Abstract: Concrete-filled stainless steel tubular (CFSST) columns have attracted increasing research interests in recent years; however, It seems that the behavior of this type of innovative column under cyclic loading has not been addressed sufficiently so far. This paper reports test results of 10 CFSST columns under constant axial load and cyclically increasing flexural loading. The main parameters varied in the experiments were axial load level, cross-sectional type, and concrete type. The influences of these parameters on strength, ductility, stiffness, and energy dissipation were investigated. It was found that CFSST columns exhibited excellent energy dissipation and ductility, even when the specimens were subjected to high axial loads. The hysteretic behavior of the tested CFSST columns was compared to that of their carbon steel composite counterparts reported in the literature. Several existing design codes were used to predict the ultimate strength and flexural stiffness of the test specimens, and some suggestions are proposed accordingly for designing CFSST columns. DOI: 10.1061/(ASCE) ST.1943-541X.0001705. © 2016 American Society of Civil Engineers.70168

Author keywords: Concrete-filled steel tubes (CFST); Stainless steel; Composite columns; Cyclic lateral loading; Strength; Ductility; Metal and composite structures.

Introduction

In recent times, the use of stainless steel in construction has attracted considerable interest from both researchers and engineers (Gardner 2005; Uy et al. 2011). Compared with conventional carbon steel, the stainless steel has several advantages, such as extremely high durability, excellent corrosion resistance, easiness of maintenance, and improved fire resistance. However, the utilization of stainless steel in real structures has been limited by its relatively high initial cost. One of the solutions to reduce the cost of stainless steel is using stainless steel and concrete composite structures in which the high cost of stainless steel is expected to be partly offset by the cheaper concrete. One such example is to fill concrete into stainless steel tubes to form concrete-filled stainless steel tubes (CFSST), as shown in Fig. 1. Indeed, this type of innovative composite construc- tion has been used in some construction projects, such as the Hearst Tower in New York and Stonecutters Bridge in Hong   Kong.

As shown in Fig. 2, the stress–strain behavior of stainless steel is quite different from that of carbon steel. Whereas carbon   steel

1Associate Professor, College of Transportation and Civil Engineering, Fujian Agriculture and Forestry Univ., 15 Shangxiadian Rd., Cangshan District,  Fuzhou,  Fujian  Province  350002,  P.R.   China.  E-mail:   feiyu

Note. This manuscript was submitted on February 3, 2016; approved on September 22, 2016; published online on November 21, 2016. Discussion period open until April 21, 2017; separate discussions must be submitted for inpidual papers. This paper is part of the Journal of Structural En- gineering, © ASCE, ISSN  0733-9445.

normally exhibits a sharp yield point followed by a flat yield pla- teau, stainless steel shows a rounded stress–strain relation without sharp yield point and demonstrates considerable strain hardening and high ductility (Gardner 2005; Quach et al. 2008; Rasmussen 2003). The different material properties may cause different struc- tural behavior in stainless steel and conventional carbon steel composite columns. This was confirmed by various studies on CFSST columns, such as stub column tests by Lam and Gardner (2008), Tam et al. (2014), and Young and Ellobody (2006), short and slender column tests by Uy et al. (2011), finite-element analy- sis on square CFSST stub columns by Tao et al. (2011), and fire tests by Han et al. (2013). Their research results indicate that the CFSST columns are more ductile and have much higher residual strengths than the conventional concrete-filled steel tube (CFST) columns (Tao et al. 2011; Uy et al. 2011). Meanwhile, a CFSST column generally has  higher  fire  resistance  than  its  carbon steel counterpart, mainly due to the differences in thermal and mechanical properties between stainless and carbon  steels.