Background Eastern span replacement of the San Francisco–Oakland Bay Bridge

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collapsed section of roadbed visible above support tower after loma prieta earthquake in 1989


it had been known on 30 years major earthquake on either of 2 nearby faults (the san andreas , hayward) destroy major cantilever span. little done address problem until 1989 loma prieta earthquake. earthquake measured 6.9 on moment magnitude scale , while epicenter distant bridge, 50-foot (15 m) section of upper deck of eastern truss viaduct portion of bridge collapsed onto deck below, indirectly causing 1 death @ point of collapse. bridge closed month construction crews removed , reconstructed fallen section. reopened on november 18, 1989, new stronger retrofit in place. failure @ transition between easternmost through-truss , westernmost double-deck causeway segment, location inertial response character of structure makes abrupt change. analysis of event completed internal staff has shown bridge close far more catastrophic failure in either through-truss or causeway segment have dropped common support structure.


it clear eastern span needed made more earthquake resistant. estimates made in 1999 placed probability of major earthquake in area within following 30 years @ 70%, although recent studies announced in september 2004 united states geological survey have cast doubt on predictability of large earthquakes based upon duration of preceding quiet periods. more recent (2008) analysis asserts increased probability of major event on hayward fault.




a 2010 view of original eastern span in foreground replacement construction beyond. portions of old eastern span considered @ risk in large earthquake.








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