To Engineer Is Human: The Role of Failure in Successful Design

To Engineer Is Human: The Role of Failure in Successful Design

by Henry Petroski
To Engineer Is Human: The Role of Failure in Successful Design

To Engineer Is Human: The Role of Failure in Successful Design

by Henry Petroski

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Overview

How did a simple design error cause one of the great disasters of the 1980s - the collapse of the walkways at the Kansas City Hyatt Regency Hotel? What made the graceful and innovative Tacoma Narrows Bridge twist apart in a mild wind in 1940? How did an oversized waterlily inspire the magnificent Crystal Palace, the crowning achievement of Victorian architecture and engineering? These are some of the failures and successes that Henry Petroski, author of the acclaimed The Pencil, examines in this engaging, wonderfully literate book. More than a series of fascinating case studies, To Engineer is Human is a work that looks at our deepest notions of progress and perfection, tracing the fine connection between the quantifiable realm of science and the chaotic realities of everyday life.

Product Details

ISBN-13: 9780679734161
Publisher: Knopf Doubleday Publishing Group
Publication date: 03/31/1992
Edition description: Reprint
Pages: 272
Sales rank: 126,069
Product dimensions: 5.17(w) x 7.99(h) x 0.56(d)

About the Author

Henry Petroski is the Aleksandar S. Vesic Professor of Civil Engineering and a professor of history at Duke University. The author of more than a dozen previous books, he lives in Durham, North Carolina, and Arrowsic, Maine.

Read an Excerpt

CHAPTER 1

BEING HUMAN

Shortly after the Kansas City Hyatt Regency Hotel skywalks collapsed in 1981, one of my neighbors asked me how such a thing could happen. He wondered, did engineers not even know enough to build so simple a structure as an elevated walkway? He also recited to me the Tacoma Narrows Bridge collapse, the American Airlines DC–10 crash in Chicago, and other famous failures, throwing in a few things he had heard about hypothetical nuclear power plant accidents that were sure to exceed Three Mile Island in radiation release, as if to present an open-andshut case that engineers did not quite have the world of their making under control.

I told my neighbor that predicting the strength and behavior of engineering structures is not always so simple and well-defined an undertaking as it might at first seem, but I do not think that I changed his mind about anything with my abstract generalizations and vague apologies. As I left him tending his vegetable garden and continued my walk toward home, I admitted to myself that I had not answered his question because I had not conveyed to him what engineering is. Without doing that I could not hope to explain what could go wrong with the products of engineering. In the years since the Hyatt Regency disaster I have thought a great deal about how I might explain the next technological embarrassment to an inquiring layman, and I have looked for examples not in the esoteric but in the commonplace. But I have also learned that collections of examples, no matter how vivid, no more make an explanation than do piles of beams and girders make a bridge.

Engineering has as its principal object not the given world but the world that engineers themselves create. And that world does not have the constancy of a honeycomb's design, changeless through countless generations of honeybees, for human structures involve constant and rapid evolution. It is not simply that we like change for the sake of change, though some may say that is reason enough. It is that human tastes, resources, and ambitions do not stay constant. We humans like our structures to be as fashionable as our art; we like extravagance when we are well off, and we grudgingly economize when times are not so good. And we like bigger, taller, longer things in ways that honeybees do not or cannot. All of these extra-engineering considerations make the task of the engineer perhaps more exciting and certainly less routine than that of an insect. But this constant change also introduces many more aspects to the design and analysis of engineering structures than there are in the structures of unimproved nature, and constant change means that there are many more ways in which something can go wrong.

Engineering is a human endeavor and thus it is subject to error. Some engineering errors are merely annoying, as when a new concrete building develops cracks that blemish it as it settles; some errors seem humanly unforgivable, as when a bridge collapses and causes the death of those who had taken its soundness for granted. Each age has had its share of technological annoyances and structural disasters, and one would think engineers might have learned by now from their mistakes how to avoid them. But recent years have seen some of the most costly structural accidents in terms of human life, misery, and anxiety, so that the record presents a confusing image of technological advancement that may cause some to ask, "Where is our progress?"

