Experiment Study And Mechanical Analysis Of Twin-PBL Shear Connectors’ In Steel-UHPC Composite Structure

For the steel-concrete composite structure bridge,shear connectors plays the role of transferring shear force,which is an important component to ensure the cooperative work of steel-concrete composite structure.Twin-PBL(Perfobond Leiste)shear connectors are widely used because of its high bearing capacity and convenient construction.However,in the long-term heavy traffic load and harsh environment,the mechanical properties of this type of shear connector degradation fast,poor durability and easy to crack and other problems,gradually become the focus of engineering and very difficult problems.To solve the above problems,ultra high performance concrete(UHPC)can replace or regular concrete.However,the ultimate shear capacity,failure mode and failure mechanism of twin-PBL shear connectors in UHPC materials are not clear,and there is no specification for reference.Therefore,based on the introduction of test and finite element analysis,the mechanical properties of twin-PBL shear connectors in steel-UHPC composite structures are studied.The main contents and results are as follows:(1)Based on the push out test,the effects of the diameter of the through reinforcement and the number of holes in the steel plate on the mechanical properties of twin-PBL shear connectors in steel-UHPC and ordinary steel-concrete composite structures are clarified.The results show that in the two composite structures,the diameter of through reinforcement and the number of steel plate openings have significant influence on the ultimate shear capacity of shear connector;compared with the ordinary steel-concrete composite structure,the ultimate shear capacity,ductility and shear stiffness of shear connector in steel-UHPC composite structure are better.(2)According to the bond failure curves and the failure characteristics of the specimens,the difference of the stress characteristics of the shear connectors in each stage of the two composite structures is discussed,and the calculation formula of the load slip curves of twin PBL shear connectors in the steel-UHPC composite structure is proposed.The results show that compared with the ordinary steel-concrete composite structure,the steel bars in the shear connector of steel-UHPC composite structure yield obviously,and shear failure is the main reason,the number of concrete cracks is less,the width is small,and the development is slow;the calculation formula of load slip curve proposed in this paper has higher accuracy and applicability.(3)Based on the theory of structural stress state,the initial failure load of twin-PBL shear connector in steel-UHPC composite structure is evaluated,and the reliability of this method is verified.The results show that the initial failure load is about 0.92 times of the ultimate shear capacity,which is in line with the definition of the design value of shear capacity in the code.(4)The software of ABAQUS is used to establishe and modifie according to the measured.On this basis,the influence of concrete strength and steel plate opening diameter on the ultimate shear capacity of twin-PBL shear connector is further discussed.Based on the test and finite element analysis results,a formula for calculating the ultimate shear capacity of twin-PBL shear connector in steel-UHPC composite structure is proposed.The results show that the finite element results are in good agreement with the experimental results;the diameter of steel plate opening has less influence on the ultimate shear capacity than the diameter of through reinforcement,the number of steel plate openings and the strength of concrete;the proposed calculation formula has high accuracy and strong applicability.(5)Based on the results of finite element analysis,the response surface method is used to optimize the design parameters of twin-PBL shear connectors,and the optimal design parameters considering the mechanical properties and economy are given.The results show that the response surface method can be used to optimize the design parameters of twin-PBL shear connector in steel-UHPC composite structure.Compared with only taking the ultimate shear capacity as the optimization objective,considering the mechanical properties and economy as the optimization objective,the ultimate shear capacity of the shear connector is reduced by about 5%,but the cost is reduced by about 12.4%.