Seismic Response Analysis Of Irregular Structure In Urban Grade Separation

Limited by the road alignment and the pursuit of beautification of the structure, theprofiled wider multi-room box structure are often used in the bifurcation junction by whichthe main bridge leading to the ramp in the viaduct project and interchange projectconstruction in the city. These irregular bridges are generally constructed of straight bridgeand curved bridge, which are combined in various ways based on the route trend. In terms ofprevious earthquake damage, the curve bridge suffers more, compared with the curve bridge,the irregular bridge is more complex in structure and character of external force, thus,anti-seismic research of it is of great significance.This paper carried out the analysis of urban interchange profiled bridge dynamiccharacteristics, response spectrum and nonlinear time history based on the engineeringbackground of an irregular bridge of Shenan Bridge in Lanzhou City. Focus on the impact onthe dynamic characteristics and seismic response of the bridge caused by different modelcategory and the boundary condition of ramp bridge. The paper suggests the principle ofselecting local model for seismic calculation of irregular bridges commonly used in theinterchange projects.The main research contents are as follows:(1) Briefly described the overview of the development of the urban interchange arbitrarybridge and damage characteristics, concluded the current status and problems of the seismicstudy of the urban interchange profiled bridge.(2)Based on the engineering background, the paper established the finite elementanalysis model of single beam and grillage of the upper structure,discussed the influence ofdifferent model categories, as well as the boundary conditions of ramp bridge in the the urbaninterchange arbitrary bridge on the dynamic characteristics.(3)Carried out the response spectrum analysis of single beam model and grillage modelrespectively, analysised the difference of two models under the elastic seismic response.Reasonable aseismatic analysis model of irregular structure in urban grade separation is putforward. The shortcoming of single beam model was pointed out.(4)Carried out response spectrum analysis of grillage model that connects different unionnumber of ramp bridges, and the influence on the seismic response of the mainline bridgecaused by union number of ramp bridges are analyzed. According to the analysis results,andcombined the different orientation of ramp bridge constraints, a reasonable calculation modelwas determined eventually.(5)Using the0°~180°rotating input method, carried out the response spectrumunidirectional drive analysis of the reasonable calculation model determined in the former sections, discussed the most unfavorable earthquake input direction of irregular structure inurban grade separation.(6) As for the practical background engineer of this paper, a lead rubber bearing modelwas set up, non-linear time history analysis was carried out, and compared with ball shapedsteel bearing in the design. Shock absorbing effect of lead core rubber support model toirregular structure in urban grade separation was studied.