Properties of High-Strength Concrete Filled Steel Tube Columns

Abstract

Abstract. High Strength Concrete Filled Steel tubes (CFST) provide a common construction material in China. The purpose of this research was to determine the axial load properties for CFST subjected to concentric and eccentric loading in a series of experiments. The results show that the magnitude of experimentally measured compressive strength increases for the core concrete, due to the confinement from the steel that is proportional to the ratio of the area of steel to the area of concrete. If the slenderness ratio is kept constant the columns bearing capacity and maximum strain decreases as the eccentricity to radius ratio increases. Formulas to estimate the load bearing capacity for short and for slender eccentrically loaded columns were established from the data. The results have been compared statistically to other published results to show that a general linear form of the capacity equation is warranted for High Strength Concrete Filled Steel tubes. Keywords:Concrete filled steel tubes, high strength concrete, bridge construction. IntroductionThe purpose of this research is to experimentally investigate the properties of concrete filled steel tubes (CFST) using a high strength concrete core. The experimental work investigates the ductility and strength properties of steel tubular columns filled with a high strength concrete core, using short and slender columns subjected to either concentric or eccentric loads. The results are compared to recent published data from the USA, Australia, and China [1][2][3][4][5][6][7][8][9][10][11][12]. The protocol for the column compression tests used both concentric and eccentric load rigs. The columns used in the experiments have length to diameter ratios ranging from 3.5 to 15. This paper outlines the literature relevant to this work, provides a methods section, outlines and summarizes the results and the key findings, and provides a conclusion. Literature ReviewCFST column types have been used in recent high-rise structures in China [13][14][15][16][17][18][19][20][21][22]. CFST structures are emerging as an important structural system for new buildings, particularly for providing earthquake resistance. Steel tubular columns filled with normal strength concrete (NSC) have been studied using slender and eccentrically loaded units [23,24], and based on these studies; a design code has been established for Chinese use [25]. A sketch of a typical CFST building connection showing a column and beam connection is drawn in Figure 1. This sketch provides the definitions of the steel wall thickness, diameter of the steel tube and the area of the concrete core of the composite tube. The schematic format of the connection detail shown in Figure 1 comes from a recent Chinese building. The connection detail has been simplified by reducing the number of bolt holes and stiffener plates. The steel plate for the beam connection transfers the load to the steel tube, which relies on the concrete to provide buckling restraint and increased strength for the given cross-sectional area.An ea...

Confinement effects for rubberised concrete in tubular steel cross-sections under combined loading

“…2g). As pointed out in available literature, the concrete core is under biaxial confinement due to the steel tube having an enhanced compressive strength [52]. The moment capacity (M u,GB ) considers an empirical coefficient, dependent on ξ, the elastic section modulus W sc = πD 3 /32, and the…”

Evaluation and improvement of shear-strength expressions for circular concrete-filled steel tubes

“…( 6) provides the shear strength as a function of the axial load, aspect ratio, as well as concrete-fill and steel-tube properties. [6][7][8][9][10][11]18] was used to evaluate current code expressions. Table 1 shows the average and coefficient of variation (COV) for the measured to predicted strength ratio for each code.…”

“…23. The figure shows that some individual specimens by Qian et al [7] and Lehman et al [10] fail in flexure where 𝑀 𝑒𝑥𝑝 > 1.1𝑀 𝑃𝑆𝐷𝑀 ; as such, these results are not included the following validation.…”

“…Experimental studies on circular CFSTs subjected to shear loading have been conducted in China (e.g., [68]), Japan (e.g., [9]) and the US (e.g., [10,11]). These investigations cover important design parameters including (1) the compressive concrete strength, (2) the yield strength of steel (𝐹 𝑦 ), (3) the shear span-todiameter ratio (𝑎/𝐷), (4) the diameter of the CFST (𝐷), (5) the axial load ratio (𝑃/𝑃 0 ), (6) the internal reinforcement ratio (𝜌 𝑖𝑛𝑡 ), and (7) the bond condition between steel tube and concrete. The collective findings from these investigations are: (1) shear failure does not occur for 𝑎/𝐷 greater than 0.5 [6,8], (2) the shear strength increased with an increase in the 𝑃/𝑃 0 ratio [8,10], (3) composite action between the steel tube and infill concrete is needed to develop the full shear resistance [10], and (4) internal reinforcement has a much smaller contribution to the total shear capacity and in many cases can be neglected [10].…”