Performance of Concrete-Filled Steel Tubular Columns with Bi-angled Structural Steel Encasement under Axial Compression—Technical Note

ABSTRACT This study investigates the axial compressive strength of steel-encased concrete-filled steel tubular (CFST) columns with the same cross-sectional area but with encasement oriented differently. A series of 6 different CFST columns of 12 specimens have been tested under axial compression, as per the guidelines in ANSI/AISC 360-16, Specification for Structural Steel Buildings. The E250 grade steel was used for the outer tube (70 by 70 by 1.6 mm) and inner angle section (ISA 25 by 25 by 3 mm). For the confinement of concrete, C40 grade was used. According to the experimental results, the influence of the bi-angled section significantly provides greater compressive strength for the cruciform-angled (double angle) CFST 01 and back-back attached (double angle) CFST 04 forms. The maximum theoretical strength composite column was derived as per the ANSI code and correlated with the experimental data. The load versus axial shortening curves were compared and commented on with differently oriented steel-encased columns. The CFST column failure pattern regarding ductility index and stiffness index has been investigated. Furthermore, the recommendation regarding the position and orientation of steel encasement has been made for bi-angled columns.