Seismic Fragility Analysis Of The Long-span Deck Steel Truss Arch Bridge

The seismic activity in southwest China is frequent and strong,and the topographic and geological conditions are complex.The arch bridge has become one of the main bridge types in this area because of its advantages.The seismic response of long-span arch bridge is affected by high-order mode and vertical ground motion,which makes the seismic response more complex and the plastic zone is not clear enough.The results of Wenchuan earthquake damage investigation show that the earthquake damage of long-span arch bridge is extreme.Once the damage occurs,it will seriously affect the rescue and reconstruction after the earthquake.Therefore,this paper uses the performance-based seismic design analysis method to analyze the vulnerability of a 1-490 m long-span steel truss arch bridge.This paper mainly studies the following aspects:(1)Based on the literature review at home and abroad,this paper systematically summarizes the development of long-span arch bridges,the seismic damage of arch bridges,the concept of seismic design and the research status of seismic vulnerability of bridge structures.(2)The main steps of seismic vulnerability analysis of bridge structures are reviewed and the seismic intensity index and seismic wave are selected.By referring to foreign codes,the failure criterion and damage index of steel structure in codes of various countries are detailed.(3)The finite element software Midas/civil program was used to establish the spatial finite element model of long-span through steel truss arch bridge,analyze its dynamic characteristics,and summarize the dynamic characteristics of the long-span through steel truss arch bridge.(4)Based on the hybrid element model of beam element and fiber element,the damage development process of the long-span deck steel truss arch bridge under the action of El Centro and longitudinal + vertical earthquake of safety assessment wave is analyzed by using the incremental dynamic analysis method(IDA),and the influence of the energy consumption of the upper arch column and arch rib on the seismic response of the whole structure under the action of earthquake is studied.(5)The nonlinear time history analysis of the hybrid beam element model is carried out by using the incremental dynamic analysis method,and the vulnerability curves of the main components(columns on the arch,chords on the arch rib)of the long-span deck steel truss arch bridge are obtained.Based on the theory of system reliability,the first-order limit method is used to calculate the system vulnerability curve of the arch bridge.