| High-strength bolt connector has the advantages of tight connection,detachable and good fatigue resistance,which can be used not only for the assembled connection of concrete slabs and steel beams in the composite bridge,but also for reinforcement of existing bridge.It has been a hotspot in the research of shear connector in composite beam.However,there are few studies on high-strength bolt connector in composite beam at present,lacking complete theoretical system and calculation method to guide engineering design,which has greatly limited its application and promotion.Supported by National Key R&D project(2016YFC0701202),the mechanical properties of high-strength bolt connector were studied.The main research contents and conclusions are as follows:(1)Twelve high-strength bolt connector specimens were tested,and the effects of pretension and preset hole size on the shear performance of high-strength bolt connector were studied.The test results show that the load process of the connector can be divided into four stages: the friction transferring force stage,the slipping stage,the elastic stage of bolt transferring force and the elastic-plastic stage.The value of pretension does not greatly affect the ultimate bearing capacity although it does significantly affect the initial slip load.The size of preset hole plays the main control role in the slipping stage of the connector,when the preset hole size approaches the bolt diameter,the length of the slipping stage will decrease as well as the value of ultimate slip.(2)The influence of significant parameters on ultimate bearing capacity and ultimate slip of high-strength bolt connector were analyzed through finite element method,such as concrete strength,size of preset hole,friction coefficient of steel-concrete interface,and diameter,ultimate tensile strength,pretension of bolt.The results show that high-strength bolt is under the combinations of tension,bending and shear in test,and the ultimate bearing capacity of it is composed of shear performance of the connector itself and sliding friction between steel beam and concrete slab.The former is mainly affected by the cross-section area and ultimate tensile strength of connector,while the latter is related to the value of pretension and friction coefficient.The sliding friction will increase significantly with the increasing of pretension,while the shear performance of the connector will decrease at the same time.Therefore,when calculating the ultimate bearing capacity of the connector,the interaction between the tensile and the shear should be considered.The ultimate slip of the connector also consists of the deformation of the connector itself and the size of the preset hole,the former is determined by the size and ultimate tensile strength of the connector and the latter is linearly related to the size of preset hole in concrete slab and steel beam.Based on the existing test data and finite element analysis results,the formulas for calculating the ultimate bearing capacity and ultimate slip of high-strength bolt connector under combinations of tension and shear are proposed.(3)Based on the existing test data and the finite element analyses of high-strength bolt connector,the influence of pretension and preset hole size on the fatigue performance of connector were studied.The research results show that the fatigue life of the connector will increase with the increase of pretension,so in the actual project,we can appropriately increase pretension to avoid premature slip and fatigue failure of the connector.The increase of the preset hole size will cause the decrease of the fatigue life,so in the real project,the size of preset hole should be minimized to ensure the fatigue life of the connector,but in the meanwhile,to ensure easy installation of high-strength bolt connector,we can arrange appropriate preset hole size firstly,and then fill the hole through grouting. |
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