Open Access
ARTICLE
Seismic Fragility Evaluation of Elevated Water Storage Tanks Isolated by Optimized Polynomial Friction Pendulum Isolators
Mojgan Mohammadi1, Naser Khaji2,*
1 Faculty of Civil and Environmental Engineering, Tarbiat Modares University, Tehran, Iran
2 Civil and Environmental Engineering Program, Graduate School of Advanced Science and Engineering, Hiroshima University, 1-4-1, Kagamiyama, Higashi-Hiroshima, Hiroshima, Japan
* Corresponding Author: Naser Khaji. Email: 
Computer Modeling in Engineering & Sciences https://doi.org/10.32604/cmes.2026.078945
Received 11 January 2026; Accepted 18 February 2026; Published online 06 March 2026
Abstract
The failure of liquid storage tanks, one of the most critical infrastructure systems widely used, during severe earthquakes can have direct or indirect impacts on public safety. The significance of their safe performance even after destructive earthquakes and their potential for operational use underscores the necessity of 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 vibration period. 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 an alternative solution by investigating the variable-curvature friction pendulum isolator (VFPI). This isolator type exhibits behavior similar to that of FPS isolators under low excitations and transforms into a pure friction system under high excitations. The study proposes optimizing this VFPI, which features a polynomial function termed the Polynomial Friction Pendulum Isolator (PFPI), 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 two well-established metaheuristic algorithms for optimization. It 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 PFPI. This underscores the potential of the proposed solution in enhancing the seismic resilience of liquid storage tanks.
Keywords
Elevated water storage tanks; variable friction pendulum isolator; long-period ground motions; metaheuristic algorithms; optimization; polynomial friction pendulum isolator
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