A Comparative Study of Various Shape Sections of Concrete-Filled Steel Tube Beams under Bending

Beam sections are commonly designed with various height-to-width ratios. Under bending, the height is more important than the width because it takes the power of three in the inertia modulus. Studies on particular concrete filled steel tube (CFST) beams—steel tubes filled with concrete—have included investigations and have been published. However, the effect of various height-to-width ratios on behavior, bending moment, and stiffness of rectangular CFST beam sections has rarely been found in the literature and is thus the focus of this study. Therefore, a CFST section available in the literature was selected. The fiber model of this section was developed in SAP2000 and verified. A total of 22 sections with the same cross-sectional area of steel, including 21 rectangular sections and one circular section, were then analyzed. The results indicated that the height-to-width ratio plays an important role in the behavior, moment capacity, and stiffness of CFST sections. Interestingly, when the height-to-width ratio equals 1.8, the rectangular and circular sections have similar mechanical properties. The results confirmed that the sections with height-to-width ratios less than 1.8 (including the square section) exhibit significantly lower mechanical properties than the circular section. When the ratio is greater than 1.8, rectangular CFST sections have negligibly higher ultimate moments than the circular CFST section. These outcomes provide useful information for structural engineers when designing CFST beams in practice, a step toward CFST frame construction.