Design Method Of High Strength Bolts In T-stub Based On Increasing Prying Force To Consider Bending Moments

T-stub connector is a simplified form of tension joint in steel structure,which is combined with high-strength bolts as a typical analysis unit.Scholars have done a lot of research on it,established the basic theory of T-shaped connection assembly,and put forward the corresponding design method.However,domestic and foreign codes generally regard bolts in axial tension,which are subjected to additional force only by prying force without considering the influence of bending moment.The test shows that there is a bending moment that can not be ignored when the bolt is in tension,which should be considered in the design.In this paper,taking the high-strength bolts with symmetrical T-stub parts as the research object,four specimens were designed to carry out the uniaxial load tensile test of T-stub parts by changing the pretightening force,the length of inner and outer plate and other influencing factors.The experimental data show that:1)The bolt is indeed in a tension-bending state,and the ratio of bending stress to total stress can reach 32.68% when yielding,and the ratio of bending stress to total stress can reach 46.69% when members without pretension are yielded.Bending stress accounts for a relatively large proportion,which can not be ignored.2)Increasing the length of the outer plate can reduce slightly the proportion of bending stress,but it has little effect on the total stress,and increasing the pretightening force can reduce the proportion of bending stress.In this paper,the expanded parameter analysis is carried out by finite element software.The effects of the changes of thickness,length and width of T-stub parts on the internal force of bolts are discussed emphatically.The analysis shows that: Increasing the length of the outer plate has little effect on the internal force of the bolt,which is negligible.When the ratio of inner and outer plate length is 1,the bending moment of the bolt decreases during the decrease of the length of the inner plate.The axial stress and bending stress of the bolt will be reduced in the same load.It’s bearing capacity has been improved.When the thickness of the upper and lower flange plates of the T-stub parts is the same,the larger the thickness of the plate is,the weaker its bending ability is.The additional force(bending moment and prying force)becomes smaller.The axial stress and bending stress of the bolt decrease.When the thickness of the upper and lower flange plates of the T-stub parts are different,Under the condition of constant bolt stiffness,the stress of the bolt mainly depends on the thin plate.Increasing the width of the T-shaped flange plate can increase its stiffness,reduce the deformation,reduce the axial stress and bending stress of the bolt,and improve the bearing capacity of the bolt.The analysis shows that the thickness of flange plate of T-stub parts is an important parameter affecting bolt stress.Therefore,When designing T-stub connectors,It is suggested that under the same conditions,The size of the T-stub part is designed to be smaller in length of the inner plate,the flange plate is thicker,width and length of outer plate is structural requirements.The bending moment influence coefficient k is obtained through theoretical and numerical simulation method of combining in this paper.The thickness correction calculation method considering the influences of bending moment is proposed.It is proved that comparing with the current domestic codes,this method can avoid the problem of stress exceeding the limit of high strength bolts to a greater extent by the Case analysis,and the safety of engineering application is higher.On this basis,combed the design method and some feasible design suggestions are put forward.