Lessons learned from the Northridge earthquake

The performance of welded connections in special moment resisting frames (SMRF) during the Northridge, California earthquake in January 1994 was influenced by many variables. The actual ground motions experienced by the buildings, the design details employed in the connections, material properties, fabrication workmanship and inspection practices. The evidences of workmanship-related problems were primarily the result of lack of conformance to the requirements specified in the AWS Structural Welding Code D1.1, Lack of emphasis on in-process visual inspection may have permitted questionable fabrication practices to go undetected. A fundamental expectation regarding the performance of the SMRF is that of 'ductility'. In concept, the seismic energies are to be absorbed by the formation of plastic hinges within the structure. The pre-Northridge connection detail is examined in light of quality, fracture and multi-directional stresses, and its relative performance regarding expectations of ductile behavior. Post-Northridge research specimens are examined with respect to the same factors, along with their relative level of ductile behavior. Details that enhance ductile behavior and the reasons that this behavior can be expected are presented. (C) 1997 Elsevier Science Ltd.