Correlation of Earthquake Ground Motion and the Response of Seismically Isolated Bridges

The seismic response of bridges seismically isolated by lead-rubber bearings (LRB) to earthquake excitations of different magnitudes is presented in this thesis. The force-deformation behavior of LRB is considered as bilinear. The specific purpose of the study is to assess the effect of seismic isolation on the peak response of bridges subjected to different base accelerations ranging from 0.05g to 0.5g in the horizontal direction transversal to the bridge axis. Thus a certain level of efficiency can be shown in respect of the particular bearing modification. Furthermore, the effect of superstructure stiffness (i.e. pier stiffness, pier layout) on the isolator efficiency is investigated in depth. The seismic response in the finite element model of the continuous span isolated bridges is obtained by solving the governing equations of motion in the incremental form using an iterative stepby-step method. To study the effectiveness of LRB, the seismic response of isolated bridges is also compared with the response of corresponding nonisolated bridges (i.e. bridges without isolation devices). The important parameters included are the flexibility of the substructure and the ground acceleration. The results show that specific design of the isolation device has a significant effect on the seismic response of the isolated bridges. The efficiency of LRB in the bridges subjected to low seismic activity is considerably smaller due to the lead mostly remaining in the elastic range. The LRB can in this case therefore not contribute hysteretic damping which is, however, the great benefit of LRB from the design point of view. Stiffer structures tend to improve the isolator efficiency and show better performance in case of low