Any popular list of technological horror stories usually comprises the latest examples of accidents, failures, and flawed products. This catalog changes constantly as new disasters displace the old, but almost any list is representative of how varied the list itself can be. In 1979, when accidents seemed to be occurring left and right, anyone could rattle off a number of technological embarrassments that were fresh in everyone's mind, and there was no need to refer to old examples like the Tacoma Narrows Bridge to make the point. It seemed technology was running amok, and editorial pages across the country were anticipating the damage that might occur as the orbiting eighty-five-ton Skylab made its unplanned reentry. Many of the same newspapers also carried the cartoonist Tony Auth's solution to the problem. His cartoon shows the falling Skylab striking a flying DC–10, itself loaded with Ford Pintos fitted with Firestone 500 tires, with the entire wreckage falling on Three Mile Island, where the fire would be extinguished with asbestos hair dryers.

While such a variety may be unique to our times, the failure of the products of engineering is not. Almost four thousand years ago a number of Babylonian legal decisions were collected in what has come to be known as the Code of Hammurabi, after the sixth ruler of the First Dynasty of Babylon. There among nearly three hundred ancient cuneiform inscriptions governing matters like the status of women and drinking-house regulations are several that relate directly to the construction of dwellings and the responsibility for their safety:

If a builder build a house for a man and do not make its construction firm, and the house which he has built collapse and cause the death of the owner of the house, that builder shall be put to death.

If it cause the death of the son of the owner of the house, they shall put to death a son of that builder.

If it cause the death of a slave of the owner of the house, he shall give to the owner of the house a slave of equal value.

If it destroy property, he shall restore whatever it destroyed, and because he did not make the house which he built firm and it collapsed, he shall rebuild the house which collapsed from his own property.

If a builder build a house for a man and do not make its construction meet the requirements and a wall fall in, that builder shall strengthen the wall at his own expense.

This is a far cry from what happened in the wake of the collapse of the Hyatt Regency walkways, subsequently found to be far weaker than the Kansas City Building Code required. Amid a tangle of expert opinions, $3 billion in lawsuits were filed in the months after the collapse of the skywalks. Persons in the hotel the night of the accident were later offered $1,000 to sign on the dotted line, waiving all subsequent claims against the builder, the hotel, or anyone else they might have sued. And today opinions as to guilt or innocence in the Hyatt accident remain far from unanimous. After twenty months of investigation, the U. S. attorney and the Jackson County, Missouri, prosecutor jointly announced that they had found no evidence that a crime had been committed in connection with the accident. The attorney general of Missouri saw it differently, however, and he charged the engineers with "gross negligence." The engineers involved stand to lose their professional licenses but not their lives, but the verdict is still not in as I write three years after the accident.

The Kansas City tragedy was front-page news because it represented the largest loss of life from a building collapse in the history of the United States. The fact that it was news attests to the fact that countless buildings and structures, many with designs no less unique or daring than that of the hotel, are unremarkably safe. Estimates of the probability that a particular reinforced concrete or steel building in a technologically advanced country like the United States or England will fail in a given year range from one in a million to one in a hundred trillion, and the probability of death from a structural failure is approximately one in ten million per year. This is equivalent to a total of about twenty-five deaths per year in the United States, so that 114 persons killed in one accident in Kansas City was indeed news.

Automobile accidents claim on the order of fifty thousand American lives per year, but so many of these fatalities occur one or two at a time that they fail to create a sensational impact on the public. It seems to be only over holiday weekends, when the cumulative number of individual auto deaths reaches into the hundreds, that we acknowledge the severity of this chronic risk in our society. Otherwise, if an auto accident makes the front page or the evening news it is generally because an unusually large number of people or a person of note is involved. While there may be an exception if the dog is famous, the old saying that "dog bites man" is not news but that "man bites dog" is, applies.

