| With the implementation of UHV and other large-scale transmission projects in China,there are higher requirements for the load capacity and spanning capacity of transmission towers.Steel tube towers are widely used in long-span transmission projects because of their better load performance and economy than angle steel towers.With the increasing transmission voltage,the height and flexibility of the transmission tower become larger and larger.Under the lateral horizontal loads such as wind load,it shows strong nonlinear characteristics.When the load reaches a certain level,the structure may enter plasticity,which leads to the decrease of bearing capacity and increased risk.But,in the current design code of transmission tower structure,there is a lack of explicit expression on the nonlinearity and dynamic response.Therefore,it is of great theoretical and engineering significance to make an accurate elastoplastic analysis of spatial structure and master the dynamic response law of steel tube transmission tower under dynamic load.The main work of this paper is as follows:Firstly,according to the spatial mechanics’ characteristics of steel tube transmission tower,the double nonlinear analysis of spatial beam structure considering material nonlinearity and geometric nonlinearity is carried out.Based on the assumption of concentrated plastic hinge and internal force space yield surface,the plastic reduction stiffness matrix considering material nonlinearity is derived and an explicit expression is formed.By using rigid body criterion,the problem of large geometric displacement and deformation is decomposed into rigid body displacement and small geometric deformation,which greatly simplifies the process of geometric nonlinear analysis.The generalized displacement control method is used to adjust the incremental step and loading direction in the incremental iteration process,and the incremental iterative calculation program for static elastoplastic analysis is compiled.The abrupt change phenomenon of the ideal elastoplastic model is modified by interpolation,so that it can satisfy the description of the plastic development process.The results of an example show that the static elastoplastic analysis method in this paper has good accuracy and can meet the needs of static elastoplastic analysis.Secondly,the static and dynamic theoretical analysis method of semi-rigid connection is discussed.The semi-rigid connection element is simulated by rotating spring,and the elastic-plastic stiffness matrix of the hybrid element of semi-rigid connection is established,which has a good analysis effect on the calculation example.Considering the coupling effect of semi-rigid connection and material nonlinearity,the calculation shows that the superposition of the two can accelerate the plastic reduction.In this paper,two semi-rigid connection models,Romberg Osgood model and boundary line restoring force model,are dynamically analyzed.The above two simplified dynamic analysis methods are used to effectively simulate the dynamic nonlinear response of uniaxial bar structure,then obtained correct simulation results.Thirdly,on the basis of static elastic-plastic analysis,the motion hardening model are used to analyze the plastic development of the structure,and the tangent stiffness matrix suitable for dynamic analysis is derived by the form of hardening matrix,so that the elastic-plastic analysis model can consider the plastic hardening of materials.The Newmark-β method is used to solve the dynamic equilibrium equation iteratively.Through the analysis and comparison of classical examples,the applicability of this elastic-plastic analysis method in dynamic problems is shown.Finally,established the calculation model of spatial steel tube transmission tower in the calculation program,and carried out the dynamic time history analysis of steel tube transmission tower.Compared and analyzed the linear and nonlinear dynamic elastoplastic response laws of transmission tower.The results show that nonlinearity will reduce the carrying capacity of the transmission tower and has an important influence on the dynamic response of the structure. |
