Behavior of super-sized thin-walled CFDST columns for wind turbine towers subjected to combined loads: Experiment

Concrete-filled double skin steel tubular columns with large hollow ratios (LHR-CFDST) have been commonly researched in the past few years. The excellent performance of this structure renders it promising as a novel form of wind turbine tower. Increasing the diameter-to-thickness ratio is one efficient way to reduce steel consumption as the size of this engineering structure continues to expand. There is a paucity of research on thin-walled LHR-CFDST. Meanwhile, these structures may be susceptible to local buckling without stiffening measures. Furthermore, the size effect of this type of structure is more complicated. This paper reports the first experimental investigation on super-sized thin-walled LHR-CFDST columns under combined compression-torsion-shear-bending loads. Two LHR-CFDST columns with varying stud spacings are discussed. Investigations are conducted into failure modes, local buckling behaviors, load-strain responses, and a few popular mechanical indices. According to the test results, the specimen with smaller stud spacing has an 8.1% greater ultimate bearing capacity. It is assumed that a more intensive stud arrangement can delay the onset of local buckling, thereby increasing the peak load. Besides, the arrangement of the studs leads to an obvious effect of section confinement, thus improving the overall performance of the specimens. The failure modes and load-displacement relationships simulated by the FE models agree well with the experimental results. Then, a modified method for predicting the ultimate strength of LHR-CFDST based on the previously summarized formulae for CFST under compression-bending-shear-torsion is proposed and utilized for the evaluation of two specimens in this research. Since the tested value of the specimen with narrower stud spacing is higher by 5.6% than the predicted value, it can be concluded that the large-scale thin-walled LHR-CFDST may be evaluated using this method, complemented by appropriate stiffened measures.