Seismic Response of Retrofitted Welded-Flange-Plate Moment Connections to Built-Up Battened Columns: A Parametric Study

This paper numerically investigates the seismic behavior of welded-flange-plate (WFP) moment connections between I-shaped beams and built-up battened columns, focusing on the modification of the connection to improve its performance. The WFP connection also features triangular rib plates, which, while not designed to bear structural loads, might influence the connection seismic performance. The first phase of the study identifies a severe strain concentration within the beam end-plate, where the out-of-plane deformation of the low- to moderately-thick end-plate significantly deteriorates the connection cyclic behavior. In the second phase, three novel retrofitting methods are proposed including: (1) insertion of trimmed rectangular continuity plates within the panel zone, (2) welding the end-plate interior face to the column flanges, and (3) attaching the end-plate to the column flange through welding a T-section steel profile. The parametric study reveals that the deployed modifications could successfully compensate for the conventional connection limitations and result in reinforced connections with substantially increased ductility and capable of maintaining their resistance, displaying a minimal resistance loss at story drifts of up to 4%. Notably, the retrofitting process enhanced the strength and energy dissipation capacity of the strengthened connections by 60% and 55%, respectively, delivering them suitable for the usage in intermediate and special steel moment frames. This research’s novelty includes: (1) identifying deficiencies in the structural detailing of the currently-practiced WFP connections to the battened columns, (2) systematically analyzing the overlooked effects of triangular rib plates on WFP connection performance, and (3) developing three innovative retrofitting strategies to enhance the connection efficacy against seismic loads.