Analytical modeling of bending of circular concrete-filled steel tubes

Concrete-filled steel tubes (CFSTs) are frequently used for piers, columns, and caissons for deep foundations because of their large compressive stiffness and axial-load capacity. Recently, other structural systems have used CFST members for girders and other members subjected to bending. Flexural behavior is the primary design issue for these applications. The bending behavior of CFST members has been investigated experimentally and these results provide a basis for understanding the response of these elements and to establish their engineering properties. However experimental results alone are not sufficient to support the engineering of these components. Complementary advanced numerical models are needed to simulate the flexural behavior of CFST to extend the experimental research and develop predictive tools required for design and evaluation of structural systems. In this study, a finite element model for CFST subjected to bending was developed. The confinement effects, composite action, and flexural behavior predicted by the proposed finite element model for CFST were verified by comparing with test results. The model was used to conduct a series of parametric studies to study the effects of D/t ratio and the impact of the materials properties. Analytical results are compared with design specification models and prior research studies. The results were combined to improve the flexural design of CFST components. Finally, a simplified model to predict the moment–drift relationship of CFST under bending was proposed.