We are both fascinated by and uncomfortable with the unfamiliar. When it was a relatively new technology, many people eschewed air travel for fear of a crash. Even now, when aviation relies on a well-established technology, many adults who do not think twice about the risks of driving an automobile are apprehensive about flying. They tell each other old jokes about white-knuckle air travelers, but younger generations who have come to use the airplane as naturally as their parents used the railroad and the automobile do not get the joke. Theirs is the rational attitude, for air travel is safe, the 1979 DC–10 crash in Chicago notwithstanding. Two years after that accident, the Federal Aviation Administration was able to announce that in the period covering 1980 and 1981, domestic airlines operated without a single fatal accident involving a large passenger jet. During the period of record, over half a billion passengers flew on ten million flights. Experience has proven that the risks of technology are very controllable.

However, as wars make clear, government administrations value their fiscal and political health as well as the lives of their citizens, and sometimes these objectives can be in conflict. The risks that engineered structures pose to human life and environments pose to society often conflict with the risks to the economy that striving for absolute and perfect safety would bring. We all know and daily make the trade-offs between our own lives and our pocketbooks, such as when we drive economy-sized automobiles that are incontrovertibly less safe than heavier-built ones. The introduction of seat belts, impact-absorbing bumpers, and emission-control devices have contributed to reducing risks, but gains like these have been achieved at a price to the consumer. Further improvements will take more time to perfect and will add still more to the price of a car, as the development of the air bag system has demonstrated. Thus there is a constant tension between manufacturers and consumer advocates to produce safe cars at reasonable prices.

So it is with engineering and public safety. All bridges and buildings could be built ten times as strong as they presently are, but at a tremendous increase in cost, whether financed by taxes or private investment. And, it would be argued, why ten times stronger? Since so few bridges and buildings collapse now, surely ten times stronger would be structural overkill. Such ultraconservatism would strain our economy and make our built environment so bulky and massive that architecture and style as we know them would have to undergo radical change. No, it would be argued, ten times is too much stronger. How about five? But five might also arguably be considered too strong, and a haggling over numbers representing no change from the present specifications and those representing five- or a thousand-percent improvement in strength might go on for as long as Zeno imagined it would take him to get from here to there. But less-developed countries may not have the luxury to argue about risk or debate paradoxes, and thus their buildings and boilers can be expected to collapse and explode with what appears to us to be uncommon frequency.

Callous though it may seem, the effects of structural reliability can be measured not only in terms of cost in human lives but also in material terms. This was done in a recent study conducted by the National Bureau of Standards with the assistance of Battelle Columbus Laboratories. The study found that fracture, which included such diverse phenomena as the breaking of eyeglasses, the cracking of highway pavement, the collapse of bridges, and the breakdown of machinery, costs well over $100 billion annually, not only for actual but also for anticipated replacement of broken parts and for structural insurance against parts breaking in the first place. Primarily associated with the transportation and construction industries, many of these expenses arise through the prevention of fracture by overdesign (making things heavier than otherwise necessary) and maintenance (watching for cracks to develop), and through the capital equipment investment costs involved in keeping spare parts on hand in anticipation of failures. The 1983 report further concludes that the costs associated with fracture could be reduced by one half by our better utilizing available technology and by improved techniques of fracture control expected from future research and development.

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.

(Continues…)


Excerpted from "To Engineer Is Human"
by .
Copyright © 1992 Henry Petroski.
Excerpted by permission of St. Martin's Press.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

Table of Contents

Prefacevii
1Being Human1
2Falling Down is Part of Growing up11
3Lessons From Play; Lessons From Life Appendix: "The Deacon's Masterpiece,"35
4Engineering as Hypothesis40
5Success is Foreseeing Failure53
6Design is Getting From Here to There64
7Design as Revision75
8Accidents Waiting to Happen85
9Safety in Numbers98
10When Cracks Become Breakthroughs107
11Of Bus Frames and Knife Blades122
12Interlude: The Success Story of the Crystal Palace136
13The Ups and Downs of Bridges158
14Forensic Engineering and Engineering Fiction172
15From Slide Rule to Computer: Forgetting How it Used to be Done189
16Connoisseurs of Chaos204
17The Limits of Design216
Afterword229
Bibliography233
Index245
List of Illustrations
I.Cartoons illustrating public concern over engineering failures
II.Models of the ubiquitous cantilever beam
III.The Brooklyn Bridge: Anticipating failure by the engineer and by the layman
IV.The Crystal Palace: Testing the galleries and finding them sound
V.The Crystal Palace and two of its modern imitators
VI.Suspension bridges: The Tacoma Narrows and after
VII.The Kansas City Hyatt Regency walkways collapse
VIII.The Mianus River Bridge collapse and its aftermath

