The Buckling Modal Analysis And Application Of Thin-walled Members Based On Force-feature

Buckling phenomenon has an extremely important impact on the load-carrying capacity of members in the design of thin-walled structures.Usually,buckling modes are divided into three main families: global,distortional and local buckling mode.However,coupling effect of two or three modes above exists in practical buckling behavior of thin-walled member.Therefore,these three classes of buckling modes could be regarded as components of arbitrary buckling behavior.Current definitions of global,distortional and local buckling modes are all based on the deformation mode,which causes some disadvantages in applicability and accuracy.The method in this thesis is derived by taking the force conditions instead of merely deformation conditions into consideration.Based on finite element analysis,a common buckling mode is decomposed according to deformation functions,and participation factors are calculated for modal identification.The problem that the coupled results of FEM buckling analysis are inappropriate for practical application is solved.For the objective above,following researches are carried out in this thesis:(1)Research on current analysis method of thin-walled member: Generalized Beam Theory and Constrained Finite Stripe Method.The derivation and solution are summarized,and the existing problems are discussed in order to compare with the method in this thesis.(2)A set of new definitions of global,distortional and local deformation mode of thinwalled member is carried out,and based on which the modal identification is achieved.Several force-based conditions are introduced into these definitions,therefore the effect of shear strain,transverse membrane strain and nonlinear longitudinal membrane strain could be considered.The three deformation modes in this thesis fully contain all kinds of deformations of thin-walled members,which are orthogonal with each other about elastic stiffness.Hence the participation factors could be calculated in terms of strain energy.(3)Axial compression members are taken for examples that show how this method works.Based on finite element method buckling analysis,modal identification is accomplished with the method in this thesis applied.Critical curves of global,distortional and local buckling are figured.(4)The applicability of this method is discussed by analyzing different thin-walled members with distinct boundary conditions and perforated members.Innovations in this thesis:(1)Several force feature conditions are introduced into the definitions of sub-deformation buckling modes of thin-walled members.(2)The modal identification and the calculation of participation factors are based on strain energy,rather than based on deformation merely.(3)The method in this thesis breakthrough the limit of finite element method in buckling analysis,that the pure mode could hardly be analyzed.