Study On The Mechanical Property Of Embedded Nut Bolted Connector In Prefabricated Steel-Concrete Composite Beams

Steel-concrete composite beams have been widely used in civil engineering because of their good mechanical properties,short construction period and comprehensive efficiency.The shear connector is a key component that directly affects the load-bearing capacity of the steel-concrete composite beam.Embedded Nut Bolted Connector(ENBC),as one of the important types of connectors,has the advantages of high resistance,high stiffness,tight connection,installable and demountable,and is a common connector for prefabricated steel-concrete composite beams.However,in the existing research,the mechanical mechanism of ENBC was not fully studied,so shear resistance of ENBC was not fully explored.The existing equations of connector were not suitable for estimating the shear resistance of ENBC,which restricted the promotion and application of ENBC.Therefore,in this study,the mechanical mechanism of ENBC were researched deeply,the embeded nut size was optimized.As a result,the shear resistance of ENBC was fully explored.And equations for ENBC design were proposed.Details as follows:(1)The valid mechanical model of ENBC was proposed.Based on the foundation beam theory,Cullen friction theory,metal cutting theory and Evans wedge tool cutting resistance model,the theoretical mechanical model of ENBC was established,and four distinct loading stages and the equations of shear resistance in each stage were proposed to reveal the mechanical behavior of ENBC,which remeded the shortage of existing research.(2)The mechanical mechanism of ENBC was revealed.Based on the push-out test results of 63 ENBC compostied specimens in 22 groups,the shear resistance,slip,loaddisplacement(L-S)curve,failure modes and steel-concrete surface image of the tested specimens were analyzed.The differences of the shear mechanical properties of ENBC,stud and HSFGBC were discussed.The effects of bolt diameter,ring width of embedded nut,pretension,concrete strength on the shear mechanical properties of ENBC were investigated.The micromechanical behavior of the steel-concrete composite surface was analyzed for the first time using image recognition technology,which verified the validity of the mechanical model and revealed the mechanical mechanism of ENBC.(3)The mechanical behavior of ENBC connectors and the composite beams was analyzed by finite element analysis.Using finite element analysis software ABAQUS,the valid finite element model of ENBC connectors was established to launch the parametric analysis of ENBC including the parameter of concrete strength,bolt diameter,embeded nut ring width and steel tensile strength of bolt.The finite element model of ENBC connectors in steel-concrete composite beam was established,and the the mechanical behavior and performance of ENBC in steel-concrete composite beams were analyzed.(4)The configuration of ENBC was optimized.Based on the mechanical mechanism of ENBC and the finite element analysis results,the recommended configuration of embeded nuts was proposed,which improved the shear resistance and shear stiffness of ENBC and stimulated the potential shear resistant porperties of ENBC.(5)A series equations for ENBC design were proposed.Based on the test results and finite element analysis results,a series equations of ENBC for design shear resistance,load-slip(L-S)curve,shear stiffness and slip were proposed considering bolt diameter,material properties,embeded nut ring width and pre-tension.