Renewable energy is important to the long-term sustainability of the nation. In particular, wind energy, a vast domestic resource, has the potential to transform the energy economy of the U.S. The U.S. Department of Energy lists the development of renewable energy sources as an immediate national need, and has set a target for the U.S. to generate 20% of its electricity from renewable energy by 2030. To obtain this goal, it is clear that transformative advances in wind generated energy technology are crucial. Specifically, wind turbine towers must be manufactured taller and cheaper. A start-up company in Boston has developed an innovative manufacturing technology, based on automated spiral welding that enables conical, slender towers to be produced on-site in an efficient process. The benefits to this are two-fold: first, the automation reduces production costs dramatically compared to traditional practices and, second, the on-site fabrication precludes transport limits that currently inhibit tower height. A critical barrier to the deployment of this technology is a lack of fundamental understanding of the buckling failure for this particular structure and, generally, for slender shells. Existing methods to predict capacity of slender tower shells are unsatisfactory, relying on overly conservative, empirically derived factors, not having a firm probabilistic basis, and never having been applied to spiral welded pipe loaded in flexure. New reliability-based analysis approaches are needed to take full advantage of innovative technology of welding and manufacturing. This project aims to probabilistically characterize the controlling limit states of slender tubes and, based on this characterization, develop a rigorous reliability-based analysis and design approach. The project assesses the strength, imperfection sensitivity, and variability of slender shell structures and includes both analytical and experimental investigations of poorly understood phenomena of (1) the probabilistic nature of local buckling and its dependence on random imperfections and (2) the variability in fracture/fatigue performance of welded connections and its dependence on plate misalignment, weld microstructure and spatial correlation of toughness. The developed analysis and design method will be coupled with manufacturing tolerances, thus allowing manufacturers to explicitly explore the cost-benefit tradeoff between manufacturing methods and tolerances and the final capacities utilized in practice.
