Research On Seismic Fragility Of Long-span Bridges Based On Monitoring Data

As the most important hub in a highway system,large-span bridges have made significant contributions to the economic and cultural development of the region.The past earthquake disasters have caused serious damage to the transportation,especially to the bridges.Therefore,the research of seismic fragility has an important significance for long-span bridges operation.Many studies have been conducted to investigate the seismic fragility of regular girder bridges,whereas only a few studies have focused on irregular cable-stayed and suspension bridges.Besides,the numerical models for the studies of theoretical seismic fragility were completely based on the design documents which could not accurately describe the static and dynamic characteristics of the on-site bridges.In this paper,Jiajiang bridge was taken as research subject,an initial finite element model was established by ANSYS.The initial finite element model has been revised based on the monitoring data,which was studied for seismic fragility in the longitudinal and transverse directions.The main content and innovation of this paper are as follows:(1)Identification of structural parameters of long-span bridges based on NexT-CMIF method has been realized.The static load test results revealed the deflection of the grider and the cable force of the sling.In the meantime,the environmental vibration monitoring data under the operating condition has been obtained by the bridge health monitoring system and processed by the Next method,which could get the frequency response function.The vertical bending modes of the main span girder and the cable forces has been identified based on the CMIF method and peak picking method.(2)Based on the pushover analysis,the failure mechanism of the tower and the damage index of the tower section have been studied,and the refined model of the tower has been simplified.Based on the design drawings,the initial finite element model of Jiajiang Bridge has been established by ANSYS.The failure mode and damage index of the tower have been obtained through pushover analysis of The refined tower model.Then,taking into account the calculation time and convergence problems of seismic dynamic analysis,the simplified model of the bridge tower has been established combined with the results of pushover analysis.(3)The initial finite element model of Jiajiang Bridge has been corrected based on the combined staticdynamic correction method.Due to the properly simplification of the structural dimensions,material parameters and boundary conditions in the theoretical modeling,there is a large error between the initial finite element model and the on-site bridge structure.In order to establish a finite element model that meets the structural accuracy requirements and the static and dynamic characteristics of the on-site structure,the sensitivity parameter analysis has been done to determine the parameters which need to be modified.Then,the objective function has been setted up based on the static and dynamic characteristics of the on-site bridge test identification,the modified finite element model has been getted combined with the optimization analysis module of ANSYS.(4)The probabilistic seismic demand fragility analysis method based on finite element correction is proposed,and the seismic fragility of the transverse and longitudinal bridge directions has been analyzed by the corrected finite element model.In this paper,based on the site conditions and seismic fortification requirements of Jiajiang Bridge,50 seismic waves have been selected from the seismic wave database provided by the Pacific Earthquake Engineering Research Center,and the spectral acceleration SA has been determined the strength parameter of ground motion parameters.The time-history analysis of the longitudinal and transverse directions of the corrected finite element model has been carried out.The PSDA method was used to obtain the fagility curve of the longitudinal and transverse directions of the Jiajiang Bridge bearing and bridge tower.It is verified that there is less coupling between the vibration of the vertical bridge and the vibration of the transverse bridge of the self-anchored suspension bridge with longitudinally floating system.Meanwhile,it is found that the bearing is easier to damage than the bridge tower under earthquake,and the 12 th bearing is the most vulnerable under the action of seismic waves,followed by 7th,11 th,8th,9 th bearing.