The Study on Axial Stiffness Model of Aluminum Alloy Gusset Joints

In recent years,single-layer aluminum alloy reticulated shells are widely used in long-span spatial structures,and the most commonly used joint form is plate joint.The joints of single-layer reticulated shells bear both axial force and bending moment.At present,most of the existing research results focus on the flexural performance of plate joints,and there is less research on their axial performance.In view of the above research status,this paper takes the axial performance of plate joints as the research object,carries out compressive tests,and establishes the corresponding numerical analysis model.The comparison results of test and numerical simulation show that the axial load-displacement curve of plate joints includes four stages:elastic stage,bolt slip stage,hole wall bearing stage and failure stage.The load-displacement curves of the test and numerical simulation are consistent,and the failure modes are all along the bolt hole at the beam end.Obviously,the numerical model is very accurate and can be used for subsequent parametric analysis.The numerical analysis models of different bolt clearance,bolt preload and bolt quantity are established to carry out parametric analysis on the axial performance of plate joints.The results of parametric analysis show that:1) with the increase of bolt clearance,the load-displacement curve of bolt embedding stage basically coincides,the bolt slip distance gradually increases,and the axial stiffness of hole wall in pressure stage is basically consistent with the ultimate load.2) With the increase of bolt preload,the initial load in bolt slip stage gradually increases,the slip distance is basically unchanged,and the load-displacement curve of hole wall bearing and failure stage completely coincide.3) With the decrease of the number of bolts,the axial bearing capacity of plate joints decreases most obviously,the shear bearing capacity takes the second place,and the reduction of flexural bearing capacity is the smallest.In the equal strength design of joints,the number of bolts should be determined according to the principle of equal axial bearing capacity.On the basis of experimental research and numerical analysis,the axial stiffness model of plate joints is studied.According to the load-displacement curve obtained from test and numerical simulation,the multi broken line simplified model can be used to describe the deformation mechanism of plate joints under axial force.Then,based on the deformation and force transmission mechanism of plate joints under axial force,the calculation formula of multi broken line simplified model is deduced.Comparing the simplified model with the experimental and numerical simulation results,it is found that the simplified model is in good agreement with the experimental and numerical simulation results in the elastic stage,sliding stage and hole wall pressure stage.In the failure stage,the ultimate bending moment of the simplified model is slightly smaller than the test and numerical simulation results.It is obvious that the derived multi broken line axial stiffness model satisfies the accuracy and safety requirements at the same time.