Flexural Performance of High-strength Prestressed Concrete-encased Concrete-filled Steel Tube Sections

The sections composed of concrete and steel, which include concrete-encased concrete-filled tubes, generally have defects due to the low tensile strength of concrete. Therefore, an appropriate method was used for the combination of concrete-filled tubes (CFT) and prestressing strands which is encased in concrete. The conventional design guidelines are commonly developed for materials with normal strength thus further investigation is required to be conducted for sections with high-strength materials. In order to develop the design process, high-strength concrete and steel have been utilized in this study to examine the effects of steel and concrete strengths on the core concrete confinement, sectional size and flexural behavior of high-strength prestressed concrete-encased CFST (HS-PCE-CFST) beams. Hence, a total of thirteen HS-PCE-CFST beams were modeled via ABAQUS finite element software. The main variables include the steel tube yield strength, compressive cylinder strength of the core and outer concrete  and the steel tube diameter to section width ratio. Furthermore, experimental results were employed to verify the finite element model. The bending moment, ductility, flexural stiffness and failure mode of beams are also examined. The results confirm that among the compressive strength of the outer and core concrete and the steel tube yield strength, change in the outer concrete compressive strength has a greater effect on the change of flexural parameters, also increasing the ratio of steel tube diameter to section width causes a minor increase in the ultimate bending moment and serviceability level flexural stiffness, but a major escalation in the initial flexural stiffness.