Experimental investigation on seismic behavior of square CFT columns with different shear stud layout Bin Wang a , Jianghao Liang a , Zheng Lu a,b, ⁎ a Research Institute of Structural Engineering and Disaster Reduction, College of Civil Engineering, Tongji University, Shanghai 200092, China b State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China abstract article info Article history: Received 5 January 2018 Received in revised form 3 October 2018 Accepted 3 October 2018 Available online xxxx This study evaluates the seismic behavior of the square concrete-filled steel tube (CFT) column under cyclic load- ing. A total of nine large-scale square CFT columns with different shear stud layout and axial compressive load ratio designed according to the recommendations of the engineering practice were investigated. Seismic perfor- mance of these specimens was discussed in terms of damage mode, force-displacement relationship, deforma- tion capacity, stiffness degradation, and energy dissipation capacity. Test results show that the axial compressive load ratio has a significant effect on the hysteresis loops of the square CFT columns. Shear stud has an obvious improvement of the local buckling of the steel tube in specimens with low axial compressive load ratio. However, it is not as much expected improvement on the local buckling of the steel tube when subjected to high axial compressive force. In addition, energy dissipation capacity of the square CFT column is shown to be insensitive to the shear stud layout. © 2018 Elsevier Ltd. All rights reserved. Keywords: Concrete-filled steel tube (CFT) column Shear stud Cyclic loading Axial compressive load ratio Seismic behavior 1. Introduction Reinforced concrete (RC) columns are extensively used in high-rise buildings in earthquake-prone regions around the world. To achieve the desirable seismic performance under moderate-to-strong earth- quakes, however, RC columns located in the bottom stories of the high-rise buildings are usually designed with large cross-sections asso- ciated with dense reinforcement. Fat RC columns not only occupy the useful space but also increase the self-weight of the whole building, which in turn lead to an amplification of the seismic force. Assembling dense reinforcement in these columns requires considerable labour and time-consuming work. Moreover, heavily congested reinforcement may result in poorly compacted concrete and construction difficulties. For these reasons, concrete-filled steel tube (CFT) columns are appeal- ing to high-rise buildings in the recent years due to these remarkable benefits [1–18], including high strength, large lateral stiffness, favourable ductility, large energy dissipation capacity, and convenience for construction. Square CFT column, as one of the types of composite members in CFT family, has been applied in modern engineering practice widely, which is attributed to the convenient connection details with other structural members, as shown in Fig. 1. An extensive experimental and numerical investigations of the square CFT columns were carried out with various loading condition [19–22] and material strength [23–26]. However, compared with the circular CFT members, square CFT columns exhibit a relatively low local-buckling resistance due to the weak interaction between the steel tube and the infilled concrete. To improve the cyclic behavior of the square CFT column, some efficient stiffening details have been proposed in terms of setting stiffeners, welding shear studs, and binding bars. Ge and Usami [27] explored the experimental studies of the square CFT column with longitudinal stiffeners. Test results showed that the significant stiffening effect of the longitudinal stiffeners on the column strength was expected, however, the stiffening effects against the buckling mode of the steel plates were not as much expected because of the relatively lower rigidity of the stiffener. Hsu and Juang [28] adopted the internal strengthening braces between the steel plates to improve the cyclic performance of the square CFT column. Parallel design concept with binding bars was proposed by Cai and He [29] to improve the concrete confinement effect and the local buckling behav- ior. In addition, Wang et al. [30] also presented the hysteretic behavior of square CFT columns with binding bars. Huang et al. [31] developed a stiffening scheme associated with welding a set of four steel tie bars crossing the corners of the steel tube. Wang et al. [32] and Yang et al. [33] conducted systematic studies on the square CFT columns with four different layouts of reinforcement stiffener under axial compres- sive loading. Test results indicated that these stiffeners could help to delay or even prevent local buckling of the steel tubes. Ding et al. [34] carried out a comparative study of axially-loaded square stirrup- confinedCFT columns. It was found that internal loop and spiral stirrups in the square stirrup-confinedCFT columns could effectively alleviate the local buckling of the square steel tube. In addition, to meet the Journal of Constructional Steel Research 153 (2019) 130–138 ⁎ Corresponding author. E-mail address: luzheng111@tongji.edu.cn (Z. Lu). https://doi.org/10.1016/j.jcsr.2018.10.004 0143-974X/© 2018 Elsevier Ltd. All rights reserved. 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