Compressive–Flexural Failure Mechanism and Bearing Capacity Calculation of Over-Ranging Tapered CFDST Members for Support Structures of Offshore Wind Turbines

Abstract

Upon the higher requirement on high-performance structures of large-scale supporting structures of offshore wind turbines, the systematic analysis on the compressive-flexural behavior and ultimate bearing capacity of tapered concrete-filled double skin steel tubular (CFDST) members designed by over-ranging parameters was performed. Investigating the entire-process mechanism, e.g., the moment–deformation response, stress development, interaction stress, and subassembly contribution, was based on the finite element (FE) analysis, where the moment–deformation curve can be distinguished by four characteristic points, and the transverse local buckling of outer tube partly weakens distribution height of interface pressure in compression zone compared to that in tension zone. Influences of material strengths and geometric parameters were examined by the parametric study, e.g., increasing tapered angle (ψ) slightly reduces the bearing capacity; the higher axial compression ratio (n) contributes a noteworthy action on the post-peak behavior and carrying capacity, e.g., the bearing capacities at n = 0.9 and n = 0.5 reduce by 64.14% and 18.44% compared to capacity at n = 0.1, respectively; influence of Do/to ratio is more significant than Di/ti ratio. Subsequently, the modified cross-sectional stress integration (CSI) method was proposed to predict the moment–strain (M-ε) curves of tapered CFDST members; meanwhile, a confined concrete model with transverse confinement stress as an explicit parameter was modified, and influences of different confined concrete models on predicting M-ε curves were compared. Finally, design methods based on the modified CSI method and limit state method were proposed as a simplified calculation method to determine the correlative relationship of axial compressive strength and moment-resisting capacity (N-M curve).