| UHPC is widely used in composite structures for its high-strength material properties.It is worth exploring how to improve the mechanical properties of structures,so as to guide the engineering design and application,as well as give full play to the structural usability and engineering value.Studies have shown that the strength of concrete is a significant factor affecting the mechanical properties of PBL shear connectors.Compared with ordinary concrete,the excellent mechanical properties of UHPC and other high-performance concrete change the failure behavior and mechanical properties of PBL shear connector embedded in it.Therefore,this paper takes structural test and finite element analysis as the main research methods to study the static performance and fatigue performance of PBL shear connector in UHPC.Six push-out specimens belong to two groups were carried out in this test,and the failure modes of the specimens were described.The force transmission mechanism of shear connector was obtained by analyzing the relationship among load,slip and strain in the process of loading.Finally,the static performance of several groups of specimens was integrated.Besides,the test values of bearing capacity were compared with those calculated by various formulas.The conclusions are as follows: Shear failure of the shear connector occurs through the steel bar,and the UHPC tenon in the core area is crushed;The stress process of two kinds of shear connectors can be divided into three stages: elastic stage,elastic-plastic stage and plastic stage;UHPC can increase the bearing capacity of PBL shear connector to about 2 times,meanwhile,the shear stiffness is more than 1.75 times.It is recommended to use the formula in JSCE to calculate the design bearing capacity of PBL shear connector in UHPC,and the formula proposed by He to calculate the ultimate bearing capacity.On the basis of experiments,the accuracy of nonlinear finite element analysis is verified.Moreover,the influence of structural parameters on the mechanical properties of shear connectors is studied by parameter analysis according to the orthogonal test method.The analysis results delicate that the influences of steel plate opening diameter,steel plate thickness and steel bar diameter on the design bearing capacity and shear stiffness of shear connectors decrease in turn;The diameter of steel plate and the thickness of steel plate are highly remarkable factors,and the influence of steel bar diameter on shear stiffness is greater than the design bearing capacity.The interaction between steel plate diameter and steel bar diameter can be neglected.The fatigue performance of PBL shear connector in UHPC was figured out via fatigue tests of 9 specimens.The fatigue life of the specimens under different loading conditions is compared,and the fatigue damage process of the shear connector is analyzed in combination with the dynamic change law of slip and the failure form of the specimens,thus the evolution law of shear stiffness of the shear connector is found.The conclusions are as follows: Load amplitude is the main factor affecting the fatigue life of shear connector,followed by load peak value;When the load amplitude is 0.4 times less of the ultimate bearing capacity and the peak value of fatigue load is less than 0.56 times the ultimate bearing capacity,the fatigue life of PBL shear connector in UHPC can reach more than 2 million times;The fatigue life of shear connector consists of two parts: the fatigue life of UHPC tenon and the fatigue life of through reinforcement;The fatigue damage process of shear connector can be divided into initial stage,development stage and failure stage;With the decrease of load peak and load amplitude,the proportion of initial stage and failure stage decreases gradually,and the proportion of development stage increases gradually.In the initial stage,the proportion is mostly less than 5%,in the development stage,the conventional proportion is between 85% ～ 90%,the proportion of failure stage is basically about 10%;Under fatigue load,the shear stiffness of PBL shear connector in UHPC will continue to decline,and the long-term stiffness presents a power function degradation law with the change of dynamic slip;The long-term stiffness of shear connector mainly presents two-stage linear degradation characteristics with the number of fatigue actions;The long-term stiffness degradation rate of shear connector in the initial stage decreases with the increase of load amplitude,and the long-term stiffness degradation rate in the development stage increases with the increase of load amplitude.The fatigue life of shear connector is evaluated by combining test data with fatigue crack propagation simulation.The fatigue life of UHPC tenon is concluded by the variation law of dynamic slip.In addition,the fatigue crack propagation life of penetrating steel bar is calculated by using the joint simulation technology of ABAQUS and FRANC3 D.Eventually,with good agreement,the fatigue life of shear connector obtained by combining them is compared with the test results,which proves the feasibility and effectiveness of the idea and method. |
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