Study On The Deterioration Mechanism In Mechanical Properties Of Composite Beams Caused By Fatigue Damage Of Stud Connectors

The steel-concrete composite beams take advantage of materials' properties,convenient to construct,has been widely used in bridge engineering.Stud connectors are usually welded on group on the flange of steel beam.Longitudinal shear force at the interface between steel and concrete is not evenly distributed among these shear connectors.Under fatigue loading,the slip increases,which reduces the shear stiffness of stud connectors and redistributes longitudinal shear force.The above process develops with the increasing number of fatigue loading.It is observed that the slip between steel beam and concrete deck increases,so does the deflection of composite beams.The major contents and conclusions of my work are summarized as follows:1.The fatigue test of three composite beams was carried out to investigate the fatigue mechanism and fatigue damage process of composite beams characterized by the failure of shear connectors.Results shows that fatigue life of composite beams is sensible to fatigue load,both the range and the peak load;Based on the deflection of composite beams and the evolution in the shear stiffness of the group of shear connectors,the fatigue damage process of composite beams characterized by the failure of shear connectors can be divided into three stages;The degradation in the shear behavior of the group of shear connectors is coupled with the fatigue damage of single shear connectors;The deflection of composite beams does not always reflect internal fatigue damage.2.Considering the nonlinear load-slip relationship of stud connectors,based on the correlation of load and slip at the interface,the "non-continuous shear transfer" model is established.The model programmed by MATALB is capable to calculate load and slip of every stud connector.Results are in good agreement with numerical models.Coefficient analysis shows that increasing the shear stiffness of steel-concrete interface can improve the stiffness of composite beam,but has its limit.3.Based on the development of slip after cyclic loading,the stiffness degradation model of stud connectors is brought into the "non-continuous shear transfer" model,to analyze the redistribution of longitudinal shear force and the stiffness degradation of composite beams after cyclic loading.Results show that the fatigue loading not only reduces longitudinal shear force but also redistributes it more evenly;the deflection of composite beams increases almost linearly with the increasing number of cyclic loading.