EN 1991-1-4:2005

SLOVENSKI STANDARD
01-oktober-2005
1DGRPHãþD
SIST ENV 1991-2-4:1998
Evrokod 1: Vplivi na konstrukcije – 1-4. del: Splošni vplivi – Obtežbe vetra
Eurocode 1: Actions on structures - Part 1-4: General actions - Wind actions
Eurocode 1: Einwirkungen auf Tragwerke - Teil 1-4: Allgemeine Einwirkungen -
Windlasten
Eurocode 1 : Actions sur les structures - Partie 1-4 : Actions générales - Actions du vent
Ta slovenski standard je istoveten z: EN 1991-1-4:2005
ICS:
91.010.30 7HKQLþQLYLGLNL Technical aspects
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN 1991-1-4

NORME EUROPÉENNE
EUROPÄISCHE NORM
April 2005
ICS 91.010.30 Supersedes ENV 1991-2-4:1995
English version
Eurocode 1: Actions on structures - Part 1-4: General actions -
Wind actions
Eurocode 1: - Actions sur les structures - Partie 1-4: Eurocode 1: Einwirkungen auf Tragwerke - Teil 1-4:
Actions générales - Actions du vent Allgemeine Einwirkungen - Windlasten
This European Standard was approved by CEN on 4 June 2004.

CEN 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 Central Secretariat or to any CEN 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 CEN member into its own language and notified to the Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 1991-1-4:2005: E
worldwide for CEN national Members.

