Practical Toughness Design Formulas for Steel Beam-columns

本课题的目的是根据目前研究人员发现的表征新的临界行为的状态参数的临界组合，推导出一套合理的、实用的钢压杆韧性设计公式。(1)将前人提出的理想悬臂梁柱的对称极限理论推广到满足一组非平稳滞回应力应变关系的双向对称截面梁柱的理论。结果表明，扩展理论预测的钢梁-柱对称极限幅值与对其滞回性能进行精确分析得到的结果非常接近。(2)在对称极限理论的基础上，研究了二阶因素对对称极限幅值的影响。发现了以下特点：(1)梁柱…的对称极限曲线具有屈服平台的骨架曲线越符合不连续性。(2)残余应力的存在总是使对称极限幅值略有增加。(3)方管梁柱翼缘的局部屈曲变形可能增加或减小对称极限幅值，这取决于状态参数。(3)建立了任意(双向)对称截面的梁柱的稳态极限理论，满足文[1]中的非线性应力应变关系。证明了对称极限曲线是对相应的稳定极限曲线的一种较好的安全逼近。(4)方钢管模型钢梁柱在等轴压下进行了递增幅值的完全反向弯曲试验。(5)得到了轴压比和名义长细比平面上的对称极限曲线，并将其作为设计的基本曲线。较少

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