Theory And Program Development Of Multi-point Seismic Motion Simulation For Layered Canyon Sites And Seismic Response Of Large Span Structures

China is a country with frequent earthquakes.The eastern part is located in the Circum-Pacific seismic belt,and the southwestern part is located at the junction between the Qinghai-Tibet Plateau plate and the Indian Ocean plate.These two seismic zones are the most abundant seismic areas in the world.With the enhancement of our country’s comprehensive strength and the rapid development of economy,more and more long-distance and long-span complex projects such as long-span bridges,long-distance tunnels and high-voltage transmission tower systems of West-to-East power transmission are gradually built and operated in these earthquake-prone areas.These projects not only bear the risk of high occurrence earthquakes,but also are affected by complex topographic and geological factors.A large number of records of earthquake disasters show that local site factors have a significant impact on the seismic response of structures.However,due to technical and economic reasons,it is assumed that the site is a single homogeneous medium and the site conditions are often assumed to be flat terrain in major seismic codes and seismic studies.Many scholars have found that in some sites with severe disasters,the terrain is usually irregular and stratified.Comparing with a single medium on a flat surface,seismic waves may undergo a series of complex refraction or reflection under the condition of irregular surface as well as inhomogeneous medium.For the SV wave and the P wave,there will be more complex wave coupling transformation problems,which leads to the completely different dynamic response from that of a single medium site on flat terrain.The accuracy of seismic response of long-distance and long-span structures depends largely on the input seismic time history of structures.Therefore,the analysis of long-distance and long-span structures considering the site effect of topographic and geological stratification has urgent theoretical and practical significance.In this paper,a double layered arc canyon under SV wave incident is taken as the research project.The main research contents are as follows:(1)Seismic scattering solutions of irregular terrain or layered sites are usually focused on the incidence of SH waves.In this paper,the difficulties of interference,scattering and P-wave conversion of relatively complex waves are overcome when SV waves are incident on such sites.The scattering frequency domain solution of the double layered arc Canyon under the incident of SV wave is derived.The correctness of the solution is verified by assigning the physical parameters of layered soils to the same values as those calculated under the condition of homogeneous media.Finally,the effects of different inci-dent frequencies and different incident angles of different SV waves on the ground motion are studied.(2)Based on the frequency domain solution of the above model,the correlation function of the canyon and the power spectrum matrix of underground ground motion are derived by using random vibration theory,which establishes the artificial ground motion foundation of SV wave incident layered arc Canyon.Using MATLAB language,the program of artificial ground motion for the layered circular arc Canyon site with SV wave incidence is developed,and the visualization of the program is achieved.(3)Based on a typical project of a continuous steel frame bridge across an arc canyon,the method and program proposed in the previous chapters are tested practically,and the results of numerical simulation analysis are analyzed in detail.The seismic response of structures with and without consideration of topographic effects is quite different.For the seismic analysis of long-span structures,the influence of complex sites on the scattering of seismic waves needs to be considered.