Wind energy generation systems - Part 6: Tower and foundation design requirements

IEC 61400-6:2020 specifies requirements and general principles to be used in assessing the structural integrity of onshore wind turbine support structures (including foundations). The scope includes the geotechnical assessment of the soil for generic or site specific purposes. The strength of any flange and connection system connected to the rotor nacelle assembly (including connection to the yaw bearing) are designed and documented according to this document or according to IEC 61400-1. The scope includes all life cycle issues that may affect the structural integrity such as assembly and maintenance.
The contents of the corrigendum of November 2020 have been included in this copy.

Systèmes de génération d'énergie éolienne - Partie 6: Exigences en matière de conception du mât et de la fondation

l'IEC 61400-6:2020 spécifie les exigences et les principes généraux à utiliser pour évaluer l'intégrité structurelle des structures de support d'éolienne terrestre (y compris les fondations). Le domaine d'application inclut l'évaluation géotechnique du sol en fonction des besoins génériques ou spécifiques au site. La résistance d'une bride et le système de connexion relié à l'ensemble rotor – nacelle (y compris la connexion au palier du dispositif d’orientation) sont conçus et documentés selon le présent document ou selon l'IEC 61400-1. Le domaine d'application inclut toutes les questions liées au cycle de vie qui peuvent avoir un impact sur l'intégrité structurelle (le montage et l'entretien, par exemple).
Le contenu du corrigendum de novembre 2020 a été pris en considération dans cet exemplaire.

General Information

Status
Published
Publication Date
20-Apr-2020
Current Stage
PPUB - Publication issued
Completion Date
21-Apr-2020
Ref Project

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IEC 61400-6
Edition 1.0 2020-04
INTERNATIONAL
STANDARD
colour
inside
Wind energy generation systems –
Part 6: Tower and foundation design requirements
IEC 61400-6:2020-04(en)
---------------------- Page: 1 ----------------------
THIS PUBLICATION IS COPYRIGHT PROTECTED
Copyright © 2020 IEC, Geneva, Switzerland

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form

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---------------------- Page: 2 ----------------------
IEC 61400-6
Edition 1.0 2020-04
INTERNATIONAL
STANDARD
colour
inside
Wind energy generation systems –
Part 6: Tower and foundation design requirements
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.180 ISBN 978-2-8322-8004-1

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC 61400-6:2020 © IEC 2020
CONTENTS

FOREWORD ........................................................................................................................... 9

INTRODUCTION ................................................................................................................... 11

1 Scope ............................................................................................................................ 12

2 Normative references .................................................................................................... 12

3 Terms and definitions .................................................................................................... 13

4 Symbols and abbreviated terms ..................................................................................... 17

4.1 Symbols ................................................................................................................ 17

4.2 Abbreviated terms ................................................................................................. 19

5 Design basis including loading ....................................................................................... 20

5.1 General ................................................................................................................. 20

5.2 Basis of design ..................................................................................................... 20

5.2.1 Basic principles ............................................................................................. 20

5.2.2 Durability ....................................................................................................... 21

5.2.3 Principles of limit state design ....................................................................... 21

5.2.4 Structural analysis ......................................................................................... 21

5.2.5 Assessments by tests .................................................................................... 22

5.3 Materials ............................................................................................................... 22

5.4 Loads.................................................................................................................... 22

5.4.1 Use of IEC 61400-1 or IEC 61400-2 load cases and partial safety

factors for loads ............................................................................................. 22

5.4.2 Superseding of IEC 61400-1 or IEC 61400-2 partial safety factors for

materials ....................................................................................................... 22

5.4.3 Serviceability load levels ............................................................................... 23

5.4.4 Load combinations in ULS ............................................................................. 24

5.4.5 Structural damping values to be used in load calculations ............................. 25

5.4.6 Definitions and methods for use of internal loads ........................................... 25

5.4.7 Definition of required load data for fatigue analysis ........................................ 25

5.4.8 Definition of required load data for extreme load level ................................... 25

5.4.9 Vortex induced vibration ................................................................................ 26

5.4.10 Loads due to geometric tolerances and elastic deflections in tower

verticality ....................................................................................................... 26

