Axial compressive behavior of thin-walled CFDST columns with large void ratio: Effects of curing age, stiffeners, and hygrothermal corrosion

Concrete-filled double-skin steel tubular (CFDST) columns with large hollow ratios (LHR) offer weight reduction and improved seismic performance, but their behavior under early-age loading, aggressive environments, and stiffened configurations remains unclear. This study investigates the axial compressive behavior of circular LHR-CFDST stub columns (hollow ratio 0.77) through 15 experiments and validated three-dimensional finite element models (FEM). The experimental results indicate that early-age loading (5 days) results in an approximately 11% reduction in ultimate load capacity compared to the 28-day benchmark. While full-length longitudinal stiffeners effectively enhance ductility by 8.7%, circumferential stiffeners prove inefficient. Prolonged hygrothermal corrosion significantly compromises structural integrity, leading to a 21.2% decrease in load-bearing capacity and a 16.7% reduction in ductility after 180 days of exposure. Furthermore, FEM analysis revealed the complex stress evolution and load transfer mechanisms between the double steel skins and the sandwiched concrete. Finally, the predictive accuracy of six major international design codes was assessed. The findings provide essential data and design recommendations for the application of LHR-CFDST columns in offshore and long-span structures.