Structural behaviour of stainless steel-high strength concrete-high strength steel double skin tubular (SHHDST) columns under compression-torsion loading

Stainless steel-high strength concrete-high strength steel double skin tubular (SHHDST) structure is a recently developed composite structure with superior mechanical performance and corrosion resistance, exhibiting competitive application potential in marine engineering, such as offshore wind turbines, sea-crossing bridges and so on. However, the marine structures may be subjected to combined compression-torsion loading during their service time, and the corresponding structural behaviour of SHHDST columns has not been investigated. This paper therefore focuses on the structural behaviour and design of the SHHDST column under combined compression and torsion. The laboratory tests were conducted on seven specimens, considering different hollow ratios, tapered angles and axial compression ratios. The test results, including torsional resistances, failure modes, load–deformation responses, structural indices, interaction relationship between compression and torsion and circumferential strains, were reported and discussed in detail. A parallel numerical modelling method was developed and validated against the test results. The validated finite element models were then employed to carry out parametric studies covering a wide range of geometric dimensions and axial compression ratios. Based on the test and numerical results, the applicability of relevant design methods, as specified in the Chinese technical specification and proposed by previous researchers, was evaluated for SHHDST columns, all exhibiting conservative failure load predictions. Finally, new design methods, with revised two end points (axial compression and pure torsion) and shapes of the codified interaction curves, were proposed and resulted in improved design accuracy and consistency for SHHDST columns under combined compression and torsion.