Fatigue behaviour of CFDST members subjected to bending

Concrete filled double-skin steel tubular (CFDST) structures show promising applications in marine engineering, bridge construction, and towering infrastructures. Such structures are subjected to high-cycle loading during service and fatigue-related issues are likely to affect the service life. 2 circular hollow sectional (CHS) and 15 CFDST specimens are designed to investigate the failure modes and performance under high-fatigue bending loads. The deflection distributions, mid-span deflection-life curves, strain distributions at weld toes, strain-life curves at different loading cycles, and strain distributions across various cross-sectional heights during fatigue loading are compared. The differences in fatigue performance under different fatigue load and the geometric parameters and their influence on static performance are clarified. Studies indicate that CFDST members exhibit superior deformation resistance and fatigue life compared to traditional steel structures. Fatigue loads cause overall deformation in the form of bending failure, with the failure mode determined by the localized failure position. Specimens with a larger hollow ratio demonstrate better fatigue performance. Meanwhile, specimens subjected to varying degrees of cyclic loading still exhibit excellent flexural behaviour under monotonic loading . Finally, a life prediction method for CFDST members is proposed considering the butt-welds.