Analysis of Seismic Failure in Skew RC Bridge

The dynamic behavior of skewed reinforced concrete (RC) box girder bridges under the effect of earthquake excitation is studied using finite element models of the Foothill Boulevard Undercrossing, S.E. Bridge, in the San Fernando Valley, Calif., which suffered a great damage during the 1971 earthquake. Linear as well as nonlinear models were considered in this study for the time-history analysis of the bridge. The time-history analyses showed that rigid-body modes dominated the earthquake response of the bridge, which led to the writers’ conclusion that under dynamic loads, short stiff skewed bridges behave essentially as rigid bodies if the deck is not rigidly fixed to the abutments. This paper gives an explanation of the seismic failure of rigid skewed RC bridges that agrees with the field observation made soon after the failure of the Foothill Boulevard Undercrossing.