Performance-based Seismic Fragility And Risk Analysis Of High Pier And Long Span Continuous Rigid Frame Bridge

With the continuous improvement of the transportation system,the construction of the western bridge across the deep trench canyon has also developed rapidly.Due to its has the advantages of strong spanning ability,good terrain adaptability and reasonable construction cost,the continuous rigid frame bridge has become the best bridge type for the western mountainous area to cross the deep trench canyon.China's existing seismic code is only applicable to piers below 40 m,while the height of continuous rigid frame bridge piers in western mountainous areas is far more than 40 m.Therefore,it is necessary to analyze the damage rules and seismic behavior of high-rise long-span continuous rigid frame bridges.It will promote the design and development of bridge structures in the western region.Based on a four-span high-rise long-span continuous rigid frame bridge in the alpine region,this paper uses the CSI Bridge large-scale finite element analysis software to simulate the bridge structure reasonably and accurately,and then the damage law and danger under the longitudinal and lateral seismic action of the structure were studied.And the risk has been carefully analyzed.The general content of this article includes the following aspects:(1)Based on reading domestic and foreign literature,the development of high-rise longspan continuous rigid frame bridge and seismic research are summarized,and the research trends of bridge vulnerability and risk based on performance considerations are introduced.The current research situation is introduced.(2)The performance-based seismic analysis method is introduced.Considering the particularity of the bridge,the performance index and damage index of the bridge structure are given,and the method of establishing the vulnerability curve are given.(3)Relying on a four-span high-rise continuous rigid frame bridge with a span of 75m+3×140m+75m,using Xtract software to analyze the bending moment-curvature of the control section,using curvature to quantify the damage of four damage states: minor damage,medium damage,serious damage and complete damage.Considering the inconsistency of the longitudinal and lateral main periods of the bridge structure and the uncertainty of the ground motion,10 adjusted actual seismic waves are input for incremental dynamic analysis,and the results are quadratic regression to obtain the regression required for vulnerability establishment.The seismic demand model with the Sa as the variable of each bridge pier section is obtained;(4)According to statistical knowledge,an expression of the earthquake vulnerability function is given.Based on the damage index of each key section and the seismic demand value under different intensity earthquakes,the seismic vulnerability curves of each key section are obtained according to the capacity demand ratio theory.The damage rules of the piers under the longitudinal and lateral earthquakes are further compared and analyzed.(5)On the basis of obtaining the seismic hazard curve of spectral acceleration Sa,the results of comprehensive vulnerability analysis are used to obtain the seismic risk function expression of the bridge structure.On this basis,the seismic demand risk of the high pier continuous rigid frame bridge is analyzed.Based on the current seismic fortification standards of highway bridges in China,the seismic performance of high-rise long-span continuous rigid frame bridges is accurately and effectively determined.The main research results and conclusions of this paper are as follows: under the action of longitudinal bridge,the damage probability and risk probability of the pier section of each pier are much larger than the pier bottom section,and the damage probability of the bottom section of each pier is to be affected by the transverse bridge.Far more than the top of the pier.According to the comprehensive analysis,the sensitivity of the short pier is greater than that of the high pier,which has little to do with the direction of the earthquake.Moreover,during the design reference period of the bridge structure,the probability of longitudinal risk damage is greater than the probability of lateral earthquake risk.The possibility of serious or complete damage to the pier is less than 5%,indicating that the bridge can be repaired and not collapsed after the earthquake.