Study On Seismic Behavior Of Long-span Partially Earth-anchored Cable-stayed Bridge

The partially earth-anchored cable-stayed bridge is a new type of cable-stayed bridge with strong spanning ability,it inherits the advantages of cable-stayed bridge and overcomes the problems of excess axial force of the girder near the towers,large tower height and small structural stiffness of traditionalfully self-anchored cable-stayed bridge with main span ofabove 1000 meters,and therefore has good development potential and application prospect.In this thesis,the dynamic characteristics and seismic performance of a partially earth-anchored cable-stayed bridge with main span of 1400 m are analyzed,and the favorable earthquake-resistant structural system is studied,and the research results have good theoretical reference for seismic analysis and design of long-span partiallyearth-anchored cable-stayed bridge.Firstly,the three-dimensional finite element model of a long-span partial earth-anchored cable-stayed bridge with main span of 1400 meters is established by Midas/civil finite element analysis software,the reasonable structural state in completion is determined,and structural dynamic characteristics are analyzed.Secondly,by using the seismic response spectrum analysis method and time-history analysis method,the seismic response of the partially anchored cable-stayed bridge is analyzed under the earthquake actionE1 and E2,the seismic behavior of long-span partially anchored cable-stayed bridge is discussed,and the influence of structural nonlinearity on seismic response is also revealed.Thirdly,through investigating the seismic performance of a fully self-anchored cable-stayed bridge with the same main span,the advantage of the seismic performance of partially earth-anchored cable-stayed bridge is proved.Finally,by changing structural design parametersincluding the earth-anchored girder length,the girder width,the girder height,the tower height,the inclination angle of stay cables,the setting of auxiliary piersin the side spans,the connection between tower and girder etc,the influence of each design parameter on structural dynamic characteristics and seismic performance of partially earth-anchored cable-stayed bridge is investigated,and its reasonable value is also discussed.The results show that:(1)long-span partially earth-anchored cable-stayed bridge hasvery long basic period,its natural frequencies are small and distribute densely,and therefore it is a kind of flexible structure.The longitudinal and transverse structural stiffness is less,the seismic effect is remarkable;(2)as compared with the fully self-anchored cable-stayed bridge with the same span,the overall stiffness is higher,and better seismic performance is achieved for partially earth-anchored cable-stayed bridge;(3)structural nonlinearity has obvious influence on the seismic response of long-span partially earth-anchored cable-stayed bridge,the nonlinear time-history analysis method is proposed to accurately predict the seismic performance;(4)under the cases that the earth-anchored girder length to main span ratioisabout 0.3,the greater girder height is set,the tower height to span ratio is about 0.2,and the auxiliary piers installed in the side spans,the partially earth-anchored cable-stayed bridge has good seismic performance.