Research On Mechanical Properties Of Aluminum Alloy Reticulated Shell Gusset Joints Considering The Influence Of Axial Force

The gusset joint has become the most commonly used joint form in single-layer aluminum alloy reticulated shells,due to its simple construction and convenient installation.Based on the existing research,the theoretical analysis and experimental research were carried out mainly for the gusset joint under the combined action of axial force and bending moment.The simplified calculation formula of the composite bearing capacity of the gusset joint and the equivalent stiffness model reflecting the semi-rigid characteristics of this kind of joint were proposed.The influence law of the semi-rigidity joint on the stability of the single-layer aluminum alloy reticulated shell was explored based on the stiffness model,and the corresponding design method was proposed.The main research findings are as follows.(1)The damage mechanism of the gusset joints was investigated by conducting axial compression and flexural tests.The axial compression specimen was crushed at the outermost bolt hole,and the flexural specimen showed fan-shaped tearing at the tensile side cover,which verified the validity of the analytical model.The results of the parametric analysis of the joints showed that increasing the preload of the bolts can significantly improve the anti-slip load,with an average increase of about 60%,and the influence of the change of bolt number on mechanical properties in axial compression was significantly higher than that of flexural case.According to the analysis results of the numerical model bearing composite load,the simplified calculation formula of composite bearing capacity was fitted,and its correlation coefficient was greater than 0.99,which indicated that the fitting accuracy of the formula was high.(2)In order to reflect the compression-bending composite working condition of the gusset joint,the numerical models were analyzed under one-way eccentric loading and reciprocal loading respectively.When one-way eccentric loading,the axial load capacity of the joint decreased with the increase of eccentric distance,with an average decrease of 18.45%;the flexural load capacity increased with the increase of eccentric distance,with an average increase of 16.98%.At the same time,the eccentric distance led to an obvious two-stage bolt slip phenomenon in the moment-angle curves.When reciprocating eccentric loading,increasing the eccentric distance caused the maximum energy dissipation area of the joint in bending resistance to increase significantly,with an average increase of about 40%,and the bearing capacity of the joint decreased by 5.42% on average compared with one-way loading.The loaddisplacement curve overlapped with the corresponding skeleton curve,but the moment-angle curve deviated less from the corresponding skeleton curve in the failure stage.(3)The calculation method of equivalent stiffness model of gusset joints was proposed according to the principle of stiffness and bearing capacity equivalence.The average errors of the equivalent stiffness model and the numerical model of eccentric loading for bearing capacity and stiffness were 3.49% and 2.99% respectively,the average error of the equivalent stiffness model and the low cyclic loading test for bearing capacity was 4.6%,and the hysteresis curves of both were in good agreement.The results of parametric analysis showed that the influence of the equivalent area length on the out-of-plane bearing capacity of the joint was small;while the increase of the arching height and the support stiffness all made the out-of-plane bearing capacity and stiffness increase significantly.(4)Stability analysis of single-layer spherical reticulated shells with rigid and semi-rigid joints respectively showed that the stable bearing capacity of the semi-rigid joint model was reduced by 24.34% on average.Parametric analysis of the reticulated shell with semi-rigid joints showed that the stable bearing capacity decreased by an average of 16.59% with the increase of the equivalent area length;when geometric nonlinearity was considered,the stable bearing capacity decreased by an average of 10.08% with the increase of the initial geometric defects,and when material nonlinearity was considered,the decrease of the stable bearing capacity was significantly smaller than the result when geometric nonlinearity was considered.The analysis of a shaped reticulated shell in Hainan showed that the stability design method of single-layer aluminum alloy reticulated shells based on the equivalent stiffness model of semirigid joints proposed in this thesis simplified the design process by integrating the design process of semi-rigid joints into the overall calculation of the reticulated shell structure.