مهدی نعمت زاده افروزی

Concrete-encased concrete-filled steel tubes (CFST) has extensive applications in the world. According to previous researches, if the CFST is placed in the compression zone, the confinement increases, and the compressive capacity of the concrete is completely used. The prestressed strands also increase the core concrete confinement and eliminate tension cracks. Therefore, in this paper, to achieve the benefits of CFST and prestressed strand, for the first time, a novel concept called prestressed concrete-encased CFST (PCE-CFST) beams were introduced. The main objective of the combination of steel tube and pre-stressed strands is to increase the core concrete compressive strength and control the concrete crack in the tension zone. Six beams were constructed using self-compacting concrete to investigate the influence of variations in the pre-stressing force level of the pre-stressed strands, the pre-stressed strands eccentricity, and the steel tubes diameter-to-thickness ratio on the structural performance of these members. The specimens were tested under four-point loading. The results showed that the pre-stressed strands increased the confinement effect on the core concrete and improved the bearing capacity, ductility, and bending stiffness. The steel tubes improved the bearing capacity, ductility, and energy absorption, while they did not significantly affect the bending stiffness. Finally, it was shown that the pre-stressed strands increased the bearing capacity, energy absorption, and bending stiffness in reinforced concrete beams.