Fragility-Based Optimal Design of Friction Pendulum Bearings in Seismically Isolated Liquid-Storage Tanks

A fragility-based probabilistic framework is proposed for the optimal design of friction pendulum (FP) bearings in seismically isolated liquid-storage tanks. The isolation period and sliding friction coefficient of the FP system, which significantly influence the seismic performance of isolated liquid-storage tanks, were analyzed as the two design parameters of the isolation system. The seismic fragility functions of the isolated tanks, generated using incremental dynamic analysis (IDA), were evaluated and used to determine the optimal ranges for these design parameters. This procedure, which yields the minimum seismic failure probability of the considered structures, was examined in the design of seismic isolation systems for two on-grade cylindrical steel storage tanks with broad and slender configurations. Moreover, the effects of including or excluding the failure mode corresponding to the excessive displacement of the isolation system from the considered failure limit states were analyzed and discussed. Finally, the present study provides recommendations for the optimal selection of design parameters for FP isolators in liquid-storage tanks.