Comparison of Peak Seismic Displacement Obtained from Simplified Analysis for Lead Rubber Bearing (LRB) Isolators with Nonlinear Response History Analysis

Document Type : Original Article

Authors

Faculty of Civil, Water, and Environmental Engineering, Shahid Beheshti University, Tehran, Iran

10.48308/ijce.2026.107087

Abstract

Seismic isolation systems are widely used to reduce earthquake-induced structural demands by increasing the fundamental period and providing additional energy dissipation. Among available isolation devices, Lead Rubber Bearings (LRBs) are commonly employed because they combine lateral flexibility with hysteretic damping. Simplified displacement-based design procedures are frequently used in practice to estimate the effective properties and displacement demands of LRB systems; however, their accuracy relative to nonlinear dynamic analysis remains an important concern. This study evaluates the accuracy of a simplified iterative design procedure for LRB isolation systems through comparison with nonlinear time-history analyses performed in OpenSeesPy. The isolated structure was modeled as an equivalent single-degree-of-freedom (SDOF) system. A parametric investigation was conducted using six characteristic strength ratios (μ = 0.03–0.30) and ten post-yield stiffness ratios (α = 0.05–0.50), resulting in sixty isolator configurations. Effective mechanical properties were first determined using the displacement-based iterative procedure. Nonlinear time-history analyses were then performed using 44 FEMA P695 ground-motion records scaled to the design earthquake spectrum for downtown Los Angeles. Peak displacement demands obtained from nonlinear analyses were statistically evaluated and compared with the design displacements predicted by the simplified procedure. Results showed that the simplified method consistently underestimated displacement demands, particularly for low characteristic strength ratios. The average prediction error exceeded 100% for μ = 0.03 and decreased to approximately 29% for μ = 0.30. The characteristic strength ratio was identified as the primary factor affecting prediction accuracy, while the influence of the post-yield stiffness ratio was relatively small. The findings indicate that simplified procedures are useful for preliminary design, but nonlinear time-history analysis is necessary for reliable estimation of displacement demands in seismically isolated structures.

Keywords

References

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Interdisciplinary Journal of Civil Engineering
Volume 2, Issue 1 - Serial Number 5
January 2026
Pages 492-506

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