Research On Interface Shear Performance Of Stud Shear Connectors With Constrained Structure

Steel-concrete composite member is a new type of member composed of steel beams,connectors and reinforced concrete.Because it can take into account the advantages of steel structure and concrete structure,it exhibits better mechanical properties than steel structure and concrete structure,and has significant advantages.It has become another important component form after steel structure and concrete structure.However,the problem of concrete cracking exposed during the use of steel-concrete composite components will cause the reduction of the stiffness of the components,lead to corrosion of the reinforced steel beams,and seriously reduce the life and durability of the components,which has become an important factor restricting the development and application of composite structures.one.The causes of the cracks in the concrete slab of the steel-concrete composite structure are relatively complex.From the perspective of the unique mechanical performance of the composite structure,there are mainly the following two reasons:(1)the "shear-pry" connection of the concrete in the composite member is cracked by partial pressure;(2)the composite structure The concrete slab in the member cracks in tension.In view of the above two problems,this research group proposes two structural measures to solve.For the "shear-pry" partial pressure cracking of concrete stud connectors,a stud shear connector with constrained structure is proposed.Additional steel plates are used to help the concrete in the negative moment zone in tension.Among them,the stud connector with restraint structure has been verified by the push-out test to verify its excellent anti-splitting performance,and the mechanical properties of the stud connector with restraint structure and in the negative bending moment region are further verified by the interfacial shear performance test in this paper.The use of additional steel plates to help concrete in tension is feasible,and a comprehensive study of the interfacial shear performance of stud connections with restrained structures is carried out.The main work and research results are as follows:(1)The stud connector with restraint structure can restrain the crack within the range of6 d,which can give full play to the advantages of high compressive strength of concrete materials,and the shear stiffness of the stud in the interface shear performance test is not higher than that in the push-out test.The shear stiffness of the stud is significantly reduced,which proves that it is feasible to use additional steel plates to replace the concrete slabs and the tensile steel bars in them in the negative bending moment area.(2)The addition of hooks in the transverse reinforcement can increase the ultimate bearing capacity of the member by 12%,which is conducive to the development of the shear ductility of the interface,so that the member can better exert its ductility after entering elastoplasticity.In addition,the stud shear connector with restraint structure can reduce the amount of transverse reinforcement against longitudinal shearing and splitting in the existing "Standards for Design of Steel Structures" by more than 70%.(3)The restraint structure of carbon fiber cloth and spiral bars for the stud connector with restraint structure can improve the later bearing capacity and ductility of the component,but it has no effect on the early stress of the component.And the failure mode of the component can be changed by adopting the strength of the concrete slab matching the diameter of the stud.(4)The formula for calculating the shear stiffness of the stud is proposed,and the shear stiffness ratio-shear angle theoretical curve that can widely evaluate the material utilization efficiency and shear efficiency of studs with different length-to-diameter ratios is proposed,and the elastic shear stiffness of the stud is defined.The limit is the shear force corresponding to a shear angle of 0.01.(5)The stud connector with constrained structure can make the stud have higher material utilization efficiency and shear resistance efficiency,and the increase of the stud diameter under the same plate thickness will reflect the adverse effect of the shear prying effect.The shear stiffness of the stud should be corrected considering the influence of the length-diameter ratio of the stud.(6)The simplified calculation model and assumption of the stud connection with restraint structure are feasible,and the calculation formula of the elastic modulus Es and the shear bearing capacity of the single stud are obtained through the numerical simulation calculation results.(7)Under the condition of constant concrete strength,the shear stiffness ratio-shear angle curve of the stud is controlled by the length-diameter ratio of the stud.