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1/92

BRITISH STANDARD

BS 6399:

Part 2:1995

Loading for

buildings

Part 2. Code of practice for wind loads

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NO COPYING WITHOUT BS1 PERMISSION EXCEPT AS PERMITTED BY COPYRIGHI LAW

—


2/92

BS6399:Part2: 1995

This British Standard, having

bee” prepared under the

direction of the Building and

Chil Engineering %ctor Board,

was published tinder the

authority of the Standards

Bozwd and comes into effect on

15 Ausust 1995

0 BSI 1 295

Nmt published (as CP 4)

November 1944

First revision (as CP 3:

Chapter V) Ausust 1952

%rfitd second revision (as CP3:

Chapter V : Part 1)

Becember 1967

Completion of second revision

(= CP 3: Chapter V : Part 2)

July 1970

Published as KS 6399: Fart 2:

Au@st 1995

The following 9S1 references

relate ro the work on this

sta”dati.

Committee reference 9/525/ 1

Draft for comment 91 I 16625 DC

ISBN06S0 23651 X

Committees responsible for this

British Standard

‘rhe preparation of this Britiih Standard was entrusted by ‘lbchnical

Committee B/525, Buildings and civil engineering structures, to Subcommittee

B/525/1, Actions (loadings) and basis of desigrr, upon which the following

bodies were represented:

British Constructional Steelwork Association Ltd.

British Iron arrdSteel Producem’ Association

British Masonry Society

Concrete Society

Department of the Environment (Building Research Establishment)

Department of the Environment (Property and Buifdings Directorate)

Department of Trarrsport (Highways Agency)

Institution of Structural En@reers

National House-building Council

Royal Institute of British Architects

Steel Construction Institute

Amendments issued since publication

Amd. No. Date

Text affected

I

I


3/92

BS6299:Part2:

Contents

Fage

Committees responsible

Inside front cover

Foreword

iv

Section 1. General

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

Scope

Informative references

Definitions

Main symbols

Outline of proceducc for calculating wirrd loads

Dyrramic claasiiication

Site exposure

Choice of method

1

1

1

2

3

7

7

8

Section 2. Standard method

2.1 Standard wind loads

9

2.2 Standad wind speeds

12

2.3 Standard pressure coefficients

20

2.4 External pressure coefficients for walls

20

2.5 External pressure coefficients for roofs

25

2.6 Internal pressure coefficients

39

2.7 Pressure coefficients for elements

41

Section 3. Directional method

3.1 Dwectional wind loads

44

3.2 Directional wind speeds

46

3.3 Dnctional pressure coefficients

51

3.4 Hybrid combinations of standard arrd dkectional methods

72

Annexes

A (normative) Necessary pruviaions for wind tunnel testing

73

B (irrfOmative) Derivation of extreme wind information

73

C (informative) Dynamic augmentation

75

D (nonnative) PmbabiIity factor and seasonaf factor

77

E (informative) ‘l&rain categories and effective height

79

F (informative) Gust peak factor

81

‘lhbles

1

2

3

4

L

6

7

8

9

10

11

12

Buifding-type faCtOr&

Dynamic pressure g= [in Pa)

Valves of dwection factor S,j

Factor .%,for standard methud

ExcemaA pressure cucfficients Cw for verticaI walk

Frictional drag coefficients

External pressure Cw coefficients for walls of circulm-plan buildhrgs

Extemaf pressure ceefficienta Cw for flat roofs of buiIdings

External presarrc coefficients Cw for monOpirch mOfs Of buildin@

External pressure coefficients C& for duopitch roofs of build@s

External pressure coefficients Cw for hipped roofs of buildings

Reduction factor for multi-bay roofs

7

9

17

20

21

25

25

26

31

31

32

35

i


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Dcr

.s : - z :

Page

13 Net pressure coefficients CP for free-standing monopitch canopy roofs 36

14 Net pre~um coefficients CP for free-standing duopitch canopy roofs

15 Reduction factors for free-standing multi-bay camopy roofs

16 Internal pressure coefficients CPi for enclosed build@s

17 Internal pressure coefficients Cpi for buildings with dominant

opmings

HI Internal

pressure coefficients Cpi for open-sided buildings

19 Internal pressure coefficients Cpi for open-tOpped vertical ~lindem

20 Net pressure coefficients CP for long elements

21 Net pressure coefficients CP for free-standing W*

22 Factom .SCind $

23 A@stment factors I“c and Tt for sites in town terrain

24 Gust peak factor gt

25 Values of L, and .Sh

26 External pressure coefficients Cp, for vertical walls of

rectangular-plan buildings

27 Reduction factom for zone A on verticaf walls of polygon&plan

buildings

28 External pressure coefficients CP, for vertical gable w~k adjacent tO

non-vertical walls and roofs

29 External pressure coefficients Cw for windward-facing nOn-vefiical

walls

30 ExtemaJ pressure coefficients Cw for flat roofs with sharp eaves

31 Reduction factor for zones A to D, H to J and Q to S of flat roofs

with parapets

32 External pressure coefficients Cm for flat roofs with curved eaves

33 External pressure coefficients Cw for flat roofs with mansard eaves

34 External pressure coefficients CP, for pitched roof zones A to J

35 Extemaf pressure coefficients CR for pitched roof zOnes K tO S

36 External pressure coefficients Cw for additional zones T to Y of

hipped roofs

37 Intemaf pressure coefficients Cpj for open-sided buildings

D. 1 Values of seasonal factor

Figures

1 Flowchart illustrating outline procedure 4

2 Basic deftitions of building dimensions

6

3 Dynamic augmentation factor C,

8

4

Size

effect factor Ca of standard method

11

5 Definition of diagonal of loaded areas

12

6 Basic wind speed

Vb

(in rds) 13

7 Definition of significant topography

14

8 Definition of topographic dimensions

15

9

lbpogmphic location factors for hills and ridges

16

10 ‘f@ographic kxation factors for cliffs and escarpments 17

11 Division of buildings by parts for lateral loads 19

12 Key to wall pressure data 21

13 Typical examples of buildhygs with m-entrant comers and recessed

bays 22

37

37

39

40

40

40

41

42

48

49

50

51

52

.52

54

55

59

60

60

61

63

66

70

72

78

ii


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Page

14 Examples of flush irregular walls

15 Key for walls of inset storey

16 Key for flat roofs

17 Key to cave details for flat roofs

18 Key for inset stomy

19 Key for monopitch roofs

W Key for duopitch roofs

21 Key for hipped roofs

22 Key for mansard and multipitch roofs

22 Key for multi-bay roofs

24 Key for free-standing canopy roofs

25 Reduction factor for length of elements

26 Key for free-stamding walls

27 Shelter factor for fences

26 Key for signboards

29 Wind directions for a rectarrgulm-plan building

26 Key to overall load

P

31 Key for vertical walls of builrlii

32 Key to vertical gable wrdls

23 Key for walls of buildings with m-entrant comers

24 Key for walls of buildings with recessed bays

35 Key to general method for flat rcofs

26 Examples of zones of flat roof of arbM’ary Plan shape

37 Additional zones around inset storey

28 Key for monopitch roofs

39 Synrmetries for pitched roofs

40 Key for duopitch roofs

41 Key for hipped roofs

42 Key to multi-bay roofs

E. 1 Effective heights br towns

F. 1 Gust peak factor gt

L&t of references

23

24

26

27

28

29

30

33

34

35

38

41

42

43

43

44

46

52

54

56

57

58

59

62

64

65

67

69

71

so

82

Inside back cover

In


6/92

Foreword

This Part of this British Standard has been prepared by Subcommittee B/525/1,

Actions (loadings) and basis of design, and supersedes CP3 : Chapter V : Part 2:

1972.

