EXPERIMENTAL STUDY ON CIRCULAR AND SQUARE CONCRETE FILLED STEEL TUBE COLUMNS SUBJECTED TO AXIAL COMPRESSION LOADS

Abstract

D. R. Panchal1, V. P. Sheta2 1Assistant Professor, Department of Applied Mechanics, FTE-MSU, Vadodara, Gujarat, India panchaldr@gmail.com 2M.E. (Structural Engineering) Student, Department of Applied Mechanics, FTE-MSU, Vadodara, Gujarat, India vpsheta63@gmail.com Abstract This paper investigates the behaviour of concentrically axially loaded circular and square high strength steel tube (Fe310 grade) columns filled with different grades (M20, M30 & M40 etc.) of concrete. The effects of grade of concrete and composite action between the steel tube and the concrete core on axial load capacity are studied & graphs of Axial load v/s vertical deflection (axial shortening curves) are plotted experimentally. Some important performance indices entitled as Ductility Index (DI), Strength factor (SI) and Concrete Contribution Ratio(CCR) are also evaluated and compared between the circular and the square shaped Concrete Filled Steel Tube (CFST) columns.By referring many research works, we can know firmly that confinement effect is restricted to short column only. So, we choose 300mm length for all the specimens of 88.9mm dia and 80×80mm size, to keep the columns stub only for getting benefit of confinement effect especially in circular sections.From the results, it has been noted that square columns have higher axial capacity when compared with circular columns of same resisting area under compression. Hence, size reduction for square column is possible. While ductility index for circular columns are quite better than square ones. Ultimate failure patterns are obtained by applying axial compression loads concentrically up to ultimate stage on circular and square CFST stub columns. as expected, the results shows a Local buckling i.e. crushing of concrete type of failure at supports. Ultimate axial load capacity of Concrete filled steel tubular columns are evaluated and compared experimentally as well as by calculations also, as per the guidelines suggested by EC4(Eurocode part-4, British Standards Institutions) code, which is the best suitable code for design of CFST columns amongst all other international codes for composite structure design. From the study it is concluded that, loads obtained by EC4 fits nearer to perfection and depicts the behaviour well enough by 15-20% error with experimental ultimate loads. The results obtained by experimental and EC4 code are validated well with the previous scholar researchers too