| Tower crane with screw attachment rod as a variable section of axial stress component,the screw section has a local mutation,and the screw section moment of inertia relative to the attached rod section has a huge gap,can significantly reduce the overall stable bearing capacity of the attached rod,and the current"tower Crane design Code"does not mention the relevant design method.Tower crane designers generally ignore the adverse effects of adjusting screw on attaching rod or roughly add a safety factor during design,which will make the design of attaching rod with screw unsafe and uneconomical.Therefore,the design method of attaching rod with screw needs to be studied urgently.In this thesis,the calculated length coefficientμ_b(μ_b>1)caused by variable section is considered to consider the adverse effects of setting the adjusting screw.Firstly,the overall stability of the attached rod with screw was studied through experiments.Considering the influence of screw length on the overall stability of the attached rod,four specimens with different screw lengths were designed,and the ultimate bearing capacity of each specimen was obtained through the material property test and axial compression test.It was found that the setting of adjusting screw significantly weakened the stable bearing capacity of the attached rod.Then the finite element software was used to calculate the four specimens,and the finite element results were compared with the test results.The maximum deviation was only7.8%,which proved the reliability and accuracy of the finite element method and could be further applied in the parameter analysis.The stability of attached rod with screw was studied by static method and Rayleigh-Ritz method respectively.It is difficult for static method to obtain the analytical formula for calculating the length coefficient.Although Rayleigh-Ritz method can obtain the analytical formula for calculating the length coefficient,due to the restriction of deformation function,it is found that the accuracy of the formula is poor and cannot be used in engineering design through comparison with finite element method,but the general influence law of each parameter is obtained.Parametric analysis of attached rod with screw was carried out by finite element software,mainly considering the screw length,the screw position,the ratio of the attached rod section moment of inertia to the screw section moment of inertia and the influence of screw material strength on the overall stability of the member.A large number of components were designed,and the finite element software was used to model the eigenvalue buckling analysis and elastoplastic buckling analysis.The length coefficient and the elastic-plastic stability bearing capacity were calculated,and the influence law of each parameter on the stability bearing capacity of the member was obtained by in-depth analysis of each influencing factor,and some design suggestions were given in combination with practical engineering.Finally,the value table of the calculated length coefficient under different screw lengths is given by the finite element parameter analysis.The calculated length coefficient can be obtained by interpolating the length of the attached rod and the ratio of the moment of inertia of the section.The calculation results of the theoretical method and the finite element method are compared to prove that the calculated length coefficient is reliable.The design method and checking calculation method of attached rod with screw are given,which can be used as reference for engineering designers. |
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