Axial compression behavior of a prefabricated F4T-section thin concrete encased steel short columns with different stirrup types

Abstract

A prefabricated F4T-section thin concrete encased steel (F4T-TCES) column with a low reinforcement ratio is proposed to address instability, corrosion resistance issues in pure steel columns, and column protrusion out of the wall. The F4T-section is a T-shaped column with internal steel featuring four flanges. Ten F4T-TCES short columns were tested under axial compression loads, examining five new stirrup types to facilitate construction and study their impact on load-carrying capacity. The effects of steel flange and web thicknesses, stirrup and longitudinal bar diameters, stirrup spacing and form, and concrete encasement thickness on axial compressive behavior were investigated through tests and finite element (FE) analysis. Results indicate that less reinforcement and thin concrete cover can restrain steel elastic buckling and fully utilize material properties. Using 8 mm diameter longitudinal bars and a 1.32 % stirrup ratio provides sufficient strength and adequate confinement. Reliable performance is achieved with a flange thickness of 12 mm, while increasing web thickness beyond 8 mm shows no significant improvement. Increasing concrete encasement thickness from 45 to 70 mm effectively reduces the cracking of the concrete cover. Specimen with stirrup type C exhibits the highest load-carrying capacity, delayed crack initiation, and narrower crack widths, with type D also performing well in crack control. All five stirrup types meet load-carrying requirements, with types C and D being easier to construct and thus preferable. Formulas for the axial compressive strength and a simplified load-axial deformation model for F4T-TCES columns are proposed and validated.