Development of Experimental Systems for Simulation of Complete Failures of Steel Structures Subjected to Earthquake Loading

这项研究的重点是发展模拟结构在地震荷载作用下完全失效的实验技术。研制了一套由超大型行程加载千斤顶、高分辨率数字位移传感器和在线数字计算机控制组成的实验系统。利用开发的系统对钢梁和钢柱的完全破坏进行了模拟试验。这里，完全失效的定义是构件完全断裂和分离，和/或构件失去承受重力载荷的能力。试验结果表明：(1)强烈的几何非线性使梁的抗力模式由弯曲转变为轴向拉伸/收缩。(2)即使在梁遭受严重损伤后，这种模式的改变也产生了额外的阻力。(3)钢柱的完全破坏是由裂缝的扩展和随后的截面断裂控制的。(4)一定量的轴向荷载延缓了裂缝的萌生和扩展，有助于提高柱的完全破坏能力。用有限元方法对试验结果进行了数值分析，结果表明，即使在几何非线性较强的情况下，有限元分析也是有效的，但当杆件拓扑结构发生较大变化时，有限元分析不能模拟试验行为。

This study focuses on development of experimental techniques for the simulation of complete failures of structures subjected to earthquake loading. An experimental system that consists of very large stroke loading jacks, high resolution digital displacement transducers, and on-line digital computer control was developed. Using the system developed, tests were conducted for the simulation of complete failures of steel beams and columns. Here, complete failure was defined such that the member was fractured and separated completely and/or the member loses the capacity of sustaining gravity load. The major findings obtained from the tests are as follows.(1) Strong geometrical nonlinearity changed the mode of beam resistance from flexure to axial elongation/contraction.(2) This change of mode generated additional resistance even after the beam sustained significant damage.(3) Complete failure of steel columns was governed by the growth of cracks and succeeding fractures of the section.(4) A certain amount of axial load retarded the initiation and growth of cracks, which assist the increase of column capacity to complete failure. Numerical analysis using the finite element method was performed to simulate the experimental results, and it was found that the analysis is effective even in the regime of strong geometrical nonlinearity but fails to simulate the experimental behavior once the member topology is altered significantly.