Axial-flexural behaviour of concrete filled double skinned steel tubular (CFDST) composite column: Experimental investigations

Abstract

Concrete Filled Double Skinned Steel Tubular (CFDST) composite column comprising of outer and inner steel tubes is a class of CFST composite columns developed for improved structural performance and is evolving. An experimental investigation is carried out on total 10 nos. of CFDST composite column test specimens including one CFST column under axial-flexural loading. Parametric study is performed considering outer square steel tube with inner steel tubes of circular and diagonally oriented square shapes as well as without inner steel tubes of square and circular shapes, not commonly found in the literature. Influence of D/t ratio and confinement of concrete sandwiched between steel tubes are examined. An effective loading mechanism, utilizing the full length of the test specimen, is developed. Ultimate load carrying capacity, longitudinal and lateral strains as well as axial and lateral displacements are extracted for test specimens. It is shown that, CFDST column with outer and inner square tubes under axial load performs well in terms of ultimate load capacity, confinement effect, displacement behaviour and ductility vis-à-vis CFST column. Experimental load-moment (P-M) interaction curve is plotted for CFDST composite column. Shape and orientation of inner square steel tube w.r.t outer square steel tube does not have detrimental effect on axial strength of the CFDST columns. Axially loaded CFDST columns exhibit significant confinement of concrete at the level of loading ∼ 20–40% of the peak load.