Contents Page
Section 1 General 9
1.1 Scope 9
1.2 Normative references 10
1.3 Assumptions 10
1.4 Distinction between Principles and Application Rules 10
1.5 Design assisted by testing and measurements 10
1.6 Definitions 10
1.7 Symbols 11
Section 2 Design situations 16
Section 3 Modelling of wind actions 17
3.1 Nature 17
3.2 Representations of wind actions 17
3.3 Classification of wind actions 17
3.4 Characteristic values 17
3.5 Models 17
Section 4 Wind velocity and velocity pressure 18
4.1 Basis for calculation 18
4.2 Basic values 18
4.3 Mean wind 19
4.3.1 Variation with height 19
4.3.2 Terrain roughness 19
4.3.3 Terrain orography 21
4.3.4 Large and considerably higher neighbouring structures 21
4.3.5 Closely spaced buildings and obstacles 22
4.4 Wind turbulence 22
4.5 Peak velocity pressure 22
Section 5 Wind actions 24
5.1 General 24
5.2 Wind pressure on surfaces 24
5.3 Wind forces 25
Section 6 Structural factor c c 28
s d
6.1 General 28
6.2 Determination of c c 28
s d
6.3 Detailed procedure 28
6.3.1 Structural factor c c 28
s d
6.3.2 Serviceability assessments 30
6.3.3 Wake buffeting 30
Section 7 Pressure and force coefficients 31
7.1 General 31
7.1.1 Choice of aerodynamic coefficient 31
7.1.2 Asymmetric and counteracting pressures and forces 32
7.1.3 Effects of ice and snow 32
7.2 Pressure coefficients for buildings 33
7.2.1 General 33
7.2.2 Vertical walls of rectangular plan buildings 34
7.2.3 Flat roofs 37
7.2.4 Monopitch roofs 40
7.2.5 Duopitch roofs 43
7.2.6 Hipped roofs 47
7.2.7 Multispan roofs 48
7.2.8 Vaulted roofs and domes 50
7.2.9 Internal pressure 51
7.2.10 Pressure on walls or roofs with more than one skin 53
7.3 Canopy roofs 54
7.4 Free-standing walls, parapets, fences and signboards 61
7.4.1 Free-standing walls and parapets 61
7.4.2 Shelter factors for walls and fences 63
7.4.3 Signboards 63
7.5 Friction coefficients 64
7.6 Structural elements with rectangular sections 65
7.7 Structural elements with sharp edged section 67
7.8 Structural elements with regular polygonal section 67
7.9 Circular cylinders 69
7.9.1 External pressure coefficients 69
7.9.2 Force coefficients 71
7.9.3 Force coefficients for vertical cylinders in a row arrangement 74
7.10 Spheres 74
7.11 Lattice structures and scaffoldings 76
7.12 Flags 78
7.13 Effective slenderness λ and end-effect factor ψ 80
λ
Section 8 Wind actions on bridges 82
8.1 General 82
8.2 Choice of the response calculation procedure 85
8.3 Force coefficients 85
8.3.1 Force coefficients in x-direction (general method) 85
8.3.2 Force in x-direction – Simplified Method 88
8.3.3 Wind forces on bridge decks in z-direction 89
8.3.4 Wind forces on bridge decks in y-direction 90
8.4 Bridge piers 91
8.4.1 Wind directions and design situations 91
8.4.2 Wind effects on piers 91
Annex A (informative) Terrain effects 92
A.1 Illustrations of the upper roughness of each terrain category 92
A.2 Transition between roughness categories 0, I, II, III and IV 93
A.3 Numerical calculation of orography coefficients 95
A.4 Neighbouring structures 100
A.5 Displacement height 101
Annex B (informative)  Procedure 1 for determining the structural factor c c 102
s d
B.1 Wind turbulence 102
B.2 Structural factor 103
B.3 Number of loads for dynamic response 105
B.4 Service displacement and accelerations for serviceability assessments of a
vertical structure 105
Annex C (informative)  Procedure 2 for determining the structural factor c c 108
s d
C.1 Wind turbulence 108
C.2 Structural factor 108
C.3 Number of loads for dynamic response 109
C.4 Service displacement and accelerations for serviceability assessments 109
Annex D (informative)  c c values for different types of structures 111
s d
Annex E (informative) Vortex shedding and aeroelastic instabilities 114
E.1 Vortex shedding 114
E.1.1 General 114
E.1.2 Criteria for vortex shedding 114
E.1.3 Basic parameters for vortex shedding 115
E.1.4 Vortex shedding action 118
E.1.5 Calculation of the cross wind amplitude 118
E.1.6 Measures against vortex induced vibrations 128
E.2 Galloping 129
E.2.1 General 129
E.2.2 Onset wind velocity 129
E.2.3 Classical galloping of coupled cylinders 131
E.3 Interference galloping of two or more free standing cylinders 133
E.4 Divergence and Flutter 134
E.4.1 General 134
E.4.2 Criteria for plate-like structures 134
E.4.3 Divergency velocity 134
Annex F (informative) Dynamic characteristics of structures 136
F.1 General 136
F.2 Fundamental frequency 136
F.3 Fundamental mode shape 141
F.4 Equivalent mass 143
F.5 Logarithmic decrement of damping 143
Bibliography 146
Foreword
This document EN 1991-1-4:2005 has been prepared by Technical Committee CEN/TC250 "Structural
Eurocode", the secretariat of which is held by BSI.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by October 2005, and conflicting national standards
shall be withdrawn at the latest by March 2010.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard : Austria, Belgium, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy,
Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia,
Spain, Sweden, Switzerland and United Kingdom.
This European Standard supersedes ENV 1991-2-4: 1995.
CEN/TC 250 is responsible for all Structural Eurocodes.
Background of the Eurocode programme
In 1975, the Commission of the European Community decided on an action programme in the field of
construction, based on article 95 of the Treaty. The objective of the programme was the elimination of
technical obstacles to trade and the harmonisation of technical specifications.
Within this action programme, the Commission took the initiative to establish a set of harmonised
technical rules for the design of construction works which, in a first stage, would serve as an
alternative to the national rules in force in the Member States and, ultimately, would replace them.
For fifteen years, the Commission, with the help of a Steering Committee with Representatives of
Member States, conducted the development of the Eurocodes programme, which led to the first
generation of European codes in the 1980s.
In 1989, the Commission and the Member States of the EU and EFTA decided, on the basis of an
agreement between the Commission and CEN, to transfer the preparation and the publication of the
Eurocodes to the CEN through a series of Mandates, in order to provide them with a future status of
European Standard (EN). This links de facto the Eurocodes with the provisions of all the Council’s
Directives and/or Commission’s Decisions dealing with European standards (e.g. the Council Directive
89/106/EEC on construction products - CPD - and Council Directives 93/37/EEC, 92/50/EEC and
89/440/EEC on public works and services and equivalent EFTA Directives initiated in pursuit of setting
up the internal market).
The Structural Eurocode programme comprises the following standards generally consisting of a
number of Parts :
EN 1990 Eurocode : Basis of Structural Design
EN 1991 Eurocode 1: Actions on structures
EN 1992 Eurocode 2: Design of concrete structures
EN 1993 Eurocode 3: Design of steel structures

