Impact of diameter to thickness (D/t) on axial capacity of circular CFST columns: Experimental, parametric and numerical analysis

Twenty-four circular Concrete Filled Steel Tube (CFST) columns divided in to three series based on their cross-sectional dimensions were subjected to uni-axial compression and their behaviour is studied. This paper aims to develop the volume of experimental database as there is shortage in data that can assess the guidance from the codes and enhances their accuracy in determining the ultimate capacities and the behaviour of CFST specimens subjected to uni axial compression. This study consists of CFST specimens having outer diameter of 76 mm, 89 mm and 100 mm with same wall thickness of 3 mm having four Length to Diameter (L/D) ratios of 3, 4, 5 and 6. Impact of D/t on the parameters like confinement (ξ), strength index (SI), relative slenderness ratio (λ), percentage contribution of steel and concrete and ductility index (DI) were studied. Further, the axial compressive load values were compared with the predicted design values of codes, namely, Eurocode – 4 (EC4), American code (AISC 360-10), Australian code (AS5100), Chinese code (DBJ13-51) and American Concrete Institute (ACI-318). A design equation is proposed to calculate the ultimate axial load and the predicted results are near to the test results. To check the accuracy of the proposed equation, experimental results of 63 CFST circular columns from the literatures were compared with proposed equation and found the results to be conservative. At last, finite element analysis using ABAQUS was done to study the behaviour of column buckling, axial load and displacement curves. Results showed good agreement with experimental test results.