Dynamic Instability of Steel Frames under Combined Stressduring Earthquake

进行了钢梁柱的双向受弯和单轴受弯试验，以及变轴向荷载试验。采用了三种加载方式：(1)单调加载试验，(2)循环加载试验，(3)计算机在线地震反应试验。这些试验的观测结果可用于校核钢构件的抗力和变形能力的设计公式，并在梁柱设计实践中研究轴力的适当限制。此外，钢梁柱的非弹性部分被建模为弹簧单元的组合，并提出了一个简单的滞回准则来模拟其非弹性行为，考虑了应变硬化和包辛格效应。基于该模型对每种荷载工况进行了分析，并与试验结果进行了比较。分析结果与试验结果吻合较好。特别是在循环加载试验的情况下，…观察到了很大的变形本文的研究成果总结如下：1.开发了一套计算机控制的测试系统，用于对虚拟复杂结构体系(如高层建筑)中的特定构件产生的梁柱试件进行不同的组合应力状态测试。在整个试验过程中，验证了该智能装车系统的有效性和准确性。将现有的计算双向受弯和受轴向荷载作用下钢压杆抗力的设计公式与试验结果进行了比较，结果表明，对于轴向荷载占屈服荷载的60%以下的情况，计算结果较为保守。然而，在梁柱的极限状态设计中，可能需要更准确地评估抗力，这需要通过更广泛的试验和分析来研究。在一些循环加载试验中，平面外方向积累了相当大的塑性变形。对于这种离面失稳现象，应进行更仔细的研究。基于非弹性节点模型的分析方法能够较好地预测钢梁柱在组合应力状态下的抗力和变形能力。这种模型简单，可以应用于大型三维钢框架的分析。较少

Steel beam-columns were tested under biaxial and uniaxial bending and varying, axial load as well. Three kinds of loading, types were applied : (1) monotonic loading tests, (2) cyclic loading tests, and (3) computer on-line earthquake response tests. Observations in these tests can be used to check the design formulae for the resistance as well as the deformability of steel members, and also to study an appropriate limitation of axial forces in the beam-column design practice.Additionally, an inelastic portion of a steel beam-column is modeled as an assembly of spring elements, and a simple hysteresis rule is proposed to simulate its inelastic behavior in including the strain-hardening and the Bauschinge's effects. Analyses based on such a model were carried out for each loading cases, and compared with the test results. The results of the analyses proved to agree fairly well with the test results. Especially in the case of the cyclic loading test, very large deformation was observed i … More n the direction where displacement was not constrained, and even such an unstable phenomenon was well simulated by the present analysis.The results of this research project are summarized as follows :1. A computer-controlled testing system was developed to provide varying combined stress states to a beam-column specimen, which would be produced in a specified member of a fictitious complicated structural system such as a high rise building. The effectiveness and the accuracy of such an intelligent loading system were confirmed during all the test procedures.2. An existing design formula to evaluate the resistance of steel beam-columns under biaxial bending and axial load was compared with the test results, and proved to give a conservative evaluation for the axial load smaller than 60 percent of the yield axial load. However, more accurate evaluation of the resistance may be needed in the ultimate limit state design of the beam-columns, and this shall be studied by more extensive sets of experiments and analyses.3. In some of the cyclic loading tests, considerable amounts of plastic deformation were cumulated in the out-of-plane direction. Such an out-of-plane instability shall be investigated more carefully.4. The analysis method based on an inelastic joint model proved to provide a good prediction of the resistance and the deformability of steel beam-columns under combined stress states. Such a modeling can be applied, because of its simplicity, to the analysis on large-scale 3-dimensional steel frames. Less