5.5 Load data and interface reporting requirements .................................................... 27

5.5.1 Purpose ......................................................................................................... 27

5.5.2 Wind turbine specification .............................................................................. 27

5.5.3 Time history data ........................................................................................... 28

5.5.4 Load origins ................................................................................................... 28

5.5.5 Load components .......................................................................................... 28

5.6 General structural design requirements ................................................................. 28

5.6.1 Secondary structural influence ....................................................................... 28

5.6.2 Fatigue analysis ............................................................................................ 28

5.7 Delivery documentation ......................................................................................... 28

6 Steel towers .................................................................................................................. 29

6.1 General ................................................................................................................. 29

6.2 Basis of design ..................................................................................................... 29

6.3 Materials ............................................................................................................... 29

6.3.1 General ......................................................................................................... 29

6.3.2 Structural steels ............................................................................................ 29

---------------------- Page: 4 ----------------------
IEC 61400-6:2020 © IEC 2020 – 3 –

6.3.3 Bolts and anchors .......................................................................................... 32

6.4 Ultimate strength analysis for towers and openings ............................................... 32

6.4.1 General ......................................................................................................... 32

6.4.2 Partial safety factors ...................................................................................... 32

6.4.3 Verification of ultimate strength ..................................................................... 32

6.4.4 Tower assessment ......................................................................................... 32

6.4.5 Detail assessments........................................................................................ 33

6.5 Stability................................................................................................................. 33

6.5.1 General ......................................................................................................... 33

6.5.2 Partial safety factor........................................................................................ 34

6.5.3 Assessment ................................................................................................... 34

6.5.4 Door frames/stiffeners ................................................................................... 34

6.6 Fatigue limit state ................................................................................................. 35

6.6.1 General ......................................................................................................... 35

6.6.2 Partial safety factor for materials ................................................................... 35

6.6.3 Assessment ................................................................................................... 36

6.6.4 Details ........................................................................................................... 36

6.7 Ring flange connections ........................................................................................ 36

6.7.1 General ......................................................................................................... 36

6.7.2 Design assumptions and requirements, execution of ring flanges .................. 36

6.7.3 Ultimate limit state analysis of flange and bolted connection .......................... 38

6.7.4 Fatigue limit state analysis of bolted connection ............................................ 38

6.8 Bolted connections resisting shear through friction ............................................... 40

6.8.1 General requirements .................................................................................... 40

6.8.2 Test-assisted design ...................................................................................... 41

6.8.3 Design without test ........................................................................................ 42

7 Concrete towers and foundations................................................................................... 42

7.1 General ................................................................................................................. 42

7.2 Basis of design ..................................................................................................... 42

7.2.1 Reference standard for concrete design ........................................................ 42

7.2.2 Partial safety factors ...................................................................................... 43

7.2.3 Basic variables .............................................................................................. 43

7.3 Materials ............................................................................................................... 45

7.4 Durability .............................................................................................................. 46

7.4.1 Durability requirements .................................................................................. 46

7.4.2 Exposure classes .......................................................................................... 46

7.4.3 Concrete cover .............................................................................................. 46

7.5 Structural analysis ................................................................................................ 46

7.5.1 Finite element analysis .................................................................................. 46

7.5.2 Foundation slabs ........................................................................................... 47

7.5.3 Regions with discontinuity in geometry or loads ............................................. 47

7.5.4 Cast in anchor bolt arrangements .................................................................. 48

7.6 Concrete to concrete joints ................................................................................... 48

7.7 Ultimate limit state ................................................................................................ 48

7.7.1 General ......................................................................................................... 48

7.7.2 Shear and punching shear ............................................................................. 48

7.8 Fatigue limit state ................................................................................................. 49

7.8.1 General ......................................................................................................... 49

