Research On Shear Force Transfer Performance Of Cold-bent Thin-wall Steel Self-tapping Screw Connection

The method of cold-formed thin-walled steel reinforcement is a new method based on increasing the section area of cold-formed thin-walled steel.In order to fully achieve the reinforcement effect,the deformation between the new and old cold-formed thin-walled steel sections must conform to the assumption of a flat section,that is,the shear force can be completely transmitted between the new and old cold-formed thin-walled steel sections,And the new and old cold-formed thin-walled steel is connected by self-tapping screws to transmit the shear force.Therefore,the shear force transmission capability of self-tapping screw connection is the focus of this study.First,the shear resistance of cold-formed thin-walled steel single-screw connectors was tested to study the effect of different screw diameters and plate thickness on the failure mode,shear bearing capacity and shear stiffness of self-tapping screws.The results show that: The shear bearing capacity and shear rigidity of a single screw connector increase with the increase of the screw diameter and the thickness of the plate.Then,according to the load-deformation curve obtained by the experiment,a constitutive model of the shear stiffness of the self-tapping screw connection is proposed,and its constitutive equation is fitted;Finally,the method of combining the nonlinear spring element and the constitutive model in the finite element simulation analysis is used to verify the feasibility and effectiveness of the finite element simulation method.Then,the two methods of test and finite element analysis are used to study the shear transfer performance of single and multiple self-tapping screw connections,and the test results are compared with the finite element analysis to verify the correctness of the finite element model.Then the finite element variable parameters of screw end distance,screw diameter,plate thickness and length of reinforcement section are analyzed for the shear transfer performance of single tapping screw,the finite element variable parameter analysis of screw arrangement,number of screws and screw spacing for shear transfer performance of multiple tapping screws.The results show that: for asingle screw connector,the effect of the screw end distance is very small,and its shear force transfer value and shear force transfer stiffness increase linearly with the increase of the screw diameter,plate thickness and length of the reinforced section;The arrangement of screws is an important influencing factor.The shear force transfer value and shear force transfer stiffness increase non-linearly with the increase of the number of screws and the distance between screws,and have a "group strengthening effect".Finally,according to the analysis results of finite element variable parameters,the design calculation formula and construction measures are proposed for the shear transmission value of single and multiple self-tapping screws.