Seismic Response Analysis Of Long-span Cable-stayed Bridge

Cable-stayed bridge, a kind of flexible structure with high redundant degrees, has unique static and dynamic characteristics and carrying out refined seismic response analysis of long-span cable-stayed bridge is of great engineering significance for its service function and safety during an anticipated earthquake. The seismic behavior of Ed Yangtze River highway bridge, a long span semi-floating hybrid cable-stayed bridge with two towers and double cable planes, is investigated based on the anti-seismic research work that has been done domestic and abroad. Three dimensional finite element model is established based on the theory of finite element method, and the vibration characteristics and seismic response of the bridge are studied with the model. The main work in this thesis as follows:(1) The development of seismic analysis methods for bridge is expounded and the basic principle of response spectrum and time-history analysis method for bridge is introduced. Proper numerical calculating method is selected in order to solve the earthquake motion equations derived from structural dynamics.(2) Spatial finite element dynamic calculation model of the whole bridge is developed, using appropriate element type, according to the structural feature of the bridge by advanced analysis program ANSYS under two boundary conditions:with or without pile foundation. By analyzing and comparing the vibration characteristics of the two FEM models mentioned above, the vibration characteristics of long-span cable-stayed bridge are summarized, and the influence of pile foundation on the self-vibration characteristics of the bridge is reached.(3) By calculating the cumulative effective mode participation mass of the bridge, the minimum number of modes for response spectrum analysis is obtained. Design acceleration response spectrum is selected according to the site condition of the bridge to calculate the seismic response of the bridge under five load conditions, namely, longitudinal, transverse, vertical and the combination of horizontal and vertical and the seismic response of the bridge under two probabilities is also checked. (4) According to the site condition of the bridge, appropriate ground motion record is selected for the time-history analysis. Considering the geometric nonlinearity of long-span cable-stayed bridge, the nonlinear time-history analysis is carried out under uniform excitation. The effect of vertical component of earthquake excitation is discussed based on the calculating results.(5) The seismic responses of the bridge under different earthquake wave velocities are calculated to verify the influence of travelling-wave effect, which is one of the three main factors contributing to the spatial variation of earthquake excitations.