‘Rds part of BS 6399 is a technical revision of CP3 : Chapter V : Part 2 and

incorporates the considerable advances made and experience gained in wind

engineering since that time. CP3 : Chapter V : M 2 will not be withdrawn

immediately so as to allow an overlap period with this Part of BS 6399.

The b=ic wind speed in thk British Standard is given as an hourly mean value;

this differs from CP3 : Chapter V : Part 2 in which it was based on a 3 s gust

value. However, the hourly mean basic wind speed is subsequently converted

into a gust wind speed for use in design (by a gust peak factor wh]ch takes

account of gust duration time, height of structure above ground and the size of

the structure). The adoption of the hourly mean value for the basic wind speed is

for technical reasons. Primarily it allows a more accumte treatment of

topography, but it alao provides the starting pohrt for serviceability calculations

involving fatigue or dynamic response of the stmcture. Its use is akw a move

towards harmonization as mean values (sometimes 10 min means) are often the

basis for wind loading calculations in European and international standards.

Structure factors are used to check whether the response of the structure can be

considered to be static, in which caae the use of the calculation methods in thk

standard is appropriate. If the response is found to be mildly dynamic the

methods can still be used but the resulting loads will need to be augmented.

Structures which are dynamic will alsu be identified but their assessment is

outside the scope of the standard.

TWOalternative methods are given:

a) a standard method, which uses a simplified procedure;

b) a directional method, from which the simplified method was derived.

The standard method gives a conservative result within its range of applicability.

Calibration haa shown that loads on typicaf buildings obtained by the standard

method are around 14 % larger than obtained from the directional method. The

degee of conservatism can be much larger close to the ground and in towns, but

decreaaes to zero around 100 m above the gruund.

In addition to reduced conservatism, the directional method assessesthe loadhg

in more detail, but with the penalty of increaaed complexity and compukitional

effort. Because of this it is anticipated that the standard method will be used for

most hand-baaed calculations and that the directional method wifl be

implemented principally by computer

Procedures are alao given to enable the standard effective wind speed to be used

with the directional pressure coefficients and for the directional effective wind

speeds to be used with the standard pressure coefficients.

CP3 : Chapter V : Part 2 allowed for the effect of ground roughness, building

size and height above gound by a single factor. This required the calculation of

separate wind speeds for every combination of reference height above gruund

and the size of the loaded area. However, a simp~] cation has been introduced in

the standard method which involves the calculation of only a single wind speed

for each reference height. The effect of size is allowed for by a separate

factor, Cc

BS 6399: Part 2 also gives values for external pressure coefficients for a greater

mnge of building configurations than did CP3 : Chapter V : Part 2.

Compliance with a British Standard does not of itseff confer immunity from

legaf obligations.

iv


7/92

BS6399:Part 2:1995

Section 1. General

1.1 Scope

‘lidsRutof BS 6399 gives methods for determining

the gust peak wind loads on buildings and

components thereof that should be taken into

account in design using equivalent static

procedures.

Two alternative methods are given:

a) a standard method which uses a sirnpliiled

pnxedure to obtain a standard effective wind

speed which ix uacd with standard pressure

coefficients to determine the wind loads for

orthogonal design cases.

NOTE 1. This procedure is virtually the same win CP3 :

Chapter V : Parr 2.

b) a directional method in which effective wind

s~ds ~d Preasurc coefficients arc determined

to derive the wind loads for each wind dtiction.

Other methods may be used in place of the two

methcds given in thix standard, provided that they

can be shown to be equivalent. Such methods

include wind tunnel tests which should be taken as

equivalent only if they meet the conditions defined

in armex A.

NUTE

2. Wind tunnel tests are recommended when the form of

the building is not covered by the data i“ this standard, when

the form of the b.ifdimg cm be changed in response to the test

resulf.? in order to give an optimized design, or when loading

data are required in more derail than is awe” in this standard.

Specialist advice should be sought for building

shapes and site locations that are not covered by

this standard.

The methods given in this Part of BS 6399 do not

apply tO bufldkgs which, by virtue of the

structural properties, e .g, maas, stiffness, natural

frequency or damping, are particularly susceptible

to dynamic excitation. These should be asaeased

using established dynamic methods or wind tunnel

tests.

NOTE 3 See

references [1] to 14] for examples of established

dynamic methcds.

NUI’E 4. If a building is susceptible to excitaticm by vortex

shedding or other aemelastic instability, tie maximum dynamic

respome may occur at wind speeds lower than the maximum.

1.2

Informative references

Thii British Standard refers to other publications

that provide information or guidance. Editions of

thexe publications current at the time of issue of

this standard am listed on the inaide back cover,

but reference should be made to the latest

editions.

1.3 Defiitionx

For the purposes of this British Standard the

following definitions apply.

1.3.1 Wind speed

1.3.1.1 basic wind speed

The hourly mean wind speed with an annual risk Q

of being exceeded of 0.02, irrespective of wind

direction, at a height of 10 m over completely flat

terrain at sea Ievei that would occur if the

ruughneas of the terrabr w uniform everywhere

(inclu~l:g urban areas, inland lakes and the sea)

and equwalent to typical open country in the

United Kingdom.

1.3.1.2 site wind speed

The basic wind speed modtiled to account for the

altitude of the site arrd the direction of the wind

being considered (arrd the aeaaon of exposure, if

required).

NUlll, In the standard metbcd only,

effectsof topographic

featuresareincludedntbe sitewindspeed.

1.3.1.3 effective wind speed

The site wind speed modfied to a gust speed by

taking account of the effective height, size of the

building or structural element Ming considered and

of permanent obstmctions upwind,

NCII’E. 1“ the direcriomd method only: the effects of

topographic featwes are omitted from the site wind s~ed.

1.3.2 Pressure

1.3.2.1 dynamic pressure

‘f’he potential pressure available from the kinetic

energy of the effective wind speed.

1.3.2.2 pressrrre coefficient

The ratio of the pressure acting on a surface to the

dy-c pKS.SUP2.

1.3.2.3 exterfud pressrrre

The pressure acting on a.frexternal surface of a

building caused by the dmct action of the wind.

1.3.2.4 intemaf pressure

The preasffrc acting on an internal surface of a

buildbrg caused by the action of the external

pressures through porosity and openings in the

external surfaces of the buildlng.

1.3.2.5 net pressure

The pressure dtiference between opposite faces of

a surface.

1


8/92

BS63Y9:Part2:lYY5

Section 1

1.3.3 Height

1.3.3.1 altitude

a) when topography is not si@lcant: the height

above mean sea level of the ground level of the

site;

b) when topography is significant: the height

above mean sea level of the base of the

topographic feature,

1.3.3.2 building height

The height of a building or part of a building above

its base.

1.3.3.3 reference height

The reference height for a part of a structure is the

datum height above Wound for the pressure

coefficients and is defined with the pressure

coefficients for that part.

1.3.3.4 obstruction height

The average height above ground of buildings,

structures or other permanent obstmctions to the

wind immediately upwind of the site.

1.3.3.5 effective height

The height used in the calculations of the effective

wind speed determined from the reference height

with slfowance for the obstmction height.

