’s chair is so large and so hard and so unyielding under the weight of Goldilocks that apparently without thinking she gains a confidence in the strength of all rocking chairs. Goldilocks next tries Mama Bear’s chair, which is not so large but is softer, perhaps because it is built with a lighter wood. Goldilocks finds this chair too soft, however, too yielding in the cushion. Yet it is strong enough to support her. Thus the criterion of strength becomes less a matter of concern than the criteria of “give” and comfort, and Goldilocks is distracted by her quest for a comfortable chair at the expense of one sufficiently strong. Finally Goldilocks approaches Baby Bear’s chair, which is apparently stiffer but weaker than Mama Bear’s, with little if any apprehension about its safety, for Goldilocks’ experience is that all chairs are overdesigned. At first the smallest chair appears to be “just right,” but, as with all marginal engineering designs, whether chairs or elevated walkways, the chair suddenly gives way under Goldilocks and sends her crashing to the floor.