Agreement between the Commission of the European Communities and the European Committee for Standardisation (CEN)
concerning the work on EUROCODES for the design of building and civil engineering works (BC/CEN/03/89).
EN 1994 Eurocode 4: Design of composite steel and concrete structures
EN 1995 Eurocode 5: Design of timber structures
EN 1996 Eurocode 6: Design of masonry structures
EN 1997 Eurocode 7: Geotechnical design
EN 1998 Eurocode 8: Design of structures for earthquake resistance
EN 1999 Eurocode 9: Design of aluminium structures
Eurocode standards recognise the responsibility of regulatory authorities in each Member State and
have safeguarded their right to determine values related to regulatory safety matters at national level
where these continue to vary from State to State.
Status and field of application of Eurocodes
The Member States of the EU and EFTA recognise that Eurocodes serve as reference documents for
the following purposes :
– as a means to prove compliance of building and civil engineering works with the essential
requirements of Council Directive 89/106/EEC, particularly Essential Requirement N°1 –
Mechanical resistance and stability – and Essential Requirement N°2 –Safety in case of fire ;
– as a basis for specifying contracts for construction works and related engineering services ;
– as a framework for drawing up harmonised technical specifications for construction products (ENs
and ETAs)
The Eurocodes, as far as they concern the construction works themselves, have a direct relationship
with the Interpretative Documents referred to in Article 12 of the CPD, although they are of a different
nature from harmonised product standards . Therefore, technical aspects arising from the Eurocodes
work need to be adequately considered by CEN Technical Committees and/or EOTA Working Groups
working on product standards with a view to achieving full compatibility of these technical
specifications with the Eurocodes.
The Eurocode standards provide common structural design rules for everyday use for the design of
whole structures and component products of both a traditional and an innovative nature. Unusual
forms of construction or design conditions are not specifically covered and additional expert
consideration will be required by the designer in such cases.