7.8.2 Reinforcement and prestressing steel fatigue failure ...................................... 49

---------------------- Page: 5 ----------------------
– 4 – IEC 61400-6:2020 © IEC 2020

7.8.3 Concrete fatigue failure ................................................................................. 49

7.9 Serviceability limit state ........................................................................................ 50

7.9.1 Load dependent stiffness reduction ............................................................... 50

7.9.2 Stress limitation ............................................................................................. 50

7.9.3 Crack control ................................................................................................. 50

7.9.4 Deformations ................................................................................................. 51

7.10 Execution .............................................................................................................. 51

7.10.1 General ......................................................................................................... 51

7.10.2 Requirements ................................................................................................ 51

7.10.3 Inspection of materials and products.............................................................. 51

7.10.4 Falsework and formwork ................................................................................ 51

7.10.5 Reinforcement and embedded steel ............................................................... 51

7.10.6 Pre-stressing ................................................................................................. 51

7.10.7 Precast concrete elements............................................................................. 52

7.10.8 Geometrical tolerances .................................................................................. 52

8 Foundations – Geotechnical design ............................................................................... 52

8.1 General ................................................................................................................. 52

8.2 Basis of design ..................................................................................................... 52

8.2.1 General ......................................................................................................... 52

8.2.2 Geotechnical limit states ................................................................................ 53

8.3 Geotechnical data ................................................................................................. 53

8.3.1 General ......................................................................................................... 53

8.3.2 Specific considerations .................................................................................. 55

8.4 Supervision, monitoring and maintenance of construction ..................................... 56

8.5 Gravity base foundations ...................................................................................... 56

8.5.1 General ......................................................................................................... 56

8.5.2 Ultimate limit state (ULS) ............................................................................... 57

8.5.3 Serviceability limit state (SLS) ....................................................................... 60

8.6 Piled foundations .................................................................................................. 62

8.6.1 General ......................................................................................................... 62

8.6.2 Pile loads ...................................................................................................... 62

8.6.3 Ultimate limit state ......................................................................................... 63

8.6.4 Serviceability limit state ................................................................................. 64

8.7 Rock anchored foundations ................................................................................... 65

8.7.1 General ......................................................................................................... 65

8.7.2 Types of rock anchor foundation .................................................................... 65

8.7.3 Geotechnical data .......................................................................................... 65

8.7.4 Corrosion protection ...................................................................................... 65

8.7.5 Anchor inspection and maintenance .............................................................. 66

8.7.6 Post tension tolerances and losses ................................................................ 66

8.7.7 Ultimate limit state ......................................................................................... 66

8.7.8 Serviceability limit state ................................................................................. 67

8.7.9 Robustness check ......................................................................................... 67

8.7.10 Rock anchor design ....................................................................................... 68

9 Operation, service and maintenance requirements ........................................................ 70

9.1 Operation, maintenance and monitoring ................................................................ 70

9.2 Periodic structural inspections .............................................................................. 70

9.3 Embedded steel structural section inspections ...................................................... 71

9.4 Bolt tension maintenance ...................................................................................... 71

---------------------- Page: 6 ----------------------
IEC 61400-6:2020 © IEC 2020 – 5 –

9.5 Structural health monitoring .................................................................................. 71

Annex A (informative) List of suitable design codes and guidelines for the calculation

basis ..................................................................................................................................... 72

A.1 General ................................................................................................................. 72

A.2 Reference documents ........................................................................................... 72

Annex B (informative) List of material for structural steel ..................................................... 73

B.1 General ................................................................................................................. 73

B.2 Structural steel ..................................................................................................... 73

Annex C (informative) Bolts ................................................................................................. 74

C.1 General ................................................................................................................. 74

C.2 Reference documents ........................................................................................... 75

Annex D (informative) Z-values for structural steel ............................................................... 76

D.1 General ................................................................................................................. 76

D.2 Definition of Z-value according to Eurocode .......................................................... 76

D.3 Reference documents ........................................................................................... 76

