The behavior of circular and square Concrete-Filled Steel Tubular (CFST) sections with various concrete (partial replacement of coarse aggregate with granite, rubber, construction and demolition debris, and fiber) strengths under axial load is presented. The effects of steel tube dimensions, shapes, and the confinement of concrete are examined. Measured column strengths are compared with the values predicted by Eurocode 4 (EC4), Australian Standards, and American Codes. 12 specimens were tested with a strength of concrete as 20 MPa and a D/t ratio 25.0 and 41.2. The columns were 75 mm in diameter, 70 mm in square, and 900 mm in length. All the three codes predicted lower values when compared to experimental results. Modified ACI/AS gives the best estimation for CFST sections with rubber, fiber and C and D debris concrete.

Circular tubular columns have an advantage over sections when used in compression members for a given cross-sectional area; they have a large uniform flexural stiffness in all directions. Filling the tube with concrete will increase the ultimate strength of the member without significant increase in cost. The main effect of concrete is that it delays the local buckling of the tube wall and the concrete itself in the restrained state, and can sustain higher stress and strain than when is unrestrained.

The use of CFSTs provides large saving in cost, as it increases the floor area by a reduction in the required cross-section size. This is very important in the design of tall buildings in cities, where the cost of letting spaces are extremely high. These are particularly significant in the lower storey of tall buildings where short columns usually exist.

CFSTs can provide an excellent monotonic and seismic resistance in two orthogonal directions. Using multiple bays of composite CFST framing in each primary direction of a low to medium-rise building provides seismic redundancy while taking full advantages of the two-way framing capabilities of CFSTs (Hajjar, 2002).

Structural Engineering Journal, Steel Tubular Slender Columns, Concrete-Filled Steel Tubular Sections, Circular Ttubular Columns, Seismic Redundancy, American Institute of Steel Constructions, AISC, Load and Resistance Factor Design Method, Local Buckling, Biaxial Effects, Fiber Reinforced Concrete, Electronic Universal Testing Machine, Monotonic Axial Loading.