Comparative Nonlinear Seismic Response of Fixed-Base and Lead-Rubber-Isolated Reinforced Concrete Building Systems

Abstract

This study examines how lead-rubber bearing (LRB) isolation changes the seismic response of a ten-story reinforced-concrete building using matched fixed-base and isolated models. Three-dimensional ETABS models were analyzed using nonlinear direct integration under the EQ-X component of the 1999 Kocaeli earthquake recorded at the Arcelik station. Nonlinear behavior was confined to 38 LRB links, while the superstructure remained linear elastic. Record import, units, scaling, spectrum screening, gravity initialization, damping, convergence, and signed response envelopes were verified. The results show that isolation lengthened the first period from 1.332 to 2.245 s and reduced the base-shear envelope from 9,066.91 to 5,778.71 kN, representing a reduction ratio of 36.3%. Story-shear reductions ranged from approximately 36.0% to 49.2%. Drift reductions from Stories 2 to 10 reached 47.6%, although the Story 1 superstructure drift increased by 96.9%. Matched absolute accelerations decreased by 52.6%, 38.6%, and 48.6% at Stories 1, 5, and 10, respectively, while the corrected center-of-mass overturning envelope decreased by 28.6%. The governing bearing displacement was 59.35 mm, corresponding to 39.6% of its 150 mm design value. The novelty and improvement of this work lie in its separation of bearing deformation from interstory drift, removal of the gravity offset from the overturning moment, comparison of matched absolute accelerations, and connection of the system response to a transparent bearing-level check.