1.3.4 Length

1.3.4.1 buifding length

The longer horizontal dimension of a buildhrg or

part of a building. 1,

1.3.4.2 building width

The shorter horizontal dimension of a building or

part of a building.’)

1.3.4.3 crosswind breadth

The horizontal extent of a buiIding or part of a

building norrmd to the direction of the wind. l]

1.3.4.4 inwind depth

The horizontal extent of a building or part of a

building paralfel to the direction of the wind. 11

1.3.4.5 diagonrd dirnenaion

The largest diagonal dimension of a loaded area,

i.e. the dimension between the most distant points

on the periphery of the area.

1.3.4.6 scaling length

A reference length determined from the

proportions of the building used to define zones

over which the pressure coefficient is Sas”med to

be constant.

1.3.5 Distance

1.3.5.1 fetch

The distance from the site to the upwind edge of

each category of terrain, used to determine the

effect of termirr roughness changes.

1.4 Main symbols

For the purposes of this Rut of BS 6399 the

following symbols apply.

A

a

B

b

c.

Cp

c

c:

c,

D

d

G

9t

H

He

H ,

Ho

h

Kb

L

LD

L,

Lu

P

P

P,

Area

Largest diagonal dimension of the loaded area

envelope (figure 5)

Crosswind breadth of building (figure 2b)

Scaling length used to define loaded areas for

pressure coefficients (2.4.1.3, 2.5. 1.2)

Size effect factor of standard method (2.1.3.4)

Net pressure coefficient (2. 1.3.3)

External prewure coefficient (2. 1.3.1)

Internal pressure coefficient (2. 1.3.2)

Dynamic augmentation factor (1.6. 1)

Inwind depth of buifding (figure 2b)

Disnreter of circular cylinders

gap across recessed bay or weU (figure 34)

gust peak factor

Buildhrg height (fw 2), eaves height or

height of inset or lower storey

Effective height (1.7.3)

Reference height (1. 7.3)

Obstruction height (1. 7.3, figure 2), or

average height of roof tops upwind of the

building

Pa.rspet height (2.5.1.4, f~re 17),

free-standhrg waif height (2.7.5.4, figure 23),

or signboard height (2.7.6, figure 24)

Building-type factor (1.6. 1)

Building length (figure 2) or length of element

between free ends (2.7.3)

Length of downwind slope of topogmphic

feature (2.2.2.2.5, figure 8)

Effective slope length of topographic feature

(2.2.2.2.4)

Length of upwind slope of topographic feature

(2.2.2.2.4, figure 8)

Net load (2.1.3.5)

Net pressure (2. 1.3.3)

Pressure on external surface (2. 1.3.1)

l) For COmPIeX pla shaWs, these lengths may be detemined from the Smalleat enclming rectangle or circle

2


9/92

Section

1

BSS399:Part 2:1995

Pi

Q

9

9.

9i

9s

r

s,

s~

s=

s~

s~

SP

s,

st

s

T,

Tt

v~

v,

v,

w

w

x

z

a

b

AS

AT

Pressure on intemaf surface (2.1.3.2)

Annual risk (pmbabi lty) of the baaic wind

speed being exceeded (2.2.2.4, 2.2.2. 5,)

Dynamic pressure

Dynamic pressure of directional method for

external pressures (3. 1.2.2)

Dynamic presxure of dkectional method for

internal pressures (3. 1.2.2)

Dynamic pressure of standard method (2.1.2)

Radius (figure 17)

Altitude factor (2.2.2.2)

Terrain and building factor (2.2.3. 1)

Fetch factor (3.2.3.2)

Dnction factor (2.2.2.3)

lbpogmphic increment (3.2.3.4)

Probability factor (2.2.2. 5)

Seasonal factor (2.2.2.4)

Turbulence factor (3.2.3.2)

lbpographic location factor (2.2.2.2)

Fetch adjustment factor (3. 2.3.2)

‘fhrbulence adjustment factor (3.2.3.2)

NIC wind speed (2.2.1, figure 6)

Effective wind speed (2.2.3, 3.2.3)

Site wind speed (2.2.2)

Buildlng width (figure 2)

width of wedge in re-entnmt comers

(figure 33)

D~tance of site from crest of topographic

feature (2.2.2.2.5, figure 8) or distance in

wind direction for buifding spacing ( 1.7.3.3)

Height of crest of topographic feature above

the upwind baae altitude (figure 8)

Pitch angfe (from horizontal) of roof (2.5) or

non-vertical W* (3.3.1.4)

comer angle of walls (3.3.1.2)

.%te altitude in metres above mean sea level

(2.2.2.2)

Altitude of upwind baae of topographic

feature in metres above mean sea level

(2.2.2.3)

Reduction factor for length of elements

(2.7.3)

Average slope of the gmmnd

Effective slope of topographic feature

(2.2.2.2.4)

‘fhngent of downwind slope of topographic

feature (figure 7)

lkrrgent of upwind slope of topographic

feature (figure 7, 2.2.2.2.4)

Whfd direction in degrees eaat of north

(2.2.2.3)

Solidity ratio of walls or frames (2.7.5) or

blockage ratio of canopies (2.5.9, figure 24)

Wind direction of degrees from normal to

building faces (figure 2) or angle around

periphery of circular-plan buildhrg (2.4.6)

1.5 Outline of procedure for calculating

wind loads

1.5.1 The outline of procedure is illustrated in the

flow chart given in figfmc 1. This shorn the stages

of the standard method, together with the relevant

clause numbem, as the boxes outlined and

connected by thick lines. The stages of the

directional method are shown as boxes outlined

with double lines and are directly equivalent to the

stages of the standard method. Various input data

are shown in boxes outlined with singfe lines.

1.5.2 The wind loads should be calculated for each

of the loaded areas under consideration, depending

on the dimensions of the building, defined in

figure 2. These may be:

a) the structure ax a whole;

b) parts of the structure, such as walls and roofs

or

c) individual stmctural components, including

cladding urrits arrd their ftinga.

Nc71Z. Wind load on a partially completed structure may he

critical and will be dependent on the method and sequence of

construction.

3


10/92

s ww:rar z: xm

CSSULIU1l 1

Stage 1: Dynamic augmentation

Input building height H, input

factor C, (1 .6.1) building type factor K, (table 1 )

Stage 2: Check limits of

No

Building is dynamic. This Pert

applicability C, < 0.25,

does not apply (see references

H


11/92

Section

1 BS63YY:MZ:1YY6

Notes to figure 1

Stage 1 Determines

the dynamic augmentation factor

fmm the basic geometric and stnctuml pmpenies of the

building,

Stage 2 Depending on this value, a check is p+?rformed

on the level of dynamic excitatim to determine:

a) whether the methods given in this k%rt of ss 6399

aPPIY and the a%ew.ment may proceed; or

b) whether the methcds given in this ~ of ss 6399

do not apply and the building should be assessed by

one of the methwls for dynmnic buildings (see

references [1] to [4]) or by wind tunnel tesfs

(see annex A).

SW, % Determines the basic hourly mean wind speed

from the map for the UK.

Sfage 4 Determines a site wind speed, still

corresponding to the hourly mean wind speeds at a

height of 10 m above ground in the standard exposure,

from the basic wind speed by applying corrections for the

site altitude, wind dbwmion and season. Up to this point,

no allowance for the exposure of the particular site has

been made and the procedure is common (except in ifs

treafment of the

effectsof

topography) to both the

sti”dard and dkectional metbd.

NCflE The derivations of the b~ic wind speed map, the

adjustments for site altitude, wind direction and season

are given in annex B.

