The Stability Analysis For The Crane Jib

The super-big crane, with longer arm, has been one of the developing trends of cranes. It requests the technicians not only to guarantee the product quality but also to save the costs as possible as it can. Most technicians accept the Finite element analysis (FEA) as a necessary skill in the engineering area. In the course of design, the strength, the stiffness, the stability, the fatigue and so on are considered. Generally, Technicians check the structure stability, according to the relating formula in the Design Rules for Cranes of the National Standard GB3811-83 of the People's Republic of China. However, in the present rules in every country, the stability problem is mainly considered by checking computations. With the internal force computed by the first order theory, considering the affect of the factors, such as the original flaws, eccentricity and the residual stress and so on, adopting the method of length calculation, the checking computations are done for the single rod. Its computation steps are clear, but it cannot combine every factors organically, especially for the thin-walled structure, which is destroyed mainly by the lost of stability. It is not enough to use the first order theory, because the nonlinear of the large-scale thin-walled structure is obvious and the distortion has an obvious affect on the structure. If only the linear method is used, there will be no way to know the safe storage of the structure and the safety cannot be guaranteed. That is why this issue is discussed in this dissertation.The first chapter introduces the developing status of the caterpillar cranes and wheel cranes at home and abroad, dissertates the developing trend of the cranes in the world, and points out the deficiencies of the development of the cranes in our nation. What coming down is the introduction of the classification, research history and status of the structure buckling problems. In the final part, illustrate an example of using the nonlinear finite element to solve the structure stability, showing the feasibility of this method.The second chapter introduces the correlating theories of mechanics, mathematics and the nonlinear finite element. In details, the buckling eigenvalue theory, based on the linear and nonlinear analysis, and the method of distinguishing the critical point style, are introduced. The theory foundation of the geometry nonlinear finite element, which prepared for the application of resolving the structure stability, is also introduced in several aspects, including the great distortion strain and stress measurements, geometry nonlinear problem's expression format, finite element equation's resolving method, balancing routes' following, selection of the load step and the loads depending on the distortion.There is lots of large finite element software, each of which has its strong point. The linear simple problems cannot exhibit the advantages of some excellent software, but the complicated problems need a consideration of the software selection. Choosing the MSC.MARC has enough reasons: As the first commercial nonlinear finite element software, MSC.MARC was greatly canonized and widely applied in the science area and industrial area, being the leader in the global nonlinear finite element software industry. Another important reason for choosing this processor is its supply of the Crisfield arc method, the Riks/Ramm arc method, the Crisfield/Riks-Ramm arc method and the Crisfield/Riks-Ramm arc method, which has different choices for different problems.The last chapter introduces several computational examples and gives the comparisons among the buckling loads analysis from the simple cavity box type beam and pipe to the complicated main arm, fixed secondary arm and the tower secondary arm. It is clear that the Newton-Raphson iteration method controlled by the arc method is closed to the Euler formula and the eigenvalue method based on the linear static force analysis. The Newton-Raphson iteration method can be seen as the asymptote of the other two methods, which validate the feasibility and the effectiveness in solving the structure stability problems. Furthermore, this method also provides much more information, such as the change history of the structure displacements, stress and strain etc, which vary with the increasing of the loads. It is convenient to hold the performance in the whole process of loading.This dissertation summarizes a reliable, complete computational scheme of the structure stability analysis: In the beginning of the calculation, the structure can be greatly simplified, using the Euler formula or related design rules to estimate the buckling loads, or directly using the eigenvalue method based on the linear and nonlinear static analysis to distill the structure buckling loads and mode; At last, the buckling loads computed by the former methods are added on the structure and a small perturbation is added to make the structure have a buckling mode, using the arc method to validate the results, which can save lots of computational time. The arc method can help the designers to obtain the stiffness curves before the structure buckled and a complete performance of the structure. It also helps the designers to determine the structure buckling loads based on the former designing experiences and overcome the puzzles on the stability problems, providing design rules for the designers.There are also some researches need to be done in this dissertation: Firstly, the material nonlinear is not considered, which will generate a great error when the plastic distortion occurs. If the affect of the material nonlinear is added in the analysis, the results may be more proper for the practical situation. Secondly, the eigenvalue method, which is effective for the original flaws, material nonlinear and the geometry nonlinear and have smaller calculating costs, is needed to exploit; thirdly, the perturbation method is also need to be researched. This method distills the buckling mode after the analysis of a certain increment step of the increment loading process. The mode is seen as the perturbation displacement to update the system coordinates and then to analyze the new balance position and coming loading path. This method can be used for the post-buckling distortion. By updating the system coordinates, this method can simplify the nonlinear analysis to the linear analysis, and can add the additional bending moment effect generated by the geometry distortion and add other nonlinear effects to the updating structures by loading. The efficiency will be enhanced a lot, however, because it is the simplification of the nonlinear problems, it can only be the reference, which is close to the actual buckling loads. All these researches are needed to be done in the future.