Study On The Failure Mechanisms And Design Methods Of The Thread-Fixed One-Side Bolted Connection

The emergence of one-side bolts provides a new idea for solving the installation problems of square column to beam joints,which has broad application prospects in prefabricated buildings.Many types of one-side bolts has been designed.Among them,the thread-fixed one-side bolt anchors the bolt shank through the threads tapped on the inner wall of the bolt hole,thereby replacing the traditional nut and realizing the one-sided bolt tightening.Compared with other types of one-side bolts,thread-fixed one-side bolts do not require special bolts and installation tools,meanwhile this type of one-side bolts could save nuts.However,the current researches on its anchoring mechanism,failure characteristics,bearing capacity and optimization methods are still insufficient.Therefore,the in-depth analyses of the mechanical properties of joints fixed through thread-fixed one-side bolts and the design methods are of great significance to promote the application of this type of connection in actual engineering.In this paper,experimental researches,numerical simulations and theoretical analysis are carried out on T-shaped joints of square column connected by thread-fixed one-side bolts and joints with different strengthening methods.The main research contents and conclusions are summarized as follows:(1)The monotonic loading tests were carried out on four thread-fixed one-side bolted joints with different column wall thicknesses.The basic failure characteristics of the joints were obtained,as well as the effect of the thickness of column wall on the failure mode and bearing capacity of the joint.Finite element models(FEMs)consistent with the tested specimens was established,which were verified through the test results.At the same time,the whole process of the joint in tension,the thread anchoring mechanism,the failure law of the internal threads on the bolt hole wall was analyzed.Besides,the influence of the parameters such as bolt diameter,bolt spacing distance and column section width on the thread anchorage was studied.(2)For the joints failed by the internal hole thread failure,a calculation method of the thread ultimate strength was proposed,which considered both the bending failure and the shear failure of threads.For the joints failed by the column wall yielding accompanied with hole thread failure,based on the yield line theory and the virtual work principle,a method for solving the yield strength of the joint was established.At the same time,a calculation method for the thread ultimate strength considering the influence of the outer deformation of the column wall on the thread anchoring effect was proposed.Comparing the calculated strength with the experimental and numerical analysis results,it showed that the proposed calculation method could accurately predict the bearing capacity of the thread-fixed one-side bolted joints.(3)In order to enhance the thread anchorage effect,six column wall reinforcement methods suitable for this type of connection were proposed and tests and numerical studies were conducted on them.The basic failure modes of various reinforced joints were obtained.The effects of different strengthening methods on the bearing capacity of the joints were compared.The failure mechanism of various reinforced joints,the interaction between the reinforcement and the column wall,and the influence of the geometric properties of the reinforcement on the mechanical properties of the joint were all deeply studied.On the basis of parametric studies,the design goal is that the ultimate bearing capacity of the joint reaches the design value of the ultimate tensile strength of the bolt shank and the column wall has no large-scale plastic deformation.The overall evaluation of various strengthening methods and design suggestions are made.(4)Based on the results of experiments and numerical analysis,the influence law of various reinforcements on the yield form of the column was analyzed,and the calculation method of the yield bearing capacity of various reinforcement joints was proposed.The contribution of the bearing capacity of the threads on the bolt hole wall on the column wall and bolt hole wall on the reinforcement member to the ultimate strength of the joint is investigated.The calculation method of the ultimate strength of various reinforced joints was proposed.Comparing the calculated bearing capacity with the results of experiments and numerical simulations,it showed that the bearing capacity calculation method proposed in this study could be used to design the thread-fixed one-side bolted joints,and the calculated ultimate strength was conservative.