According to Art. 3.3 of the CPD, the essential requirements (ERs) shall be given concrete form in interpretative documents
for the creation of the necessary links between the essential requirements and the mandates for harmonised ENs and
ETAGs/ETAs.
According to Art. 12 of the CPD the interpretative documents shall :
a) give concrete form to the essential requirements by harmonising the terminology and the technical bases and indicating
classes or levels for each requirement where necessary ;
b) indicate methods of correlating these classes or levels of requirement with the technical specifications, e.g. methods of
calculation and of proof, technical rules for project design, etc. ;
c) serve as a reference for the establishment of harmonised standards and guidelines for European technical approvals.
The Eurocodes, de facto, play a similar role in the field of the ER 1 and a part of ER 2.
National Standards implementing Eurocodes
The National Standards implementing Eurocodes will comprise the full text of the Eurocode (including
any annexes), as published by CEN, which may be preceded by a National title page and National
foreword, and may be followed by a National annex.
The National annex may only contain information on those parameters which are left open in the
Eurocode for national choice, known as Nationally Determined Parameters, to be used for the design
of buildings and civil engineering works to be constructed in the country concerned, i.e. :
– values and/or classes where alternatives are given in the Eurocode,
– values to be used where a symbol only is given in the Eurocode,
– country specific data (geographical, climatic, etc.), e.g. wind map,
– the procedure to be used where alternative procedures are given in the Eurocode.
It may also contain
– decisions on the use of informative annexes, and
– references to non-contradictory complementary information to assist the user to apply the
Eurocode.
Links between Eurocodes and harmonised technical specifications (ENs and ETAs)
for products
There is a need for consistency between the harmonised technical specifications for construction
products and the technical rules for works . Furthermore, all the information accompanying the CE
Marking of the construction products which refer to Eurocodes should clearly mention which Nationally
Determined Parameters have been taken into account.
Additional information specific for EN 1991-1-4
EN 1991-1-4 gives design guidance and actions for the structural design of buildings and civil
engineering works for wind.
EN 1991-1-4 is intended for the use by clients, designers, contractors and relevant authorities.
EN 1991-1-4 is intended to be used with EN 1990, the other Parts of EN 1991 and EN 1992-1999 for
the design of structures.
National annex for EN 1991-1- 4
This standard gives alternative procedures, values and recommendations for classes with notes
indicating where National choice may be made. Therefore the National Standard implementing
EN 1991-1-4 should have a National Annex containing Nationally Determined Parameters to be used
for the design of buildings and civil engineering works to be constructed in the relevant country.
National choice is allowed for EN 1991-1-4 through clauses:
1.1 (11) Note 1
1.5 (2)
see Art.3.3 and Art.12 of the CPD, as well as clauses 4.2, 4.3.1, 4.3.2 and 5.2 of ID 1.
4.1 (1)
4.2 (1)P Note 2
4.2 (2)P Notes 1, 2, 3 and 5
4.3.1 (1) Notes 1 and 2
4.3.2 (1)
4.3.2 (2)
4.3.3 (1)
4.3.4 (1)
4.3.5 (1)
4.4 (1) Note 2
4.5 (1) Notes 1 and 2
5.3 (5)
6.1 (1)
6.3.1 (1) Note 3
6.3.2 (1)
7.1.2 (2)
7.1.3 (1)
7.2.1 (1) Note 2
7.2.2 (1)
7.2.2 (2) Note 1
7.2.8 (1)
7.2.9 (2)
7.2.10 (3) Notes 1 and 2
7.4.1 (1)
7.4.3 (2)
7.6 (1) Note 1
7.7 (1) Note 1
7.8 (1)
7.10 (1) Note 1
7.11 (1) Note 2
7.13 (1)
7.13 (2)
8.1 (1) Notes 1 and 2
8.1 (4)
8.1 (5)
8.2 (1) Note 1
8.3 (1)
8.3.1 (2)
8.3.2 (1)
8.3.3 (1) Note 1
8.3.4 (1)
8.4.2 (1) Notes 1 and 2
A.2 (1)
E.1.3.3 (1)
E.1.5.1 (1) Notes 1 and 2
E.1.5.1 (3)
E.1.5.2.6 (1) Note 1
E.1.5.3 (2) Note 1
E.1.5.3 (4)
E.1.5.3 (6)
E.3 (2)
Section 1 General
1.1 Scope
(1) EN 1991-1-4 gives guidance on the determination of natural wind actions for the structural design
of building and civil engineering works for each of the loaded areas under consideration. This includes
the whole structure or parts of the structure or elements attached to the structure, e. g. components,
cladding units and their fixings, safety and noise barriers.
(2) This Part is applicable to:
– Buildings and civil engineering works with heights up to 200 m. See also (11).
– Bridges having no span greater than 200 m, provided that they satisfy the criteria for dynamic
response, see (11) and 8.2.
(3) This part is intended to predict characteristic wind actions on land-based structures, their
components and appendages.
(4) Certain aspects necessary to determine wind actions on a structure are dependent on the location
and on the availability and quality of meteorological data, the type of terrain, etc. These need to be
provided in the National Annex and Annex A, through National choice by notes in the text as indicated.
Default values and methods are given in the main text, where the National Annex does not provide
information.
(5) Annex A gives illustrations of the terrain categories and provides rules for the effects of orography
including displacement height, roughness change, influence of landscape and influence of
neighbouring structures.
(6) Annex B and C give alternative procedures for calculating the structural factor c c .
s d
(7) Annex D gives c c factors for different types of structures.
s d
(8) Annex E gives rules for vortex induced response and some guidance on other aeroelastic effects.
(9) Annex F gives dynamic characteristics of structures with linear behaviour
(10) This part does not give guidance on local thermal effects on the characteristic wind, e.g. strong
arctic thermal surface inversion or funnelling or tornadoes.
(11) This part does not give guidance on the following aspects:
– wind actions on lattice towers with non-parallel chords
– wind actions on guyed masts and guyed chimneys
– torsional vibrations, e.g. tall buildings with a central core
– bridge deck vibrations from transverse wind turbulence
– cable supported bridges
– vibrations where more than the fundamental mode needs to be considered
NOTE 1 The National Annex may provide guidance on these aspects as non contradictory
complementary information.
NOTE 2 For wind actions on guyed masts, guyed chimneys and lattice towers with non-parallel chords,
see EN 1993-3-1, Annex A.
NOTE 3 For wind actions on lighting columns, see EN 40.
1.2 Normative references
The following normative documents contain provisions which, through references in this text,
constitute provisions of this European standard. For dated references, subsequent amendments to, or
revisions of any of these publications do not apply. However, parties to agreements based on this
European standard are encouraged to investigate the possibility of applying the most recent editions
of the normative documents indicated below. For undated references the latest edition of the
normative document referred to applies.
EN 1990 Eurocode: Basis of structural design
EN 1991-1-3 Eurocode 1: Actions on structures: Part 1-3: Snow loads
EN 1991-1-6 Eurocode 1: Actions on structures: Part 1-6: Actions during execution
EN 1991-2 Eurocode 1: Actions on structures: Part 2: Traffic loads on bridges
EN 1993-3-1 Eurocode 3: Design of steel structures: Part 3-1: Masts and towers
1.3 Assumptions
(1)P The general assumptions given in EN 1990, 1.3 apply.
1.4 Distinction between Principles and Application Rules
(1)P The rules in EN 1990, 1.4 apply.
1.5 Design assisted by testing and measurements
(1) In supplement to calculations wind tunnel tests and proven and/or properly validated numerical
methods may be used to obtain load and response information, using appropriate models of the
structure and of the natural wind.
(2) Load and response information and terrain parameters may be obtained from appropriate full
scale data.
NOTE: The National Annex may give guidance on design assisted by testing and measurements.
1.6 Definitions
For the purposes of this European Standard, the definitions given in ISO 2394, ISO 3898 and ISO
8930 and the following apply. Additionally for the purposes of this Standard a basic list of definitions is
provided in EN 1990,1.5.
1.6.1
fundamental basic wind velocity
the 10 minute mean wind velocity with an annual risk of being exceeded of 0, 02, irrespective of wind
direction, at a height of 10 m above flat open country terrain and accounting for altitude effects (if
required)
1.6.2
basic wind velocity
the fundamental basic wind velocity modified to account for the direction of the wind being considered
and the season (if required)
1.6.3
mean wind velocity
the basic wind velocity modified to account for the effect of terrain roughness and orography
1.6.4
pressure coefficient
external pressure coefficients give the effect of the wind on the external surfaces of buildings; internal
pressure coefficients give the effect of the wind on the internal surfaces of buildings.
The external pressure coefficients are divided into overall coefficients and local coefficients. Local
coefficients give the pressure coefficients for loaded areas of 1 m or less e.g. for the design of small
elements and fixings; overall coefficients give the pressure coefficients for loaded areas larger than
10 m .
Net pressure coefficients give the resulting effect of the wind on a structure, structural element or
component per unit area.
1.6.5
force coefficient
force coefficients give the overall effect of the wind on a structure, structural element or component as
a whole, including friction, if not specifically excluded
1.6.6
background response factor
the background factor allowing for the lack of full correlation of the pressure on the structure surface
1.6.7
resonance response factor
the resonance response factor allowing for turbulence in resonance with the vibration mode
1.7 Symbols
(1) For the purposes of this European standard, the following symbols apply
NOTE  The notation used is based on ISO 3898:1999. In this Part the symbol dot in expressions indicates
the multiplication sign. This notation has been employed to avoid confusion with functional expressions.
(2) A basic list of notations is provided in EN 1990, 1.6 and the additional notations below are specific
to EN 1991-1-4.
Latin upper case letters
A area
A area swept by the wind
fr
A reference area
ref
B background response part
