| Because of its own advantages,the beam string structure system is widely used in various large public buildings,agricultural irrigation,building decoration,structural reinforcement and other fields.Because of the introduction of prestress,the structure would have large geometric nonlinear deformation before bearing the external load,which leads to great changes in the overall performance of the structure,so it is difficult to carry out the overall optimization in the preliminary design.After the overall scheme of the structure have been preliminarily selected,the performance of cable strut joint needs to be analyzed as the key components in the structural detail design,and the appropriate joint type should be selected according to the specific project.The role of cable strut joint is to effectively transfer the cable load to the strut,but in the process of structural tension,there is inevitable friction at the joint,which leads to the loss of prestress and overestimates the bearing capacity of the structure.At present,most of the finite element software can’t effectively simulate the friction slip at the joint in the process of structural tension.Based on the overall performance of the structure,this paper optimized the form of the preliminary design of the truss string structure,analyzed the performance of two kinds of commonly used cable strut joints in detail design,and finally putted forward a simple method to analyze the friction slip of the cable strut joints in the process of tensioning,so as to achieve the purpose of accurately applying the design prestress to the structure.The related researches are as follows:(1)In the initial shape selection stage,the overall performance of the structure was optimized.On the MATLAB platform,genetic algorithm was used to call SAP2000 through the command flow to optimize the shape selection of the structure under different states and realize the "shape finding" and "force finding";Through the optimization of 10 groups of models,it was concluded that the rise,cross section of truss chord height,sag,pretension and span of the truss showed a significant linear rising trend,the spacing of web members basically remains unchanged,while the number of struts changed in the range of 6 ～ 13.(2)Combined with an 80 m truss string project,the nonlinear friction contact was considered for two common cable strut joints of string structure.The influence of friction coefficient and joint angle on prestress loss was analyzed by ANSYS,and the anti-sliding performance of the joint was obtained under different bolt pretensions.It was found that the maximum prestress loss rate of the two kinds of joints would not exceed 3% under different friction coefficients and pretensions;The maximum friction stress of the plate joint was 45.4% less than that of the spherical joint,the slip distance was 50.8% greater than that of the spherical joint,and the friction force was255% greater than that of the spherical joint.(3)A simple method for analyzing the friction and slip of cable strut joints was proposed.Based on the vector finite-element theory and Coulomb friction model,the friction slip of cable strut joints in the process of tension was analyzed step by step with the friction force at the joints as the equivalent load.The test and numerical examples showed that the maximum error of the method was 7.3% and 4.7%respectively.This paper analyzed the slippage of 80 m truss string structure in the process of tension,and obtained the prestress loss rate and the internal force of each member under different friction coefficient.The results followed that the prestress loss rate increased linearly with the increase of friction coefficient in the range of low friction.When the friction coefficient reached 0.2,the prestress loss rate was basically maintained at about 2.5%. |
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