Flexural Test on a Full-Scale 60-kW Wind Turbine-Tower Telescopic Steel Pipe

A full-scale static test to failure was conducted on 6-m (236.22 in.)-long steel pipes constituting a segment of a telescopic wind tower with a 60-kW wind turbine. The diameter of the circular cross section of the steel pipes was 900 mm (35.43 in.), and the nominal thickness was 10 mm (0.39 in.). The steel grade was 355 MPa (51,488 psi). The tests were conducted in a force-controlled mode in a four-point bending test with a shear-to-span ratio of 2.05. The flexural limit states developed in the form of ovalization of the cross section and of local buckling. The buckling occurred in the plastic range because of the diameter-to-thickness ratio of the section. Although local buckling caused slight strength degradation, the reduction due to the shear-to-moment interaction and ovalization of the cross section was very significant (58%), while the recorded response revealed a good amount of postbuckling ductility (2.42). A finite-element analysis with ABAQUS code was also conducted for comparison with the experimental results and for validation of the simplified proposed model. By properly modeling the imperfection effects due to the roundness of the steel tube, good correlation of the structural response and failure mode, and with the analytical model, were also achieved.