C wind load factor for bridges
E Young’s modulus
F resultant friction force
fr
F vortex exciting force at point j of the structure
j
F resultant wind force
w
H height of a topographic feature
I turbulence intensity
v
K mode shape factor; shape parameter
K interference factor for vortex shedding
iv
K reduction factor for parapets
rd
K correlation length factor
w
K non dimensional coefficient
x
L length of the span of a bridge deck; turbulent length scale
L actual length of a downwind slope
d
L effective length of an upwind slope
e
L correlation length
j
L actual length of an upwind slope
u
N number of cycles caused by vortex shedding
N number of loads for gust response
g
R resonant response part
Re Reynolds number
R , R aerodynamic admittance
h b
S wind action
Sc Scruton number
S non dimensional power spectral density function
L
St Strouhal number
W weight of the structural parts contributing to the stiffness of a chimney
s
W total weight of a chimney
t
Latin lower case letters
a factor of galloping instability
G
a combined stability parameter for interference galloping
IG
b width of the structure (the length of the surface perpendicular to the wind direction if
not otherwise specified)
c altitude factor
alt
c dynamic factor
d
c directional factor
dir
c (z) exposure factor
e
c force coefficient
f
c force coefficient of structures or structural elements without free-end flow
f,o
c lift force coefficient
f,l
c friction coefficient
fr
c aerodynamic exciting coefficient
lat
c moment coefficient
M
c pressure coefficient
p
c probability factor
prob
c roughness factor
r
c orography factor
o
c size factor
s
c seasonal factor
season
d depth of the structure (the length of the surface parallel to the wind direction if not
otherwise specified)
e eccentricity of a force or edge distance
f non dimensional frequency
L
h height of the structure
h obstruction height
ave
h displacement height
dis
k equivalent roughness
k peak factor
p
k terrain factor
r
k torsional stiffness
Θ
l length of a horizontal structure
m mass per unit length
m equivalent mass per unit length
n natural frequency of the structure of the mode i
i
n fundamental frequency of along wind vibration
1,x
n fundamental frequency of cross-wind vibration
1,y
n ovalling frequency
p annual probability of exceedence
q reference mean (basic) velocity pressure
b
q peak velocity pressure
p
r radius
s factor; coordinate
t averaging time of the reference wind speed, plate thickness
v onset wind velocity for galloping
CG
v critical wind velocity for interference galloping
CIG
v critical wind velocity of vortex shedding
crit
v divergence wind velocity
div
v mean wind velocity
m
v fundamental value of the basic wind velocity
b,0
v basic wind velocity
b
w wind pressure
x horizontal distance of the site from the top of a crest
x-direction horizontal direction, perpendicular to the span
y-direction horizontal direction along the span
y maximum cross-wind amplitude at critical wind speed
max
z height above ground
z average height
ave
z-direction vertical direction
z roughness length
z , z reference height for external wind action, internal pressure
e i
z distance from the ground to the considered component
g
z maximum height
max
z minimum height
min
z reference height for determining the structural factor
s
Greek upper case letters
Φ upwind slope
fundamental alongwind modal shape
Φ
1,x
Greek lower case letters
galloping instability parameter
α
G
combined stability parameter of interference galloping
α
IG
δ logarithmic decrement of damping
aerodynamic logarithmic decrement of damping
δ
a
logarithmic decrement of damping due to special devices
δ
d
structural logarithmic decrement of damping
δ
s
ε coefficient
bandwidth factor
ε
frequency factor
ε
variable
η
ϕ solidity ratio, blockage of canopy
slenderness ratio
λ
opening ratio, permeability of a skin
µ
up-crossing frequency; Poisson ratio; kinematic viscosity
ν
θ torsional angle; wind direction
air density
ρ
standard deviation of the turbulence
σ
v
standard deviation of alongwind acceleration
σ
a,x
ψ reduction factor for multibay canopies
mc
reduction factor of force coefficient for square sections with rounded corners
ψ
r
reduction factor of force coefficient for structural elements with end-effects
ψ
λ
end-effect factor for circular cylinders
ψ
λα
ψ shelter factor for walls and fences
s
exponent of mode shape
ζ
Indices
crit critical
e external ; exposure
fr friction
i internal ; mode number
j current number of incremental area or point of a structure
m mean
p peak; parapet
ref reference
v wind velocity
x alongwind direction
y cross-wind direction
z vertical direction
Section 2 Design situations
(1)P The relevant wind actions shall be determined for each design situation identified in accordance
with EN 1990, 3.2.
(2) In accordance with EN 1990, 3.2 (3)P other actions (such as snow, traffic or ice) which will modify
the effects due to wind should be taken into account.
NOTE  See also EN 1991-1-3, EN 1991-2 and ISO FDIS12494
(3) In accordance with EN 1990, 3.2 (3)P, the changes to the structure during stages of execution
(such as different stages of the form of the structure, dynamic characteristics, etc.), which may modify
the effects due to wind, should be taken into account.
NOTE  See also EN 1991-1-6
(4) Where in design windows and doors are assumed to be shut under storm conditions, the effect of
these being open should be treated as an accidental design situation.
NOTE  See also EN 1990, 3.2 (2) (P)
(5) Fatigue due to the effects of wind actions should be considered for susceptible structures.
NOTE  The number of load cycles may be obtained from Annex B, C and E.
Section 3 Modelling of wind actions
3.1 Nature
(1) Wind actions fluctuate with time and act directly as pressures on the external surfaces of enclosed
structures and, because of porosity of the external surface, also act indirectly on the internal surfaces.
They may also act directly on the internal surface of open structures. Pressures act on areas of the
surface resulting in forces normal to the surface of the structure or of individual cladding components.
Additionally, when large areas of structures are swept by the wind, friction forces acting tangentially to
the surface may be significant.
3.2 Representations of wind actions
(1) The wind action is represented by a simplified set of pressures or forces whose effects are
equivalent to the extreme effects of the turbulent wind.
3.3 Classification of wind actions
(1) Unless otherwise specified, wind actions should be classified as variable fixed actions, see EN
1990, 4.1.1.
3.4 Characteristic values
(1) The wind actions calculated using EN 1991-1-4 are characteristic values (See EN 1990, 4.1.2).
They are determined from the basic values of wind velocity or the velocity pressure. In accordance
with EN 1990 4.1.2 (7)P the basic values are characteristic values having annual probabilities of
exceedence of 0,02, which is equivalent to a mean return period of 50 years.
NOTE  All coefficients or models, to derive wind actions from basic values, are chosen so that the
probability of the calculated wind actions does not exceed the probability of these basic values.
3.5 Models
(1) The effect of the wind on the structure (i.e. the response of the structure), depends on the size,
shape and dynamic properties of the structure. This Part covers dynamic response due to along-wind
turbulence in resonance with the along-wind vibrations of a fundamental flexural mode shape with
constant sign.
The response of structures should be calculated according to Section 5 from the peak velocity
pressure, q , at the reference height in the undisturbed wind field, the force and pressure coefficients
p
and the structural factor c c (see Section 6). q depends on the wind climate, the terrain roughness
s d p
and orography, and the reference height. q is equal to the mean velocity pressure plus a contribution
p
from short-term pressure fluctuations.
(2) Aeroelastic response should be considered for flexible structures such as cables, masts, chimneys
and bridges.
NOTE  Simplified guidance on aeroelastic response is given in Annex E.
Section 4 Wind velocity and velocity pressure
4.1 Basis for calculation
(1) The wind velocity and the velocity pressure are composed of a mean and a fluctuating component.
The mean wind velocity v should be determined from the basic wind velocity v which depends on the
m b
wind climate as described in 4.2, and the height variation of the wind determined from the terrain
roughness and orography as described in 4.3. The peak velocity pressure is determined in 4.5.
The fluctuating component of the wind is represented by the turbulence intensity defined in 4.4.
NOTE  The National Annex may provide National climatic information from which the mean wind velocity
v , the peak velocity pressure q and additional values may be directly obtained for the terrain categories
m p
considered.
4.2 Basic values
(1)P The fundamental value of the basic wind velocity, v , is the characteristic 10 minutes mean wind
b,0
velocity, irrespective of wind direction and time of year, at 10 m above ground level in open country
terrain with low vegetation such as grass and isolated obstacles with separations of at least 20
obstacle heights.
NOTE 1 This terrain corresponds to terrain category II in Table 4.1.
NOTE 2 The fundamental value of the basic wind velocity, v , may be given in the National Annex.
b,0
(2)P The basic wind velocity shall be calculated from Expression (4.1).
v = c ⋅ c ⋅ v
b dir season b,0
(4.1)
where:
v is the basic wind velocity, defined as a function of wind direction and time of year at 10 m
b
above ground of terrain category II
v is the fundamental value of the basic wind velocity, see (1)P
b,0
c is the directional factor, see Note 2.
dir
c is the season factor, see Note 3.
season
NOTE 1 Where the influence of altitude on the basic wind velocity v is not included in the specified
b
fundamental value v the National Annex may give a procedure to take it into account.
b,0
NOTE 2 The value of the directional factor, c , for various wind directions may be found in the National
dir
Annex. The recommended value is 1,0.
NOTE 3 The value of the season factor, c , may be given in the National Annex. The recommended
season
value is 1,0.
NOTE 4 The 10 minutes mean wind velocity having the probability p for an annual exceedence is
determined by multiplying the basic wind velocity v in 4.2 (2)P by the probability factor, c given by
b prob
Expression (4.2). See also EN 1991-1-6.
n
1 − K ⋅ ln(− ln(1 − p)) 
(4.2)
c =  
prob
 
