The earthquake that occurred in Northridge, California on January 17, 1994, unexpectedly fractured a great number of steel moment frame connections. They failed in a brittle manner even though they were designed to respond in a ductile manner under seismic loading. The joint failures in the popular flange- welded, web-bolted beam-to-column connections included fractures of the beam flange welds, the beam flanges at the edge of the weld access holes, and the column flanges. Another fracture mode comprised divots of steel pulled from the face of the column flanges. Comprehensive elastic, plastic, and buckling analyses using finite element models coupled with full scale beam-to-column connection assembly tests have shown that this connection is fundamentally flawed because of large stress and strain gradients and large vertical shears in the beam flange/weld at column face. However, by introducing horizontal beam web slots in the proximity of the beam flanges, both the stress and strain gradients and the vertical shears in the beam flange/weld are dramatically reduced. This proprietary connection design that essentially "salvages" this popular and economical connection can be used for both retrofitting and new construction.

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