Seismic Fragility Analysis Of Flying Pigeon Single Tower Cable-stayed Bridge

With the continuous pursuit of bridge aesthetics,many beautiful special-shaped cable-stayed bridges have been built in various countries in the world.In recent years,scholars have conducted in-depth studies on the seismic performance of cable-stayed bridges with conventional main towers,and yield fruitful results.However,few studies have been conducted on the seismic performance of special-shaped cable-stayed bridges.Therefore,based on a flying pigeon-type single-tower cable-stayed bridge,this dissertation adopts a numerical analysis method to carry out seismic vulnerability analysis.The main research contents are as follows:(1)An analytic model of a flying pigeon single-tower cable-stayed bridge is established.Based on the analysis results of dynamic characteristics,15 seismic waves are selected by the dual-frequency wave selection method.IDA analysis of longitudinal and transverse seismic waves and nonlinear time-history analysis of multiple seismic waves are carried out.The curvature and axial force distribution along the height direction of the tower and the control section for seismic vulnerability analysis of the main tower are obtained.(2)Considering the uncertainty of ground motion and taking PGA as the seismic intensity parameter,IDA analysis of 15 seismic waves in the longitudinal and transverse direction is carried out.Through regression analysis,probabilistic seismic demand models of longitudinal and transverse control sections with PGA as variables are obtained.(3)The section curvature is used as the damage index of the main tower and the transition pier.The moment and the curvature analysis of the control section of the main tower and the transition pier are carried out by using X-TRACT software.Based on the analysis results,the index values of each control section under different damage limit states are quantified.The relative displacement of piers and beams is used as the damage index of the bearing,and the index values of the bearing under different damage limit states are quantified according to the design parameters of the bearing.(4)Considering the uncertainty of material strength,a simplified analysis method is adopted to analyze the vulnerability of the main tower,the transition pier,and support based on the traditional reliability theory.The transcendence probability of each component under different damage conditions,and the vulnerable parts and damage sequence of the main tower,the transition piers,and the supports are obtained.The results show that the main tower of the flying pigeon single-pylon cable-stayed bridge is the most vulnerable to longitudinal seismic action at the variable section of the tower bottom.The section at the bottom of the tower is the most vulnerable to damage under the transverse bridge earthquake.Under the influence of longitudinal and transverse ground motion,the vulnerability of the main tower and transition pier is ranked as follows:the main tower > the side span transition pier > the middle span transition pier;Comparison of longitudinal and transverse bridge vulnerability of the main tower:longitudinal > transverse;Transition pier longitudinal and transverse bridge vulnerability comparison: transverse > longitudinal.