Base isolation of structures is a viable and an economical solution for earthquake protection. Passive control devices such as isolation bearings have been commonly used in the construction of new bridges and retrofit of existing bridges during the last 30 years. Base isolation shifts the response of the structure to a higher fundamental period thus reducing the corresponding pseudo-acceleration in the design spectrum and attracting lesser earthquake-induced forces.
Friction Pendulum System (FPS) is an innovative and viable isolation bearing that is becoming a more widespread application for the earthquake protection of structures. FPS consists of a spherical stainless steel surface and a lentil-shaped articulated slider covered by a Teflon-based high bearing capacity composite material. The two constituents of the sliding isolator mechanism is the restoring force provided by the concavity and friction force opposing the direction of motion.

The objectives of this study are to assess the performance of bridges with Friction Pendulum Systems (FPS), with a particular emphasis on evaluating the parameters of bridges and model parameters for the bearings which govern the seismic response of typical bridges.  This is accomplished by developing rigorous analytical models of isolators with particular emphasis on the Friction Pendulum System (FPS) and to use these models to investigate the response of seismically isolated bridges (SIBs).  The research tasks to accomplish these objectives are the following: 

• Identify the characteristic aspects of the FPS that contribute to the force-deformation response.  Develop the nonlinear kinematics formulation of the isolator model.
• Implement the model into a nonlinear dynamic evaluation platform and validate response using experimental data.
• Develop detailed 3-D bridge models isolated with the FPS and identify the influence of the modeling assumptions of the isolator on the response of the bridge.
• Modify the FPS model to represent the Lead-Rubber Bearings (LRB) force-deformation response.