Optimal Seismic Isolation Design for A Highway Bridge with Nonlinear Base Isolator Modeling

We have recently presented the following paper at 7th National Seismic Conference on Bridges and Highways (Oakland, CA, May 20-22, 2013)

Optimal Seismic Isolation Design for A Highway Bridge with Nonlinear Base Isolator Modeling

Yili Huo and Bulent N. Alemdar

ABSTRACT

Time history analysis is the recommended analysis method for seismic isolation of bridges in many design codes. This type of analysis imposes much more work to structural engineers for isolation design than traditional non-isolation design. Optimal choices of seismic isolation design parameters play a crucial role in mitigating bridge superstructure damages. This study utilizes fragility method and generic algorithm search to address optimal seismic isolation parameters. These methods can be very beneficial for bridge engineers to expedite and provide supplemental information during design process. To demonstrate this, a two-span concrete bridge is chosen in this study and an elastomeric rubber bearing isolator is placed between the pier column top and girder. A series of numerical studies is conducted with the aforementioned methods to find optimal design parameters of the rubber isolator in regards with minimizing damages in the bridge. Performance-Based Earthquake Engineering framework by PEER is followed during the numerical study to evaluate the bridge damages equipped with the isolation bearing. It is found that the characteristic yielding strength and the post-yielding stiffness of the bearings are crucial for seismic damage mitigation, but the pre-yielding stiffness and several other hysteretic controlling constants are not influential. The identified design parameters could be adopted for isolation design of bridges with similar properties. The proposed methods for searching optimcal isolation design could be useful in bridge engineering practice.