Seismic Retrofit of Welded Steel Moment Connections With Highly Composite Slabs

Abstract eng:
In the 1994 Northridge earthquake, connection damage initiated from the beam bottom flange was prevalent. The presence of a concrete slab and resulting composite action was speculated as one of the critical causes of the prevalent bottom flange fracture. Close review of past experimental studies recently conducted by the author clearly indicated that conventional seismic steel moment connections with highly composite slabs were much more vulnerable to the bottom flange fracture. In this study, seismic retrofit schemes are presented for welded steel moment connections with highly composite floor slabs typical of existing steel moment frames in Korea. Because top flange modification of existing beams is not feasible due to the presence of a concrete floor slab, bottom flange modifications by using welded triangular or straight haunches, and by beam web strengthening with heavy shear tab were cyclically tested and analyzed. Test results of this study showed that the retrofit schemes used is effective in eliminating the detrimental effects associated with high composite action and can ensure excellent connection plastic rotation exceeding 4% rad. Side effects as a result of each retrofit scheme as well as design recommendations are also presented.

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