Behavior of self-compacting concrete columns reinforced longitudinally with steel tubes

This study investigates the behavior of self-compacting concrete (SCC) specimens reinforced with small-diameter steel tubes in lieu of reinforcing bars. Twenty specimens were cast and tested. Four specimens were reinforced with normal steel bars (reference specimens) and the remaining 16 with steel tubes. All specimens contained steel helices with a pitch of either 50 mm or 75 mm. Deformed steel bars of 16-mm diameter were used in the four reference specimens as longitudinal reinforcement. Steel tubes of 33.7-mm outside diameter with 2-mm wall thickness (ST33.7) and steel tubes of 26.9-mm outside diameter with 2.6-mm wall thickness (ST26.9) were used as longitudinal reinforcement in the remaining 16 specimens. The specimens were divided into five groups with four specimens in each group. From each group, one specimen was tested under concentric load, one under 25-mm eccentric load, one under 50-mm eccentric load, and one under flexural load. Although the nominal yield tensile strength of the steel bars was 150 and 250 MPa greater than the nominal yield tensile strength of steel tubes ST33.7 and ST26.9, respectively, the results revealed that steel tube reinforced self-compacting concrete (STR SCC) specimens have ultimate load similar to reference specimens. Ductility of concentrically loaded STR SCC specimens was higher than that of the reference specimens. This study also reveals the challenges associated with using steel tubes as longitudinal reinforcement in STR SCC column specimens due to slip of steel tubes in concrete and explores remedial measures for the slip of steel tubes