ACI ITG-9R-2016 Report on Design of Concrete Wind Turbine Towers.pdf

1、Report on Design of Concrete Wind Turbine TowersReported by ACI Innovation Task Group 9ACI ITG-9R-16First PrintingOctober 2016ISBN: 978-1-945487-35-4Report on Design of Concrete Wind Turbine TowersCopyright by the American Concrete Institute, Farmington Hills, MI. All rights reserved. This material

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11、Concrete Practice (MCP).American Concrete Institute38800 Country Club DriveFarmington Hills, MI 48331Phone: +1.248.848.3700Fax: +1.248.848.3701www.concrete.orgThis report examines the benefits of the design of concrete towers for land-based wind turbines with heights in excess of 325 ft (100 m), in

12、comparison to those of round steel tubular towers. These benefits include reduced cost, increased stiffness, and superior service life performance. Construction alternatives, design criteria, design methodologies, and guidance for preliminary design of concrete towers are presented.The report recogn

13、izes that final tower design requires close coordination with the turbine supplier. The report is intended for those involved in developing preliminary tower designs. Concrete towers designed for maximum wind forces can be satisfactory for preliminary design, but the final design requires checking f

14、or all loads, especially fatigue and dynamic effects from wind and turbine operations. Design of connections and their proportions require an understanding of fatigue requirements during preliminary design for the connection design to remain valid during final checks.Keywords: concrete tower; full-h

15、eight tower; hybrid tower; precast elements; prestressing; slipformed; spread footings; turbine; wind; wind farm.CONTENTSCHAPTER 1INTRODUCTION, p. 21.1Introduction, p. 21.2Scope, p. 3CHAPTER 2NOTATION AND DEFINITIONS, p. 32.1Notation, p. 32.2Definitions, p. 3CHAPTER 3WIND FARM DEVELOPMENT AND TOWER

16、SUPPLY CHAIN, p. 33.1Introduction, p. 33.2Certification and design, p. 5CHAPTER 4CONCRETE TOWER TYPES, p. 64.1Hybrid concrete towers, p. 64.2Full-height concrete towers, p. 64.3Construction types, p. 64.4Construction considerations, p. 84.5Tolerances, p. 94.6Tower size and cost, p. 9CHAPTER 5TOWER D

17、ESIGN, p. 115.1Tower frequency design, p. 115.2Service level design, p. 125.3Prestressing, p. 135.4Modeling, p. 135.5Fatigue, p. 155.6Preliminary design guidance, p. 15CHAPTER 6DESIGN LOADS AND LOAD COMBINATIONS, p. 156.1Loads and load combinations, p. 166.2Load factors, p. 17CHAPTER 7DESIGN LOADS,

18、p. 177.1Basic weights and loads, p. 177.2Wind profile, p. 187.3Earthquake loads, p. 18Charles S. Hanskat, ChairACI ITG-9R-16Report on Design of Concrete Wind Turbine TowersReported by ACI Innovation Task Group 9Roger J. BeckerRick DamianiCharles W. Dolan*Neil M. HawkinsKevin L. KirkleyGary J. KleinN

19、ina KristevaDan A. Kuchma*James D. LockwoodKirk B. Morgan*Markus Wernli*Principal authors.ACI Committee Reports, Guides, and Commentaries are intended for guidance in planning, designing, executing, and inspecting construction. This document is intended for the use of individuals who are competent t

20、o evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the material it contains. The American Concrete Institute disclaims any and all responsibility for the stated principles. The Institute shall not be liable for any

21、 loss or damage arising therefrom.Reference to this document shall not be made in contract documents. If items found in this document are desired by the Architect/Engineer to be a part of the contract documents, they shall be restated in mandatory language for incorporation by the Architect/Engineer

22、ACI ITG-9R-16 was adopted and published October 2016.Copyright 2016, American Concrete Institute.All rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by electronic or mechanical device, printed, written, or

23、 oral, or recording for sound or visual reproduction or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors.17.4Normal operating fatigue loads, p. 187.5Temperature loads, p. 187.6Abnormal operating conditions, p. 18CHAPTER 8

24、CONCRETE RESISTANCE, p. 198.1Strength design, p. 198.2Serviceability design, p. 198.3Joints and connections, p. 19CHAPTER 9FOUNDATION DESIGN, p. 199.1Rock anchor foundations, p. 199.2Pier-type deep foundations, p. 209.3Spread footings, p. 209.4Termination of reinforcement and prestress, p. 229.5Towe

25、r-foundation structural integrity, p. 22CHAPTER 10CONCLUSION AND RECOMMENDATIONS, p. 22CHAPTER 11REFERENCES, p. 23Authored documents, p. 23CHAPTER 1INTRODUCTION1.1IntroductionTowers for wind turbines in North America typically have been constructed of steel and are of the round tubular types, althou

26、gh early towers for kW-rated turbines included lattice-type truss structures. Lattice tower designs are undergoing resurgence for multi-MW turbines, as the tubular towers have reached their shipping limitations. Steel has offered the industry several economic and production advantages for towers les

27、s than 325 ft (100 m) tall. Steel towers can be prefabricated, readily transported over existing high-ways, and efficiently erected on the wind farm site. Whereas concrete towers are widely used in Europe, many wind farm designers in North America have not considered concrete towers due to several p

28、erceived limitations, including the lack of:(a) Understanding the length of time to construct concrete towers(b) Familiarity with the fatigue properties of concrete(c) Industry standards for concrete tower design(d) Historical cost dataTo address these concerns, this report describes the advan-tages

