Response spectra and design spectrum of ground fissures site under seismic action.

To make efficient use of land resources and minimize the seismic destruction of structures in the ground fissures zone, the shaking table tests and 3-dimensional numerical calculation of the soil were completed, based on the ground fissures site in Xi'an (Class II, with the shear wave velocity Vs ranging from 250 m/s to 500 m/s). Influence laws of ground motion characteristics and geological structure characteristics on seismic response spectra were revealed. Based on the statistics and analysis of seismic waves of the ground fissures site, standardized design response spectra and mathematical formula of the ground fissures site were determined. The findings indicated that: the ground fissure exerted an amplifying influence on seismic waves and changed their spectral characteristics. Moreover, the amplification effect increased with the increasing of the dip angle of ground fissure. These amplified seismic excitations heightened the response of the superstructure, with more pronounced effects observed on the hanging wall compared to the footwall, showing "hanging-wall/footwall effect". Besides, the structural response was related to the spectral characteristics of seismic waves. Bedrock waves with rich high-frequency components were more likely to resonate with SDOF systems with short period, while Jiangyou waves and El Centro waves with more low-frequency components had more intense resonance responses. With the increasing of fault distance, the characteristic period T increased, but platform value of response spectra β decreased. The value of β was between 2.52 and 3.62. The distributed patterns were respectively ∨-shaped and ∧-shaped. The research results of the design spectra can be used in the seismic design of the superstructure in the ground fissures site.