Study On Structural System And Seismic Performance Of Long-span Suspension Bridges

Suspension bridge is a kind of typical long-span flexible structures,which is very sensitive to the dynamic action such as the wind and earthquake.The dynamic response and performance of the bridge under the seismic action is therefore becoming an important research issue.By taking the Runyang Bridge over the Yangtze River as example,structural dynamic characteristic and seismic performance are investigated by MIDAS/CIVIL in order to investigate its seismic behavior and also explore favorable seismic structural system.The research results have a good theoretical significance and engineering value to the seismic design of long-span suspension bridges.Firstly,by using MIDAS/Civil finite element analysis software,a 3D finite element model of a suspension bridge with main span of 1,490 m is established,the dynamic characteristics are analyzed.Secondly,by using the response spectrum method and time history analysis,seismic response of the bridge under seismic action of E1 and E2 is analyzed,the seismic behavior and also the effect of structural nonlinearity on seismic response of suspension bridge are revealed.Moreover,the dynamic characteristics and seismic response are compared to those of the cable-stayed bridge and cable-stayed-suspension hybrid bridge with the same main span.Finally,through changing the span arrangement,the suspension to span ratio,the ratio of rise to span of main cable,the ratio of side span to main span,the height of the stiffening girder,the central buckle and the support system of stiffening girder 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 results show that:(1)the dynamic characteristics of long-span suspension bridge are the same as those of flexible structures,the natural frequency is relatively small,and the fundamental period is very long,and the natural frequencies of vibration modes of the girder are generally low.(2)The seismic responses of the tower and stiffening girder are remarkable under longitudinal and transverse seismic actions.The influence of structural nonlinearity on seismic response of suspension bridges is remarkable,and therefore the time history analysis method should be used to accurately predict the seismic behavior of long-span suspension bridges.(3)As compared with the cable-stayed bridge and cable-stayed-suspension hybrid bridge with the same main span,structural displacement and internal force are less,and better seismic performance is achieved for the suspension bridge.(4)Better dynamic characteristics and seismic performance are achieved for long-span suspension bridges through using the three-span continuous system,increasing the ratio of rise to span ratio,reducing the length of the side span,increasing the height of the stiffening girder and setting the central buckle.