Bending Behavior Of Thin-walled Circular Tubes With Large Diameter-to-thickness Ratio

The wind industry continues to grow rapidly throughout the world. The growthof wind turbine installations has led to an increased interest in the behavior ofcircular thin-walled wind turbine tower. The turbine tower is mainly subjected tobending moment caused by lateral wind load or earthquake load and the ratio ofvertical load is quite small. Commonly, the diameter-to-thickness ratio of circularsteel tubes used in strucutrues is less than100. Up till to now, there has been littleresearch work for thin-walled circular steel tubes. Thus, it’s necessary to carry onthe study of the mechanical behavior of wind turbine tower with largediameter-to-thickness ratio. The main works are as follows:(1) Eight bending tests were performed up to failure on different sizes ofthin-walled tubes with diameter-to-thickness ratios D/t ranging from75to150.Observation and research were carried out for the specimen on failure modes,ultimate bending strength, deformation, ductility and rotation ability. The test resultsindicated that the failure mode was varied with the change of D/t ratio and localbuckling appeared when it reached or nearly reached its peak load. Immediatelyafter the local buckling occurred at the mid-span section, the radial deformation wassomewhat confined to this region as the increase of deformation. In general, thepeak for large D/t ratio was very sharp and the load-carrying capacity droppedrapidly, showing little ductility capacity.(2) The finite element software ABAQUS is used to develop the model toanalyse the bending behaviour of tubes with large D/t ratio and the results werevalidated by the experiments conducted in this paper. Besides the materialnonlinearity and geometric nonlinearity, the initial geometric imperfection of towertube was also considered in the analysis.(3) Different steel yeild strength, D/t ratio ranging from50to500andamptitude of initial geometric imperfection were considered in the finite elmentanalysis to evaluate how failure modes, ultimate strength, ductility and rotationability of thin-walled tubes with large D/t ratio are influenced by these parameters.The results show that thin-walled circular tubes with large D/t ratio are highlysusceptible to local geometrical imperfections. Both AISC Specification and AS4100code are utilised to compare with the experimental results.