Comparative Dynamic Response Analysis of Fixed-Base vs. Base-Isolated Steel-Concrete Composite Frames Under Seismic Excitation

Objectives: The study compares a Lead Rubber Bearing (LRB) base isolated system with a traditional fixed-base system in order to assess the seismic resistance of a G+12 high-rise steel-concrete composite structure. The main objective of the study is to analyze the decrease in seismic requirements and evaluating the capability of LRB for safeguarding vital urban infrastructure. Methods: To capture the nonlinear hysteretic behavior of an LRB isolator, it was analyzed and designed in ABAQUS software. The comparative time history analysis was carried out in ETABS software using IS 1893:2016 guidelines. Storey drift, displacement, peak floor acceleration and base shear are among the measures used to evaluate the structural reaction. Findings: The LRB isolator system performed better, reducing storey drift by 10.83% (X), while the structure’s base reactions reduced by 20.86% (X) and 3.95% (Y). The reaction of the building was successfully moved away from hazardous earthquake frequencies, although lateral displacement increased by 38.82% and the natural time period extended by 24.53%. The implementation of LRB base isolation resulted in a major reduction of internal forces in the structural beams. The bending moment decreased by 19.24% and also the shear force decreased by 7.97% compared to the fixed-base structure. Novelty: The study integrates nonlinear isolator features derived from ABAQUS into ETABS time history analysis to give a localized high reliability comparison specifically for high rise composite structures. It highlighted the critical "acceleration attenuation" effect, proving that LRB base isolation is essential in composite design to transition from life-safety to modern functional recovery standards. Keywords: Lead rubber bearing, Composite structure, Base isolation, Storey drift, Time history analysis