Comparative probabilistic fragility assessment of a 10-storey fixed-base and friction-pendulum base-isolated RC frame under near- and far-field earthquake motions

Abstract

This study conducts a comparative probabilistic fragility assessment of a representative 10-storey reinforced concrete (RC) frame considered in fixed-base and friction-pendulum base-isolated configurations under near- and far-field earthquake motions. A collection of 44 seismic records, grouped into far-field (FF), near-field with fling-step effect (NFFS), near-field with directivity effect (NFD) and elevated peak ground acceleration (PGA) to peak ground velocity (PGV) ratio (NFD-GT-150, >150 cm/s/g), and near-field with directivity effect and reduced PGV/PGA ratio (NFD-LT-150, <150 cm/s/g), was analysed. Using incremental dynamic analysis (IDA) and probabilistic seismic demand modelling (PSDM), vulnerability curves were constructed for five structural response metrics: maximum interstorey drift ratio (IDR_max ), maximum roof drift ratio (RDR_max), maximum top floor acceleration (RA_max ), maximum base shear force (BS_max), and maximum isolator displacement (ID_max ), spanning four damage levels: slight, moderate, extensive, and collapse. Findings indicate that proximate seismic excitations (NFD-GT-150, NFFS) substantially elevate vulnerability across all damage levels, with NFD-GT-150 yielding the highest probabilities of exceedance (e.g., 99.38 % for fixed-base collapse at 0.8g PGA). Base isolation decreased IDR_max by up to 88.1 % at the collapse level under FF at 0.2g PGA, though its efficacy waned under NFD-GT-150 conditions. IDR_max and ID_max emerged as the most responsive metrics, consistently displaying elevated exceedance probabilities. The PGV/PGA ratio proved a vital predictor of seismic damage, with NFD-GT-150 raising collapse exceedance probability by 32.5 % over NFD-LT-150 at 0.4g PGA for base-isolated frames. These insights stress the importance of integrating PGV/PGA considerations and proximate seismic effects into design standards to bolster the durability of base-isolated structures in fault-proximate zones. Since the investigation is limited to one 10-storey regular RC frame, the results should be interpreted as a detailed case-study assessment rather than as generalized conclusions for all RC building heights and configurations.