Practical Toughness Design Formulas for Steel Beam-columns

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The purpose of this project is to derive a rational and practically useful set of toughness design formulas for steel beam-columns on the basis of the critical combinations of state parameters which characterize the new critical behaviors found by the present investigators. The following results have been obtained:(1) The symmetry limit theory for idealized cantilever beam-columns due to the senior investigators has been extended to the theory for beam-columns with biaxially symmetric cross-sections obeying a set of non-stationary hysteretic stress-strain relations. It has been demonstrated that the symmetry limit amplitudes of a steel beam-column predicted by the extended theory agree very closely with those obtained by an accurate analysis of its hysteretic behavior.(2) The effects of second-order factors on the symmetry limit have been investigated on the basis of the symmetry limit theory. The following characteristics have been found.(1) The symmetry limit curve for a beam-column … More obeying a skeleton curve with a yield plateau has a discontinuity.(2) The symmetry limit amplitude is always and slightly increased by the presence of residual stresses.(3) Local buckling deformation of a flange of a beam-column of a square tube may increase or decrease the symmetry limit amplitude depending upon the state parameters.(3) A steady-state limit theory has been developed on a beam-column with an arbitrary (biaxially) symmetric cross-section obeying the nonlinear stress-strain relations in (1). It has been proved that a symmetry limit curve is a good approximation of the corresponding steady-state limit curve from the safe side.(4) Model steel beam-columns of square tubes have been subjected to a program of completely reversed bending of stepwisely increasing amplitudes under constant axial compression. It has been demonstrated that the symmetry limit curve due to the theory provides fairly good predictions of the experimental results.(5) The symmetry limit curve on a plane of axial force ratio and nominal slenderness ratio for a sufficiently large value of the prescribed tip deflection amplitude has been obtained and proposed as a design fundamental curve. Less