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To Forgive Design: Understanding Failure

To Forgive Design: Understanding Failure

by Henry Petroski
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When planes crash, bridges collapse, and automobile gas tanks explode, we are quick to blame poor design. But Henry Petroski says we must look beyond design for causes and corrections. Known for his masterly explanations of engineering successes and failures, Petroski here takes his analysis a step further, to consider the larger context in which accidents occur.

In To Forgive Design he surveys some of the most infamous failures of our time, from the 2007 Minneapolis bridge collapse and the toppling of a massive Shanghai apartment building in 2009 to Boston's prolonged Big Dig and the 2010 Gulf oil spill. These avoidable disasters reveal the interdependency of people and machines within systems whose complex behavior was undreamt of by their designers, until it was too late. Petroski shows that even the simplest technology is embedded in cultural and socioeconomic constraints, complications, and contradictions.

Failure to imagine the possibility of failure is the most profound mistake engineers can make. Software developers realized this early on and looked outside their young field, to structural engineering, as they sought a historical perspective to help them identify their own potential mistakes. By explaining the interconnectedness of technology and culture and the dangers that can emerge from complexity, Petroski demonstrates that we would all do well to follow their lead.

Product Details

ISBN-13: 9780674065840
Publisher: Harvard
Publication date: 03/30/2012
Edition description: New Edition
Pages: 432
Sales rank: 1,241,185
Product dimensions: 5.60(w) x 8.30(h) x 1.30(d)

About the Author

Henry Petroski is the Aleksandar S. Vesic Professor of Civil Engineering and Professor of History at Duke University.

Read an Excerpt

From Chapter Five: A Repeating Problem

Regardless of their professional roots, dentists and engineers alike have to know a good deal about mechanics, materials, and maintenance. They have to understand the forces at play on a bridge, whether it be between two sound teeth or between two soft river banks. Dentists and engineers have to understand the holding strength of amalgams and epoxies and of steel and concrete. And they have to understand the importance of limiting deterioration, whether it takes the form of practicing prophylaxis to control dental caries or of painting steel to prevent corrosion. But the growth of decay and corrosion are insidious. Thus it is perhaps with regard to the promotion of regular checkups that dentistry has the most to offer engineering, in the sense that it makes evident even to the nontechnical lay person how important regular and thorough examinations and inspections are to insure the health of our oral infrastructure and, by analogy, our national infrastructure. In a routine dental checkup, the structures in our mouth are gone over with picks and probes to detect the small irregularities that can be harbingers of worse to come, to find the imperfections that can lead to cracks and the cracks that can lead to spontaneous fractures, to locate and fill cavities that left unchecked can threaten an entire tooth. Every year or so, x-rays are taken, and suspicious areas compared with benchmark images from an earlier visit. Given that we all have—or at least once had—teeth, we know the importance of regular dental examinations and prophylactic care.

Indeed, everyone knows, perhaps by having learned the hard way, that neglecting one’s teeth can be a sure way to their deteriorating beyond repair. We seem not yet to have fully learned that the same applies to our bridges, roads, and other public works. But going to the dentist can get us thinking about a lot more than our teeth. The experience can remind us of knowledge and lessons about good engineering practice that are forgotten at our peril. When we go to the dentist with a broken tooth, we are likely to learn that the tooth probably had had a crack in it. The crack may have gotten started quite a while back, maybe when a sharp blow from a mating tooth nicked the enamel but so slightly that even a dentist could not easily detect it. Over time, as we chomped on three meals a day, plus snacks, a little crack grew ever so slowly into a larger one. In mechanical terms, the forces imparted to the tooth in the course of chewing alternately opened and closed the crack and in the process extended it ever so slowly further into the tooth. As long as we did not chomp our teeth together too suddenly or use them as if they were a pair of pliers, the crack was stable and the tooth was safe. Eventually, however, the crack would reach a point where little force was required to get it to fast forward like a crack in a window pane tapped ever so gently with maybe just a firm finger.

Even perfect teeth are subject to repeated thermal stresses induced by hot and cold liquids and to repeated impacts due to the nature of eating and chewing food, forces sometimes supplemented by the grinding that takes place in some of us while we sleep. Such actions also can cause hairline cracks to start and grow over time, thus weakening a tooth and setting it up for breaking when it comes down upon an unexpected small piece of bone in a hamburger or part of a shell in an oyster stew. However started, progressed, and ended, this is the process of fatigue-crack initiation, growth, and fracture, something engineers have to take into account when designing bridges and roads over which traffic repeatedly bumps and bounces. Over seasons of freezing and thawing temperatures, and years of being chewed up by passing cars and trucks, our concrete and asphalt roads develop cracks that grow into gaps and into the cavities known as potholes.

Table of Contents

Preface ix

1 By Way of Concrete Examples 1

2 Things Happen 26

3 Designed to Fail 48

4 Mechanics of Failure 81

5 A Repeating Problem 107

6 The Old and the New 128

7 Searching for a Cause 150

8 The Obligation of an Engineer 175

9 Before, during, and after the Fall 199

10 Legal Matters 223

11 Back-Seat Designers 241

12 Houston, You Have a Problem 270

13 Without a Leg to Stand On 302

14 History and Failure 327

Notes 363

Illustrations 395

Index 397

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