Engineering and History
Petroski, Henry, ASEE Prism
ENGINEERS DESIGN the future; historians analyze the past. These oversimplifications may highlight some fundamental differences between the practice of engineering and history, but when taken as indicative of divergent and exclusionary objectives, they can lead to both inferior engineering and inferior history.
In their enthusiasm for advancing the state-of-the-art by pushing the limits of cutting-edge technology, some engineers do not look back at the history of their field. They do not see it as relevant. Even if they do have an armchair interest in the history of what they are currently engaged in, they tend to compartmentalize that interest or see it as an avocation they will pursue in their retirement.
This was the situation among suspension-bridge engineers, especially in the 1920s and '3Os. In a remarkable technological leap, Othmar Ammann designed the George Washington Bridge to have a main span almost double that of the previous record holder. The daringness of this, plus the shallowness of the long deck of the bridge provided a paradigm for subsequent suspension bridge designers to follow. Bridges with less and less stiff decks resulted, culminating in the Tacoma Narrows Bridge that twisted itself apart in a moderate wind.
While the undisputed leaders in the field of bridge design were following Ammann's lead, they were also disregarding the history of suspension bridges. Although they knew about the wind susceptibility of wooden-decked bridges of a century earlier, they considered it irrelevant to the design of modern steel structures.
Yet in 1840, no less an engineer than John Roebling had distilled from his study of historic failures of suspension bridges what was necessary to do in order to design a bridge that could stand up to the wind. He explicitly stated that the deck of a successful suspension bridge must be heavy, have a stiffening truss and have supplementary cables to check unwanted motion.
Roebling incorporated these necessary features into the Brooklyn Bridge, but in subsequent decades, they were systematically eliminated from the bridges of Ammann and his contemporaries. First, the cable stays were done away with as redundant, leaving those on the Brooklyn Bridge to be a somewhat quaint but distinguishing feature. …