Seismic Vulnerability Analysis Of Semi-floating Cable-stayed Bridges Based On PSDA

With the improvement of China’s infrastructure construction,the use of various highway bridges and railway bridges is becoming more and more extensive,which plays a pivotal role in the transportation work of modern society.However,China is a country with frequent earthquakes,and when an earthquake occurs,the destruction of bridges will directly affect traffic traffic,causing unpredictable losses.Therefore,it is necessary to conduct seismic analysis of bridges,cable-stayed bridges belong to high-order super-static structures,and the structural response is complex under seismic load,and the post-earthquake damage assessment of cable-stayed bridges is of great significance to ensure the performance of the structure and post-earthquake disaster relief.Through the seismic vulnerability analysis of bridge structures,the damage degree of bridges can be predicted from the perspective of probability,which provides a certain theoretical basis for subsequent maintenance and reinforcement.Taking a semi-floating cable-stayed bridge in southwest China as the research background,this paper analyzes the seismic vulnerability of cable-stayed bridges under the framework of"performance-based earthquake engineering"proposed by the Pacific Earthquake Engineering Research Center in the United States,and establishes the seismic vulnerability curve of cable-stayed bridges by studying the probabilistic relationship between structural seismic demand and ground motion parameters（PSDA）.The main work is as follows:（1）Establish a finite element model using Open Sees software to conduct detailed simulation of cable-stayed bridge components,and use Midas Civil finite element software to verify the natural vibration characteristics of the model.Select the ductile curvature ratio of the bridge tower and pier column respectively（μ_φ）"And the maximum displacement of the support(D_max)are engineering requirements parameters.Through moment-curvature analysis of vulnerable sections of bridge towers and piers,the indicators of the control section under different damage limit states are quantified.".（2）The seismic probability demand analysis of the cable-stayed bridge is conducted.Using the maximum seismic peak acceleration（PGA）as the ground motion intensity parameter index,100 natural seismic waves were selected based on the site characteristics of the cable-stayed bridge to consider the uncertainty of the seismic load.At the same time,the Latin hypercube random sampling method was used to consider the uncertainty of the structure itself and generate 100 ground motion structure sample pairs,After conducting nonlinear time history analysis on each sample model,the seismic probability demand model of the bridge is obtained through linear regression analysis.（3）Conduct seismic vulnerability analysis for cable-stayed bridges.Based on structural damage assessment and seismic probability demand analysis,seismic vulnerability curves of bridge components in the longitudinal and transverse directions are established,and comparative analysis is conducted to determine the sequence of damage of bridge components under seismic loads.（4）Establish seismic vulnerability curves for structural systems.Based on the characteristics of cable-stayed bridges,a system structural system model is established.According to the system reliability theory,the first order limit estimation method is used to establish and compare the seismic vulnerability curves of the longitudinal and transverse directions of the cable-stayed bridges.（5）Conduct seismic vulnerability analysis on the isolated system cable-stayed bridge.Using friction pendulum isolation bearings to replace ordinary sliding bearings of cable-stayed bridges,the effect of isolation bearings on structural seismic vulnerability was studied.Seismic isolation bearings can significantly improve the seismic vulnerability of bridge piers and tower components in both the longitudinal and transverse directions,effectively reducing the probability of different damage to bridge towers and piers,but at the same time increasing the relative displacement of the bearings,increasing the risk of damage to the bearings.