Study On Seismic Failure Characteristics And Dynamic Response Of Soil-frame Structure System In Ground Fissure Areas

As a typically urban geological hazard,ground fissures are widely distributed and seriously harmful.These active ground fissures not only have posed great damage to building structures,ancient buildings and metro projects,but also caused a series of ecological environment problems,which severely restrict the urban planning and construction of the area.With the activity of ground fissure being stable and the rapid development of urban construction,how to effectively utilize land resources and reduce the potential geo-hazards caused by ground fissures is one of the research focuses in civil engineering.Taking the f₄ ground fissure in Xi’an（Northwest University-Northwestern Polytechnical University）as the research object,a series of shaking table tests were designed and conducted based on the physical models of ground fissure site and soil-structure system in ground fissure areas.The results of the shaking table test were supplemented by means of numerical simulation.The seismic damage characteristics and dynamic responses of soil and soil-frame structure system in the ground fissure site were studied systematically.On this basis,the seismic design response spectrum in the ground fissure site was developed by least square fitting method.The major research works and achievements in this paper are as follows:（1）Based on the similarity theory,a series of shaking table tests were designed and conducted by the authors aimed at understanding the seismic response on the earth fissure site during strong earthquakes.It mainly solved a series of key problems such as the treatment of boundary effects,the design and production of model,the simulation of ground fissures,the arrangement of measuring points and the establishment of test loading system.Simultaneously,it obtained shaking table test means and methods for simulating ground fissure site,which laid the foundation for numerical simulation.（2）By observing the experimental phenomena and analyzing the experimental data,the seismic failure characteristics and dynamic characteristics of the ground fissure site during strong earthquakes were found.The distribution disciplinarian of ground motion parameters（ground motion intensity,strong-motion duration and frequency spectrum characteristics）on the ground fissure site was observed and compared.The Hilbert-Huang transform（HHT）was used to analyze the development trend of seismic damage of soil in the ground fissure site.Test results showed that the dynamic response and damage of the soil on the hanging-wall were more serious than those on the footwall,especially in the near ground fissure area,which showed obvious"hanging-wall and footwall effect"and spatial non-consistent seismic.（3）Based on the distribution disciplinarian and the characteristics of geological structure of ground fissures,the multi-scale 3D dynamic model of the ground fissure site was established by ABAQUS,and the results of the numerical simulation were verified by means of physical model test.On this basis,the influences of input seismic wave and geological structure on the dynamic response of ground fissure site were found.The results showed that the input direction,amplitude,frequency spectrum and strong-motion duration of seismic wave had significant influence on the dynamic response of soil in ground fissure site,but the degree of influence was different.The soil of structure stratification and staggered layers,vertical dip angle and platform series had obvious influence on the propagation of seismic waves in the soil medium,which not only changed the amplitude and spectrum characteristics of seismic wave,but also changed the time when seismic wave propagates to the surface.（4）It has been the first time to design and complete shaking table model test of frame structure across ground fissure,and the hoisting device of the finished model was invented.The seismic failure characteristics and dynamic responses of the frame structure across the ground fissure under non-uniform seismic excitation were found.By comparing the numerical results with the test results,the response laws of acceleration,displacement and seismic shearing force of frame structure on the common site and on the ground fissure site were compared and analyzed,and the scope of the dynamic amplification effect on the ground fissure site was determined.（5）Through the response spectrum analysis of SDOF on the ground fissure site,the failure mechanism of structure across ground fissure was further studied,and the influence of geological structure on seismic response spectrum was obtained.The relationship between fissure distance with characteristic period and peak platform value of response spectrum was analyzed,and the least squares piecewise fitting calibration method was used to fit the standardized seismic design response spectrum on the ground fissure site.