Experimental Investigations on Axial–Flexural Behaviour of Slender Concrete Filled Steel Tubular Columns

Axial–flexural behaviour of Concrete Filled Steel Tubular (CFST) column specimens utilizing routinely used Indian hollow steel tube sections is investigated. Eighteen test specimens comprising of circular, square and rectangular geometrical shapes are considered. A simple mechanism is developed with pinned end conditions to utilize full testing length of slender CFST column. Maximum load, axial shortening and lateral displacement parameters are evaluated to quantify axial–flexural behaviour of slender CFST column test specimens. Normalized ratios in terms of confinement factor, steel and concrete contribution ratio, ductility index, strength index and load carrying capacity are estimated to study efficacy of geometrical shapes of CFST column test specimens. It has been found that square CFST column outperforms circular and rectangular CFST column for resisting maximum load with global buckling as predominant mode of failure. The maximum load carrying capacity of circular, square and rectangular CFST test specimens under concentric loading is found to reduce for eccentric loading with increased eccentricity. Concentrically loaded CFST column test specimens show local buckling as predominant failure against global buckling failure under eccentric loading. Design code EC4 estimates load and moment for CFST column test specimens in close agreement to experimental values. Dissection of the CFST test specimens reveal that concrete infilled hollow steel tube cracked due to tensile and compressive stresses ensuring perfect bond assumption between steel and concrete elements. © 2022, The Institution of Engineers (India).