Stage 6 .ksses.ses the exposure of the site in term of the

terrain mugtmes and the effective height. llu?e

categories of terrain roughness are used to define the site

exposure. The effective height depends cm the degee of

shelfer provided by neighbo”ri”g buildings or other

permanent obstmcfiom.

Stage k Having assessed the exposure of the site, this

St&3e

offers

the choice between the standard nwtbcd a“d

the directional method. The standard method @ves

conservative values for standard orthogonal load czses,

and a simplified method for buildin@ up to 1C4 m in

height and for signirlcant to fmgmphy. The directional

methcd gives a more precise value for any given wind

direction, particularly for sites in towns, and where

topography is significant. A simple rule for assessing the

significance of tofmsraphy is provided.

Stage 7 Determines the effective wind W&&S required

by either method. The effective wind speed is a gust

wind sp+ed appropriate to the site exposure and the

height of the building. h the scmdard method this

correspmds to a datum size of loaded area, while in the

directional method this cm’resfmnds to the size of the

loaded area under consideration.

s~e 8 Converts the effective wind speed into an

equwalent dynamic pressure.

Stage 9 Selects pressureoefficients corresponding to

the form of the building. In the standard method these

coeffkienb correspond to a number (usually two or

three) of orthogonal load cases, while in the directional

methcd they correspond to the wind directions being

considered (usually twelve).

St-x. 10 Determines the wind loads from the dynamic

pressure,pressureoefficients, dynamic augmentation

factor and, in the standard method, by the size effect

factor, to gtve the characteristic wind load for static

design.

5


12/92

Bsw99:Partz: YY5

Section 1

a) Fixed dimensions length, width, height

—.

44

‘B

k~x

Wind

rml

D

General caae Orthogonal caaas

h) Variable dimemiom: crosswind breadth, imvind depth, wind angle

c) Obstruction height and upwind paci”g

Figure 2. Basic definitions of building dimensions

6


13/92

Section 1

BS 6299: Part 2:1995

1.6 Dynamic classtilcation

1.6.1

Dyn am ic a ugm e n t at ion fa ct or

Th e

methods of this standard employ equivalent

static loads to represent the effect of fluctuating

loads which is applicable only to buildings which

are not susceptible to dynamic excitation.

The standard permits equivalent static loads to be

used for the design of mildly dynamic structures by

the introduction of a dynamic augmentation factor.

The value of this factor depends upon the actual

height H of the building above ground and on a

building-type factor ~b obtained from table 1, for

the form of construction of the buildlng.

The dynamic augmentation factor C, is given for

typical buildings in figure

3 .

‘fhble 1. Building-type fsctor ~b

&p-e

of

buUdf@

Welded steel unclad frames

Bolted steel and reinforced concrete

unclad frames

Fort-d sheds and similar light structures

with few internal walls

Framed buildings with structural walls

around M- and staim only (e.g. office

build~ of open plan or with

partitioning)

Framed buildmf@ with structural walk

around lifts and stairs with additional

masonry subdivision walls (e. g.

aptiment buildings), buildings of

ma.?arry construction and

timber-framed housing

:

f&

?3

4

2

1

0.5

NOTE. Thevaluesof thefacfarsKb and C, have been derived

for typical building structures with typical frequency and

damping chamcfe tstics, under typical UK wind speeds, without

accounting for topogmphyor tsme.inoughness effects. More

accurate values of these factam may be derived using annex C

when tbe buifding characteristics am “ot typical, or when the

effectsof topographyand terrain mugtmessneed tobe

taken

into account.

1.6.2 Lfndts of applicability

This Part of Ef36399 does not apply when the

value of dynamic augmentation factor exceeds the

limits shown in figure 3. Buildin@ faffing outside

these imk? should be assmsed using established

dynamic methods.

NCllll See

referemes[1] to

[4]

for

f“rtber information o“

analysis of dynamic structures.

1.7 Site exposure

1 .7 .1 Ge n e rs f

Th e

site wind speed

V,

refers to a standard open

country exposure at a height of 10 m above

ground. ‘lb obtain the effective wind speed the

effects of varying gruund roughness, the height

and d~tance of obstructions upwind of the site and

the effects of topography should be taken into

account.

1.7.2 Ground roughness categories

Three categories of terrain are considered:

a) sea the sea, and inland areas of water

extending more than 1 km in the wind direction

when closer than 1 km upwind of the site;

b) country: all terrain which is not defined as sea

or town;

c) bum: built up aress with an average level of

mof tops at least

Ho =

5 m above ground level.

NOTE 1. Permanent forest and woodland may be treated 8..s

town categmy.

NUIT 2. ‘l&rain Categories are explained i“ more detail in

annex E.

1 .7 .3 Re fe re nc e h eigh t an d e ffe ct ive h eigh t

L 7 .3 .1 Th e

reference height

H , is

defined for the

building form in the appropriate pressure

coefficient tables and deftition figures, but can

conservatively be taken as the maximum height of

the building above ground level.

1.7.3.2 For buifdings in country terrain, or

conservatively for buildings in town terrain, the

effective height Ife should be taken as the

reference height

HP

1 .7 .3 .3

For buildings in town terrain, the effective

height & depends on the shelter affofied by the

avemge level of the height Ho of the roof tops of

the buildings, or of the height of other permanent

obstructions, upwind of the site and their upwind

spacing X. These dimensions are defined in

figure 2. The effective height He should be

determined as follows.

a) Ifxs2Ho

then

He is

the greater of

He = H r – 0.8H0 or He = 0 .4H ,;

b) If X >

6H0

tiien

H e is given

by

He = H r;

c) fn

the range 2Jfo < X c

6H0

He is the greater of

He =

H , -

1.2H0 + 0.2X

or He = 0 .4HP

NOTE. 1. the absence of more accurate information, the

obstmction bwgbt Ho may be estimated from the average

number of storeys of .pwi”d buildings by raking the typical

storey height as 3 m. Furrher guidance is given i“ annex E.

7


14/92

BsfxfYY: I’a r tz:lYY5

sec on

@

Limits of applicability

Shaded regionoutaidescopeof thisPart

0.4

0.3

0.2

0.1

0

1

10

100 1000

Building height, H (m)

Figure 3 . Dyn am ic au gm en t a t ion fa c t or C,

1.8 Choice of method

1.8.1 For alf structures less than 100 m in height

and where the wind loading can be represented by

equivalent static loads (see 1.6), the wind loading

can be otained either by the standard method

described in section 2 or by the directional method

given in section 3,

1.8.2 The standard method provides values of

effective wind speed to be used with the standard

pressure coefficient (clauses 2.3 to 2.5) to

determine orthogonal load cases, corresponding to

the wind direction notionally normal or parallel to

the faces of the buifding. The standard method

uses a simplilled allowance for signiilcant

topography, as defined in figure 7.

1.8.3 The directional method gives values of the

effective wind s~ed for different wind directions,

taking into account the term.in appropriate to the

wind dnction behrg considered, to be used with

the directional pressure coefficients. It gives better

estimates of effective wind speeds in towns and for

sites affected by topography.

L 8.4 However, m the standard method gives

conservative values of both effective wind speed

(below 100 m) and pressure coefficient, it may

sometimes be appropriate to use a hybrid

combination of both methods, either

a) standard effective wind speeds with

directional pressure coefficients; or

b) directional effective wind speeds with

standard pressure coefficients.

Combination a) k aurxouriate when the form of

the building is ‘well ‘defied, but the site is not; the

caaes of relocatable buildings or

standard

mass- pruduced designs are typical examples.

