Citation: Shaker, F.M.F.; Daif, M.S.; Deifalla, A.F.; Ayash, N.M. Parametric Study on the Behavior of Steel Tube Columns with Infilled Concrete—An Analytical Study. Sustainability 2022, 14, 14024. https://doi.org/10.3390/ su142114024 Academic Editors: Dalei Wang, Tao Chen, Qing Zhang and Yue Pan Received: 3 September 2022 Accepted: 9 October 2022 Published: 28 October 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). sustainability Article Parametric Study on the Behavior of Steel Tube Columns with Infilled Concrete—An Analytical Study Fattouh M. F. Shaker 1 , Mohammed S. Daif 1 , Ahmed Farouk Deifalla 2, * and Nehal M. Ayash 1, * 1 Civil Engineering Department, Faculty of Engineering at Mataria, Helwan University, Cairo 11718, Egypt 2 Structural Engineering and Construction Management, Future University in Egypt, New Cairo 11835, Egypt * Correspondence: ahmed.deifalla@fue.edu.eg (A.F.D.); nehal82ayash@m-eng.helwan.edu.eg (N.M.A.) Abstract: Concrete-filled steel tube (CFST) columns are used in tall buildings and bridges, and they pro- vide more rigidity and higher bearing capacity, but buckling affects their behavior. There is an exceptional need to study the behavior of these columns under various conditions. The numerical method is benefi- cial in supplementing the experimental works and is used to explore the effects of various parameters because of the limitations in cost, apparatus, and time of the experimental program. The various pa- rameters, such as the different slenderness ratios, i.e., column-height-to-cross-section-dimension (H/D), different steel-tube-thickness-to-column-dimension (D/t), and different compressive strength of concrete to yield strength of steel tube ratio (fc/fy) under concentric axial loading are considered in this current study. Firstly, a finite element model used the “ANSYS” software program and was constructed to validate the results of the experimental works. The extensive numerical models were carried out to extensively widen the study in this field. The numerical work was conducted on sixty- four specimens. Moreover, the analytical calculations from the different international codes/standards were compared with the numerical results to test their reliability in predicting the ultimate carrying loads. The study provided results that show the improvement effect of CFST columns with the high compressive strength of infilled concrete, while no remarkable enhancement effect with the high yield strength of steel tube was observed. Increasing the columns’ diameter is more effective in enhancing the load capacity (about three times more) than increasing the tube thickness (about 1.3 times). Ring stiffeners for long CFST columns (H/D > 12) do not lead to any enhancement of the column behavior due to yielding occurring firstly at the location of the rings. ECP205-2007 is the most conservative design code in predicting the load capacity of CFST columns, while the AIJ design code is good at predicting the ultimate load failure compared to the other codes/standards. Eurocode 4 provides underestimation values of the load-carrying capacity of CFST columns. Keywords: numerical analysis; infilled concrete; steel tube; stiffeners; buckling 1. Introduction Compared to conventional reinforced concrete columns, in concrete-filled steel tubes (CFSTs), the steel tube lies at the outer perimeter, enhances the stiffness, and has a much greater modulus of elasticity than the concrete. Additionally, it confines the concrete core, which increases the compressive strength and the ductility of the column. While the infilled concrete forms an ideal core to withstand the compressive load, it also delays and often prevents local buckling of the steel. Concrete-filled steel tube columns (CFSTs) were used for many decades as a composite structural element due to their numerous structural advantages, such as high strength, high ductility, fire resistance, and considerable energy absorption capacities. Nowadays, composite structures are considered to be an advanta- geous system for carrying loads in different building structures, such as bridges, high-rise buildings, subway stations, workshop buildings, electricity pylons and poles, and other types of structures. The sustainability of this type of construction has been investigated Sustainability 2022, 14, 14024. https://doi.org/10.3390/su142114024 https://www.mdpi.com/journal/sustainability