Study On Fatigue Life Prediction Of Steel Structure With Steel-Concrete Composite Beam Bridge

Steel-concrete composite girder bridge has the advantages of good overall performance,fast construction speed,good economic benefits and beautiful appearance.It is a common bridge type for small and medium span bridges.The steel-concrete composite girder bridge is inevitably subjected to alternating external loads such as vehicle loads during operation.The supporting steel beam of concrete bridge deck is usually welded by steel plate,and high strength bolts are used to splice between beam sections.In the welding process,due to the influence of welding heat and other factors,there will inevitably be stress concentration and welding defects,and the initiation position of fatigue cracks is usually easy to occur at the stress concentration of these structural details.For continuous girder bridges,it is necessary to consider the stress response and fatigue life calculation of the negative bending moment zone under vehicle load.Therefore,this paper takes a steel-concrete composite beam skew bridge as the research object,uses the finite element software to establish its three-dimensional finite element model,carries out fatigue vehicle loading,analyzes the fatigue damage prone position of H-shaped steel beam and evaluates the fatigue life.Firstly,the key parameters such as the type,weight,axle load and wheelbase of the fatigue vehicles used in this paper are determined by consulting the fatigue vehicles in the specifications of various countries.Based on the actual engineering case,the geometric model and finite element model of the inclined bridge of the steel-concrete composite continuous beam are established.The finite element analysis is carried out on the two working conditions of the dead load and the dead load plus vehicle load during the operation period,and the stress and strain contours of the bridge deck and the steel beam under the corresponding load conditions are obtained.At the same time,the shear connection degree of the steel-concrete composite beam is calculated,and the failure mode and fatigue details of the steel-concrete composite beam bridge are determined.According to the calculation results and experience,the fatigue failure locations of the steel beam are selected,which are the weld between the stiffener and the web,the weld between the stiffener and the lower flange,and the weld between the web and the lower flange plate.The fatigue vehicle model in the ’General Specification for Design of Highway Bridges and Culverts’ is selected and the APDL command flow is written to load four typical transverse wheel load conditions on the continuous steelconcrete composite beam skew bridge.The stress history of the focus points at different working conditions and different positions is extracted,and the stress history with large stress response is counted by rain flow.The stress spectrum at the most unfavorable position is obtained,and the maximum stress amplitude and frequency in the stress spectrum are statistically analyzed.Finally,based on the nominal stress method,the fatigue damage calculation and fatigue life prediction are carried out at the most unfavorable position.The results show that under the fatigue vehicle load,the fatigue damage at the most dangerous point of the fatigue details on the No.1 main girder of the steel beam is larger,and the fatigue failure occurs first at the connection between the upper web and the lower flange of the No.1 main girder.