Nonlinear Stress Analysis And Research On Truss Boom With Auxiliary Bracing

According to the development of large tonnage crawler cranes and the use of high-strength steel pipe, slenderness lattice boom continues to be used. However, the boom length’s increase is limited due to the problem of the boom’s poor stiffness, increasing arm length is the only way to achieve the desired lifting height and amplitude. It has become particularly important to research the nonlinear problem of the slenderness lattice boom. Auxiliary bracing can significantly improve the stress state of the boom system and solve the problem of boom’s poor stability, but the calculation theory about auxiliary bracing is still immature. Commonly using FEM test algorithm spends a lot of time and cost for the complexity of modeling and nonlinear convergence problems.For above problems, the moment and deflection formula of the boom is derived by analyzing the force of the lattice boom based on the theory of second-order effects and the deflection differential equation. Firstly, the effect of the boom weight, the arm head moments and the auxiliary bracing force to the boom has been calculated without considering the impact of the boom axial force. Then, the impact of the additional moment caused by the axial force on the boom stress is calculated. Finally, the calculation result is superposed on the condition of constant axial force. Then the boom stress can been obtained based on the axial bending component mechanical characteristics. Since the complexity of the boom deflection calculation and in order to achieve the stress and deflection simultaneously, the nonlinear numerical algorithm is improved. Meanwhile, the boom stress’s calculation is increased. Based on MATLAB platform the boom stress and deflection can be obtained simultaneously. And with actual example the design criteria of optimal length of the auxiliary bracing is analyzed.The main research is as followed:(1) Refer to the relevant literatures, the mechanical characteristics of the lattice boom is analyzed in-depth, the stress formula is derived based on P-8effect and the second-order effects analysis method by considering the deformation of the boom is proposed. Using this algorithm can quickly get every section stress of the boom.(2) In view of the low stiffness of the auxiliary bracing and pull plate, the effect of the auxiliary bracing and pull plate’s elongation to the boom stress results is analyzed. The result shows that the influence with the elongation is minimal. The effect can be ignored on the premise of meeting the design requirements.(3) For the second-order effects analytical calculation does not consider the impact of the webs. So the boom moment of inertia is equivalent and then the webs effect is calculated. And practical examples show that the webs shear does not much affect the boom stress result. To simplify the calculation, the webs shear can be ignored.(4) The nonlinear numerical algorithm is improved. Meanwhile, the boom stress calculation is increased. The practical examples show that boom stress and deflection can be obtained fast by using this algorithm. Meanwhile, on practical cases, the design criteria of the auxiliary bracing length is analyzed and the optimum auxiliary bracing length of different boom length are identified.