Fragility Analysis Of Tower Of Cable-Stayed Bridge Under The Interactions Of Earthquakes And Winds

The cable-stayed bridge has large span and high tower height,so earthquakes,winds and other disasters have brought great challenges to the safety of cable-stayed bridge.Multi disaster analysis has become the focus of cable-stayed bridge research.Taking the cable tower of a long-span cable-stayed bridge as an example,considering the influence of cable and main beam,the finite element model of cable tower is obtained through static and dynamic equivalence;The vulnerability method is used to analyze the seismic vulnerability and wind disaster vulnerability of cable tower;Considering the actual action mode of earthquake and wind,the influence of wind speed on vulnerability is considered as well,the longitudinal multi disaster vulnerability of cable-stayed bridge tower under the Interactions of Earthquakes and Winds is studied.The main research contents of this paper are as follows:(1)Taking the static and dynamic characteristics of the whole bridge model of cable-stayed bridge as a reference,the simplified model of cable tower is established by using equivalent stiffness method and additional mass method.The analysis shows that the dynamic response of the cable tower simplified model is basically the same as that of the cable tower under the whole bridge state.In order to improve the analysis efficiency,the vulnerability analysis can be carried out by using the cable tower simplified model.(2)Based on the vulnerability analysis method,the damage index of the cable tower is determined,the bending curvature of each section of the cable tower is analyzed by XTRACT to quantify the damage index,and then the vulnerability of each section of the cable tower is studied through OpenSees nonlinear time history analysis.The results show that under the action of 8-degree design earthquake,there is no obvious damage to each section of the cable tower,the exceedance probability of slight damage under rare earthquake is less than 15%,and the maximum is 44%under extremely rare earthquake.(3)Based on the harmonic superposition method,the fluctuating wind speed at different heights of the cable tower is simulated,transformed into the time history curve of concentrated force according to the code,and the time history analysis is carried out.The influence of wind speed on the displacement of the cable tower is studied,and then the vulnerability of the cable tower to wind disaster is analyzed.The results show that under the action of design reference wind speed,the damage probability of cable tower is very small,the maximum exceedance probability of slight damage is about 0.2%,and the cable tower will not be damaged by wind in the design state.(4)Through the nonlinear time history analysis of the cable tower of cable-stayed bridge under the interactions of design earthquake and wind,rare and extremely rare earthquake and wind speed in different return periods,its influence on the internal force and top displacement of the cable tower is studied,and the vulnerability of the cable tower under the interactions of earthquakes and winds is analyzed.The results show that the addition of wind load will increase the dynamic response of the cable tower,but its influence degree decreases with the increase of PGA,and the damage of the cable tower will be more serious under the interactions of earthquakes and winds;The higher the wind speed is,the greater exceedance probability of the cable tower under the interactions of earthquakes and winds,and the increment of exceedance probability increases with the increase of wind speed;Under the action of 8 degree rare earthquake,the exceedance probability of slight damage to the cable tower is 14.58%.When considering the interactions of earthquake and design reference wind,the probability is about 23%.The vulnerability of the cable tower increases significantly under the interactions of earthquakes and winds.