Annex E (informative) Simplified buckling verification for openings in tubular steel

towers ................................................................................................................................... 77

Annex F (informative) Fatigue verification ............................................................................ 80

F.1 General ................................................................................................................. 80

F.2 Specific details ..................................................................................................... 80

Annex G (informative) Methods for ring flange verification ................................................... 81

G.1 Method for ultimate strength analysis according to Petersen/Seidel ...................... 81

G.1.1 Basics ........................................................................................................... 81

G.1.2 Calculation method ........................................................................................ 81

G.1.3 Extension by Tobinaga and Ishihara .............................................................. 84

G.2 Method for fatigue strength analysis according to Schmidt/Neuper ........................ 85

G.2.1 Basics ........................................................................................................... 85

G.2.2 Formulas for the tri-linear approximation ........................................................ 86

G.3 Reference documents ........................................................................................... 87

Annex H (informative) Crack control – Guidance on 7.9.3 .................................................... 88

H.1 General ................................................................................................................. 88

H.2 Crack control based on Eurocode 2 ...................................................................... 88

H.3 Crack control based on Japanese standards ......................................................... 88

H.4 Crack control based on ACI 318 ............................................................................ 89

H.5 Reference documents ........................................................................................... 89

Annex I (informative) Finite element analysis for concrete................................................... 90

I.1 General ................................................................................................................. 90

I.2 Order and type of elements ................................................................................... 90

I.3 Constitutive modelling ........................................................................................... 91

I.4 Solution methods .................................................................................................. 91

I.5 Implicit approach .................................................................................................. 91

I.6 Steps in conducting of a finite element analysis .................................................... 92

I.7 Checking results ................................................................................................... 92

I.8 Reference documents ........................................................................................... 93

Annex J (informative) Tower-foundation anchorage ............................................................. 94

J.1 General ................................................................................................................. 94

J.2 Embedded anchorages ......................................................................................... 94

J.3 Bolted anchorages ................................................................................................ 95

---------------------- Page: 7 ----------------------
– 6 – IEC 61400-6:2020 © IEC 2020

J.4 Grout .................................................................................................................... 95

J.5 Anchor bolts .......................................................................................................... 95

J.6 Embedded ring ..................................................................................................... 95

J.7 Anchorage load transfer ........................................................................................ 96

Annex K (informative) Strut-and-tie section ......................................................................... 97

K.1 General ................................................................................................................. 97

K.2 Example of a rock anchor foundation .................................................................... 98

K.3 Reference documents ......................................................................................... 101

Annex L (informative) Guidance on selection of soil modulus and foundation rotational

stiffness .............................................................................................................................. 103

L.1 General ............................................................................................................... 103

L.2 Soil model ........................................................................................................... 103

L.3 Dynamic rotational stiffness ................................................................................ 105

L.4 Static rotational stiffness ..................................................................................... 106

L.5 Reference documents ......................................................................................... 107

Annex M (informative) Guidance for rock anchored foundation design ............................... 108

M.1 General ............................................................................................................... 108

M.2 Corrosion protection ........................................................................................... 108

M.2.1 Standard anchors ........................................................................................ 108

M.2.2 Corrosion protection of bar anchors ............................................................. 109

M.3 Product approval ................................................................................................. 110

M.4 Rock anchor design ............................................................................................ 110

M.5 Grout design ....................................................................................................... 110

M.6 Testing and execution ......................................................................................... 110

M.7 Suitability/performance test ................................................................................. 111

M.8 Acceptance/proof test ......................................................................................... 111

M.9 Supplementary extended creep tests .................................................................. 111

M.10 Reference documents ..................................................
...

