Nonlinear Seismic Responses Of The Powerhouse Of A Hydropower Station Under Near-fault Ground Motions Oblique Input

Water energy resourcesare richin the Southwest and Northwest regions of China,but the area is prone to strong earthquakes,it is difficult to avoid the location of hydropower projects.Powerhouse of hydropower station is the core strcuture of hydroelectric power project,it's seismic safety faces severe challenges.Near-fault ground motions have unique motion characteristics such as long-period and larg'e amplitude velocity and displacement pulse,genera:lly do not meet the vertical incidence assumption,and often cause serious damage to powerhouse of hydropower station.It is an important topic for designers and researchers to carry out seismic safety evaluation of powerhouse of hydropower station under near-fault ground motions.In this paper,through theoretical derivation and numerical simulation,the pulse characteristics of near-fault ground motions and incidence angle on seismic response of powerhouse of hydropower station are studied.The main conclusions include:(1)Based on the continuous condition of madia interface and free surface boundary condition,the theoretical displacement expression of free surface under planeSV-wave and P-wave oblique incidence are derived.The nonlinear effect law of the seismic wave inc.idence angle on the free surface displacement is discussed.Compared with vertical incidence,the free surface horizontal and vertical displacement show different degrees of magnification or reduction with the increase of the seismic wave incidence angle.The free surface horizontal displacement maximum can be increased by 49%under plane SV-wave oblique incidence,the free surface horizontal displacement maximum increased from 0 m to 1.743m under plane P-wave oblique incidence.(2)According to thewave field of differemt boundaries,considering different seismic wave's time delays,the displacement,velocity,and stress generated by the incidence wave,reflected wave,and derived reflected wave are added overlay,the free field displacement,velocity and stress at theboundary are obtained,the viscoelastic artificial equivalent nodal force is obtained,and the seismic wave three-dimensional oblique incidence input is realized.The displacement numerical calculation of the surface center point of the boxed foundation under of plane SV-wave and P-wave three-dimensional oblique incidence input is carried out.And compared with the previous theoretical solution,the correctness of the three dimensional oblique incidence input method is verified.(3)Five groups of near-fault pulse and non-pulse ground motion records were selected according to the engineering site category.Based on seismic wave three dimensional oblique incidence input method,the nonlinear seismic response research of powerhouse strcuture under plane SV-wave and P-wave oblique incidence input carried out for an actual powerhouse of hydropower station.The damages,energies,interlayer displacement angles and reinforcement stress of upper structure and other responses of powerhouse strcuture under near-fault plane SV-wave decrease with the increase incidence angle(00-300).The damages,energies and other responses of powerhouse strcuture under near-fault plane P-wave increase with the increase incidence angle(0°-65°).At the same incidence angle,pulse-like ground motions have stronger damage ability than non-pulse ground motions.It provides reference for seismic safety and evaluation research of powerhouse.