Evaluation of Hybrid Strong Flange I-Sections under Compression

Hybrid I-sections are frequently designed with slender webs and thick flanges, and greater material strength in the flanges. Under the fundamental load case of pure compression or bending, a compressed flange will approach fully plastic capacity before failure, whereas the web develops only its local buckling capacity, a long-overlooked failure mechanism not currently integrated into design-ready tools. This paper provides the first systematic experimental and numerical assessment of the effect of hybridity on strong flange sections, establishing the experimentally grounded and numerically validated basis required to quantify this behavior and incorporate it into design-oriented strength models. We present the test method, results, and analysis of 13 stub column tests on hybrid stainless steel I-profiles exhibiting strong flange behavior. The tested sections are comprised of web and flange plates made from a combination of austenitic and duplex stainless steels and carbon steel, fabricated by tungsten inert gas (TIG) welding. Tensile coupon tests were conducted on each constituent plate to measure material properties. Geometric imperfections for the web and flanges of each column were measured by pairing an adapted computer numerical control (CNC) machine with a linear variable differential transformer. The stub columns were compressed under a constant displacement rate while strains were measured at multiple locations using a video extensometer (VE) alongside digital image correlation (DIC). A finite-element model of the compression tests was developed in ABAQUS and validated against the experimental results. The influence of individual geometrical and material properties on buckling mechanisms and ultimate strength was analyzed. The experimental results in this paper provide the essential foundations to then develop a new direct strength method (DSM) formulation that explicitly captures the governing behavior of hybrid strong flange I-sections, addressing a key gap in current design practice.