Finite element–based optimal seismic retrofit and performance evaluation of RC frames using an integrated steel frame–ENTA damper system

초록

This study proposes an optimal seismic retrofit strategy for reinforced concrete (RC) frames using an integrated steel frame-ENTA damper system and evaluates its structural performance through experimental and numerical investigations. The proposed retrofit concept combines the stiffness enhancement provided by an external steel frame with the energy-dissipation capability of replaceable external nonlinear tensile-axial (ENTA) dampers, forming a hybrid energy-dissipating retrofit system. Full-scale cyclic tests were conducted on two-story RC frames representing both as-built and retrofitted configurations to examine their load-displacement response, hysteretic behavior, and damage progression under seismic loading. A nonlinear finite element (FE) model was developed and validated using the experimental results, showing good agreement with discrepancies of less than 5% in peak strength and approximately 3% in displacement capacity. The validated model was subsequently used to conduct parametric analyses to investigate the influence of the retrofit height ratio (RH) of the external steel frame and the thickness-to-width ratio (t/B) of the ENTA damper on the global structural response. The results indicate that the proposed retrofit system significantly improves lateral strength, stiffness, ductility, and energy dissipation capacity while effectively shifting damage from the primary RC members to the replaceable damper components. Increasing RH primarily enhances global stiffness, whereas increasing t/B significantly improves both stiffness and hysteretic energy dissipation. An optimal retrofit configuration was identified with RH ranging from 0.5 to 1.0 and t/B between 0.027 and 0.045, providing a balanced improvement in structural strength, ductility, and energy absorption efficiency. Seismic performance evaluation using the capacity spectrum method further confirms that the retrofitted frame satisfies the Life Safety performance level under design-level seismic demand, demonstrating the potential of the proposed retrofit system for enhancing the seismic resilience of existing RC frame structures.

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