Clarification of the occurrence mechanism of out-of-plane deformation of steel beam-columns subjected to cyclic bending and theoretical prediction of the critical states

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Theoretical and experimental investigations have been carried out in order to clarify the occurrence mechanism of out-of-plane deformation in steel beam-columns subjected to reversed cyclic bending and to establish a prediction method of the in-plane behavior limits.1. For a 4 degree-of-freedom model of cantilever space beam-column, which consists of a rigid frame and elastic-plastic springs with linear strain-hardening characteristics, the existence of in-plane behavior limits has been proved and the occurrence mechanism of out-of-plane deformation has been clarified by obtaining the analytical solution in a closed form of the entire hysteretic response of the model to a cyclic bending program with gradually increasing amplitude. A theory, which can predict in-plane behavior limits without tracing the entire hysteretic response, has been established.2. The in-plane behavior limit theory has been extended to a one-dimensional continuum beam- column model with four flanges and the analy … More tical solutions to the in-plane behavior limits have been obtained.3. The in-plane behavior limit theory has been developed for a more realistic model of space beam-column. This theory is expected to provide the basic data used in constituting improved design formulas for steel beams and columns. (1)A new FEM model has been proposed, which permits large deflection analysis of elastic-plastic behavior of a steel space beam-column with an arbitrary shaped solid cross-section taking into account warping deformation of cross-sectional planes. (2)The in-plane behavior limit theory has been constructed for this model. The relations between stress rates and strain rates associated with the increment variation of steady state have been derived for all patterns of variation except those from the states of alternating plasticity for the materials subject to Prager's and Zieglar's kinematic hardening,laws. (3)A computer program for the numerical analysis based upon this limit theory has been made.4. Completely reversed cyclic bending tests with step-wisely increasing amplitude have been carried out for steel beam-column specimens with square tubular and H-shaped cross- sections. The test results have demonstrated the existence of in-plane behavior limits and steady state limits and confirmed several major findings from the theoretical studies. Less