A Numerical Method for Predicting Critical Behavior of Elasto-plastic Frame with Elements Obeying Deteriorating Stress-strain Relation

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In the beam-column FEM analysis of ultimate or critical behavior of elasto-plastic frames, the stiffness matrix consistent with the constitutive law must be generated. In such an analysis, local buckling of steel member and large deformation of concrete material will be estimated by elements which obey elastic-deteriorating plastic stress-strain model and which have an appropriate length. A conventional iterative procedure for generating consistent stiffness matrix of a frame model with elastic-deteriorating plastic elements frequently leads to a pitfall of cyclic process. An algorithm for generating consistent stiffness matrix has been presented for predicting the static equilibrium path of elastio-plastic frames by the head investigator. The algorithm utilizes an eigenvector of stiffness matrix of the comparison frame. In the numerical analyses of the buckling behaviors of bars and of the collapse behaviors of portal frames, the algorithm has been verified. These simulations demonstrate that the algorithm functions effectively for generating the consistent stiffness matrix and for sellecting the control path-parameter in the vicinity of critical point. However, the algorithm has not been utilized in analyzing the critical behavior of the frame with elements obeying deteriorating stress-strain relation. The effect of the similar strategy for generating consistent stiffness matrix in such case is confirmed in this study. The algorithm provides an apt selection of the control path-parameter for execution of numerical analysis.