Impulsive seismic response of bridge column-cap beam joints

The results of dynamic tests on six half-scale reinforced concrete bridge column-cap beam joints are discussed. The loading protocol used included the effects of impulsive near-field ground motions. Cyclic loading with increasing amplitudes followed this impulsive loading. Three of the specimens incorporated nominally ductile reinforcement details typical of pre-1971 construction practice in California. The three other specimens incorporated ductile reinforcement details typical of current design practice in California. The impulsive loading was particularly detrimental to the pre-1971 specimens. Shear failure in the joint was initiated during the impulsive loading, causing early-strength degradation. The joints incorporating ductile reinforcement details suffered minimal damage during the impulsive loading and continued to perform well during the subsequent loading cycles. The increased capacity exhibited by both types of joints during the impulsive loading can be accounted for by modifying the steel and concrete properties for the high strain rate induced during the impulsive loading.