Earthquake resistant design formula for steel beam-columns with regard to deterioration phenomena under repeated loading

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1. The symmetry limit and steady-state limit have been theoretically predicted for a unit sub-frame consisting of one elasto-plastic column and four elastic beams cut out from a multistory multibay planar frames. Beam-column design formulas and diagrams have been proposed based upon these theoretical prediction results.2. Repeated bending tests of steel beam-columns with box and H-shaped cross sections subjected to constant axial compression have been performed to clarify the cyclic growth phenomena of out-of-plane deformation.3. It has been revealed by the symmetry limit theory that an unknown type of overall collapse behavior characterized by a cyclic growth of bow-like-shaped overall deflection mode is possible to occur in multistory multibay weak-beam planar frames subjected to repeated horizontal top displacement. A numerical response analysis of the frames is performed to verify the theoretical predictions.4. A computer analysis program has been developed to predict the symmetry limit and steady-state limit of planar frames with arbitrary shapes. Several new types of critical behavior have been found by means of this program.5. The original symmetry limit theory for beam-columns subjected to repeated lateral displacement has been extended to the problem of beam-columns subjected to repeated lateral force.