Study On Mechanical Properties Of Stainless Steel-aluminum Composite Joints In Aluminum Alloy Tower Structure

In recent years,with the rapid development of communication,5G era has come,which puts forward higher requirements for the construction of communication infrastructure.The traditional communication tower is generally a steel structure.Still,in coastal and heavy pollution environments,the traditional steel structure is very easy to corrosion,resulting in the decline of bearing capacity and damage.In contrast,aluminum alloy materials have light and high strength and corrosion resistance.However,due to its unique chemical characteristics,aluminum alloy is not easy to weld,and welding strength reduction is more serious.Electrochemical corrosion will occur when connecting with traditional steel.Therefore,it is necessary to study the aluminum alloy tower structure joints.Based on an aluminum alloy three tube communication tower as the prototype,a new type of stainless steel-aluminum composite fabricated joint is proposed,aiming at the aluminum alloy material is not suitable for welding and the welding deformation is significant.Its full-scale test and finite element analysis are carried out to explore its mechanical response,ultimate bearing capacity and failure mode under tension and compression load.Based on the numerical simulation,the new joint angle aluminum gusset plate and the joint’s connection properties are studied.The parametric analysis is carried out to study the influence of the sleeve thickness and length on the joint’s mechanical properties.To explore the influence of diameter thickness ratio on the ultimate bearing capacity of aluminum alloy single tube tower,the ultimate bearing capacity of aluminum alloy single tube tower with different diameter thickness ratio was studied by numerical simulation:（1）Stainless steel-aluminum composite joint design.Three kinds of stainless steel-aluminum composite joint connection schemes are proposed,and the finite element models are established,respectively.The mechanical responses of the three joint connection schemes under the design load are obtained by applying the tension and compression design load cases.The analysis results show that the stainless steel sleeve external joint can ensure the upper and lower aluminum alloy main pipe work together,and each part’s stress is more reasonable.Therefore,this kind of joint is selected to arrange the connection form and size of each part of the tower structure node reasonably,and the rationality of the connection form is verified by theoretical calculation.（2）Test and numerical simulation analysis of stainless steel-aluminum composite joints.The mechanical response,ultimate bearing capacity,and failure mode of four joints under tension and compression load are obtained by refined finite element analysis.By using the self-designed loading frame,the full-scale tests of TA and TC joints are carried out,and the mechanical responses of each part of the joints under the tensile design load are obtained.The test results and finite element results are compared and analyzed.The results show that the test results and finite element results are better,and the accuracy of finite elements is verified.（3）Joint connection properties and joint parameterization analysis.TC joints are selected to analyze the properties of angle aluminum profile-gusset plate connection and overall connection by using finite element software,and the moment rotation curve of joint connection is obtained.For angle aluminum-gusset plate connections,considering the axial force of the angle aluminum profile,bolt preload,and end restraint of the angle aluminum profile,the moment angle curve is closer to that of a hinge joint.For the whole joint,it can be seen from the moment rotation relationship that the overall joint connection belongs to the obvious semi-rigid connection.The TC joint is selected for parametric analysis.With the increase of the sleeve thickness,the ultimate tensile capacity of the joint is increasing.The prototype joint’s ultimate tensile capacity is about1.6 times the design load,which has met the design requirements.It is not significant to continue to increase the sleeve thickness.The results show that the joints’compressive load-displacement curves with different sleeve thicknesses have the same trend,and the sleeve thickness has little effect on the joints’ultimate compressive capacity.With the increase of sleeve length,the ultimate tensile bearing capacity difference is less than 5%,while the ultimate compressive bearing capacity is the same.which indicates that the sleeve length has little effect on the ultimate tensile and compressive bearing capacity of the joint,and the bolt spacing length specified in the code can be met in the design.（4）Bearing capacity analysis of aluminum alloy single tube tower.The model of aluminum alloy single tube tower with diameter thickness ratio between 40 and 150 is established.Considering the influence of material nonlinearity and geometric nonlinearity,the linear elastic analysis,and nonlinear ultimate bearing capacity analysis are carried out.A single tube tower’s mechanical properties under the combined action of wind load and vertical load are obtained.Then the relationship curve of diameter-thickness ratio-allowable stress is obtained.The design strength correction factor₍（9）is proposed,which can reference the design of the aluminum alloy single tube tower.This paper has 105 pictures,28 tables,and 104 references.