Flexural behavior of assembled aluminum alloy-concrete‑carbon steel double-skin tubular column

In this study, an assembled aluminum alloy-concrete‑carbon steel double-skin tubular (ACSDST) column for jacket legs of offshore platforms was proposed. Six specimens, including five assembled ACSDST columns and one non-assembled ACSDST column, were experimentally tested to explore the resulting flexural behavior. The corresponding failure modes, moment-deflection curves, strain distribution, flexural strengths, flexural stiffness, and overall vertical deflection curves were investigated. The failure of the assembled ACSDST column occurred at the outermost high-strength bolt holes on the tensile side, accompanied by the tensile fracture of the aluminum alloy tube and concrete. The bolt holes could reduce the effective bearing area of the outer aluminum alloy tube, leading to reduced flexural strength in the assembled ACSDST column than that of the non-assembled ACSDST column. Nevertheless, the assembled ACSDST column exhibited a high ultimate flexural capacity. Subsequently, a finite element (FE) model was developed and validated against experimental results. Further, the effects of various parameters on the flexural behavior of the assembled ACSDST columns were analyzed. The diameter-to-thickness ratio of the outer tube had a significant impact on the flexural capacity, whereas the effect of concrete strength was limited. The effects of pretension of high-strength bolts and 0.2 % proof stress of aluminum alloy could be neglected. The suitability of the existing codes for predicting the flexural capacity of assembled ACSDST columns was also evaluated. Finally, a new design model was proposed.