Residual Stress and Global Deflection Limits for Future Hot-Rolled Steel Asymmetric I-Beams

Abstract

Medium-span to long-span floor systems in residential and commercial construction have commonly used steel–concrete composite construction. These composite floor systems have become more structurally efficient with the use of built-up asymmetric steel beam sections. Although structural efficiency is important, a fast and cost-effective solution is paramount. The research presented herein is being conducted for the AISC on hot-rolled asymmetric I-beams (A-shapes) for potential future addition to the AISC Steel Construction Manual. The aim is to adequately proportion these hot-rolled shapes so they match or improve built-up asymmetric beam structural efficiency while increasing the speed and economy of steel–concrete composite floor systems. The initial focus has been placed on steel behavior as a result of the manufacturing process, where residual stresses and deformations can be an issue due to uneven cooling. A better understanding of residual stresses is critical for accurate calculation of the lateral torsional buckling strength during deck casting and placement. In addition, steel mills have expressed concern regarding global deformation of an asymmetric I-shape. As a result, an extensive thermomechanical finite-element modeling approach, using nonlinear thermomechanical properties of steel, was devised to simulate the cooling process of hot-rolled steel shapes. A single model requires up to 50 h of processing time using the Texas A&M high-performance computing center. The modeling procedure was validated against accepted residual stress experimental test measurements. Proof-of-concept (POC) A-shape beams were also produced by Nucor. The POC beam cooling profiles were used as further validation. Then, a parametric study was executed that individually altered the top flange width and thickness of two different-depth W-shapes. The parametric study identified a maximum flange width-to-thickness ratio to satisfy a reasonable residual compressive stress limit. The study also found that, despite concerns, global deformations are not an issue for realistic proportions of future hot-rolled asymmetric I-beams.