IEC 61400-6
Edition 1.0 2020-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Wind energy generation systems –
Part 6: Tower and foundation design requirements
Systèmes de génération d'énergie éolienne –
Partie 6: Exigences en matière de conception du mât et de la fondation
IEC 61400-6:2020-04(en-fr)
---------------------- Page: 1 ----------------------
THIS PUBLICATION IS COPYRIGHT PROTECTED
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About IEC publications

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---------------------- Page: 2 ----------------------
IEC 61400-6
Edition 1.0 2020-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Wind energy generation systems –
Part 6: Tower and foundation design requirements
Systèmes de génération d'énergie éolienne –
Partie 6: Exigences en matière de conception du mât et de la fondation
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.180 ISBN 978-2-8322-8803-0

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC 61400-6:2020 © IEC 2020
CONTENTS

FOREWORD ........................................................................................................................... 9

INTRODUCTION ................................................................................................................... 11

1 Scope ............................................................................................................................ 12

2 Normative references .................................................................................................... 12

3 Terms and definitions .................................................................................................... 13

4 Symbols and abbreviated terms ..................................................................................... 17

4.1 Symbols ................................................................................................................ 17

4.2 Abbreviated terms ................................................................................................. 19

5 Design basis including loading ....................................................................................... 20

5.1 General ................................................................................................................. 20

5.2 Basis of design ..................................................................................................... 20

5.2.1 Basic principles ............................................................................................. 20

5.2.2 Durability ....................................................................................................... 21

5.2.3 Principles of limit state design ....................................................................... 21

5.2.4 Structural analysis ......................................................................................... 21

5.2.5 Assessments by tests .................................................................................... 22

5.3 Materials ............................................................................................................... 22

5.4 Loads.................................................................................................................... 22

5.4.1 Use of IEC 61400-1 or IEC 61400-2 load cases and partial safety

factors for loads ............................................................................................. 22

5.4.2 Superseding of IEC 61400-1 or IEC 61400-2 partial safety factors for

materials ....................................................................................................... 22

5.4.3 Serviceability load levels ............................................................................... 23

5.4.4 Load combinations in ULS ............................................................................. 24

5.4.5 Structural damping values to be used in load calculations ............................. 25

5.4.6 Definitions and methods for use of internal loads ........................................... 25

5.4.7 Definition of required load data for fatigue analysis ........................................ 25

5.4.8 Definition of required load data for extreme load level ................................... 25

5.4.9 Vortex induced vibration ................................................................................ 26

5.4.10 Loads due to geometric tolerances and elastic deflections in tower

verticality ....................................................................................................... 26

5.5 Load data and interface reporting requirements .................................................... 27

5.5.1 Purpose ......................................................................................................... 27

5.5.2 Wind turbine specification .............................................................................. 27

5.5.3 Time history data ........................................................................................... 28

5.5.4 Load origins ................................................................................................... 28

5.5.5 Load components .......................................................................................... 28

5.6 General structural design requirements ................................................................. 28

5.6.1 Secondary structural influence ....................................................................... 28

5.6.2 Fatigue analysis ............................................................................................ 28

5.7 Delivery documentation ......................................................................................... 28

6 Steel towers .................................................................................................................. 29

6.1 General ................................................................................................................. 29

6.2 Basis of design ..................................................................................................... 29

6.3 Materials ............................................................................................................... 29

6.3.1 General ......................................................................................................... 29

6.3.2 Structural steels ............................................................................................ 29

---------------------- Page: 4 ----------------------
IEC 61400-6:2020 © IEC 2020 – 3 –

6.3.3 Bolts and anchors .......................................................................................... 32

6.4 Ultimate strength analysis for towers and openings ............................................... 32

6.4.1 General ......................................................................................................... 32

6.4.2 Partial safety factors ...................................................................................... 32

6.4.3 Verification of ultimate strength ..................................................................... 32

6.4.4 Tower assessment ......................................................................................... 32

6.4.5 Detail assessments........................................................................................ 33

6.5 Stability................................................................................................................. 33

6.5.1 General ......................................................................................................... 33

6.5.2 Partial safety factor........................................................................................ 34

6.5.3 Assessment ................................................................................................... 34

6.5.4 Door frames/stiffeners ................................................................................... 34

6.6 Fatigue limit state ................................................................................................. 35

6.6.1 General ......................................................................................................... 35

