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.
