Ductility of Structural Steel Members Governed by Fracture

1. 大型试验中断裂的实验模拟采用冷弯方钢管进行断裂试验。结果表明，断裂过程由裂纹萌生、裂纹贯通和最终断裂三个阶段组成。以均匀伸长率和Charpy冲击值为代表的力学性能对断口有显著影响。在改变材料强度、焊接条件、缺口形状、尺寸和加载程序的断裂试验中，发现裂纹起裂应变受与材料相关的均匀应变控制。此外，裂纹起裂应变不受尺寸的影响，这一事实对实践是有用的。含脆柱结构的抗震性能对含脆柱钢框架的动力响应分析表明，这种框架存在动力渐进破坏的风险。为避免破坏，应赋予框架比普通延性框架更大的强度，并提出了强度放大系数。大地震时避免钢结构脆性断裂的设计指南是在裂纹起裂保守预测断裂的基础上建立的。

1. Experimental Simulation of Fracture in Large-Scale TestingFracture test was done by using cold-formed square steel tubes. It was found that the fracture process is composed of crack initiation, crack penetration, and final fracture. The mechanical properties represented by uniform elongation and Charpy impact value have a significant influence on the fracture.2. Crack Initiation StrainFrom fracture testing, in which material strength, welding condition, notch shape, size, and loading program are changed, it was found that the crack initiation strain is governed by the uniform strain pertinent to the material. Furthermore, the fact is useful for practice that the crack initiation strain is not affected by size.3. Seismic Performance of Structures Having Brittle ColumnsDynamic response analysis of steel frames having brittle columns showed that such frames have the risk of dynamic progressive failure. In order to avoid the failure, the frame should be assigned more strength than ordinary ductile frames, and the strength amplification factor is proposed.4. Design GuideDesign guide to avoid brittle fracture in steel structures during a big earthquake is established on the basis that the fracture is conservatively predicted by the crack initiation.