1 − K ⋅ ln(− ln(0,98))
 
where:
K is the shape parameter depending on the coefficient of variation of the extreme-value distribution.
n is the exponent.
NOTE 5 The values for K and n may be given in the National Annex. The recommended values are 0,2
for K and 0,5 for n.
(3) For temporary structures and for all structures in the execution phase, the seasonal factor c
season
may be used. For transportable structures, which may be used at any time in the year, c should
season
be taken equal to 1,0.
NOTE  See also EN 1991-1-6.
4.3 Mean wind
4.3.1 Variation with height
(1) The mean wind velocity v (z) at a height z above the terrain depends on the terrain roughness
m
and orography and on the basic wind velocity, v , and should be determined using Expression (4.3)
b
v (z) = c (z)⋅c (z)⋅v (4.3)
m r o b
where:
c (z) is the roughness factor, given in 4.3.2
r
c (z) is the orography factor, taken as 1,0 unless otherwise specified in 4.3.3
o
NOTE 1 Information on c may be given in the National Annex. If the orography is accounted for in the
O
basic wind velocity, the recommended value is 1,0.
NOTE 2 Design charts or tables for v (z) may be given in the National Annex.
m
The influence of neighbouring structures on the wind velocity should be considered (see 4.3.4).
4.3.2 Terrain roughness
(1) The roughness factor, c (z), accounts for the variability of the mean wind velocity at the site of the
r
structure due to:
the height above ground level
the ground roughness of the terrain upwind of the structure in the wind direction considered
NOTE  The procedure for determining c (z) may be given in the National Annex. The recommended
r
procedure for the determination of the roughness factor at height z is given by Expression (4.4) and is
based on a logarithmic velocity profile.

