The 6.8 magnitude Northridge earthquake that shook California's San Fernando Valley on January 17 in 1994, did not cause the collapse of any steel structures but connections, confidently designed and constructed in the past with traditional code simplification and common site welding techniques, were discovered not to meet our expectations.
This paper reviews connection failures during the 1994 Northridge earthquake and the design philosophy and examines the post-Northridge earthquake experimental and analytical researches. Possible causes of the moment connections damage are categorized into three classes; welding-related factors, design-related factors, and material-related factors. For the analyses, the idealizations of the moment connection considering each factor are studied. From the idealization of the moment connection, the five-plate model is analyzed to investigate the stress concentration and stress state of the connection. The equivalent design crack models are investigated using the fracture mechanics approach.
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