Research On The Influence Of Additional Constraints In Push-out Test On The Bearing Mechanism Of Perfobond Shear Connectors

Perfobond shear connectors are widely used in steel-concrete composite structures because of their simple construction,high shear bearing capacity,good ductility and excellent fatigue resistance.However,since the existing literature does not consider the difference between the actual restrained state of the test piece and the combined structure,the results of the calculation formulas of the bearing capacity of the perfobond connector proposed by the researcher are quite different.In order to clarify the influence mechanism of constrained reinforcement and contact friction between the test piece and the test pedestal,this paper carried out the launching test and numerical analysis,and proposed the calculation method of the bearing capacity of the perfobond connector considering the influence of the additional constraint.And the results are as follows:(1)The difference between the commonly used perfobond specimen and the actual composite bridge perfobond connection structure was analyzed.Taking the presence or absence of constrained steel bars and the contact friction between the test piece and the test bench as the main parameters,3 sets of 9 perfobond test pieces were designed and produced.Monotonic static loading was used to launch the test,and the study showed that additional constraints such as constrained steel bars and friction between the test piece and the test pedestal have obvious mechanical behaviors such as the failure mode of the perfobond connector,steel bar strain and load-slip curve.influences.The two have successively increased the ultimate bearing capacity of the connector by 19% and 29%,and the friction force at the bottom of the test piece has improved the rigidity and ductility of the connector more significantly.(2)A refined finite element analysis model was established for the launch test,and the effects of the diameter,position,and contact friction coefficient of different constrained steel bars on the mechanical behavior of perfobond shear connectors were simulated and analyzed.The research shows that additional constraints affect the penetration of the steel bar and concrete tenon The shear,bending,tensile and compressive bearing capacity of the concrete are improved to different degrees,and the upper and lower connectors are slightly affected;the ultimate bearing capacity of the connector increases with the height,diameter and bottom contact friction coefficient of the constrained steel bar to the concrete surface Large and increased;constrained rebar and contact friction have obvious constraints on the stress and deformation of the concrete in the adjacent area,inhibiting the lateral shear deformation of the concrete tenon,and thus improving the bearing capacity of the perfobond connector.(3)Establish and simplify the calculation model of the bearing capacity of the perfobond connector,analyze the constraint mechanism of the friction force between the steel bar and the bottom of the specimen in the connector,and determine the form of the influencing parameters of the two through the action of bending moment and contact friction.Based on the existing research results,the formula for calculating the ultimate bearing capacity including the influence of the parameters of the transverse restraint steel,the coefficient of contact friction,the size of the opening,the thickness of the opening steel plate,the strength of the concrete,the size and strength of the penetration steel bar,and the main literature The calculation formula is better than the accuracy,and it has a good reference value for predicting the bearing capacity of perfobond connectors considering the effect of additional constraints.