The most common wind tower structure, a tapered tubular steel monopole, is currently limited to heights of ~80m due to transportation constraints which arise because tower sections are manufactured at centralized plants and transported to site for assembly. The need to transport the sections imposes a limit on their size, whereby maximum tower diameters are dictated by bridge clearances rather than by structural efficiency. New manufacturing innovations, based on automated spiral welding, may enable on-site production of wind towers, thereby precluding transportation limits and permitting the manufacture of taller towers, which can harvest the steadier, stronger winds at higher elevations. Taller towers, however, are expected to have crosssections with slenderness that is uncommon in structural engineering (i.e., diameter-to-thickness ratios up to ~500) and much larger than those of conventionally manufactured towers (i.e.,

One of the barriers to reducing the cost of wind-generated energy is the cost of manufacturing wind turbine towers which are usually designed with conical steel shells. Such towers are currently manufactured manually at centralized plants and then transported in sections to the installation site. The necessity of transporting these sections often limits the base diameter of large tower designs, requiring an increased use of material when compared to an optimized (i.e. least-weight) design. A new manufacturing technology, based on an adaptation of spiral welding, enables on-site and automated fabrication of taller, more economical towers. On-site fabrication precludes transport-based limits that currently inhibit turbine size and automated fabrication enables production at lower cost than other methods. Spiral welding is a mature technology in the pipeline industry where resistance to internal and external pressures is the primary loading mode, however, for wind turbine towers, flexure is the primary loading mode and the design of spirally-welded tubes for this application is not fully established. Moreover, this application of spiral welding requires requires larger diameter-to-thickness ratios than are currently used in the pipeline industry. This paper examines existing design standards for slender shells and assesses their applicability to shells manufactured by spiral welding. The research considers two limit states, local buckling and fatigue, and emphasizes the differences in imperfections and weld details between traditional turbine towers and those manufactured with spiral welding.

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