Stochastic Seismic Response Analysis Of Long-span Multi-tower Composite Girder Cable-stayed Bridge

In recent years,the construction of long-span cable-stayed bridges has developed rapidly,with a larger span and a more novel structure.At the same time,strong earthquake ground motion activities are more frequent.Cable-stayed bridges are the key points in the traffic network,and their seismic performance cannot be neglected.The ground motion has obvious randomness,and the deterministic seismic response analysis method can only analyze individual samples of structural seismic response,which has no universal significance.It is more scientific and reasonable to take seismic action as a stochastic process and use stochastic vibration theory to analyze seismic response.The thesis uses the stochastic vibration method to systematically study the seismic dynamic response of Nanjing No.5 Yangtze Bridge under construction.The main research contents are as follows:1.The stochastic seismic excitation methods for long-span bridges are systematically sorted out,including the power spectrum model of stochastic ground motion,the spatial effect model of ground motion,the pseudo excitation method and the theory of the pseudo excitation method for solving the absolute displacement.the approach of pseudo excitation method for solving absolute displacement in finite element software is given.2.The finite element space model of Nanjing No.5 Yangtze Bridge was established and the dynamic characteristics were analyzed.The results show that the longitudinal stiffness of the bridge is relatively strong and the lateral stiffness is relatively weak.After considering the pile-soil effect,the stiffness of the right half-bridge is less than that of the left half-bridge.3.Using ANSYS combined with pseudo excitation method based on absolute displacement solving method analyzes the stochastic seismic response of long span composite girder cable-stayed bridge under uniform excitation and multi-dimensional-multi-point nonuniform stationary stochastic seismic response analysis.The results show that the singledimensional seismic excitation causes the structure to have a large response in the excitation dimension,and the coupling effect is obvious under the longitudinal and vertical excitation.The laterally uniform excitation produces a small response in the longitudinal and vertical directions,and the three-dimensional uniform excitation is greater than the response produced by only longitudinal or vertical uniform excitation.The non-uniform excitation considered the spatial effect of ground motion.The calculation results show that the traveling wave effect has a significant impact on the seismic response of the bridge,and there is no uniform law to follow.The traveling wave effect must be included in the seismic response analysis of the bridge;Whether considering coherence has a significant impact on structural seismic response,the response when considering the partial coherence effect is slightly smaller than the response when considering the completely coherence effect;Because the soil properties of the piers at the site of Nanjing No.5 Yangtze Bridge are close to each other and the thickness of the soil cover is not much different,the local site effect has little effect on the seismic response of the structure.Considering the local site effect,it mainly affects the lateral seismic response of the structure.4.The parameters analysis of bridge is carried out from the perspective of earthquake resistance.The results show that the composite structure cable tower can improve the overall stiffness of the bridge,reduce the seismic response of the structure and reduce the stress level of the tower.For the longitudinal diamond-type tower of Nanjing No.5 Yangtze Bridge,when the length of the lower beam of the tower increases,the longitudinal stiffness of the cable tower decreases,and the lateral stiffness changes are not obvious.The increase of the length of the lower beam can effectively reduce the internal seismic response of the tower.Considering the deformation and stress of the structure under earthquake,the longitudinal partial restraint system is suitable for the cable-stayed bridge.