Tensile Behavior Study On Hollo-bolts

The tensile zone in semi-rigid connection with Hollo-bolts used may occur premature failure firstly and then resulting in lower reliability indexes of the whole structure,which can be attributed to the sleeve of Hollo-bolt may be cut off or the whole Hollo-bolt may be pulled out from the bolt hole when Hollo-bolt suffers to tensile load.Therefore,measures must be taken to improve the tensile behavior of Hollo-bolt.However,there are mainly two deficiencies in today’s researches and they show as follows:(1)Researches on improving the tensile performance of Hollo-bolt considering the bonding effect of concrete are limited to structure level,and there still needs some relevant research methods and experimental dates on improving the tensile performance of Hollo-bolt in direct tension when bonding effect of concrete were considered.Moreover,the mechanisms of Hollo-bolt modified by welding anchor reinforcements when embedded in concrete are also unknown.(2)Researches on Hollo-bolt used in T-stub connection mainly focus on the traditional T-stub connection,whereas there are few research reports on T-stub connection formed through two angle back-to-back.What’s more,necessary experimental and theoretical studies on the tensile performance of Hollo-bolt in T-stub connections which influenced by variables such as the bonding effect of concrete,thickness of the Angle.etc are still seriously lack.To this end,with great engineering significance,the tensile performance studies of Hollo-bolt were carried on both component level and structure level respectively in this paper.Additionally,the main theoretical and experimental research methods and results based on the above research insufficient were listed as follows:Firstly,this paper employs the bonding effect of concrete to improve the tensile behavior of Hollo-bolt with new device for pulling out tests used and the experimental variables mainly include bolt type,concrete strength grade and without or with the filling of concrete into tubes.etc.Furthermore,tests mainly examined the tensile response of Hollo-bolts,including the stiffness,strength,ductility and fracture energy,with emphasis on the bonding effect of concrete.The result shows that the tensile performance of modified Hollo-bolt considering the bonding effect of concrete was approximately close to or even superior to that of a standard bolt in the same grade.Secondly,fifteen Finite element(FE)models of Hollo-bolts under axial tension were done by using finite element software ABAQUS.The accuracy and reliability of FE models were verified by comparing with experimental results and reference test results,which has made good preparations for proposing Tri-Stiffness Models in the latter chapter.Thirdly,Mechanism analysis on Hollo-bolt Type A,Type B and Type C were proposed based on the relevant research of the university of Nottingham.Meanwhile,according to stiffness principle of spring in series and parallel,quantitative analysis about stiffness contribution of sleeve,center shank,anchor reinforcements and concrete was given based on component method respectively.What’s more,on the basis of existing researches on bolt stiffness,Tri-Stiffness Models for Hollo-bolts Type A,Type B and Type C were proposed and verified based on a large number of finite element simulations and the result shows that Tri-Stiffness Models for Hollo-bolts can be used for stiffness prediction in engineering structure.Lastly,seven specimens of T-stub connections to CFST columns under static tensile load have been done,where the T-stub connections newly formed by Angles.Failure modes,tensile load-displacement relationships and strain-time curves in the key place of T-stub connections were recorded in this test.Additionally,mechanism and the influence regulations of bolt type,thickness of the steel tube column wall and thickness of the Angle.etc on T-stub connections were also predominantly explored in this paper.