Quantification of Fundamental Frequencies of 3D Basins and Structures and Site-City Interaction Effects on Responses of Structures

摘要

Large-scale commercialization in Indian metrocities has made realtors develop new construction sites by filling land depressions with loose soil, which may behave as small three-dimensional (3D) basins. This study presents the development of empirical relations to predict the fundamental frequency of basins (FB 03D) and structures (FS 03D) on rock for different shape ratios to study the effects of site-city interactions (SCIs) on the response of structures under a double resonance condition. The S-wave responses of the various considered basins, structures, and site-city models are simulated using the finite-difference method. Analysis of the simulation results reveals that the FB 03D of the basin and the FS 03D of the structure depend strongly on the shape ratio, on average matching with those obtained using the SV-wave response of the section of the respective basin/structure. However, the spectral amplification factor (SAF) obtained at FB 03D/FS 03D for the basin/structure is much larger than that obtained using the SV-wave response of a section of the respective basin/structure. Empirical relations are developed to predict the FB 03D of basins and FS 03D of structures in terms of the shape ratio and one-dimensional (1D) fundamental frequency of the respective model. Analysis of 3D SCI effects reveals a reduction of the SAF at the fundamental frequency of the structure in the basin (FSB 03D) with an increase of the number of structures as compared with that at the fundamental frequency (FSB 03D) of a standalone structure in the basin, being on the order of about 60 % in the case of a city with 25 structures. This finding indicates the need for 3D SCI studies in urban environments for cost-effective earthquake engineering.