6.6.2 Partial safety factor for materials ................................................................... 35

6.6.3 Assessment ................................................................................................... 36

6.6.4 Details ........................................................................................................... 36

6.7 Ring flange connections ........................................................................................ 36

6.7.1 General ......................................................................................................... 36

6.7.2 Design assumptions and requirements, execution of ring flanges .................. 36

6.7.3 Ultimate limit state analysis of flange and bolted connection .......................... 38

6.7.4 Fatigue limit state analysis of bolted connection ............................................ 38

6.8 Bolted connections resisting shear through friction ............................................... 40

6.8.1 General requirements .................................................................................... 40

6.8.2 Test-assisted design ...................................................................................... 41

6.8.3 Design without test ........................................................................................ 42

7 Concrete towers and foundations................................................................................... 42

7.1 General ................................................................................................................. 42

7.2 Basis of design ..................................................................................................... 42

7.2.1 Reference standard for concrete design ........................................................ 42

7.2.2 Partial safety factors ...................................................................................... 43

7.2.3 Basic variables .............................................................................................. 43

7.3 Materials ............................................................................................................... 45

7.4 Durability .............................................................................................................. 46

7.4.1 Durability requirements .................................................................................. 46

7.4.2 Exposure classes .......................................................................................... 46

7.4.3 Concrete cover .............................................................................................. 46

7.5 Structural analysis ................................................................................................ 46

7.5.1 Finite element analysis .................................................................................. 46

7.5.2 Foundation slabs ........................................................................................... 47

7.5.3 Regions with discontinuity in geometry or loads ............................................. 47

7.5.4 Cast in anchor bolt arrangements .................................................................. 48

7.6 Concrete to concrete joints ................................................................................... 48

7.7 Ultimate limit state ................................................................................................ 48

7.7.1 General ......................................................................................................... 48

7.7.2 Shear and punching shear ............................................................................. 48

7.8 Fatigue limit state ................................................................................................. 49

7.8.1 General ......................................................................................................... 49

7.8.2 Reinforcement and prestressing steel fatigue failure ...................................... 49

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7.8.3 Concrete fatigue failure ................................................................................. 49

7.9 Serviceability limit state ........................................................................................ 50

7.9.1 Load dependent stiffness reduction ............................................................... 50

7.9.2 Stress limitation ............................................................................................. 50

7.9.3 Crack control ................................................................................................. 50

7.9.4 Deformations ................................................................................................. 51

7.10 Execution .............................................................................................................. 51

7.10.1 General ......................................................................................................... 51

7.10.2 Requirements ................................................................................................ 51

7.10.3 Inspection of materials and products.............................................................. 51

7.10.4 Falsework and formwork ................................................................................ 51

7.10.5 Reinforcement and embedded steel ............................................................... 51

7.10.6 Pre-stressing ................................................................................................. 51

7.10.7 Precast concrete elements............................................................................. 52

7.10.8 Geometrical tolerances .................................................................................. 52

8 Foundations – Geotechnical design ............................................................................... 52

8.1 General ................................................................................................................. 52

8.2 Basis of design ..................................................................................................... 52

8.2.1 General ......................................................................................................... 52

8.2.2 Geotechnical limit states ................................................................................ 53

8.3 Geotechnical data ................................................................................................. 53

8.3.1 General ......................................................................................................... 53

8.3.2 Specific considerations .................................................................................. 55

8.4 Supervision, monitoring and maintenance of construction ..................................... 56

8.5 Gravity base foundations ...................................................................................... 56

8.5.1 General ......................................................................................................... 56

8.5.2 Ultimate limit state (ULS) ............................................................................... 57

8.5.3 Serviceability limit state (SLS) ....................................................................... 60

8.6 Piled foundations .................................................................................................. 62

8.6.1 General ......................................................................................................... 62

8.6.2 Pile loads ...................................................................................................... 62

