Collapse Mechanism Analysis Of Long-Span Continuous Beam Bridge Subjected To Strong Earthquake

With the continuous progress of bridge construction in the dangerous mountainous areas of the west,the requirements for crossing capacity of bridges are gradually increasing,which makes a growing number of long-span continuous beam bridges emerge.At the same time.Numerous earthquakes have happened in our country in recent years.There are frequent accidents in terms of bridge structure damage or collapse and so forth,which causes a series of severe casualties and huge amount of economic losses.The safety of long-span continuous girder bridge,especially the anti collapse ability under strong earthquake,has become an important factor for bridge construction in western mountainous areas.Therefore,it is of great significance to carry out the collapse analysis of long-span continuous bridge under strong earthquake and determine the critical state of collapse.This paper describes the research status of bridge collapse at home and abroad,and summarizes the key problems to be solved in the collapse analysis of long-span continuous beam bridge.Based on the strong nonlinear explicit dynamic analysis module of ANSYS/LS-DYNA,a three-dimensional finite element model of long-span continuous bridge is established.The nonlinear dynamic analysis(collapse analysis)of long-span continuous bridge under strong earthquake was carried out.In the process of nonlinear dynamic analysis,the influence of reinforcement strength and reinforcement ratio on pier damage is analyzed,and the influence of multi dimension of ground motion on collapse mechanism is analyzed.The main research work is as follows:(1)Based on the research results at home and abroad,the refined finite element model of long-span continuous girder bridge is established by using ANSYS/LS-DYNA explicit dynamic finite element program;(2)Based on the established calculation model,considering the impact of bridge collision,the whole process of multi span continuous beam bridge from elasticity,damage to collapse under earthquake is calculated and analyzed.The dynamic characteristics of the model under the action of unidirectional seismic wave and multidirectional seismic wave are studied,and the structural shape and internal force changes of the collapse of long-span continuous beam bridge in earthquake are explored;(3)The main collapse modes of long-span continuous girder bridges under strong earthquakes are as follows: the stress at the bottom of the fixed pier first reaches the maximum value and plastic hinge appears.Therefore,the fixed pier appears bending failure.With the aggravation of the failure,the vertical displacement of the fixed pier increases,resulting in the loss of support of the whole bridge,which is considered that the bridge has collapsed;The proposed damage index D can make a reasonable and effective evaluation on the damage state of long-span continuous beam model;(4)Based on the established calculation model,the effects of different reinforcement strength and diameter on pier damage are compared.Based on the damage index D,the influence law of the strength and diameter of steel bar on the dynamic response of bridge structure under earthquake is reasonably expounded.The research results can be acted as references for seismic design and anti-collapse measures of long-span continuous bridges.