Collapse fragility of structures subjected to basin amplified ground motion: Influence of basin parameters

Abstract

The seismic amplification due to sedimentary basins often increases the strength demands of structures located inside a basin, and so the understanding of the collapse fragility subjected to these amplified ground motions is significant. However, the influence of basin amplification on spectral acceleration is not directly included in most seismic design codes. For the first time, the influence of various basin parameters such as basin depth, basin width, basin-to-bedrock impedance ratio, and source-to-basin distance are addressed in terms of collapse fragilities. The very focus of this study is to characterize the effect of basin parameters on the collapse fragility of structures with time natural periods T = 0.3 s, T = 1.0 s and T = 3.0 s by means of synthetic ground motions. Various basin models with different configurations are created, and earthquake shaking is simulated for a Mw 7 magnitude earthquake on a finite fault with 5 different rupture scenarios. The response of structures with natural periods 0.3 sec, 1.0 sec, and 3.0 sec are computed by incremental dynamic analysis, and fragility curves are derived for the collapse limit state. From the study, it has observed that the fragility variation with basin geometry is significant for taller structures. Basin depth significantly affects fragility, particularly for T = 1.0 and 3.0 s structures, with a decreasing trend in fragility as depth increases beyond 5 km. The results of this study also suggest that structures in the basin exhibit greater variability in response, likely due to complex seismic waves interaction inside deep sediment basins. From the insights of study on effect of basin materials on structural fragility, it is clear that the higher impedance ratios lead to significantly higher structural vulnerability. The computed fragility parameters are compared with those of HAZUS for low-rise (C1L, S1L), mid-rise (C1M, S1M), and high-rise (C1H, S1H) moment-resisting frames made of steel and concrete.