Combination b) is appropriate when only the

standmd orthogonal load cases are required, but a

better allowance for site exposure is desired

because topogmphy is signifkant and/or the site is

in a town. Such hybrid combinations should be

app~ed only in accordance with 3.4.

“-)

8


15/92

BS6399:Part2:lW5

Sec t ion 2 . St an d a rd m et h od

2.1 Standard wind loads

2.1.1

Wind

direction

2 .1 .1 . 1 T h e standard method requires assessment

for orthogonal load cases for wind dmections

normal to the faces of the buifdmg, as shown in

figure 2b. When the building is doubly-symmetric,

e.g. rectangular-plan with flat, equal- duopitch or

hipped roof, the two orthogonal cases shown in

figure 2b are sufficient, When the building is

singly-symmetric, three orthogonal cases are

required, e.g. for rectangular-plan monopitch

buildings: wind norrnaf to high eaves; wind normal

to low eaves; wind pwallel to eaves. When the

buifdlng is asymmetric, four orthogorwd cases are

n?quired.

2.1.1.2 For each orthogonal case, the range of

wind dmctions *45” either side of the direction

normal to the building face should be considered.

When symmetry is used to reduce the number of

orthogonal load cases, both opposing wind

directions, e.g. Q =

Oo rmd O = 180° should be

considered arrd the more onerous dmction used.

2.1.2 Dynamic prsssure

2.1.2.1 The value of the dynamic pressure q, of

the standard method is given by

q , =

0.613Ve2

(1)

where

q , i s

the dynamic pressure (in Pa*);

t ’ , i s the effective wind speed from 2.2.3

(in rots).

2.1.2.2 Values of dynamic pressure q~ for various

values of

Ve a r e

given in table 2.

2.1.3

Wind

load

2 .1 .3 . 1 Er t em a l su ea ce p r ssa ur w

T h e pressure acting on the external surface of a

buildhg P, i s gNen by

where

9s is the dynamic pressure from 2.1. Z

Cw is the extemaf pressure coefficient for the

buifding surface given irr 2.4 and 2.5

c,

is the size effect factor for external

pressures defined in 2.1.3.4.

2.L3.2 I n t er n a l su ~a ce p rssa ur vs

T h e pressure acting on the internal surface of a

building, pi, is given by

Pi =

q , cp l ca

(3 )

where

9,

is the dynamic pressure from 2.1.Z

CPi is the internal pressure coefficient for the

buifding given in 2.6

c, is the size effect factor for internal


2.1.3.3 Nst su@ace

P re a s u rw

T h e

n et pressure p a ct in g a cross a sur fa ce is given

by the following.

a) For enclosed buildings

P= Pe -Pi

(4)

where

pe is the external pressure given irr 2.1.3.1;

Pi

i s

the internal pressure given in 2.1.3.2.

b) For free-standing canopies and building

elements

P = %% G

(5)

where

9,

is the dynamic pressure from 2.1. Z

Cp

is the net pressure coefficient for the

canopy surface or element given in 2.5.9

and 2.7

P, -

q,cwc,

(2) Ca

is the size effect factor for external


uc pressure

q~ (i n Pa )

+0 + 1.0 + 2.0

61

245

552

981

iCi30

74

270

589

1 0 3 0

1 5 9 0

38

297

628

1080

1660

‘Ihble 2. Dyrrs

Y

‘e

mls

10

2 0

3 0

4 0

5 0

6 0 2210 \2280 I 2360

.lP a -l J /m2

T

I

C4

120

324 353

668 709

1130 1190

1720 17 30

2430

2510

T

6.0

+ 6.0

136 i 57

383

414

751 794

1240 1300

1850 1920

2590 2670

a

7.0 + 8.0 + 9.0

177 199

221

447 481

516

839 885 932

1350 1410

1470

1990

2060 2130

2750 2830

2920

9


16/92

BSfX399: F’art2:1995

Section 2

2 . 1 .3 . 4 S u e @ectf ac t Or

T h e size effect factor Ca of the standard method

accounts for the non-simultaneous action of gusts

acnmsanextemalsurfaceand for the response of

internal pressures. Values of size effect factor are

given in figure4, dependent onthe site exposure

(see 1.’7) and the diagonal dnenaion a.

For external pressures the diagonal dimension a is

the largest diagonal of the area over which load

sharfng takes place, as illustrated in figure 5. For

internal pressures an effective diagonal d]menaion

is defined in 2.6 which is dependent on the

internal volume.

For all individual stmctural components, claddlng

units and their ftings, the diagonal dimension

should bc taken as a = 5 m, unless there is

adequate load sharing capacity to justify the use of

a diagonal length ~eater than 5 m.

2.1.3.5 Su@ace l o a d s

T h e net load P on an area of a building surface or

element is gjven by

P=PA (6 )

where

P

is the net pressure acroas the surface;

A

is the loaded area.

Load effects, for example bending moments and

shear fomes, at any level in a building should be

baaed on the diagonal dimension of the loaded area

above the level being considered, as illustrated in

figure 5C.

2.1.3.6 Ovemll l o a d s

T h e ovem f l

load

P on a

building is taken as the sum

of the loads on individual surfaces with allowances

for non-simultaneous action between faces and for

mildly dynamic response.

T h e overall horizontal loads are given by

P = 0.85( X Pf m n t - EP, ,J (1 + C,) (7)

where

,zPf m n t i s the horizontal component of surface

load summed over the

windward-facing walls and roofs;

ZP.W

is the horizontal component of surface

load summed over the leeward-facing

walls and roofs;

c, is the dynamic augmentation factor

fmm 1.6.1;

but tafdng the inwind depth of the building,

D, a s

t h e smaller of width Wor length L in the

determination of P f m n t and Prem

N OTE 1. Th e fa ct or 0.85 a ccoun ts for t he n on -sim ult a neou s

a ct ion bet w een fa ces.

NOTE 2. As t he effect of int erna l pressure on t he front a nd

rea r fa ces is eq w d a nd opposit e w hen t hey a re of eq ua l size,

in ter na l pr es mu e ca n be ig nor ed in t he ca lcula t ion -of over all

h or izon ta l loa ds on en closed buildin gs on level g roun d.

Wher e t he combina tion

of the orthogonal loads is

critical to the design, for example in deriving

stresses in comer columns, the maximum stresses

caused by wind in any component may be taken as

80 % of the sum of the wind stresses resulting from

each orthogonal pair of load caaes.

2.1.3.7 .@m m et r i c l oa d s

Unless specific rules are given for particular forms

of buifdlng (e.g. free-standing canopies (2.5.9.1)

and signboards (2. 7.6)), an aUowance for

aaymmetw of loading should be made, as follows.

For overalf loads on enclosed buildhga, 60 % of the

load on each waif or roof pitch should be applied in

turn, keeping the loads on the rest of the building

at the design values.

Where the inffuence function for a structural

component haa regions of negative value, 100 % of

the design loads to areas contributing to the

positive regions and 60 % of the design loads to

areas contributing to the negative regions should be

applied.

NIX % ‘his procedw e shcmld k used t o a ccount for t orsiona l

effecfs on buildin gs a nd is eq uiva lent t . a boriz.n ta l

displa cement of t he force on ea ch fa ce of 10 % of t he fa ce

w idt h fr om t he cem xe of t he fa ce.

