Ask A Scientist© Engineering Archive

Index Key:   ENG031
Author:      zuni
Subject:     Golden Gate Bridge
Text:        During the San Francisco Earthquake the Oakland Bay Bridge fell.  
Why did not the Golden Gate Bridge fall?

Response #:  1 of 1
Author:      dipper
Text:        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.