Effect of Material Parameters on Performance of Welded Steel Moment Frame Connections

在1994年北岭地震中，100多座钢框架结构出现了脆性连接断裂，1995年日本地震后也出现了类似的断裂。 尽管从那时起对大型和小型结构进行了广泛的实验室测试，但尚未确定导致这些焊接接头脆性断裂的因素。 最近的研究脆性断裂的原因主要集中在这些连接的结构设计。 然而，这些焊接接头中的钢的局部材料特性对于这些连接的原因和失效可能具有同等重要性。 焊接钢抗弯连接件的设计修改旨在降低整体应力。 它们对减轻局部压力作用甚微。 本研究项目的目的是开发一种改进的焊接工艺，在“临界区”将形成细晶组织由于总是存在的高应力而通常产生裂纹的连接的断裂韧性将大大降低，并且由于临界区域中较高的断裂韧性，连接中固有的三轴应力将具有较小的破坏性。 因此，焊接梁柱接头将表现出增强的性能，并可避免脆性断裂。 焊接产生的残余应力将通过应力扫描声学成像测量，这是一种新开发的声学显微镜技术，可以以高空间分辨率绘制应力图。 这项研究涉及与日本东京大学和京都大学的日本研究人员的积极合作。

More than 100 steel moment resisting frame buildings exhibited brittle connection fracture during the Northridge earthquake of 1994 and similar fractures were also observed following the Earthquake of 1995 in Japan. Despite extensive laboratory testing of large and small scale structures since then, factors leading to brittle fractures in these welded joints have not yet been identified. Recent studies on the causes for the brittle fracture have focused primarily on the structural design of these connections. However, local material properties of the steel in these welded joints are probably of equal importance to the causes and the failure of these connections. Design modifications in welded steel moment resisting connections deal with reducing global stresses. They do little to reduce local stresses. The aim of this research project is to develop a modified welding procedure specifically designed to ensure that ductile, fine grained microstructure will develop in the "critical region" of the connection where cracks commonly initiate due to the high stresses which are invariably present will be considerably reduced and triaxial stresses which are inherent in the connection will be less damaging due to the higher fracture toughness in the critical region. As a result the welded beam-to-column joint will exhibit and enhanced performance and brittle fracture may be avoided. The residual stresses due to welding will be measured by Scanning Acoustic Imaging of Stress, a newly developed acoustic microscopy technique, that allows stresses to be mapped with high spatial resolution. This research involves active collaboration with Japanese researchers at the University of Tokyo and Kyoto University in Japan.