Abstract: An experimental study was performed to investigate the structural behavior of thin-walled rectangular concrete-filled tubular (RCFT) columns。 This study mainly focused on the effects of a high-strength steel slender section on the overall eccentric compression capacity。 The test parameters included the width-to-thickness ratio of steel plates, yield strength of steel plates, and use of stiffeners。 Five specimens were tested under eccentric axial loading。 In the slender-section specimens, despite early local buckling, significant postbuckling reserve strength developed。 Consequently, the predictions of a current specification significantly underestimated the load-carrying capacity of the slender-section specimens。 The specimens strengthened with vertical stiffeners exhibited enhanced strength and ductility, attaining the plastic capacity of the composite section。 Furthermore, a design method of vertical stiffener was developed for high-strength steel RCFT columns。 DOI: 10。1061/(ASCE)ST。1943-541X。0001724。 © 2016 American Society of Civil Engineers。71995

Author keywords: Concrete-filled tube; High-strength steel; Slender section; Stiffener; Eccentric axial loading; Metal and composite structures。

Introduction

In concrete-filled steel tube (CFT) columns, the concrete crushing is restrained by the lateral confinement of the steel tube, while the local buckling of the steel tube is restrained by the infill concrete。 For this reason, CFT columns exhibit excellent structural perfor- mance。 Furthermore, in the CFT columns, unlike concrete-encased steel columns, the steel plates are located at the perimeter of the cross section。 Thus, the contribution of the steel section to flexural capacity can be maximized, particularly when high-strength steel is used。 From the viewpoint of constructability, the use of high- strength steel is also beneficial since the welding and lifting weights can be reduced by using thin plates。 When high-strength steel and high-strength concrete are utilized together, the cross section area can be significantly reduced, which is preferable for architectural design and planning。 Recently in Japan, high-strength CFT col- umns with 780 MPa (tensile strength) steel and 150 MPa concrete were used in practice (Matsumoto et al。   2012)。

However, when the yield strength of the steel tube  exceeds 600 MPa (yield strain  of  approximately  0。003),  early crushing of concrete can occur before yielding of the high-strength steel (Kim et al。 2014)。 For  this  reason,  current  design  codes limit the yield strength of steel for composite members。 In ANSI/AISC

1Graduate Student, Dept。 of Architecture and Architectural Engineer- ing, Seoul National Univ。, 1 Gwanak-ro, Seoul 151-744, Korea。 E-mail: hojun1032@gmail。com

2Senior Researcher, Building Structure Research Group, POSCO Global R&D Center, 100 Songdogwahak-ro, Incheon 406-840, Korea 

3Professor, Dept。 of Architecture and Architectural Engineering, Seoul National Univ。,  1 Gwanak-ro, Seoul 151-744, Korea。 E-mail:     

Note。 This manuscript was submitted on February 10, 2016; approved on October 12, 2016; published online on December 5, 2016。 Discussion period open until May 5, 2017; separate discussions must be submitted for inpidual papers。 This paper is part of the Journal of Structural 

360 (AISC 2010) and Eurocode 4 (CEN 2004), the yield strength of steel is limited to 525 and 460 MPa, respectively (Leon et al。 2007)。 However, in the case of CFT columns, since the infill concrete is laterally confined by the steel tube, the limitation of the yield strength needs to be  reconsidered。

For more than a decade, experimental studies have been con- ducted on rectangular CFT (RCFT) columns and beam-columns using high-strength steel (yield strength ≥600 MPa)。 Despite the advantages of high-strength steel, in order to restrain local buck- ling, current design codes require thick plates or low width-to- thickness ratios (bt=tt)。 Thus, the majority of previous experiments for high-strength RCFT columns were performed for columns with compact or noncompact sections。 Uy (2001b) tested columns, beams, and beam-columns with bt=tt ¼ 20。0 ∼ 40。0。 Sakino et al。 (2004) and Fujimoto et al。 (2004) reported extensive experimental studies on columns and beam-columns (bt=tt ¼ 16。5 ∼ 48。2), as parts of U。S。–Japan cooperative research。 Varma et al。 (2002, 2004)  tested  beam-columns  focusing  on  monotonic  and cyclic