Investigation On Shear Performance Of Flexible-sleeves Composite Perfobond Strip Connectors

The steel-concrete composite beam is usually composed of upper concrete slab and lower steel beam,which can give full play to the respective mechanical properties of steel and concrete materials.Therefore,steel-concrete composite beams have broad application prospects in the field of bridge engineering.In order to ensure the synergistic force between the concrete slab and the steel beam,the good shear performance of the shear connection between the two interfaces is very important.The perfobond connector（Perfobond Leiste,PBL for short）is a new type of shear connector that resists external loads by transverse rebars and concrete dowels in the perforated plate holes.PBL has the advantages of high bearing capacity and good fatigue resistance,so it is favored in the construction of steel-concrete group（mixed）bridges.In recent years,with the deepening of the research on PBL,the disadvantages of rigid shear resistance caused by excessive initial stiffness have gradually emerged.Aiming at the optimization of the mechanical properties of PBL,our research group proposed a composite PBL with flexible sleeves around the transverse rebar to reduce the early stiffness of the connector,and the single-hole push-out test confirmed the good stress-deformation performance of the connector.On the basis of the previous research,this thesis aims at the uneven shear phenomenon caused by the porous arrangement of PBL in engineering practice,combined with the project of the Natural Science Foundation of Guangdong Province "Research on the flexural performance and design method of fabricated high-strength steel-UHPC composite beams"（No.2020A1515011355）,through the introduction of test,numerical simulation and theoretical analysis methods,the force transmission mechanism and shear resistance calculation of porous composite PBL are studied.The main research contents and achievements are as follows:（1）By summarizing the force transmission mechanism,failure mode,influencing factors and bearing capacity calculation method of conventional PBL,the key influencing parameters were clarified;Calculation formula for shear resistance of through reinforcement for bending-tension deformation.（2）The push-out test of 16 porous PBLs was carried out,and the effects of the number of holes,the thickness of the sleeve and the length of the sleeve on the shear resistance of the composite PBL were studied.The results show that: setting flexible sleeves around the through transverse rebars or increasing the number of holes in the steel plate can make the failure mode of the transverse rebars of porous PBL gradually change from shear failure to bending-tension failure;the flexible sleeve can make the force of each hole PBL tend to be uniform,and reduce the initial load non-uniformity coefficient of the key group;increasing the thickness of the sleeve can significantly improve the stiffness and ductility of the PBL,but it will reduce the bearing capacity of the connector;in addition,reducing the length of the sleeve will reduce the ductility of the PBL,but the bearing capacity will be reduced.Less affected.（3）The finite element calculation model of porous PBL was established,and the effects of concrete strength,diameter of transverse rebars,and diameter of openings on the mechanical properties of PBL were studied.The results show that increasing the concrete strength can significantly improve the shear stiffness and bearing capacity of the porous composite PBL,but reduce the ductility;increasing the diameter of the through-bar has little effect on the initial stiffness of the porous composite PBL,but the ultimate bearing capacity and ductility are significantly improved;Increasing the opening diameter can improve the shear stiffness and bearing capacity of the connector,but the ductility of the connector will decrease.（4）Based on the flexural-tensile deformation model of the transverse rebar,a calculation formula for the bearing capacity of the single-hole composite PBL considering the influence of the thickness of the sleeve is established;by introducing the porous reduction factor,the shear bearing capacity of the porous composite PBL is further given.formula.The results show that the calculation results of the proposed formula are in good agreement with the experimental results and numerical simulation results,and can be used for the calculation of the bearing capacity of the porous composite PBL.