8.6.3 Ultimate limit state ......................................................................................... 63

8.6.4 Serviceability limit state ................................................................................. 64

8.7 Rock anchored foundations ................................................................................... 65

8.7.1 General ......................................................................................................... 65

8.7.2 Types of rock anchor foundation .................................................................... 65

8.7.3 Geotechnical data .......................................................................................... 65

8.7.4 Corrosion protection ...................................................................................... 65

8.7.5 Anchor inspection and maintenance .............................................................. 66

8.7.6 Post tension tolerances and losses ................................................................ 66

8.7.7 Ultimate limit state ......................................................................................... 66

8.7.8 Serviceability limit state ................................................................................. 67

8.7.9 Robustness check ......................................................................................... 67

8.7.10 Rock anchor design ....................................................................................... 68

9 Operation, service and maintenance requirements ........................................................ 70

9.1 Operation, maintenance and monitoring ................................................................ 70

9.2 Periodic structural inspections .............................................................................. 70

9.3 Embedded steel structural section inspections ...................................................... 71

9.4 Bolt tension maintenance ...................................................................................... 71

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9.5 Structural health monitoring .................................................................................. 71

Annex A (informative) List of suitable design codes and guidelines for the calculation

basis ..................................................................................................................................... 72

A.1 General ................................................................................................................. 72

A.2 Reference documents ........................................................................................... 72

Annex B (informative) List of material for structural steel ..................................................... 73

B.1 General ................................................................................................................. 73

B.2 Structural steel ..................................................................................................... 73

Annex C (informative) Bolts ................................................................................................. 74

C.1 General ................................................................................................................. 74

C.2 Reference documents ........................................................................................... 75

Annex D (informative) Z-values for structural steel ............................................................... 76

D.1 General ................................................................................................................. 76

D.2 Definition of Z-value according to Eurocode .......................................................... 76

D.3 Reference documents ........................................................................................... 76

Annex E (informative) Simplified buckling verification for openings in tubular steel

towers ................................................................................................................................... 77

Annex F (informative) Fatigue verification ............................................................................ 80

F.1 General ................................................................................................................. 80

F.2 Specific details ..................................................................................................... 80

Annex G (informative) Methods for ring flange verification ................................................... 81

G.1 Method for ultimate strength analysis according to Petersen/Seidel ...................... 81

G.1.1 Basics ........................................................................................................... 81

G.1.2 Calculation method ........................................................................................ 81

G.1.3 Extension by Tobinaga and Ishihara .............................................................. 84

G.2 Method for fatigue strength analysis according to Schmidt/Neuper ........................ 85

G.2.1 Basics ........................................................................................................... 85

G.2.2 Formulas for the tri-linear approximation ........................................................ 86

G.3 Reference documents ........................................................................................... 87

Annex H (informative) Crack control – Guidance on 7.9.3 .................................................... 88

H.1 General ................................................................................................................. 88

H.2 Crack control based on Eurocode 2 ...................................................................... 88

H.3 Crack control based on Japanese standards ......................................................... 88

H.4 Crack control based on ACI 318 ............................................................................ 89

H.5 Reference documents ........................................................................................... 89

Annex I (informative) Finite element analysis for concrete................................................... 90

I.1 General ................................................................................................................. 90

I.2 Order and type of elements ................................................................................... 90

I.3 Constitutive modelling ........................................................................................... 91

I.4 Solution methods .................................................................................................. 91

I.5 Implicit approach .................................................................................................. 91

I.6 Steps in conducting of a finite element analysis .................................................... 92

I.7 Checking results ................................................................................................... 92

I.8 Reference documents ........................................................................................... 93

Annex J (informative) Tower-foundation anchorage ............................................................. 94

J.1 General ................................................................................................................. 94

J.2 Embedded anchorages ......................................................................................... 94

J.3 Bolted anchorages ................................................................................................ 95

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J.4 Grout .................................................................................................................... 95

J.5 Anchor bolts .......................................................................................................... 95

J.6 Embedded ring ..................................................................................................... 95

J.7 Anchorage load transfer .................................................................................

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