Effects of subfreezing temperature on the seismic response of lead rubber bearing isolated bridge

Seismic isolation is one of the most effective ways to minimize structural damage during and immediately after any seismic event. The objective of base isolation is to provide enough horizontal flexibility during seismic excitation while providing adequate performance under all service load. Rubber based isolation systems, such as elastomeric bearings and Lead Rubber Bearings (LRBs), have been widely used as seismic isolators for bridges. Due to their superior performance and combined isolation and energy dissipation functions in a single compact unit, LRBs have gained much popularity in the bridge industry. However, the main constituent of LRB, rubber, is very sensitive to low temperatures and related duration of exposure. At low temperature, rubber undergoes crystallization stiffening which substantially effects the mechanical properties of LRB. The objective of this study is to evaluate the seismic performance of a base isolated bridge at subfreezing temperature. The bridge is seismically isolated using LRBs and assumed to be located in Montreal, Quebec, Canada where a temperature variation between + 35 degrees C to -35 degrees C is expected. Using a detailed 3D finite element model of the bridge and considering the bridge component material properties and bearing properties at summer and winter service temperatures, the performance of the isolated bridge is evaluated in terms of isolator force-deformation relationship, force demand in the substructure, deck acceleration, and shear strain in the isolation bearing. Finally, fragility curves are developed to evaluate the effect of subfreezing temperature on the seismic response of LRB isolated bridges. Analysis results show that freezing condition may have a notable effect on the component fragility as well as the bridge system fragility.