2.1.3.8 F i ct i on a l d m g com pon en t

When deriving overalf forces on the building

(see 2.4.5 and 2.5. 10) the contribution of the

frictional forces should be taken to act in the

direction of the wind and should be added to the

contribution of the normal pressure forces

from 2.1.3.6 using vectorial summation.

10


17/92

I

Section 2 BS6299:Part2 :1995

1

.m

0.

0s0

o.m

a m

“7”

,

,,, ,,

0.00

0.%

1 ?0

100 10C O

Diagonal dimensiona (m)

I @ t o I I nes on figure 4

E ffect ive height S it e I n count y closest dist a nce t o sea (km)

S it e in t ow n: closest dist a nce t o sea

H ,

(km)

m

Oto15 t o 20 A A B B A B B

>20 t o 30 A A A B A

A

B

>30 t o 50 A A A

B A A

B

>50 A A

A B A A B

Figure 4. Size effect factor Ca of standard method

11


18/92

BSS399:Fart2 :1995

Sec t ion 2

&a

A

a ) D ia gon als f or loa d on in dividu al

b) D ia gona l for tot i loa d on com bined

faces

faces

a

E N

for shear at bsse of shaded parl

A+i2 xf0rc1ad

C ) Dia gona ls for loa d on element i of fa ces

d) D ia gom l for t ot a l loa d on ga ble

e) D ia gcm a l for t ot al loa d .“ r oof pit ch

Figu r e 5 . De ffit ion of d iagon a l o f losd ed m ess

2.2 Standard wind speeds

NU l?3 In considet ig t he ra nge of w ind direct ions *45”, in

a cccm da m?e w it h 2.1.1.2. t w o a mxoa .h es a re u ossible:

2 .2 .1

Basic wind

s p e e d

. .

a ) t he most onerous va lue of ea ch fa ct or in equa tion 8 is

Th e x eom a uh ica l variation of basic wind sDeed Vb

t a ken, lea ding t o a single conserva tive va lue of V,;

shou~d b> ~btained directly from fisure 6.- -

NU fE . The m et hod used t o derive t be ba sic w ind speed fm m

t he rnet eomlw jca l da ta is descriimd in a nnex B .

2 .2 . 2 Site wind s p e e d

2 .2 .2 .1 Geneml

T h e site wind speed V, for any particular direction

should be calculated from where

v,=vbx.$ax.$dxssxs~

(8)

where

Vb is

the basic wind speed from 2.2.1;

S. is an altitude factor (see 2.2.2.2);

Sd is a direction factor (see 2.2.2.3);

s, is a seaaons.1factor (see 2.2.2.4);

SD

is a probability factor (see 2.2.2.5).

b) ==m ..~ Of V, = e m a de a t int e~ th in@ t he ~ ge

of dir ect ion a nd t he la rgest va lue used.

[n pra ct ice, opt ion b) w ill not produce sign in ca nt ly low er

va lues t ha n a ) un less t be cmnbi”a tio” of loca tion , exposure

a nd t opogra ph y of t he sit e is un usua l.

2.2.2.2 A l t i t u de f a ct or

2 .2 .2 .2 .1 T h e altitude factor Sa should be used to

adjust the basic wind speed Vb for the altitude of

the site above sca level. Its calculation in the

standard method depends on whether topography

is considered to be significant, as indicated by the

simple criteria in f~re 7. When topogmphy is not

considered significant, Sa should be calculated

using the procedure in 2.2.2.2.2. When topography

is signifhint, S1 should be calculated using the

procedure in 2.2.2.2.3 for the wind direction

-

yielding the largest value of S=, typically the

diection with the steepest slope upwind of the site.

12


19/92

I

Sec t ion 2

BS6 2 9 9 :Pa r t 2 :1 9 9 5

r

63 C row n copy rig ht , B uild in g R esea rch E st a blish men t

Figure

6.

Bas ic win d sp eed Vb (in r id s )

13


20/92

BS6399:Fart 2:1995

Section 2

J

. S IOW l engt h

.)

Hill

a nd ridge (upw ind slope > 0.05; dmvmvind slope > 0.05)

Wind

P

\ d_”ddow

yo< 0.05

b) E sca rpm ent (O.3 > upw ind slope > 0.05; dmvnw ind$lope < 0.05) a ndcliff(upw ’ind

slope > 0,3; dmvm+ inds lope < 0.05)

F igu re 7 . De fii t ion of s ign it lc am t t opograp hy

2 .2 .2 . 2 . 2 When topography is not considered

significant Sa should be calculated from

s. = 1 + o.oolzf~ (9)

where

As is the site altitude (in metres above mean

sea level).

NOTE 1“ this cm t he va lue of S = , ba sed .“ t he sit e a lt it ude,

com pen sa t es f or r es id ua l t opog ra ph y ef fect s.

2 .2 .2 .2 .3 W h en

topography is considered

significant Sa, should be taken as the greater of

Sa=

1 + o.oolzl~ (lo)

where

A~ is the site altitude (in metres above mean sea

level); or

s= = 1 + o.oolzf~ + 1.2v& (11)

where

AT is the altitude of the upwind baae of

significant topography (in metres above

mean sea level);

we

is the effective slope of the topographic

feature;

s is a topographic location factor.

2 .2 .2 .2 .4 T h e

relevant dmensions of the

topography are defined in figure 8. ‘RVO

pararnetem, effective slope we and effective slope

length L, are defined in terms of these dimensions

by the following.

a) For shallow upwind slopes 0,05 < v 0.3:

We = 0.3 and

L , = Z /O.3 .

1 4


21/92

Sec t ion 2

BS6 2 9 9 :Pa r t 2 :1 9 9 5

Whd

Xo

‘~

a )

Hill

a nd r idge (Vu >0.05, VD > 0.05)

‘ k—Lu —i

b) E sca rpment (0.3 > Vu >0.0.5, WD < 0.05) a nd cliff (VU >0.3, VD < 0.05)

f@Y

J%

h

x

z

As

‘T

v“

w

Lengt h of t he dow nw ind slope in t he w ind dimxt ion

Lengt h of t he upw ind slope in t he w ind dir ect ion

H orizont al disfa nce of t he sit e fr om t he crest

Effectiveheightof the feature

Sitealtitude

in m eow s a bove mea n sea level

Alt it ude of upw in d ba se of t opogr aph ic fea tur e

U pr nnd S I OW Z{k i. t he ~ d d~ On

D ow n win d slope

Z IL~

in t he w in d dir ect ion

Figu re 8 . De ft it ion of t opograph ic d im en sion s

15


22/92

BS6399:Fart 2:1995

Section 2

2.2.2.2.5 Values of the topographic location b) downwind of thecrest(X > O), the horizontal

factors are given for hills and ridges in figure 9 positiorr ratio is X/LDfor hills and ridges, and

and for cliffs and escarpments in figure 10. In XL for cliffs and escarpments.

reading the value ofs f-mm these fi&ree., the

location with respect to the crest of the feature is

In all &ses, the height ab&e ground &-~io is

Z/Le.

scaled to the lengths of the upwind

L u

or

N UI ’E . 1. c-s

transitionaletweenhillsandridgesin figw? 8a

downwind

L D

slopes as follows:

andcliffsandexarpmenfsn figure 8b, i.e. w hen t he

dow nw ind slope lengt h ~ is much longer t ha n t he upw ind

a) upwind of the crest (X < O), the horizontal

slope

lengt h ~ it ma y be difficult t o decide w hich m odel is t he

position ratio is X /L u for all types of topography;

moreappropriate1“t his cm, a va lue of s ma y b? der ived fr om

both

figures

9 a nd 10, a nd t he sma ller va lue used.

