Using fibres and fly ash in concrete-filled steel tube columns

The aim of the present study is to experimentally investigate the behaviour of concrete-filled steel tubular columns under axial loading. The grade of concrete used is M20 and the yield strength of the steel is 250 MPa. Fly ash is used as partial replacement (25%) of cement and 0·5, 1·0 and 1·5% polypropylene fibres are added to the concrete; the optimum mix is selected based on the mechanical properties of the concrete and used as a filler material for the columns. Twenty-seven columns of different cross-sections, such as circular, rectangular and square cross-sections with length-to-depth ratio of 2 to 11·83, and two different concrete infills are tested. The load–deflection response of axially loaded columns is obtained. The strength of the columns is predicted theoretically by various international design standards, including Eurocode 4 (BS EN 1994-1-1). A comparative study is made between the experimental and theoretical values. From the investigations, it is inferred that the partial replacement of cement by fly ash and addition of fibres in the concrete is advantageous as infill material in concrete-filled steel tubular columns.