Performance of Post-Tensioned Concrete-Filled GFRP Tubes for Wind Turbine Towers in Remote Areas

Abstract

Providing sustainable energy infrastructure in remote areas of Canada presents significant challenges such as limited access to materials and skilled labour, large distances between neighbouring communities, and maintenance requirements. Wind turbines are a form of decentralized sustainable energy production that are well-suited for remote areas, though conventional tower structures made of steel or concrete are heavy (requiring large foundations), can be difficult to transport, and have relatively short service lives because of deterioration from corrosion and/or fatigue. Glass Fibre Reinforced Polymer (GFRP) tubes are increasingly used for utility poles because they are light in weight and easily connected on-site, thereby reducing transportation costs and emissions while simplifying erection and foundation requirements. Moreover, GFRP materials have a high tensile strength and improved durability to corrosion and fatigue compared to steel and concrete. In other applications (e.g., bridge piers), GFRP tubes have also been used as structural formwork and filled with concrete to produce a composite system with enhanced performance; the concrete adds strength and stiffness while the outer tube confines the concrete core and provides resistance to bending. Hence, concrete-filled FRP tubes (CFFTs) present a promising unexplored solution for wind turbine towers in northern remote areas. The research presented in this thesis consists of two phases: experimental work and numerical modelling. Three hollow tapered CFFTs with different diameters were constructed and tested to assess their structural performance. Post-tensioned steel tendons were used to increase the stiffness of the tower and reduce the deflection caused by lateral loads. The towers were large scale, with heights of 5.8 m and base diameters between 460 mm and 535 mm and were tested as vertical cantilevers by fixing them to a large reusable foundation block. The outcomes of the experimental tests include: (I) understanding the response of CFFT wind turbine towers under static loads; (II) dynamic properties of prestressed CFFT towers for use as wind turbine towers; and (III) design recommendations and analysis of CFFT wind turbine towers for remote areas. Furthermore, in the second phase of the project, a finite element model was developed and validated using the experimental results to conduct parametric studies. The results confirmed that post-tensioned CFFT towers provide adequate stiffness, strength, and dynamic performance for wind turbine applications in remote areas. Failure mechanisms observed experimentally were well captured by the models, supporting their use in design optimization. The parametric investigations further clarified the (I) effect of different prestress force levels on the lateral load–deflection behaviour, (II) influence of GFRP thickness on structural response, (III) impact of concrete confinement modelling on structural performance, and (IV) effect of different elastic moduli for the GFRP tube on the lateral load–deflection behaviour of the tower. Together, these results improve understanding of the structural behaviour of CFFT wind turbine towers and offer guidance for their practical application in remote northern energy infrastructure.