-1.5

-1.0 -0.5 0 0.5 1.0

1.5 2.0 2.5

I

X/Lu x/LD

Horizontalpositionratios

Figure 9. lbp ograp h ic lo ca t ion fac t or s fo r h ills an d r id ge s

16


23/92

Section

2

i

BS6299:Fart 2:1995

U pw i.d of cr est .~ ,C fow nw in dofcr et i

4“ 2.0

; 1.5

0

.-

@ 1.0

u

c

3

0

~ 0.5

a

>

2

m

g 0.2

?

0.1

-1.5 -1.0 -0.5 0

0.5 1.0

1.5 2.0 2.5

X/Lu X/Le

Horizontalpositionratios

Figure

1 0. ‘lbp ogr aph ic loca t ion fa c to r s fo r c fiffs an d e s ca r pm en t s

2 . 2 .2 . 3 D i r w ? c t i o nf a c t o r

‘Ik ble 3 . Vfd ue s o f d ir ec t io n fa ct or &

Th e

direction factor Sd maybe used to adjust the

D irect ion v D irect ion fa ct or S ~

bssic wind speed to produce wind speeds with the

same risk of being exceeded in any wind direction.

0° North

0.78

Values am given in table 3 for all wind dmtilons in

30°

0.73

30” intervals (where the wind direction ix defined

in the conventional manner an east wind is a wind

60°

0.73

direction of v = 90°

a n d b lo ws

from the east to 90° Esst 0.74

the site). J.fthe orientation of the building is

120”

0.73

unknown or ignored, the value of the dim?ction

factor should be taken ss Sd = 1.00 for all

150°

dmctions.

0.80

180” South 0.85

NU 1’E . When t he direct ion fa ct or is used w it h ot her fa ct om t ha t

ha ve a dbecdona l va r ia don, va lues fr om ‘Ale 3 should be

210”

0.93

in t er pola ted for t he specific direct i.” being considera l, or t ie

la rgest t sbula ted va lue in t be ra nge of w ind direct ion ma ybe

240°

1.00

selected.

270° West

0.99

300”

0.91

330”

0.82

360° North 0.78

NOTE.

I n t errela tion ma y be used w it hin t his t a ble.

17


24/92

BS6299:Part2 :1995

Section 2

2.2.2.4

S e a s o r r a l f a c t o r

T h e seaaonaf factor S, may be used to reduce the

basic wind speed for buildings which are expected

to be exposed to the wind for specific subarmual

periods, in particular for tempmary works and

buildings during construction. Values which

maintain the risk (probabtity) of being exceeded of

Q -0.02 in the stated period are given in

annex D.

For permanent buildlrrgs and buildings exposed to

the wind for a contirrrrous period of more than

6 months a value of 1.0 should be used for S,.

2.2.2.5 Pr v ba bi l i t f I f a ct o r

A pmbabiity factor SP may be used to change the

risk of the basic wind speed being exceeded from

the standard value of Q . 0.02 annually, or in the

stated subannurd period if S’Sis alao rraed.

Equation D.1 gives .SP,together with a number of

values for other levefs of risk.

For alf normal design applications, where

adjustments for risk arc made through the partial

factors, the standard value of risk, Q = 0.02, is

used and SP = 1.0.

2.2.3 Effective win d sp ee d

2 .2 .3 .1

‘f’be effective wind speed

V,

should be

calculated from

ve=v, xs~

(12)

where

V, is the site wind speed obtained from 2.2.2,

for the range 6 = +45° around the

notiorrrd orthogonal wind directions defined

with the pressure coefficient data for each

form of buifding;

.%

is the terrain arrd building factor obtained

from 2.2.3.3.

2.2.3.2 For buildings with height ff greater than

the cmaswind breadth

B

for the wind dmction

being considered, some reduction in later-alloads

may be obtained by dividhrg the building into a

number of parts m follows

a) buildings with height

H l ea s

than or equal to

B

should be considered to be one part, as in

figure ha;

b) buildings with height II greater than B but less

than 2B should be considered to be two parts,

comprising a lower part extending upwards from

the ~ound by a height equal to

B

and an upper

part which is the remainder, as in figure 1lb;

c) buildings with height H greater than 2B should

be considered to be multiple parts, comprising a

lower part extending upwards fmm the ground

by a height equal to

B, a n

upper part extending

downwards from the top by a height equal to

B ,

and a middle region between upper and lower

parts which may be dMded into a number of

horizontal parts, as in figure 1lc.

The reference height

H ,

for each part should be

taken as the height to the top of that part.

2.2.3.3 The terrain and building factor Sb should

be obtained directly from table 4 and takes account

of .

a )

the effective height H e determined from L 7.3;

b) the closest diatarrce of the site from the sea in

the range of wind direction O = t45° around

the notional wind direction for the orthogonal

load case, as defiied with the pressure

coefficient data for each form of building

c) whether the site is in country terrain or at

least 2 km irrside town terrain.

NCTE.

Forall

sit es inside t ow ns (except exa ct ly a t t he upw ind

edge or a t a di.w a nce of 2 km fmm t he upw ind edge) t he

simp~ ,ca tions of t he sra nda rd m et hod prcduce a huger va lue of

S b t ha n t he direct iona l met hcd. I f t he loa ds pr oduced by t he

sfa nda rd met hod a re crit ica l t o t he design , t he use of t be

hy hrid combi”a tio” given i“ 3.4.2 sh ould & con sider ed.

18


25/92

Section 2

BS6399:Part 2:1995

a ) On e pa rt w hen

H s B

_FBF _

1

‘T

Hr=H

H

T

Hr=B

v

////’////////////////////

b) Tw opa rt s w hen B < H s 7.,9

~-

~LYA.

IH, =H

1 Hr=z l;, =

A

——

H

A

fH=B

v

r

/ / / / / / / / / / / / / / / / / / / / / / / /

c) Mult ipie pa rt s w henfl > ZE

Ngu re 1 1 . Divis ion of bu ild in gs by p a r t s fo r

la t er al lo ad s

H-6

19


26/92

BS6399:Fs.rt2 :1995

Section 2

‘fh ble 4 . I%c tn r .Sbfo r s t an d ar d m e t hod

S it e in coun tr y

] S it e in t ow n, ext ending 22 km .pw Ind from t he sit e

E ffect ive height I C losest dist a nce t o sea

H e

km

%----+=

5 1.65

10

1,78

15

1.s5

20

1.90

30

1.96

50

2.04

100 2.12

2

1.40

1.62

1.78

1,85

1.90

1.96

2.04

2.12

1.35

1,57

1,73

1.82

1.s9

1.96

2,04

2.12

I

Effective

height 1

C losest dist ance t o sea

I

W

I

+

100 m

1.26 52

1.45

6

1.62

10

1.71 15

1.77 20

1.85 30

1.95 50

2.07 100

k

m

2

1.18

1.50

1.73

1.85

1.90

1.96

2.04

2.12

1,15 1,07

1.45

1.36

1.69 1.58

1,s2 1.71

1,89 1.77

1.96

1.s5

2.04

1.95

2,12 2.07

NOTE 1. [nt erpa ia t ion ma y be used w it hin ea ch mble.

N(TE 2. The iRures in t his ta ble ha ve been derived from r efer ence [5]

NOTE 3. Va lues = .me a dia a on?.1 dim ension a = 5 m

NOr2 4. I f H , > 100 m use t he direct iona l m et hod of sect ion 3.

