Parametric Analysis of Flexural Strength and Structural Efficiency in Steel I-Beams: The Influence of Depth, Flange Compactness, and Lateral Bracing

Abstract

The flexural design of steel I-beams is governed by a complex interaction between cross-section geometry and stability limits, yet comprehensive comparative data on the performance of compact, non-compact, and slender flange sections across a practical range of depths is often lacking. This study presents a systematic parametric analysis of the nominal flexural strength and structural efficiency of I-sections with depths ranging from 1000 mm to 2500 mm, designed and evaluated in strict accordance with SNI 1729:2020. The investigation considers three distinct flange classifications (compact, non-compact, and slender) under fully, partially, and minimally braced conditions to simulate varying degrees of lateral-torsional buckling (LTB). The results establish a clear performance hierarchy, demonstrating that compact flange sections provide superior strength and material efficiency, achieving up to 18.14 kNm/cm². Non-compact sections deliver intermediate capacity, typically 60-64% of compact sections, and are consistently governed by flange local buckling (FLB) for common bracing spacings. Slender sections exhibit severely limited performance, with capacities of only 13-14% of compact sections, rendering them inefficient for primary flexural members. The analysis quantifies the significant economic penalty of inadequate bracing for compact sections, while demonstrating its ineffectiveness for non-compact and slender sections under FLB governance. This research provides a definitive, data-driven framework and practical guidelines for structural engineers to optimize section selection, balancing structural performance with material economy in steel beam design.