PSI - Issue 70

Oberoi Kabrambam et al. / Procedia Structural Integrity 70 (2025) 74–81

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1. Introduction Concrete-Filled Steel Tube (CFST) is a composite structural member that consists of a hollow steel tube filled with concrete. This combination allows CFST members to benefit from the strengths of both materials which helps in creating an efficient system for resisting compression, bending, and shear forces. CFST members offers high flexural strength, compressive strength, confinement, energy absorption capacities and can also prevent and delay global and local buckling (Han et al., 2014). The concrete which is present inside the CFST protects the internal steel elements from corrosion. The concrete core helps in protecting the steel from heat and the steel provides fire resistance for the concrete core so the CFST as a whole provides good fire resistance without the need for any other additional protection. Because of high strength and more load carrying capacity of the CFST even in smaller cross-sectional areas, it allows for more useable floor areas in buildings. Shuttering is not required in CFST construction which helps in reducing construction time and cost. CFST members are found in buildings, bridges, towers etc. Xu et al. (2016) performed experimental and numerical evaluation of hexagonal stub column and beam under axial compression test and bending test. They used irregular hexagonal cross-sectional shape. They inspect specimens with varying steel ratios and compared them with hollow counterparts to assess the influence of core concrete, they found that the infill concrete increases compressive strength and ductility. Xu et al. (2016) studied the seismic behavior of the column base for the hexagonal CFST along the strong axis experimentally. The experimental results conducted by them show that the concrete-encased column bases exhibit higher strength with good ductility and high energy dissipation capacity. Ma et al. (2018) performed finite element analysis of hexagonal concrete-encased CFST columns under axial compressive forces and cyclic bending moments. They performed parametric analysis to investigate the influence of various parameters on force-displacement envelope curve of the hexagonal concrete-encased CFST columns. Mazlan and Al Zand (2022) numerically studied the flexural behavior of double-skin hexagonal CFST beam under 4-point bend test for static load. They found that using double skin significantly reduces outward buckling during failure. Ami and Patel (2023) evaluate the structural performance of short hexagonal CFST column stiffened by CFRP strips through nonlinear analysis and numerical simulation. They found out that using CFRP strips increases confinement of the steel tube and increases the strength of column by up to 35%. As we can see from the literature, 4-point bend test of single skin regular hexagonal CFST beam has not been done so the key significance of my study is to study how the change in the strength of concrete affect the ultimate moment capacity of hexagonal CFST beam, its local buckling behavior and yielding of the steel tube at the ultimate point.

Fig. 1. Sectional dimension of hexagonal CFST.

Fig. 2. Canton tower (Han et al., 2014)