z
cz()=⋅k ln for z ≤z≤z

rr min max
(4.4)
z
0
cz()=≤cz( ) for z z
rrmin min
where:
z is the roughness length
k terrain factor depending on the roughness length z calculated using
r 0
0,07

z
(4.5)
k=⋅0,19

r

z
0,II

where:
z = 0,05 m (terrain category II, Table 4.1)
0,II
z is the minimum height defined in Table 4.1
min
z is to be taken as 200 m
max
z , z depend on the terrain category. Recommended values are given in Table 4.1 depending on five
0 min
representative terrain categories.
Expression (4.4) is valid when the upstream distance with uniform terrain roughness is long enough to
stabilise the profile sufficiently, see (2).
Table 4.1 — Terrain categories and terrain parameters
z z
0 min
Terrain category
m m
0 Sea or coastal area exposed to the open sea 0,003 1
I Lakes or flat and horizontal area with negligible vegetation and
0,01 1
without obstacles
II Area with low vegetation such as grass and isolated obstacles
0,05 2
(trees, buildings) with separations of at least 20 obstacle heights
III Area with regular cover of vegetation or buildings or with isolated
obstacles with separations of maximum 20 obstacle heights (such 0,3 5
as villages, suburban terrain, permanent forest)
IV Area in which at least 15 % of the surface is covered with buildings
1,0 10
and their average height exceeds 15 m
NOTE: The terrain categories are illustrated in A.1.

