Seismic Performance Enhancement of Steel Knee-Braced Frames through Optimization of Knee Length and Supplemental Supports

The strategic use of replaceable structural fuses is pivotal for achieving seismic resilience, as it localizes damage and facilitates post-earthquake repair. This study addresses a critical gap in the design of steel Knee-Braced Frames (KBFs) by systematically quantifying the influence of the knee element's length a key yet poorly understood parameter on the global seismic performance. Through a detailed finite element parametric study in ABAQUS, validated against experimental results, we demonstrate a fundamental performance trade-off: while longer knee elements successfully protect primary columns by concentrating plasticity, they precipitate a severe degradation in initial stiffness (up to 41%) and energy dissipation capacity (up to 79%). To mitigate this limitation, we propose a novel enhanced KBF system incorporating supplemental supports that enable a dual-phase response. This system functions as a conventional KBF under moderate seismic demands, while the supports engage during intense shaking to provide a secondary stiffening mechanism and enhance energy absorption. Nonlinear dynamic analysis under the Northridge earthquake record confirms the superiority of the proposed system, showing a 38.14% reduction in peak lateral displacements compared to the conventional configuration. Our findings provide both a critical understanding of KBF geometry-performance relationships and a practical, optimized design solution for enhancing structural resilience.