Study On Influence Caused By Bolt-connection Defect On Mechanical Properties Of Bolt-ball Joint

As one of the most frequently-used node forms in large span space structure,the bolt-ball joint has been applied widely in engineering for a series of advantages,including suitability for industrialized production and great installation efficiency.However,due to the possible processing deviation and large quantities of connective components,construction deficiencies are prone to occur during the installation procedure,such as installation eccentricity and screwing-length insufficiency of high-strength bolt.Also,these defects have negative effects on the mechanical properties of joints and their connecting members,bringing hidden problems to the structural safety.Therefore,the mechanical properties of the bolt-ball joints and their jointing element with installation defects are deeply studied in this thesis,which provides a great reference significance to understand and assess the safety performance of such structures.Hence,aiming to the main bearing model of bolt-ball joints and their connecting rods,the research contents are as follows:1.Simulation analysis of bending resistance under the consideration of screwing-length defectUtilizing the established finite element model of threaded bolt-ball joints,the screwing-length variation is simulated by changing the number of thread engagement,and this simulation method is verified through existing experimental data.On above basis,the bending resistance of three kinds of common joints,namely,M20,M24 and M27,are simulated under different screwing lengths,obtaining the key mechanical indexes such as moment-rotation curve,initial rotational stiffness and ultimate bending moment under different conditions.Besides,the changing law of these indexes over screwing-length is found out,therewith,the bending mode and failure mechanism of bolt-ball joints under various screwing-length defects are also given.2.Experimental research on tensile property under the consideration of screwing-length defectBased on the detailed experimental design with insufficient screwing-length,the static tensile tests are carried out on three common joints(M20?M24?M27)under different screwing-length.By dint of the experimental phenomena and primary response indicators such as strain on critical positions and integrated deformation in the course of experiment,the vital performance indexes are obtained through careful analysis,including load-displacement curve,yield load and ultimate load under different conditions.Subsequently,the working mechanism and failure mode of bolt-ball joints under different screwing-length are explored,and the degradation law of the tensile strength along with insufficient screwing-length is offered.Furthermore,after performing an elaborate numerical simulation analysis,the validity of this method is demonstrated by comparing the simulative results with experimental data,which could be regarded as a technical reference for similar research on tensile performance of bolt-ball joints.3.Study on compressive bearing capacity of components with installation eccentricityIn order to investigate the influence of installation eccentricity on the bearing capacity of connecting elements,the compression test considering joints installation eccentricity is carefully designed,and the initial defects such as initial bending and initial eccentricity are measured in detail,hereby giving the assumption of initial defects distribution pattern of the test components.According to the compression tests on M20,M24 and M27 with installation eccentricity to varying degrees,the failure mechanism of the joint members with different eccentricity is revealed,moreover,the deterioration law of stable bearing capacity is also proposed.Finally,with the simulating and analyzing the compressive performance through a fine finite element model considering installed eccentric defects,the reliability of the simulation method is proved by results comparison between simulation and experiment,which provides a technical support for bearing capacity analysis and safety performance assessment of space steel structures with installed eccentric defects.