29、 and options for concrete towers greater than 325 ft (100 m) in height.Figure 1.1 illustrates a tower and highlights several key terms used in this report. The tower height is measured from the foundation interface to the mounting ring. A yaw bearing, which permits the horizontal rotation of the tur

30、bine, attaches to the mounting ring. The turbine and main bearing shaft are located in the nacelle, which is attached to the yaw bearing. The blades are attached to the main bearing shaft and, for tower design purposes, are included in the nacelle weight. The hub height is measured from the top of t

31、he foundation to the center of the main bearing shaft. The swept area of the blade is a circle based on the blade radius. Additional details of the top of the tower are given in Chapter 4.As the wind turbine power levels increase above 2.5 MW, the towers needed to support the turbines are exceeding

32、325 ft (100 m) in height. In moderate wind areas, such as the southeastern United States, taller towers are beneficial for 1 to 2.5 MW turbines to capitalize on the more desir-able wind patterns. For turbines in the 5 to 10 MW range, turbines using a 325 ft (100 m) or larger rotor diameter are now u

33、nder development. Towers for these turbines would exceed 325 ft (100 m) in height to the nacelle mounting ring interface. At this height, several of the advantages of the current steel towers are lost due to their larger size, their lower stiffness, and the necessity for on-site completion. Under th

34、ese conditions, concrete towers become practi-cable alternatives and economically attractive. According to Engstrm et al. (2010), using a hub height of 410 ft (125 m), it is possible to save up to 30 percent of the tower cost by selecting a technology other than the conventional welded steel tower.

35、Lattice towers and wooden towers were deter-mined to be economical. Engstrm et al. (2010) concluded that there are several interesting tower alternatives worthy of further development, including steel towers with slip critical joints, concrete, hybrid concrete/steel, wood, and lattice construction.

36、Umut et al. (2011) point out that as the height of the tower increases, the stiffness demands become critical. Concrete towers have greater ability than steel to adjust stiffness to meet the performance requirements of the original equipment manufacturer (OEM) suppliers.Fig. 1.1Wind turbine tower.Am

37、erican Concrete Institute Copyrighted Material www.concrete.org2 REPORT ON DESIGN OF CONCRETE WIND TURBINE TOWERS (ACI ITG-9R-16)1.2ScopeAll references to turbine technology in this report are limited to horizontal axis turbines of the upwind, three-blade variety. Other variants of the horizontal ax

38、is turbines, such as the two-blade and down-wind blade orientation, have advan-tages and disadvantages in the categories of dynamic loads and blade/tower interference, but they are not addressed in this report. Refer to Wind Vision 2015 (U.S. Department of Energy 2015) for more information regarding

39、 horizontal axis turbines. This report is primarily for land-based towers, although reference is made to offshore towers when those data are applicable.CHAPTER 2NOTATION AND DEFINITIONS2.1NotationEc= modulus of elasticity of concrete, lb/in.2(Pa)Esec= secant modulus of elasticity of concrete, lb/in.

40、2(Pa)fcmax= maximum stress in the concrete stress-strain curve occurring at 0, lb/in.2(Pa)k = parameter based on modulus of elasticity and strain conditionsn = ratio of actual strain-to-strain at maximum stressVhub= velocity of wind at height of hub, mph (km/h)Vin= cut-in wind speed; lowest wind spe

41、ed at the hub height at which the wind turbine starts to produce power in the case of a steady wind without turbulenceVout= cut-out wind speed; highest wind speed at the hub height at which the wind turbine is designed to produce power in a steady wind without turbulenceVp= wind speed for power gene

42、ration of the turbine, mph (km/h)Vref= reference or design wind speed for the turbine, mph (km/h)Wi= weight of segment i, lb (N)yi= lateral deflection of a segment, ft (m)z = height above ground level, ft (m)0= strain in concrete corresponding to maximum stressc= strain in concretecu= maximum concre

43、te strain = tower natural frequency, 1/s2.2DefinitionsACI provides a comprehensive list of definitions through an online resource, “ACI Concrete Terminology (CT-16),” https:/www.concrete.org/store/productdetail.aspx?ItemID=CT16.CHAPTER 3WIND FARM DEVELOPMENT AND TOWER SUPPLY CHAIN3.1Introduction3.1.

44、1 Wind farm developmentA wind farm consists of several wind turbines distributed over a large area (Fig. 3.1.1a). Because the visual impact and land requirements are signifi-cant, the development of a wind farm is complex and often requires considerable public input. Figure 3.1.1b presents a simplif

45、ied schematic of wind farm development that is typical of the hub heights of wind farms erected in the United States. Although the schematic suggests linear devel-opment, interaction between the developer, turbine original equipment manufacturer (OEM), tower designer, contractor, and other parties i

46、s more complex. For example, some site evaluations, such as wind profiles, are ongoing activities that are simultaneous with obtaining the final project funding.A licensed design professional (LDP) for wind farms may have one of many roles, including tower design for the OEM supplier, independent en

47、gineer, or tower designer for the contractor. Each role varies by project and the time the engi-neering service is required. A tower design LDP may enter the project early or late, depending on the OEM background with concrete tower design. An independent engineer LDP may be retained during the find

48、ing process or by the certi-fication agency to validate the design. The independent engineer certification role is shown as a dashed line in Fig. 3.1.1b for early involvement and a solid line as part of final approval. If the towers are procured on a design-build basis, the tower design LDP may work

49、 directly for the contractor.The towers are typically provided under the turbine OEM contract and are not within the scope of the LDPs retained for the project. The towers, however, are a significant part of the project cost and, therefore, could require input at the evalua-tion stage of the project, particularly with higher hub heights.Early identification of the tower type and construction method may offer more economical solutions than inferred in the flowchart, and may be essential for developing a reliable cost basis