Stability Analysis Of 300 Ton Crane Boom Based On Geometric Nonlinear Method

Today’s boom crawler crane truss structure in the process of manufacturing to use more advanced technology and better high strength steel,which makes people demand,amplitude,and the height of crane load to further improve.For the boom itself,this phenomenon leads to its structure tends to lattice structure,towering,gentle characteristics.The truss arm structure belongs to the thin long beam and rod system,and it will generally deform due to the stability of the rod system before reaching the failure strength of the material after being subjected to the load,so as to fail to meet the set use requirements.We call this situation instability.Because the instability phenomenon is more hidden in the process of its generation,often not easy to detect,the damage is very huge,so the crawler crane truss arm stability check calculation is a major focus in its design process.In this paper,the development and research status of beam and bar systems,especially truss boom structures,in geometric nonlinear analysis methods and stability problems are studied.The contents of linear stability and geometric nonlinear stability theory are explained,and the similarities and differences between linear analysis method and nonlinear analysis method are found out.The deformation mode and instability process of the statically indeterminate structure represented by the truss arm in terms of geometric nonlinearity are described.The geometrical nonlinear analysis of the main boom of crawler crane is carried out by using the finite element analysis software to find out the influence of the boom amplitude,length,dead weight and horizontal side load on the maximum bearing capacity and instability mode of the structure itself.This analysis not only obtained the buckling load of the structure considering the geometrical large deformation factors,but also summarized the structural force and deformation process.According to the "load-displacement" curve trend of each special node in different working conditions,the concrete phenomenon of the boom deformation in different stages of the curve is found,and the influence of each bar on the whole is understood,so as to provide suggestions for improving the structural stability in the design process.The whole content of this article is as follows:1.Based on geometric nonlinear stability analysis method,solid model and finite element model of main boom with different lengths of 300 ton crawler crane were established;An incremental equilibrium equation of finite element is derived as a mathematical model;2.The "load-displacement" curves of the lifting points of the main boom with different lengths under different working conditions and loading modes were obtained.The calculated results are much higher than the allowable lifting weight of the performance table.Taking the range of 26m as an example,the maximum critical buckling load is 2.4 times of the rated load,and the rated working condition is safe.At the same time,with the increase of the arm length,the ratio of the critical buckling load decreased from 2.2%of the short arm 86m to 27.7%of the long arm 122m,when the critical buckling load was calculated by considering the initial deformation and side load.Through comparison,the influence of the length,amplitude and loading mode of the truss crane on the bearing capacity limit of the crane under the requirement of service is obtained;3.The critical buckling loads calculated by linear and geometrically nonlinear methods are compared.In the same example,the linear method results in larger values,ranging from a maximum 3.9%difference ratio for the short arm 86m to a maximum 40.5%difference ratio for the long arm 122m.As the length of the boom increases,the flexibility of the boom increases.It is necessary to use geometric nonlinear analysis method to calculate the stability of lattice crane;4.The load-displacement curve and the buckling mode diagram of the boom are analyzed.After the length of lifting boom increases,the instability modes in this calculation example change in different ways,and the instability mode also develops from the overall structural instability caused by the instability of the belly bar at 13m near the boom root to the instability caused by the middle part of the boom at 67m.Targeted strengthening schemes are also proposed to provide a basis for improving the bearing stability of the structure.