Research On Seismic Vulnerability Of Irregular Concrete-filled Steel Tube Tied Arch Bridges

With the development of Expressway in our country,CFST arch bridge is widely used in long-span bridges.As an important part of transportation line,once the bridge is damaged by earthquake,it will not only directly affect the transportation capacity,but also cause incalculable economic loss.Therefore,it is necessary to study its seismic performance.In many anti-seismic theories,performance-based anti-seismic design uses reasonable anti-seismic performance objectives and anti-seismic measures to carry out anti-seismic design of bridges,which is of great significance for bridge design.In this paper,Jiuyin Road concrete-filled steel tube tied arch bridge across Beida River is used as the research background.Midas / civil is used to establish a finite element model,and incremental dynamic analysis method is used to study the vulnerability of bridge components.The boundary estimation method draws the vulnerability curve of the bridge system.The main research contents are as follows:(1)Introduce the theory of seismic vulnerability analysis and the method of establishing the vulnerability curve.At the same time,the principle of Incremental Dynamic Analysis(IDA)is explained,the process of seismic vulnerability analysis based on IDA method and the steps of vulnerability analysis of bridge structure are summarized.(2)Based on the research background of Jiuyin road crossing Beidahe concrete-filled steel tubular special tied arch bridge,the finite element model is established by MIDAS / civil,the dynamic characteristics of the bridge are calculated,and the damage criterion and damage index of the bridge are determined by calculation.The research shows that the out of plane stiffness of the arch rib is lower than in plane stiffness,so when designing this kind of arch bridge,we must pay attention to its lateral stability.The bridge has large torsional stiffness and good integrity.(3)Based on factors such as the site type at the bridge site and the natural vibration period of the structure,a series of seismic records were selected from the US PEER seismic database.Using the incremental dynamic analysis method,the IDA curve of the arch rib under the action of the cross-bridge earthquake is established.The seismic performance and the destruction process of the key section of the arch rib are analyzed in detail.The nonlinear dynamic time history analysis method is used to calculate the arch bridge.Seismic response,research on seismic vulnerability of bridge components based on the capability demand model.Studies have shown that: the key section of the arch rib has the best seismic performance,and the arch arch foot may be the first to break.The key section of the bridge structure shows that the bearing is the first to break,and the arch rib seismic performance Good,so the earthquake prevention of the support should be strengthened.(4)The series and parallel models were used to establish the arch bridge system analysis model.Based on the basic theory of system reliability,the fragility curve of the arch bridgesystem was calculated using the first-order limit estimation method and the second-order limit estimation method.Studies have shown that the damage probability of bridge systems is greater than the damage probability of a single component.Therefore,the traditional use of the vulnerability of components to evaluate bridge systems is unsafe.The vulnerability of the system based on the second-order reliability calculation is more accurate than that of the first-order reliability calculation.