Experimental and analytical study on the behaviour of circular concrete filled steel tubes in cyclic bending

In the present study, a comprehensive experimental investigation is conducted on eight Concrete-Filled Tube (CFT) specimens subjected to bending loads under cyclic conditions. The loading regimes included constant and variable amplitude cycles. Strain was precisely measured using strategically placed gauges, and the data generated load-displacement and moment-curvature curves. A novel analytical model is developed and calibrated to match the experimental outcomes; this model incorporates the Mander stress-strain relationship for confined concrete and the Ramberg-Osgood model for steel. The study provides new insights into the mechanical behaviour of CFTs under bending, particularly in terms of strain distribution, load-displacement characteristics, and failure modes. This research serves as a strong foundation for future finite element modelling and design optimization of CFT structures, enhancing their safe and efficient use in engineering applications.