Coupled behaviour and design of stainless steel-high strength concrete-high strength steel double skin tubular (SHHDST) columns for offshore wind turbine tower

Offshore wind turbines have become the key to wind power development, but their supporting structures face harsh conditions (severe corrosion, complex loads). Therefore, stainless steel-high strength concrete-high strength steel double skin tubular (SHHDST) structures are proposed as the novel wind turbine towers, which are often subjected to combined compression-bending-torsion load. This paper focuses on the coupled behaviour of tapered SHHDST columns with large hollow ratios under combined compression-bending-torsion loads. An experimental programme, including material tests and column tests, was conducted on seven columns within common wind turbine tower parameter ranges. The test results were fully reported and discussed, comprising the failure modes, load−deformation responses, structural indices, strain distributions and developments. Numerical models were developed and validated based on the test results, which were then employed for the parametric studies, considering an extended range of geometric dimensions and loading conditions. Design analysis was conducted by evaluating the applicability of the existing design methods, yielding conservative and scattered resistance predictions. Finally, a new design method, consisting of the revised shape and three endpoints (axial compression, pure bending and pure torsion) of the modified interaction surfaces, was proposed and provided improved predictions on structural resistances of SHHDST columns under combined loads.