Evaluation of pre-Northridge steel moment-resisting frame joints

Abstract

The 1994 Northridge earthquake caused widespread and unexpected damage to steel moment-resisting joints and connections. Shortly following the earthquake, the Federal Emergency Management Agency funded a series of full-scale tests of steel moment-resisting joints and connections to characterize the behavior of pre-earthquake connections and to evaluate the efficacy of a selected number of repair schemes. Twelve pre-earthquake connections were tested. Three of the twelve connections were tested by the authors to failure, and then repaired and re-tested. The response of the pre-earthquake connections was highly variable and uniformly poor. Premature fractures were observed in all twelve connections, and the types of fractures were similar to those observed in the field following the earthquake. The mean beam plastic rotation was 0.005 rad: one-sixth of the target value of 0.03 rad. The response of those moment-resisting connections that were repaired by replacing fractured weld and parent metal with toughness-rated weld filler metal was also poor. On the basis of the studies described in the paper, the rotation capacity of large-size moment-resisting connections built prior to the Northridge earthquake is smaller than the target values established following the earthquake; rehabilitation of earthquake-damaged moment-resisting connections by re-welding only will likely be ineffective; beam-column panel zones should be designed to remain elastic for the forces associated with plastic hinging in the beams; design equations for continuity plates should be revised; and design checks for flange compactness should be based on expected rather than nominal material properties. Copyright © 1998 John Wiley & Sons, Ltd.