Secondary prying of column flange in Tee-connections: Experimental investigation and mechanical modeling

Column flange failure due to secondary prying effect needs to be addressed when designing Tee-connections associated with deep beams in seismic areas. This study investigates experimentally the effect of column flange thickness and the associated secondary prying on the response of double Tee moment connections. The objectives of this study are: (1) to provide insight as to whether continuity plates are necessary in columns when designing and detailing Tee-connections, (2) and to quantify the secondary prying forces and the contribution of the column flange ductility to the overall ductility of the connection. The results of a series of seven component tests on column flange/thick Tee connected back-to-back are presented and discussed providing all possible failure modes and yielding mechanisms encountered in the column flange. The component tests are subjected to both monotonic and cyclic loadings and cover the range of thin, medium, and thick column flanges connected to thick Tees. A proposed mechanical model is developed and is able to predict the strength, stiffness, ductility, and all possible failure modes of the column flange. The results show that increasing the column flange thickness decreases the secondary prying forces and increases the strength and stiffness capacities of the connection. Detailing columns without continuity plates reduces the fabrication cost and eliminates the need to weld in regions of low notch toughness. Adding the secondary prying failure mode check to the current ANSI/AISC 358-16 and Eurocode 3 part 1-8 guidelines is recommended to ensure a safe design.