Interviews

Exclusive Author Essay
Writing About Things

For as long as I can remember, I have been fascinated by things large and small. I wanted to know what made my watch tick, my radio play, and my house stand. I wanted to know who invented the bottle cap and who designed the bridge. I guess from early on I wanted to be an engineer.

In Paperboy I have written about my teenage years, during which I delivered newspapers when I wasn't taking apart one of my mother's kitchen appliances. The newspaper itself is a thing of wonder for me, and I recall in some detail how we delivered it in the 1950s, folding it into a tight package and flipping it from a bicycle. My bike, a Schwinn, consumed a lot of my time and attention as a teenager, and it is a kind of character in my memoir. My family, friends, and teachers naturally also appear, but it is the attention to things as well as people that ties Paperboy to my other books.

Like a lot of writers, I write books to try to understand better how the world and the things in it work. My first book, To Engineer Is Human, was prompted by nonengineer friends asking me why so many technological accidents and failures were occurring. If engineers knew what they were doing, why did bridges and buildings fall down? It was a question that I had often asked myself, and I had no easy answer. Since the question was a nontechnical one, I wrote my book in nontechnical language. I am pleased that engineers and nonengineers find the book readable and helpful in making sense of the world of things and the people who make things.

There is a lot more to the world of things than just their breaking and failing, of course, and that prompted me to write another book for the general reader. The Pencil is about how a very familiar and seemingly simple object is really something that combines complex technology with a rather interesting history. The story of the pencil as an object has so many social and cultural connections with the world that it makes a perfect vehicle for conveying the general nature of design, engineering, manufacturing, and technology.

Pencils, like everything else, have changed over time, and I explored that idea further in The Evolution of Useful Things. This book is about invention and inventors and how and why they continue to make new things out of old. In it, I describe inventors and engineers as critics of technology, fault-finders who can't leave things alone. Their quest for perfection leads to very useful new things, such as paper clips, zippers, Post-t® notes, and a host of other inventions whose stories I tell in the book.

As an engineer, I am also interested in large things, and bridges are some of the largest things made. Engineers of Dreams is about the bridging of America, telling the stories of some of our greatest spans, including the George Washington, Golden Gate, Eads, and Mackinac bridges. It also tells the story of the engineers who designed and built these monumental structures, emphasizing that their personalities and the political and technical climate have a great deal to do with what bridges look like and how they work.

Engineers do more than build bridges, and I have told the stories of many of their other achievements in Remaking the World. Among the great projects described in this book are the original ferris wheel, Hoover Dam, the Panama Canal, the Channel Tunnel, and the Petronas Towers, now the tallest buildings in the world. The stories of these world-class things are true adventures in engineering, and it does not take a degree in engineering to appreciate them or understand their making and their working.

As much as I like large and unique structures, I have continued to return to more commonplace ones in my writing. The Book on the Bookshelf had is origins one evening while I was reading in my study. As I looked up from my chair, I saw not the books on my bookshelves but the shelves themselves, and I wondered about the first bookshelves. My search for an answer led me to the discovery that our practice of storing books vertically on horizontal shelves with the spines facing outward was not at all the way it was originally done. In fact, our seemingly natural way of placing books on shelves had to be invented over the course of many centuries. Writing The Book on the Bookshelf reinforced my belief that there is a fascinating story behind even the simplest and most familiar of objects.

As long as there are things to wonder about, there are stories to be written about them. That makes me happy, because writing about things seems to be my thing. (Henry Petroski)

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