Experimental and analytical studies of seismic response of highway bridges isolated by rate-dependent rubber bearings

The mechanical behavior of a majority of rubber bearings used for seismic isolation is known to exhibit rate dependence. Although this feature has been known for years, few studies have attempted to quantitatively evaluate the influence of this characteristic on the seismic response of an isolation system at the structural level. In this study, experimental and analytical investigations were conducted to probe the seismic response of highway bridges isolated by rate-dependent rubber bearings. Three types of such bearings were investigated: natural rubber bearings, high damping rubber bearings (HDRBs), and super high damping rubber bearings (SHDRBs). To achieve the study objective, real-time hybrid simulation (RTHS) tests were performed on a typical multi-span continuous girder highway bridge under various earthquake ground motion intensities. In the RTHS tests, a velocity loading method was adopted and the bearings were physically tested in a real-time scale and larger time scales such that the bearings were exerted under different loading rates. The influence of the rate-dependent behavior of bearings on the seismic response of the bridge was investigated by conducting a series of parametric studies. The test results indicated that the seismic response of the bridge was significantly affected by all three types of rate-dependent rubber bearings, especially HDRBs and SHDRBs. Finally, a newly proposed rate-dependent analytical model and the traditional rate-independent bilinear model for rubber bearings were used in the numerical simulation. A comparison of the simulation results indicated that the proposed model performed better than the bilinear model in the seismic response analysis.