Studying the Effectiveness of Steel Frames Using Different Bracing Systems under Earthquake Loads by Nonlinear Static Analysis

Abstract

Traditional methods used in designing earthquake-resistant structures do not adequately account for performance levels and seismic risk. This has necessitated the development of alternative approaches that provide a more accurate representation of a structure's actual behavior during an earthquake. Performance-Based Engineering has emerged as a method that ensures precision and efficiency in the analysis, evaluation, and design processes. The significant drifts and displacements observed in steel frames require the application of strengthening techniques to control these displacements and ensure stability under lateral loads. Bracing has proven effective in enhancing performance by providing high stiffness and resistance while simultaneously reducing displacements. In this study, a three-dimensional analysis was conducted on two steel structures: Structure A (four stories) and Structure B (eight stories), both reinforced with four types of central bracing systems (X-bracing, V-bracing, IV-bracing, and Diagonal (D) bracing), using nonlinear static analysis. The results indicated that adding bracing significantly improved performance by increasing elastic stiffness, lateral stiffness, and resistance while reducing relative drifts and displacements. For structure A, Diagonal (D) bracing was identified as the most efficient pattern, offering the highest resistance, lowest drift, and superior elastic and lateral stiffness. For structure B, X-bracing proved to be the most resistant, exhibiting the least drift while providing high stiffness.