Equilibrium considerations of the updated Lagrangian formulation of beam‐columns with natural concepts

Abstract
Bathe and co‐workers'1,2 updated Lagrangian formulation is reviewed for a two‐dimensional beam‐column element. From this review a physical interpretation and properties are derived for the matrices of the method. A variant of Argyris and co‐workers'4,5 natural concept is introduced in the updated Lagrangian formulation, and a new method to derive element matrices arises. A detailed derivation of the matrices of the twodimensional beam‐column element is presented to clarify further the UL formulations. Explicit expressions for these matrices, computed with the use of symbolic manipulation,17 are also presented to illustrate the concepts discussed. Finally, numerical results are shown to compare and evaluate different methods and matrices.

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