This study addresses a critical gap in seismic design codes by evaluating the nonlinear performance of multi‐tiered eccentrically braced frames (MT‐EBFs) and offering practical recommendations for future provisions. MT‐EBFs, an advanced variation of conventional EBFs, incorporate multiple tiers of links and braces within a single story, making them well‐suited for buildings with large interstory heights while enhancing energy dissipation capacity. While previous research has demonstrated that directly connecting intermediate I‐shaped links to braces can effectively eliminate lateral‐torsional buckling (LTB), such configurations pose significant fabrication and constructability challenges. Therefore, this study focuses on more practical gusset‐plate connections using both I‐shaped and box links. Two‐ and three‐tier configurations are designed in accordance with AISC 341‐22, and a comparative assessment is conducted on the buckling behavior of intermediate links and their connections. Nonlinear static pushover analyses are performed using detailed 3D finite element models to investigate LTB and column instability. Results show that intermediate I‐shaped links are highly susceptible to LTB, which compromises overall frame performance. In contrast, box links effectively mitigate local buckling in the link zone, though they tend to shift failure to adjacent members such as braces or columns. Notably, in frames with box links, such instabilities emerge only at drift levels exceeding expected seismic demands, making them a more robust and reliable option. These findings underscore critical instability mechanisms in MT‐EBFs and reveal that current seismic provisions fall short in addressing the unique demands of multi‐tiered configurations, emphasizing the need for performance‐based design updates.
Rezaee et al. (Thu,) studied this question.
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