(2) The terrain roughness to be used for a given wind direction depends on the ground roughness and
the distance with uniform terrain roughness in an angular sector around the wind direction. Small
areas (less than 10% of the area under consideration) with deviating roughness may be ignored. See
Figure 4.1.
Figure 4.1 — Assessment of terrain roughness
NOTE  The National Annex may give definitions of the angular sector and of the upstream distance. The
recommended value of the angular sector may be taken as the 30º angular sector within ±15° from the
wind direction. The recommended value for the upstream distance may be obtained from A.2.
(3) When a pressure or force coefficient is defined for a nominal angular sector, the lowest roughness
length within any 30° angular wind sector should be used.
(4) When there is choice between two or more terrain categories in the definition of a given area, then
the area with the lowest roughness length should be used.
4.3.3 Terrain orography
(1) Where orography (e.g. hills, cliffs etc.) increases wind velocities by more than 5% the effects
should be taken into account using the orography factor c .
O
NOTE  The procedure to be used for determining c may be given in the National Annex. The
O
recommended procedure is given in A.3.
(2) The effects of orography may be neglected when the average slope of the upwind terrain is less
than 3°. The upwind terrain may be considered up to a distance of 10 times the height of the isolated
orographic feature.
4.3.4 Large and considerably higher neighbouring structures
(1) If the structure is to be located close to another structure, that is at least twice as high as the
average height of its neighbouring structures, then it could be exposed (dependent on the properties
of the structure) to increased wind velocities for certain wind directions. Such cases should be taken
into account.
NOTE  The National Annex may give a procedure to take account of this effect. A recommended
conservative first approximation is given in A.4.
4.3.5 Closely spaced buildings and obstacles
(1) The effect of closely spaced buildings and other obstacles may be taken into account.
NOTE  The National Annex may give a procedure. A recommended first approximation is given in A.5. In
rough terrain closely spaced buildings modify the mean wind flow near the ground, as if the ground level
was raised to a height called displacement height h .
dis
4.4 Wind turbulence
(1) The turbulence intensity I (z) at height z is defined as the standard deviation of the turbulence
v
divided by the mean wind velocity.
NOTE 1 The turbulent component of wind velocity has a mean value of 0 and a standard deviation σ . The
v
standard deviation of the turbulence σ may be determined using Expression (4.6).
v
σ = k ⋅ v ⋅ k (4.6)
v r b I
For the terrain factor k see Expression (4.5), for the basic wind velocity v see Expression (4.1) and for
r b
turbulence factor k see Note 2.
I
NOTE 2 The recommended rules for the determination of I (z) are given in Expression (4.7)
v
σ k
v I
I (z) = = for z ≤ z ≤ z
v min max
(4.7)
v (z) c (z) ⋅ ln(z / z )
m o 0
I (z) = I (z ) for z < z
v v min min
where:
k is the turbulence factor. The value of k may be given in the National Annex. The recommended value
I I
for k is 1,0.
I
c is the orography factor as described in 4.3.3
o
z is the roughness length, given in Table 4.1
4.5 Peak velocity pressure
(1) The peak velocity pressure q (z) at height z, which includes mean and short-term velocity
p
fluctuations, should be determined.
NOTE 1 The National Annex may give rules for the determination of q (z). The recommended rule is given
p
in Expression (4.8).
qz()=+[1 7⋅I ()z ]⋅ ⋅ ρ⋅v ()z=c ()z⋅q
pv m eb
(4.8)
where:
ρ  is the air density, which depends on the altitude, temperature and barometric pressure to be
expected in the region during wind storms
c (z) is the exposure factor given in Expression (4.9)
e
q (z)
p
c (z) =
e
q
b
(4.9)
q is the basic velocity pressure given in Expression (4.10)
b
qv=⋅ ρ⋅
bb
(4.10)
NOTE 2 The values for ρ may be given in the National Annex. The recommended value is 1,25 kg/m .
NOTE 3 The value 7 in Expression (4.8) is based on a peak factor equal to 3,5 and is consistent with the
values of the pressure and force coefficients in Section 7.
For flat terrain where c (z) = 1,0 (see 4.3.3), the exposure factor c (z) is illustrated in Figure 4.2 as a
O e
function of height above terrain and a function of terrain category as defined in Table 4.1.

Figure 4.2 — Illustrations of the exposure factor c (z) for c =1,0, k =1,0
e O I
Section 5 Wind actions
5.1 General
(1)P Wind actions on structures and structural elements shall be determined taking account of both
external and internal wind pressures.
NOTE  A summary of calculation procedures for the determination of wind actions is given in Table 5.1.
Table 5.1 —Calculation procedures for the determination of wind actions
Subject Reference
Parameter
peak velocity pressure q
p
basic wind velocity v 4.2 (2)P
b
reference height z Section 7
e
terrain category Table 4.1
characteristic peak velocity pressure q 4.5 (1)
p
turbulence intensity I 4.4
v
mean wind velocity v 4.3.1
m
orography coefficient c (z) 4.3.3
o
roughness coefficient c (z) 4.3.2
r
Wind pressures, e.g. for cladding, fixings and structural

parts
external pressure coefficient c Section 7
...