Effect of base slab mass and number of rubber layers on base isolation system performance in enhancing building dynamic response

Abstract

Purpose Traditional designs might not withstand earthquake forces adequately, potentially leading to structural damage. This paper aims to examine the impact of varying the base slab mass and the number of rubber layers in isolators on the performance of isolation systems to improve the seismic performance of buildings. Design/methodology/approach The isolated structure is modeled as a two-degree of freedom system, and its corresponding equation of motion is established. Displacement expressions for the base slab and roof are derived using the mode superposition method. Findings A base isolation system improves the buildings’ behavior, particularly when higher rubber layer numbers and a heavier base slab are assumed. At an excitation frequency of 8 rad/s, an increase in the rubber layer numbers from 9 to 11 led to a 30% reduction in relative displacement. At an excitation frequency of 6 rad/s, a 40% reduction in relative displacement was observed passing from a base slab mass (mb) of 7.5 tons with damping ratios of 12% and 10% in the first and second modes to a mass (mb) of 30 tons with lower damping ratios of 9.5% and 4.2%. Originality/value The high damping ratio in the isolation mode significantly increases the damping ratio of the fixed-base building. However, higher damping ratios in the first and second modes do not necessarily lead to better seismic performance. Besides, an increase in the base slab mass and the number of rubber layers enhances the dynamic response of the isolated structure by shifting its fundamental frequency away from the excitation frequency.