Magazine article ASEE Prism

Skimping on Repairs

Magazine article ASEE Prism

Skimping on Repairs

Article excerpt

THE EMBARRASSING problems with a cracked eye-bar and a failed fix that plagued the San Francisco-Oakland Bay Bridge last fall reminded me of some analogous problems I once had with my Volkswagen Beetle.

A bridge is not unlike a machine, in that each is an assemblage of parts that move relative to one another. As large as the bridge parts might be, their movements are typically relatively slight and not easily noticeable to the untrained, unaided eye. Nevertheless, every bridge does flex whenever a vehicle passes over it. For the Bay Bridge, this happens about 270,000 times a day.

A bridge is also moved by larger forces. Gusts of wind can lift and drop it as turbulence can an airplane. In 1989, the Loma Prieta earthquake shook the Bay Bridge so violently that a section of its upper deck fell onto the lower roadway, killing a young woman motorist. That incident ultimately led to the design of a replacement for the East Bay spans of the bridge, a project that is ongoing.

Movements repeated over time can cause cracks to grow in steel components. If the progressive damage to the bridge is not detected and arrested before the cracks become too large, collapse attributable to metal fatigue can occur. This is why inspections and proper preventive maintenance are so important.

My VW was certainly nowhere near as important as the Bay Bridge, but, like all machines, the small automobile was made up of parts that moved and vibrated. In that car, I could feel the effects of wind gusts and potholes much more than I could in our heavier family car.

One morning, sensing much greater vibration than normal, I stopped to see what was going on. Opening the engine compartment, I saw that the generator was no longer firmly attached; the steel strap that clamped it to the engine block was cracked almost in two. It was a classic example of metal fatigue, and the strap had to be replaced.

Not being near an auto supply store, I went into a hardware store to get something to make a quick fix. …

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