Assessment of the performance of a novel T-Stub-enhanced ConXL moment connection under fire

Box columns are widely recognized for their satisfactory performance in structural applications; however, their complex fabrication, particularly with the use of continuity plates, remains a significant drawback. The ConXtech® ConXL™ (referred to as ConXL) moment connection addresses this limitation, offering advantages such as improved industrialization processes and construction quality. This study proposes an innovative enhancement to the ConXL connection by incorporating a T-stub for application with unfilled box columns. The enhanced connection is analyzed through parametric and numerical investigations, with a particular focus on its behavior under fire. The results indicate that all types of ConXL connections maintain stable hysteresis curves, even at elevated temperatures of up to 600 °C. These connections achieve rotations exceeding 0.04 radians without forming plastic hinges, confirming their suitability for use in special moment frames. Additionally, the incorporation of the T-stub significantly enhances the performance of the ConXL connection, especially under high-temperature conditions. Comparative analysis revealed that the T-stub increased the connections' ultimate strength by factors of 1.08, 1.11, 1.10, and 1.87 at temperatures of 20, 200, 400, and 600 °C, respectively. Predictive equations for the behavior of the enhanced system are proposed, offering a practical tool for structural design and analysis practitioners.