Seismic Behavior of Bridges with Isolation Bearings of Different Properties Under Long and Short Earthquake Durations

This paper evaluates the structural behavior of bridges subjected to seismic excitation of short and long durations. The bridge is of three spans and of continuous deck. It is studied under two cases of properties for the lead rubber isolation bearings. One of the bearings is of yield strength 500 MPa and the second is of yield strength 150 MPa. Dynamic nonlinear time history analysis is performed using three short-duration and three long-duration earthquakes all of which are matched to the response spectrum of the Egyptian loading code. Three dimensional finite element modeling is made for the bridge. The studied behavior items for the isolation bearings are maximum bearing longitudinal displacement, maximum bearing vertical displacement, and maximum bearing vertical residual displacement. Also, the base shear of piers, the maximum displacement at the top of the piers, and the maximum deck acceleration at locations top of the piers are studied. The analysis revealed that the two types of used bearings have small effect on the base shear, both the longitudinal pier displacements and deck accelerations were similar for all the cases, short duration earthquakes result in higher vertical displacements for the bearings, and the two types of bearings produce small residual displacements.