Seismic Performance and Resilience Comparison of a Fixed-Base Versus Base-Isolated Design of a Six-Story Steel Frame Building at a Near-Fault Site in Los Angeles

This paper studies the seismic performance and resilience of two different seismic designs of a 6-story steel building at a near-fault site in Los Angeles: (i) a fixed-base special moment frame (FB-SMF); and (ii) a base-isolation using triple friction pendulums and a SMF for the superstructure (BI-SMF). The fixed-base design is optimized to satisfy the minimum strength requirements of ASCE 7–16 (basis of the International Building Code, IBC-21), while the base isolated design exceeds the code minimum requirements to enhance seismic performance and reduce functional recovery time. The triple pendulum isolators are designed in accordance with the Seismic Isolator Standard for complying with ASCE 7–16 requirements for achieving target reliability of structural stability. The two buildings are analyzed using three-dimensional nonlinear response history analysis for eleven site-specific horizontal ground motion pairs developed for the design earthquake as well as risk-targeted maximum considered earthquake. The nonlinear behavior of the isolation devices as well as that of the SMF is explicitly modeled. The response is quantified in terms of story forces, drifts, and floor accelerations. A seismic loss and functional recovery time comparison of the designs is conducted using the SP3 platform. The study indicates the significant improvement of seismic performance and reduction of functional recovery time using base-isolation. The limitations of the code-minimum analysis procedure for the fixed-base SMF are revealed.