Investigations On Tensile Performance Of Thread-fixed One-side Bolted Connections To Square Hollow Section Tube

Thread-fixed one-side bolts(TOBs)have a good application prospects in the field of beam to hollow section column endplate connection.Compared to other one-side bolts,the bolt hole for thread-fixed one-side bolts is drilled using a traditional magnetic drill first,then tapping threads on the hole wall.TOBs bolted endplate connection does not require special tools and techniques both in the factory manufacture andon-site installation.It also avoid the loss of pre-tension force.In this paper,a series of experimental and finite element analyses are carried out to investigate the tensile behavior of TOB bolted endplate connection to Square Hollow Section(SHS)column,and corresponding design method are proposed.Based on the component method proposed by EC3-1-8,it can simplify the analysis ofthe tension zone of the beam to SHS column endplate connection to a TOB bolted endplate connection to SHS column.Then,the tensile and bending behavior of beam to SHS column endplate connection can be studied.The results of static experiment on TOBs bolted connection with and without backing plates show that a total of five failure modes are observed,and two types of failure modes include special thread shear failure.Specimens show five failure modes:Failure mode I:Thread shear failure,Failure mode Ⅱ:Thread shear failure accompanied with bending failure of column wall,Failure mode Ⅲ:Bolt shank failure,Failure mode Ⅳ:Bolt shank failure accompanied with bending failure of column wall and Failure mode V:Complete bending yielding of SHS column wall.The TOBs are expected to possess sufficient strength and stiffness under the cooperation of the backing plates.Moreover,the brittle thread shear failure wcan be avoided by adding the backing plates.The effects of different parameters—the bolt diameter(d),the column wall thickness(tc)and the bolt guage distance(g)—on the yield strength of TOBs bolted connection are investigated.The results show that with the improvement of the above parameters,the yield strength of the connection is also improved.Then,a FEM is proposed to study the behavior of TOBs bolted endplate connection to SHS column under tension.The developed FEM could accurately predict the strength of the connection,and the load-displacement curve obtained from the FEM simulation is in good agreement with the tested curve.The parameter of the tube wall width which is not studied in the experiment is supplemented.It has been found that as the tube width increases,the yield tensile strength of the connectiont will decrease and the yield line pattern will change.Failure mode of the connection isrelated tobolt diameter to column wall thickness ratio ψwhen the material properties remain constant.When ratio ψ was between 2.46 and 4.91,the connection failed by mode I,hole threads shear failure.This law can help engineersavoid the possible brittle failures that include thread shear failure and bolt failure in the design.It can be ensured the threads on the column wall provided enough anchoring strengthwhen the thread length should be longer than 1.1 times of bolt diameter.Calculation methods of the tensile bearing strength of the TOBd bolted connection under different failure modes are giventhrough numerical analysis,and the predicted bearing strengths calculated by the ptoposed formula are compared with the results of experiments and simulations.The results show that the formula proposed in this paper can predict well the failure mode and yield strength of the conncetion.A new Dumbbell yield line pattern on SHS column wall is presented.The corresponding calculation method for calculating the yield bearing strength of the SHS column wall is obtained based on the principle of virtual work.The prediction values of the column wall yield bearing strength calculated by using the traditional Gomes model,Yeomans model and proposed analytical model are respectively compared.It can be seen that the proposed analytical model significantly improved the accuracy and stability of prediction.A more safe and reliable prediction of yield strength can be obtained using the proposed model.