Study On Structural System And Seismic Performance Of Super Long-span Cable-stayed Bridges

To meet the needs of the construction of sea-crossing bridges,the span length of cable-stayed bridge continues to increase,and it becomes more flexible.Structural safety under the seismic action has become a key issue affecting its design and construction.By taking a super long-span cable-stayed bridge with main span of 1400 m as example,the seismic response and the effects of design parameters on the seismic performance of the bridge are analyzed to investigate its seismic behavior and also explore favourable seismic structural system.The research results have a good theoretical significance and engineering value to the seismic design of super long-span cable-stayed bridges.Firstly,by using MIDAS/Civil finite element analysis software,a 3D finite element model of a cable-stayed bridge with main span of 1400 m is established,and the dynamic characteristics is analyzed.Secondly,by using the response spectrum method and time history analysis,seismic response of the bridge under seismic action of E1 and E2 are analyzed,the seismic behavior and also the effect of structural nonlinearity on seismic response of cable-stayed bridge are reavled.Moreover,the dynamic characteristics and seismic response are compared to those of the suspension bridge and cable-stayed-suspension hybrid bridge with the same main span.Finally,by changing the girder stiffness,the tower structure,the tower height,the ratio of side span to main span,the number of auxiliary piers in side spans and the anchorage system of stayed cables etc,the bridge schemes are designed respectively,the dynamic characteristics and seismic responses are analyzed,and the key design parameters and also their reasonable value are proposed.The research results show: 1)The seismic responses of the tower and girder are significant under longitudinal and transverse seismic actions.The influence of structural nonlinearity on seismic response of the bridge is remarkable,and therefore the time history analysis method should be used to accurately predict the seismic behavior of super long-span cable-stayed bridges.2)Compared to the suspension bridge and cable-stayed suspension bridge with the same span,the cable-stayed bridge has higher structural stiffness and greater seismic responses.3)Better seismic performance can be achieved for super long-span cable-stayed bridges through increasing the girder width and height,employing the A-shaped tower and also decreasing its height,setting several auxiliary piers in side span,reducing the side span length,and setting several stayed cables as earth-anchored.