Vulnerability assessment of seismically isolated elevated liquid storage tanks using optimized friction pendulum isolators with elliptical surfaces

The failure of elevated liquid storage tanks during severe earthquakes can have direct or indirect impacts on public safety. The significance of their safe performance even after destructive earthquakes and the potential for their operational use underscore the necessity for appropriate seismic design. Hence, seismic isolation, specifically base isolation, has gained attention as a seismic control method to reduce damage to these infrastructures by increasing their period of vibration. One prevalent type of seismic isolator used for tanks and other structures is the friction pendulum system (FPS) isolator. However, due to its fixed period or frequency, it may be susceptible to resonance effects during long-period earthquakes. This research explores a solution by investigating the variable curvature friction pendulum isolator (VFPI) as an alternative. This isolator type exhibits behavior similar to FPS isolators under low excitations and transforms into a pure friction system for high excitations. The study proposes optimizing this VFPI by introducing a suitable optimization function to minimize the acceleration transmitted to the superstructure, thereby improving the dynamic performance of the elevated storage tank. The research utilizes a metaheuristic algorithm for optimization and evaluates the effectiveness of the proposed isolator through time history analysis using the state space procedure under various ground motion records. Results, particularly under long-period ground motions, indicate a substantial reduction in the dynamic response of an elevated liquid storage tank equipped with the optimized VFPI. This underscores the potential of the proposed solution in enhancing the seismic resilience of liquid storage tanks.