Exploratory Study of Partial Isolation of Highway Bridges

A special class of seismically isolated bridges shares a common feature in that both ends of the superstructure are restrained and isolators over the columns of bridge uncouple the superstructure from the ground motions. They are defined as partial isolation bridges. From measured acceleration responses, the effectiveness of full seismic isolation had been confirmed widely. However, the seismic isolation behavior in the partial isolation has not been widely observed. The effectiveness of partial isolation is evaluated in this study. The static design procedures for linear and nonlinear partially isolated bridges are developed. Results from the static analysis of linear and nonlinear partially isolated bridges, compared with conventional and fully isolated bridges, demonstrate that the effectiveness of nonlinear partial isolation is close to full isolation for reducing the yield force and displacement of the columns in some parameter ranges. However, increased displacement demands at the abutments are observed. Nonlinear time history analyses of the different bridge models under earthquake excitations are carried out to investigate the accuracy of the design procedure for nonlinear partial isolation. In addition, an example shows the application of nonlinear partial isolation to a practical bridge.