Mechanical behaviour of axially-loaded concrete-filled double-skin corrugated steel tubes: Concrete constitutive model and numerical analysis

Concrete-filled double-skin corrugated steel tubes (CFDCSTs) have been proven to offer satisfactory structural performance and durability, suitable for applications in bridge piers, towers, and high-rise buildings. However, the unique confinement provided by double-skin thin-walled corrugated steel tubes (CSTs) combined with a hollow section results in a distinct confinement effect and mechanical behaviour. This research gap hinders further analyses and development of practical design methods. Therefore, this study develops a novel stress-strain constitutive model for sandwiched concrete that considers both the hollow ratio and confinement effect based on detailed stress state analyses and existing test data; then employs an efficient finite element modelling method to conduct in-depth numerical analyses under axial compression. Results indicate that the radial and hoop stresses in sandwiched concrete material are unequal, and the average hoop stress is generally higher, especially at high hollow ratios. The maximum vertical compressive stress occurs near the middle of the sandwiched concrete layer, and both maximum and average values reduce as the hollow ratio increases. The hoop stress of the outer CST typically ranges between 0.45 and 0.9 times the yield strength at the peak load, whereas that of the inner CST is low. Finally, a formula calculating the cross-sectional axial compressive load-bearing capacity of CFDCSTs is derived based on the above mechanistic analysis.