Experimental and numerical investigation on the flexural behavior of concrete-filled elliptical steel tube (CFET)

Concrete-filled elliptical steel tube (CFET) is a novel type of composite member, which has great potential to be used as piers and columns in bridges and airport terminals because of its low flow resistance coefficient and reasonable distribution of major-minor axis. Pure bending loading conditions are not frequently occurred in practical engineering, but the flexural researches are important since it's the basis of mechanical property researches under complex loading. However, little attention to the flexural behavior of CFETs has been paid at present. Hence, the main objective of this paper presents a combined experimental and numerical investigation on the flexural behavior of CFETs. Flexural tests were carried out to investigate the behavior of CFETs under bending. The moment vs. curvature curves during the whole loading process was analyzed in detail, and all the specimens behaved in a very ductile manner. Besides, the composite action between the steel tube and core concrete was discussed and clarified based on experimental results. Furthermore, FE (Finite element) model with precise material constitutive models was established to investigate the flexural mechanical of CFETs comprehensively, in terms of the full curves analysis on the moment vs. curvature curves, development of the stress and strain distribution in the steel tube and core concrete, and composite action. It should be noted that there existed bond slip in the interface between the core concrete and steel tube during the loading process. Then, the parametric studies with various factors were performed. Finally, design formulas were proposed to predict the ultimate moment and flexural stiffness of CFETs. The predicted results showed satisfactory agreement with the experimental and FE results. Moreover, the difference among the experimental, FE and predicted results using the related design codes were illustrated. The results of this study are expected to provide a reliable reference for design and application in concrete-filled elliptical steel tube (CFST) structures.

Automated summary

This study investigates the flexural behavior of concrete-filled elliptical steel tubes (CFET) through experimental and numerical methods, revealing a ductile behavior in all specimens and discussing the composite action between the steel tube and core concrete. By establishing a finite element model with precise material constitutive models, the flexural mechanics of CFETs were comprehensively studied, including analysis of moment vs. curvature curves, stress and strain distribution, and composite action. Bond slip at the interface between the core concrete and steel tube was observed during loading, and design formulas were proposed to predict the ultimate moment and flexural stiffness of CFETs with satisfactory agreement between predicted and experimental/FE results.