Bay Bridge Collapse Due to Vibrations. Engineers working on San Francisco's ill-starred Bay Bridge have fingered a culprit in the repair job that went awry, forcing the bridge's closure: metal fatigue caused by harmonic resonance. The phenomenon, in which small vibrations at key frequencies gradually build up until they are large enough to damage a structure, is the scourge of bridge architects everywhere. At first, many experts had fingered wind as the culprit in the accident. Heavy winds lashed the Bay Area late Tuesday afternoon. At 5 pm that day, several massive pieces of metal crashed 100 feet down from the bridge superstructure onto the roadway, striking a truck and damaging a car.
