Contents lists available at ScienceDirect Structures journal homepage: www.elsevier.com/locate/structures Numerical analysis of thin-walled round-ended concrete-filled steel tubular short columns including local buckling effects Mizan Ahmed a,b , Qing Quan Liang a, ⁎ a College of Engineering and Science, Victoria University, PO Box 14428, Melbourne, VIC 8001, Australia b Department of Civil Engineering, Monash University, Clayton, VIC 3800, Australia ARTICLE INFO Keywords: Concrete-filled steel tubes Round-ended Fiber element modeling Nonlinear analysis Local buckling ABSTRACT The behavior of thin-walled round-ended concrete-filled steel tubular (RECFST) short columns loaded axially is characterized by the local-buckling of the flat steel walls and the concrete confinement exerted by the round- ended steel walls. A numerical modeling method implementing fiber analysis is presented in this paper for the determination of the behavior of short thin-walled RECFST columns subjected to axial loads. The mathematical simulation method explicitly incorporates the progressive local buckling of the flat steel walls as well as concrete confinement induced by the round-ended tube walls. A new constitutive model is developed by analyzing the available test results for determining the lateral pressures on the concrete confined by the round-ended tube walls. A coefficient of strength degradation is provided to quantify the residual strength of the encased concrete. The independent test results are utilized to assess the accuracy of the computational modeling scheme. Comparative investigations are carried out to evaluate the accuracy of the numerical models of RECFST columns presented by other investigators. The computer modeling program designed is utilized to quantify the structural responses of thin-walled RECFST composite columns subjected to the variations of material and geometric parameters. A design equation is given for designing thin-walled RECFST columns considering local buckling and concrete confinement effects. The applicability of the current design standards for circular and rectangular CFST columns to RECFST columns is assessed by utilizing experimental data. It is found that the current design codes need to be modified to be used to design RECFST thin-walled columns. The proposed computer simulation program and design equation are demonstrated to accurately yield the performance of RECFST columns under axial loading. 1. Introduction Thin-walled round-ended concrete-filled steel tubular (RECFST) columns as depicted in Fig. 1 combine the advantages of rectangular and circular concrete-filled steel tubular (CFST) columns in terms of the load-carrying capacity, ductility, and energy absorption and have been used as bridge piers in modern bridges, such as the Weihe bridge and Houhu bridge in China [1]. The round-ended tube walls provide ef- fective confining pressures on the filled concrete when subjected to axial compression, which improves the ductility and strength of the columns compared to traditional reinforced concrete columns. As dis- cussed by Shen et al. [2] and Hassanein and Patel [3], the degree of concrete confinement in RECFST columns lies in that between circular and rectangular CFST columns owing to their uncommon shape. Therefore, it is of importance to develop a constitutive model that can accurately determine the degree of concrete confinement in RECFST columns to predict their structural performance. One of the major failure modes associated with RECFST thin-walled columns is the out- ward local-buckling of the flat steel walls. This localized failure sig- nificantly affects the behavior of short RECFST columns in compression, and thus should be considered in any nonlinear numerical modeling procedures for RECFST columns. Experimental programs have been carried out by several in- vestigators, such as Wang [1], Wang et al. [4], Ding et al. [5] and Pi- quer et al. [6], to investigate the responses of RECFST columns. Wang [1] carried out tests on six RECFST slender columns loaded either concentrically or eccentrically. The normal strength concrete with an average cube strength of 34.8 MPa was used to construct the test spe- cimens. The columns failed in a ductile manner except those that filed dude to welding fracture. Test results reported by Wang [1] on slender RECFST columns showed that the ultimate loads of eccentrically loaded RECFST columns were greatly reduced by the loading eccentricity. The https://doi.org/10.1016/j.istruc.2020.08.051 Received 1 July 2020; Received in revised form 11 August 2020; Accepted 17 August 2020 ⁎ Corresponding author. E-mail address: qing.liang@vu.edu.au (Q.Q. Liang). Structures 28 (2020) 181–196 2352-0124/ © 2020 Institution of Structural Engineers. Published by Elsevier Ltd. All rights reserved. T