ستون های لوله ای فولادی پر شده از بتن مسلح فولادی تحت چرخه محوری و عرضی Steel‑reinforced concrete‑flled steel tubular columns under axial and lateral cyclic loading

Introduction Composite columns have higher strength and ductility efciency due to composite action between steel and concrete core. In this type of composite column, the concrete can be plain such as (CFT) or reinforced concrete with steel bar (RCFT). Current studies (Xiamuxi and Hasegawa 2012; Endo et al. 2000; Hua et al. 2005; Xiamuxi and Hasegawa 2011) show that RCFT columns have better performance regarding moderate and severe earthquake excitations, higher toughness, and ductility in comparison with CFT columns. A new form of concrete-filled steel tube (CFT) column, namely steel-reinforced concrete-flled steel tubular (SRCFT) column, has been proposed recently (Ellobody and Young 2006; Elchalakani and Zhao 2008). The new composite column consists of a steel tube outside and a reinforcing steel section inside to reinforce concrete, as shown in Fig. 1. Hamidian et al. (2016) have investigated the axial compressive behaviors of concrete-flled steel tube columns reinforced with diferent spiral pitch spacing. They found that the rate of pitch spacing has an important role on the postyield behavior of the reinforced concrete-flled steel tube. The results show that as the rate of pitch spacing decreases, the post-yield behavior of SRCFTs improves. In addition, the efectiveness of the pitch spacing rate on the post-yield behavior of a SRCFT column is more than the thickness rate of the steel tube. Wang et al. (2004) investigated the strength and ductility of cross-shaped steel-reinforced concrete-flled tube (SRCFT) columns subjected to axial compressive loads. The results showed that composite columns had higher strength, energy absorption capacity, and ductility performance due to the composite action between steel tube, reinforcing steel section, and concrete. Chang et al. (2012) present a numerical study of cyclically loaded cross-shaped steel-reinforced concrete-flled tube (SRCFT) and the mechanical performance of SRCFT columns under cyclic loading. They found that the presence of the section steel could carry the lateral load and reduce the tensile zone of the concrete section. The structural steel section could provide a confnement efect on the concrete core and increase the load-carrying capacity and post-peak strength of SRCFT columns. Lai and Ho (2016) mentioned that the composite action could not be fully developed because of various dilatation attributes of concrete and steel tube in the elastic stage. In addition, due to the inelastic outward buckling of steel tube, CFT columns might sufer serious degradation. Qin and Xiao (2013) have been conducted a research on concrete-flled steel tube columns subjected to cyclic lateral force. They found that the ratio of diameter to thickness and the material properties strongly afect the seismic behavior of CFT columns. Better performance could be observed for CFT columns with smaller tube diameter to thickness ratio and higher material strengths.