Comparison of seismic resistance between LRB and FPB on energy dissipation per cycle and equivalent damping

Abstract To evaluate and compare the seismic performance of isolators, this study aims to compare lead rubber bearings (LRBs) and friction pendulum bearings (FPBs) using energy dissipated per cycle (EDC) and equivalent damping as key performance indicators. Compressive-shear and compressive-friction tests were conducted in accordance with the Bridge Seismic Isolator Test Guidelines (draft) published by the Ministry of Land, Infrastructure and Transport (MOLIT), and standard formulas were applied to calculate the effective stiffness and equivalent damping ratio. Two seismic isolators, LRB and FPB, which have different mechanical properties, were used in experimental specimens. LRB specimens (Ø500 mm × 300 mm) consist of steel reinforcing plates, rubber layers, and a lead core. FPB specimens (Ø725 mm × 169 mm) have the main and sub-friction plate. The shear stiffness, EDC, and equivalent damping were calculated and used to evaluate seismic resistance. As a result, shear stiffness, EDC, and equivalent damping were shown to be more than the design value of seismic resistance. However, FPB specimens show a higher value of EDC than LRB specimens. The differences in EDC values affected the variables of the compressive-friction test. The equivalent damping ratio of the LRB and FPB specimens did not show significant differences. From the test results, it is confirmed that the LRB and FPB can be used to dissipate a seismic load as seismic isolators.