Earthquake induced dynamic axial force in reinforced concrete (RC) bridge bent columns will not only change the yield strength of the columns but also change their stiffness

which is seldom considered by the common lumped plasticity line model. Based on the fiber element model results that taking into account the influence of dynamic axial force on strength and stiffness simultaneously

the axial force stiffness interaction effect on the seismic responses of RC double column bridges was analyzed. The results show that

axial force stiffness interaction has a large effect on the seismic responses of the double column bridge in the elastic range

and it does not alter the ultimate capacity of the columns. Since the stiffness of the columns under compression and tension dynamic axial forces offset each other

the global displacement of bridge bent with equal columns is relatively unaffected by the axial force stiffness interaction

however

the differences of the column member forces are manifest. For the short column controls the global stiffness

the axial force stiffness interaction has significant influences on both the global displacement and member force responses. The influences become larger as the irregularity of the bridge bent increases

so the interaction between axial force and member stiffness should be sufficiently considered in seismic analyses.