Golden Gate Bridge
Date: Around 1993
During the San Francisco Earthquake the Oakland Bay Bridge fell.
Why did not the Golden Gate Bridge fall?
The Golden Gate bridge and the Oakland Bay Bridge differ in
construction, in that the Golden Gate bridge is a suspension bridge, and the
Oakland Bay Bridge is a series of individually supported spans. The
earthquake in SF actually changed the locations of the footings of the Bay
Bridge enough to change the length of the spans. As the distance increased
between each span, the center sections fell down. On the other hand, the
Golden Gate, being a suspension bridge, has no real solid relationship between
the bridge span and the footings in the channel. The footings can move a
considerable distance, and the worst that would happen is that the suspension
cables would change tension. In that way, a suspension bridge is far superior
to a conventional span. On the down side, however, suspension bridges have an
annoying tendency to break into harmonic resonances with the right vibrational
input. One bridge, a long time ago, broke into oscillation and actually fell
after a dog trotted across it at a constant rate. Do not worry though, all
suspension bridges now are built using enough different materials to prevent
things like that from happening.
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Update: June 2012