Spirally welded steel wind towers: Buckling experiments, analyses, and research needs

• Spirally welded wind tower tubes are slender and prone to local buckling.
• Relevant experimental and analytical literature are reviewed.
• Experimental data for slender tubes in flexure is lacking.
• Accurate prediction of strength of slender tubes is challenging.
• Experimental and analytical research needs are identified.

The most common wind tower structure, a tapered tubular steel monopole, is currently limited to heights of ~ 80 m 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 cross-sections 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., diameter-to-thickness ratios up to ~ 300). Tubular structures with highly slender cross-sections are imperfection-sensitive, and the welding process is known to influence imperfections. To account for this sensitivity, slender tubes are usually designed based on empirical knockdown factors, however there are few experiments of tubes in flexure with slenderness as high as what is expected for spirally welded wind towers, and there are no experiments on tubes within this slenderness range and manufactured with spiral welding. This paper reviews the state-of-the-art for designing spirally welded tubes as wind towers and identifies deficiencies. Relevant experimental and analytical research is summarized and research needs to efficiently design tapered spirally welded steel tubes as wind towers are identified.