A Technical Overview of ASCE/AWEA RP2011:Recommended Practice for Compliance of Large Land-Based Wind Turbine Support Structures

This paper provides a technical overview of a new reference document titled "ASCE/AWEA RP2011: Recommended Practice for Compliance of Large Land-Based Wind Turbine Support Structures." This paper discusses the features of RP2011 as a design and permitting resource for structural engineers and plan reviewers engaged in utility-scale wind farm tower design or permitting. The US wind industry has been developing utility-scale wind farms for over three decades, and in that time there has been no clear guidance in the US for the design and permitting of wind turbine support structures. In the absence of specific design guidelines or standards, demonstrating building code (i.e., "Code") compliance has been a challenge, especially since the wind industry primarily utilizes international (European) design standards. The lack of guidance may have been tolerable in the early days when large utility-scale wind energy projects were very few, but conditions and priorities in the US are changing. There is an increased demand for green/renewable energy in lieu of fossil fuels, and there is now more interest in American energy independence from foreign sources. RP2011 is specifically targeted to help and inform structural engineer designers and plan reviewers of wind farm towers. Since wind turbine support structures are addressed neither in the Code nor in any Code reference standard, design professionals might not be aware of the many idiosyncrasies and complexities involved in wind industry tower design. Design professionals will learn about several key issues in wind tower design: (1) how to properly apply Code wind and seismic provisions; (2) the importance of fatigue assessment and the reconciliation of Eurocode and AISC fatigue provisions; (3) the importance of frequency separation; and (4) cautionary examples where general attempts to apply Code provisions would result in unconservative tower designs that do not meet wind industry standards. To address these and other issues, an effort was started in late 2009 to develop a US Recommended Practice for the design and permitting of wind energy structures. This task was undertaken by a joint committee of the American Society of Civil Engineers (ASCE) and the American Wind Energy Association (AWEA) with the main goal of reconciling the regulatory requirements of US Code versus those of international wind industry commercial certification. The result of this effort is ASCE/AWEA RP2011.