Experimental Study On Static Performance Of Shear Group Studs Between Concrete Slab And Steel Beam Of Assembled Composite Beams

Steel-concrete composite beams have a very wide range of strain in all kinds of buildings and bridge structures.With the rapid development of social construction industry,prefabricated composite structures emerge as the times require.The fabricated composite structure can reduce the field work and shorten the construction period in the actual construction,which has the advantages of "rapid construction" and "prefabricated assembly".In order to explore the influence of the size of assembled group nail shear key on its mechanical properties,the constitutive equation of a single group nail shear key was studied.Nine group nail shear key push out tests were completed by using the electro-hydraulic servo loading system.Using the finite element analysis software ABAQUS to establish the finite element model of the push out test of the composite beam group nail shear key,and analyze the mechanical performance of the group nail shear key in the whole loading process.Based on the test results and finite element analysis,the load slip curve of single assembled group nail shear key is segmented,and the expressions of each stage and key points of the slip curve are analyzed.The main work of this paper is as follows:1.Taking the group of nails(number of bolt rows)and construction methods(assembly and cast-in-place)as parameters,the push out test of four groups and nine group of nail shear keys was designed and carried out.The failure mode,interface slip,strain of steel and concrete,bearing capacity and other influencing factors of prefabricated group nail shear keys were studied.In particular,aiming at the difficulty of local slip distribution test,a slip test device with a minimum measuring distance of2 cm was developed,which was proved to have high resolution,accuracy and good practicability in the test.2.In the push-out test of prefabricated group nail shear key,the failure mode of the test piece is as follows: the pre cast concrete first appears cracks along the edge of the reserved hole,then develops about 45 ° diagonal cracks down along the corner under the reserved hole,and finally the bolt is cut.The load displacement curve and the load slip curve can be divided into three stages: elastic stage,plastic stage and plastic stage.The slip tends to decrease along the vertical direction.There is a local mutation in the section with stud connection,and the overall performance is "big at both ends and small in the middle".3.The shear bond of group nail is mainly made up of the bond force between stud,steel beam and post cast concrete.In the stage of elastic loading,most of the loads are concentrated at the root of the stud.The deformation of the stud is mainly bending deformation,and the deformation at the toe of the stud is the largest.Under the action of the bond force and friction force between the steel plate and the concrete,the post cast concrete is under the action of tensile force,and at the same time,the deformation occurs with the sliding of the interface between the concrete plate and the steel flange plate.In the elastic stage of load interface slip curve of assembled group nail shear key,most of the linear stiffness is determined by studs,and a few of them are determined by concrete.The more the number of studs,the greater the contact surface between post cast concrete and steel beam,the greater the linear stiffness.The shear capacity of single nail of assembled group nail shear key is rs-157 kn,rs-259 kn and rs-360 kn respectively.4.In the monotonic loading process,the cast-in-place concrete slab basically has no crack compared with the fabricated concrete slab,which has better integrity,stronger binding effect on the stud,and the stud is closer to the pure shear state.The more favorable the stud is to bear the force,the larger the volume of the steel and concrete contact surface of the cast-in-place push-out specimen,and the greater the shear rigidity of the interface.This is because in the actual loading process,the stud can be seen as a cantilever beam.Because of the construction reasons,there is a certain gap between the prefabricated concrete plate and the steel beam surface in the test piece pushed out by the assembled group stud shear key,which increases the force arm of the stud,which is adverse to the stud’s force.The stud is more likely to occur shear failure,which reduces the shear bearing capacity.The assembled group stud shear force The shear capacity of key interface is lower than that of cast-in-place group nail shear key interface.5.In order to analyze the whole process of load interface slip curve of assembled group nail shear key,and further help to complete the derivation of load interface slip constitutive model of single group nail of assembled composite beam,The finite element analysis software was used in this paper to carry out the numerical simulation of the typical push out test of assembled group nail shear key.The calculated results are compared with the experimental results,and they are in good agreement.6.Based on the study of the geometric characteristics of the load slip curve of the shear key,the interface slip constitutive curve is segmented.By studying the important parameters of load interface slip curve of single assembled group nail shear key,based on the typical form of constitutive curve,the expression of each parameter is put forward,and the constitutive equation of load displacement curve(slip curve)of single assembled group nail shear key is finally established.Its advantage is that the form of group nail shear key is determined,and the elastic shear resistance of shear key can be directly obtained without test The results show that the difference between the calculated value and the test value the agreement is good.