Mechanical Behavior Of High Strength Bolts In T-stub Based On Moment Distribution

The T-stub connector is commonly used equivalent simplified unit in high strength bolted beam-column connection.In recent decades,scholars at domestic and abroad had established the basic theory of high-strength bolts T-stub connector by experiments and research,and had further discussed the impact of prying force on connection failure mode.The prying force increases the bolts' internal force,and reduces the bearing capacity of bolts,causing bending moment of the flange plate at the T-stub connector where bolts located.China,the United States and Europe countries have standard considering the effect of prying force,but the bolts are considered as axially loaded members,thus the moment of bolt is ignored.In this paper,the author makes deeply study on mechanical behavior of tensile bolts in T-stub by experiment and finite element analysis,based on that the bolt were yield by axial force and moment.In this paper,the experiment object is high strength bolted T-stub connector.Six parameters are changed to design seven samples,and they are: the diameter of bolt,the length of bolt,the pretightening force of the bolt,the flange thickness,the inner flange length and the outer flange length.The effects of different parameters on internal force of the bolt are obtained by tensile test.Research shows that the bending stress increases with the increasing of load,when yield,bending stress in total stress ratio can be more than 40%.The change of the size parameters can change the failure mode and the ultimate bearing capacity.The increase of thickness of the flange and bolt diameter can improve the bearing capacity.The increase of length of inner flange can reduce the bearing capacity and increase the prying force.The increase of length of outer flange and the bolts have little effect on the bearing capacity of bolts.The finite element software ANSYS is used to expand parameters to analysis 23 equal dimension solid models.The analysis results show that the prying force(the contact force between T-stub flange and bottom plate is an ubiquity distributed force in all samples,and the action point of prying force gradually detaches from the center of bolt with the increases of load.The bolt is in tensile-bending state subjected to bending moments.The arm of contact force and bolt's bending moment relate to the load of sample,diameters of bolt,thickness of flange,length of inner flange,length of outer flange and length of bolt.In this paper,a new model of T-stub connector is presented,and the calculation method of bolt's axial force and bending moment is proposed by calculating the arm of contact force and the moment distribution ratio.The results show that the calculated results of the fitting formulas considering the parameters are in great agreement with the finite element analysis results,and the results are proved to be safe and useful by comparing with calculation example.