Development of Numerical Models for KBMFs Under Cyclic Loads

Abstract

This article presents the development of a numerical model to investigate Knee-Brace Moment Frames (KBMFs) subjected to cyclic loading. The KBMF system integrates the seismic resistant characteristics of Moment Resisting Frames (MRFs) and Eccentrically Braced Frames (EBFs). This structural system utilizes short and stocky braces to resist seismic actions. The analytical results obtained from the numerical simulation were validated against experimental data of KBMF specimens under cyclic loading. The comparison demonstrates that the proposed analytical model can satisfactorily predict the structural response. Consequently, this modeling approach can be effectively utilized for the analysis and design of KBMF structural systems in the future. This study presents the comprehensive numerical model development and validation using SeismoStruct to investigate the non-linear behavior of Knee-Brace Moment Frames (KBMFs) and Buckling-Restrained Knee Braces (BRKBs) subjected to cyclic loading and non-linear static (Pushover) analysis. The KBMF configuration functions as a primary structural fuse that dissipates seismic energy through short, dedicated bracing members while preserving the structural integrity of primary beams and columns. A 2D non-linear analytical model was constructed utilizing lumped plasticity formulations coupled with fiber-section discretized elements to accurately capture material and geometric non-linearities. The reliability of the numerical frame model was rigorously verified against experimental testing data using quantitative metrics, including lateral peak load, initial elastic stiffness, and total cumulative dissipated energy. The comparative evaluation demonstrated exceptional consistency; relative errors between numerical predictions and physical experiments were 2.97% - 3.73% for ultimate strength, 5.33%$ for initial stiffness, and 8.31%$ for energy dissipation, well within an acceptable threshold of 8.5%. The proposed modeling methodology proves to be a robust and viable analytical framework for the seismic design and retrofitting of steel frame structures.