An Idealized Structural Unit model of a tubular bracing member is developed considering the influence of local buckling which takes place after the ultimate strength is attained. That is,
(1) The simplified method which was proposed in the 1 st report for a tubular member subjected to eccentric axial thrust is expanded so that the ultimate strength can be evaluated under general end loads and distributed lateral load. This method is applied to determine the ultimate strength of a member in the framework of the Idealized Structural Unit Method (ISUM) analysis.
(2) An approximate method is proposed to determine the internal forces at a cross section after the ultimate strength is attained. Using these internal forces, strain distribution is determined. The occurence of local buckling is checked based on this strain at every load increments.
(3) After the local buckling has started, its influence is reflected upon the full plastic strength interaction relationship through plastic nodal displacements of the element. A formulation to derive the elastic-plastic stiffness matrix is described considering the influence of local buckling.
Several examples are analyzed applying the newly developed element. The calculated results are compared with those by the finite element method analysis and experiment, and its validity and usefulness are demonstrated.
