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“To Engineer is Human: The Role of Failure in Successful Design,” by Henry Petroski, Vintage Books, NY, 1992. This 251-page paperback describes the engineering design process for civil engineers especially for structures like bridges and skyscrapers.

Petroski uses historical examples and recent failures to make his points. A major one is the 1981 failure of the skybridges at the Hyatt Regency Hotel in Kansas City. The result was 115 killed and 200 injured–at the time the largest loss of life in an engineering failure. The very high atrium was bridged on the second, third and fourth floors to connect hotel rooms on one side to meeting rooms on the other. The second and fourth floor bridges ran on top of each other and were supported by steel rods from the ceiling. The original design had called for long rods supporting both bridges, but difficulty with a threaded nut for the upper bridge caused a design modification using two rods. The rod for the lower bridge was suspended from the upper bridge rather than from the ceiling beam. This overloaded the upper bridge resulting in a failure while people danced on the bridges.

Similarly the book uses the Brooklyn Bridge in 1883 and the failure of the Tacoma Narrows bridge in 1940 to emphasize the need to consider other forces such as the effect of winds on the structure. Early railroad bridges were wood, but soon switched to iron bridges. Many failed until engineers learned to accommodate heavier loads and the reciprocating nature of steam engines. Safety factors and planning for partial failures make for successful designs. Stress cracking is described in detail. Corrosion and poor maintenance have contributed to recent bridge failures. The DC-10 crash in Chicago in 1979 was due to a stress failure of the pylon holding the engine. An unauthorized maintenance procedure had damaged the pylon causing stress cracks.

Stress cracking is a factor in the service life of nuclear power plants. Flaws are difficult to detect. Radiation increases the temperature below which the steel becomes brittle. Inspection can be difficult. The design service life is based on best estimates, but catastrophic failure is possible if the cracks are undetected. A Liberty ship sank unexpectedly in World War II due to stress cracks from welding. Cracks in a set of stainless steel knives introduces the description of metal processing steps and their possible effects on cracking.

Petroski notes that traditionally engineers did their design calculations with slide rules. That meant optimization of designs was a laborious process requiring repeated calculations to arrive at safe but cost effective designs. As the calculations are estimates, safety factors are commonly added. Modern computers make more precise optimization practical. That has resulted in lighter, more economical structures, but with less margin for error.

The constant pressures to reduce costs force engineers to explore new materials. Engineers usually base their work on proven designs, but new materials and cost constraints drive innovation in a competitive world. Crystal Palace in Hyde Park London for the 1851 World Exposition is cited as an innovative modular design using glass walls.

The book is thorough, informative and well written. The examples from the ‘80s makes it a bit dated. An update might include building failures such as the collapse of the World Trade Center towers on 911 and bridge failures such as the Minneapolis I-35 bridge in 2007 or the Miami bridge collapse in 2018. Those considering careers in engineering will want to read it. Photos. Bibliography. Index.
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