Modeling of Prestressed Concrete-Filled Circular Composite Tubes Subjected to Bending and Axial Loads

This paper presents a nonlinear model used to predict the load–deflection responses and axial load–moment interaction curves of pretensioned concrete-filled circular composite tubes. The model accounts for the prestressing effect, which not only improves serviceability, but also activates a confinement mechanism of the concrete core restrained by the tube. The enhanced performance of confined concrete is considered. In the compression side, the tube is modeled as a biaxially loaded membrane, subjected to longitudinal compressive and hoop tensile stresses, and failure is detected using the Tsai–Wu biaxial strength envelope. Progressive failure of layers of fibers at various directions within the tube leads to stiffness degradation, and is modeled using the classical lamination theory–ultimate laminate failure approach. The model is verified using experimental results and used in a parametric study to evaluate the effects of prestress level, amount and material type of prestressed reinforcement, and thickness and laminate structure of the tube. It was shown that ignoring concrete confinement would highly underestimate the flexural strength. The tube’s thickness and laminate structure have a much larger effect on flexural strength than the number of prestressing strands.