Torsional Resistance of High Strength Concrete Filled Steel Tube Beams Stiffened Internally with Steel Bars

The torsional behavior of twelve concrete-filled steel tube (CFST) specimens was experimentally investigated. CFST specimens were reinforced by internal cross-rods with different spacing (0, 50, 100, 150, 200, and 250) mm, different thicknesses of the steel tube (1.5 and 2) mm, and a compressive strength of 65 MPa (high strength concrete). Each sample was tested, and the results were examined. According to the results, the infill concrete prevented buckling failure in CFST specimens. The steel tube and concrete worked together since cutting steel tubes caused diagonal cracks in the infill concrete of CFST specimens. The results also showed that the CFST's torsional moment capacity increased due to the concrete infill, further aiding the steel tubes' performance. Internal stiffening in the steel tubes and concrete infill improved the failure mode, mechanical properties, and CFST specimens’ behavior under torsion.