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

Abstract 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.