Research On Nonlinear Stability Of Crane Truss Boom

In order to meet the needs of developing the engineering practice, more and more slender crane booms are designed and their stability problem is increasingly outstanding. Crane boom is a complex slender space structure, thus, its stability problem is a typical nonlinear extreme point instability problem. Traditional stability analytical method only can solve the bifurcation buckling problem of abstract beam or the one that can be simplified as abstract beam. With the development of the finite element method and computer technology, the eigenvalue buckling is widely used to solve the stability problem in all kinds of complex structure. However, eigenvalue buckling analysis assumes that the boom only has small deformation and assumes a linear relationship between stress and deformation before the boom is instability. In practice, the boom has already large deformation which cannot be ignored and the relationship between stress and deformation is nonlinear, therefore, nonlinear stability analysis is significant necessary.Based on the predecessors’ research results, the following work has been done. The boom system’s mechanics model is built by analyzing the mechanics characters of the boom system. According to the mechanics model, FEM model is built referring to the geometry dimensions of the boom with selecting appropriate FEM element. By Studying the nonlinear iterative process, the algorithm which can automatic generate load increment (even negative incremental) is present. This method is called Arc-length method and it can ensure the convergence when the iterative calculation closes to the extreme point in the iterative process. As it even can generate negative load increment, the load-displacement curve after the extreme value point can be tracked too. At last, the boom’s nonlinear full-range analysis is conducted and the full-range load-displacement curve is obtained with taking geometric nonlinearity into consideration.A 750 ton crawler crane’s boom system is taken for an instance and lots of full-range load-displacement curves are obtained by conducting nonlinear full-range analysis in different boom combinations and different ranges. By analyzing these curves, the limit loads which are closer to the true engineering practice instability load are obtained. This proves that full-range load-displacement curve which can be obtained by nonlinear full-range analysis can clearly illustrate the boom’s stability performance and it’s necessary to do the nonlinear full-range analysis.In addition, the calculation result is summarized and analyzed. The influence of different factors on the stability is obtained. Some Suggestions are proposed for the actual lifting work. What’s more, practical problems that may encounter in the actual nonlinear process stability calculation have been discussed in detail.