SIST EN IEC 61400-6:2020

SLOVENSKI STANDARD
01-september-2020
Sistemi za proizvodnjo energije na veter - 6. del: Stolp in obravnava temeljnih
zahtev (IEC 61400-6:2020)
Wind energy generation systems - Part 6: Tower and foundation design requirements
(IEC 61400-6:2020)
Windenergieanlagen - Teil 6: Auslegungsanforderungen an Türme und Fundamente
(IEC 61400-6:2020)
Systèmes de génération d’énergie éolienne – Partie 6: Exigences en matière de
conception du mât et de la fondation (IEC 61400-6:2020)
Ta slovenski standard je istoveten z: EN IEC 61400-6:2020
ICS:
27.180 Vetrne elektrarne Wind turbine energy systems
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 61400-6

NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2020
ICS 27.180
English Version
Wind energy generation systems - Part 6: Tower and foundation
design requirements
(IEC 61400-6:2020)
Systèmes de génération d’énergie éolienne - Partie 6 : Windenergieanlagen - Teil 6: Auslegungsanforderungen an
Exigences en matière de conception du mât et de la Türme und Fundamente
fondation (IEC 61400-6:2020)
(IEC 61400-6:2020)
This European Standard was approved by CENELEC on 2020-05-26. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2020 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 61400-6:2020 E

European foreword
The text of document 88/751/FDIS, future edition 1 of IEC 61400-6, prepared by IEC/TC 88 "Wind
energy generation systems" was submitted to the IEC-CENELEC parallel vote and approved by
CENELEC as EN IEC 61400-6:2020.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2021-02-26
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2023-05-26
document have to be withdrawn
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.

Endorsement notice
The text of the International Standard IEC 61400-6:2020 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards
indicated:
ISO 148-1 NOTE Harmonized as EN ISO 148-1
ISO 9001 NOTE Harmonized as EN ISO 9001
ISO/IEC 17025 NOTE Harmonized as EN ISO/IEC 17025

Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available here:
www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 61400-1 2019 Wind energy generation systems - Part 1: EN IEC 61400-1 2019
Design requirements
IEC 61400-2 - Wind turbines - Part 2: Small wind turbines EN 61400-2 -
IEC 61400-3-1 2019 Wind energy generation systems - Part 3-1: EN IEC 61400-3-1 2019
Design requirements for fixed offshore wind
turbines
ISO 2394 2015 General principles on reliability for - -
structures
ISO 22965-1 - Concrete - Part 1: Methods of specifying - -
and guidance for the specifier
ISO 22965-2 - Concrete - Part 2: Specification of - -
constituent materials, production of
concrete and compliance of concrete
ISO 22966 - Execution of concrete structures - -
ISO 6934 series Steel for the prestressing of concrete - -
ISO 6935 series Steel for the reinforcement of concrete - -
ISO 9016 2012 Destructive tests on welds in metallic EN ISO 9016 2012
materials - Impact tests - Test specimen
location, notch orientation and examination
ISO 12944 series Paints and varnishes - Corrosion protection - -
of steel structures by protective paint
systems
EN 1993-1-9 2005 Eurocode 3: Design of steel structures - - -
Part 1-9: Fatigue
EN 1993-3-2 2006 Eurocode 3: Design of steel structures - - -
Part 3-2: Towers, masts and chimneys -
Chimneys
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

– 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

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

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

– 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 . 111
Annex N (informative) Internal loads – Explanation of internal loads . 112
Annex O (informative) Seismic load estimation for wind turbine tower and foundation . 114
O.1 General . 114
O.2 Vertical ground motion . 114
O.3 Structure model . 114
O.4 Soil amplification . 115
O.5 Time domain simulation . 116
O.6 Reference documents . 116
Annex P (informative) Structural damping ratio for the tower of wind turbine . 117
P.1 General . 117
P.2 First mode structural damping ratio . 117
P.3 Second mode structural damping ratio . 118
P.4 Higher mode damping . 118
P.5 Reference documents . 119
Annex Q (informative) Guidance on partial safety factors for geotechnical limit states . 120
Q.1 General . 120
Q.2 Equilibrium . 120
Q.3 Bearing capacity . 120
Q.4 Sliding resistance . 121
Q.5 Overall stability . 121

IEC 61400-6:2020 © IEC 2020 – 7 –
Q.6 Reference documents . 122
Bibliography . 123

Figure 1 – Flange notations as an example of an L-flange . 31
Figure 2 – Door opening geometry . 35
Figure 3 – Flange gaps k in the area of the tower wall . 37
Figure 4 – Bolt force as a function of wall force . 39
Figure 5 – S-N curve for detail category 36 . 40
Figure 6 – Thermal effects around tower cross-section . 44
Figure 7 – Illustration of rock anchor length . 70
Figure E.1 – Circumferentially edge-stiffened opening . 78
Figure E.2 – Definition of W and t according to JSCE . 79
s s
Figure G.1 – Simplification of system to segment model . 81
Figure G.2 – Locations of plastic hinges for different failure modes . 82
Figure G.3 – Geometric parameters . 83
Figure G.4 – Modification factor 𝛌𝛌 for different 𝜶𝜶 [1] . 85
Figure G.5 – Tri-linear approximation of the non-linear relation between bolt force and
tension force of the bolted connection . 86
Figure K.1 – Example for the design of a deep beam using the strut-and-tie method . 97
Figure K.2 – Simple shapes of strut-and-tie models . 97
Figure K.3 – Three examples for carrying load in a deep beam . 98
Figure K.4 – Strut-and-tie models for a rock-anchor foundation . 101
Figure K.5 – Top tie reinforcement in a rock-anchor foundation. 101
Figure L.1 – Example stress-strain relationship for soil . 103
Figure L.2 – Loading and unloading behaviour of soil . 104
Figure L.3 – Variation of shear modulus with soil strain. 105
Figure L.4 – Reduction in rotational stiffness due to load eccentricity. 106
Figure L.5 – Illustrative example of reduction in foundation rotational stiffness due to
increasing load eccentricity . 107
Figure M.1 – Section through rock and anchor . 108
Figure M.2 – Typical anchor configuration with corrosion protection . 109
Figure N.1 – Representation of internal loads . 113
Figure O.1 – Structure model for response spectrum method . 115
Figure P.1 – First mode damping ratio for the steel tower of wind turbine . 118

Table 1 – Flange tolerances . 37
Table 2 – Summary of geotechnical limit states . 53
Table B.1 – National and regional steel standards and types . 73
Table C.1 – Comparison of bolt material in ISO 898-1, JIS B1186 and ASTM A490M-12 . 74
Table E.1 – Coefficients for Formula (E.3) . 78
[1]
Table H.1 – Limit value of crack width based on Japanese standards . 89
Table P.1 – Damping coefficients . 117
Table Q.1 – Minimum partial safety factors for the equilibrium limit state (European
and North American practice) . 120

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Table Q.2 – Minimum partial safety factors on for the equilibrium limit state (JSCE) . 120
Table Q.3 – Minimum partial material and resistance factors for the bearing resistance
limit state, ULS . 121
Table Q.4 – Minimum partial material and resistance factors for the sliding resistance
limit state, ULS . 121
Table Q.5 – Minimum partial material and resistance factors for the overall stability
limit state, ULS . 122

IEC 61400-6:2020 © IEC 2020 – 9 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
WIND ENERGY GENERATION SYSTEMS –

Part 6: Tower and foundation design requirements

FOREWORD
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