2.3 Standsrd pressure coefficients

2 .3 .1 .4

Pressure coefficients me given for spec~lc

3uIfaces. or uarta of surfaces, of buildings or

2 . 3 .1 Ge n e r a l

2 .3 .1 .1

The wind force on a building or element

should be calculated by the procedure given in

2.1.3 using appropriate pressure coefficients that

are dependent on the shape and form of the

buifdmg,

NOTE The

sfa nda rd pressur e coefficient s ma y be used for

b.ildi”gs a “d elemen ts of genera lly simila r sha pe. Wh ere t he

building or eim nemt sha pe fa lls oufside t he scow of t he

t a bula t ed P B.E coefficient s in Z.4 t o 2.5 or in 3.3, or w her e

mor e det ailed da ta a re r eq uired, pressure ccefficie”t s ma y h e

obfa ined from w ind t unnel t ests a s defined in 1.1.

2.3.1.2 The standd extemaf pressure coefficients

aet out in 2.4 and 2.5 apply to buifding stmctures

that me predominantly flat faced, and to walk of

circular-plan buifd@s. The majority of

conventional buildin~, such as cuboidaf, or

composed of cuboidal elements, with different roof

forms such as flat, monopitcb, duopitch, hipped

and mansard, are included.

Where considerable variation of pressure occurs

over a surface it has been subdivided into zones

and pressure coefficients have been provided for

each zone.

2.3.1.3 When calculating the wind load on

individual structural components and cladding

units and their ftings, it is essential to take

account of the pressure difference between

oPPosite faces of each elements. Extemaf pressure

coefficients are given in 2.4 and 2.5 and internal

pressure coefficients in 2 .6 for use with procedures

given in 2 . 1 ,

element& V&en the procedure of 2.1.3.~ is

applied, they give the wind loads acting in a

direction normal to that ptilcular surface,

2.3.1.5 For certain buildhgs a wind load due to

frictional drag should be taken into account (see

2.1.3.8, 2.4.5 and 2.5.10).

2.4

External pressure coefficients for

walls

2 .4 .1 R ec t a n gu la r -p la n b uild in gs

2 .4 .1 .1 External preesure coefficients for vertical

walls of rectangular plan buildings are given in

table 5, dependent on the proportions of the

buifdings as shown in figure 12.

2.4.1.2 Vafues of pressure coefficient for

windward and leeward faces are given in tsble 5

for buildlngs with

D/H s 1

and for buildings with

D/H ? 4 where

D i s

the inwind depth of the

buildlng, which varies with the wind direction

being considered (see figure 2), and H i s the height

of the wall includkg any parapet.

NOTE. Values of pr es su re coef ficien t f or in t er med ia t e D/H

r a tios m a y be in ter pola t ed .

2.4.1.3 The loaded zones on the side face should

be divided into veti]ca.1 strips from the upwind

edge of the face with the dimensions shown in

figure 12, in terms of the scafing length b given by

b = B or b = 2 H , whichever is the smaller, where

B i s

the crosswind breadth of the building, which

depends on the wind direction being considered

(see figure 2b) and

H i s

the height of the wall,

including any parapet.

20


27/92

Section 2

BS6299:Part2 :1995

Plan

Plan

W=D

d—h

-n]

L=D

Wind

L=8

%~~=

a) Loa d ca ses w ind on long fa ce a nd w ind on short fa ce

D

Elavatim

of

side faca

-m

- Ix?b

Wind

],,/,

k% “1.-

A B ‘=Hr

A B

c

H=Hr

////////////////////////////////

BuildingwithD > b BuildingwithD S b

h) K eyt opressure coefficient m n eson side fa ce

Figure 12. K eyt ow a ll pr essnr e da t a

I ml-u,. . m.A-—., --------- .--s4%-,..-..” P s-. .,-..+ ,.. .1 .-11.

I

~’edward (front)

+0.8 +0.6

Side face Zone A

-1.3 –1.6

Leeward (rear)

-0.3

–0.1

Zone B

–0.8

-0.9

face

Zone C

-0.4

-0,9

NUIX. Interpolationmaybe usedin therange1 < D/H


28/92

BSS399:Fart 2:1995

Section 2

2.4.2 Polygonal buildings c) The side walls of re-entrant corne~ and

Extemaf pressuce coefficients for the vertical walls

recessed bays facing downwind, for example the

of buildlngs with comer angles other than 90°

downwind wing of f~rc 13a, should be assumed

should be obtained using the procedures set out to be part of the leeward (rear) face.

in 3 .3 .1 .2 .

2 .4 .3 .2 For internal wells and rcceased bays in side

2 .4 .3 Bu ild in gs wit h r e -e n t ra n t c om e rs ,

r e c e s s e d bays o r in t e rn al we fls

2 .4 .3 .1

The external pressure coefficients given in

table 5 should be used for the vertical walls of

buildings containing re-entrant comers or recessed

bays, aa shown in figure 13, subject to the

following.

a) Where the re-entrant comer or recessed bay

results in one or more upwind wings to the

building, shown shaded in figures 13a,

13b and 13c, the zones on the side walls are

defined using the crosswind breadth B = B1 and

B3 and the height H of the wing.

faces (see figure 13d) where the gap acro~ the

weU or bay is smaller than the scaling length b, the

following apply.

a) External pressure coefficient for the walls of a

well is assumed to be equal to tbe roof

coefficient at the location of the weU given in

clause 2.5;

b) External pressure coefficient for the walls of

the bay is assumed to be equal to the side wall

coefficient at the location of the bay.

Where the well or bay extends acroas more than

one pressure zone, the mea-average of the pressure

coefficients should be taken.

b) The zones on the side walls of the remainder 2.4.3.3 If the gap across the well or bay is greater

of the building are defined using the crosswind than the scaling length b, the external pressure

breadth B = B2 and the height H of the building. coefficients should be obtained fmm 3.3.1.5.

Wind

d

b)

c)

d)

F igu re 1 3. Typ ic a f e xam p le s of bu ild in gs wit h r e -e n t r a n t c orn er s a n d

r ec es se d ba ys

22


29/92

I

Sec t ion 2 BS6 2 9 9 :Pa r t 2 :1 9 9 5

2.4.4 Buildings with irregular or inset faces

b) Cut-out upwind, as in fiire 14b and 14d.

2.4.4.1 I r r c g u l a r j f u s h f a c e s

T h e loaded zones on the face are divided into

External

pressure coefficients for t h e

flush waifs of

vertical strips immediately downwind of the

buildings with corner cut-outs in elevation, as

upwind edges of the upper and lower part of the

face formed by the cut-out. The scaling length bl

illustrated in figure 14, which include, for example,

for the zones of the upper part is determined

buildings with a lower wing or extension built flush

fmm the height H I znd crosswind breadth B1 of

with the main building, should bs derived as

the upper inset windward face. The scaling

follow.

length & for the zones of the lower Dart is

a) Cut-out downwind, as in fii 14a and 14c.

det&&ed from the height

H 2

and &osswind

The loaded zones on the face should be divided

breadth BZ of the lower windward face. The

into vertical strips fmm the upwind edge of the

reference height for the upper znd lower pzrt is

face with the dimensions shown in figure 12, in

the respective height above ground for the top of

terms of the scaling length b, making no special

ezch part.

allowance for the presence of the cutout. The

The pressure coefficients for zones A, B and C

scaling length b is determined from the height II

may then be obtained fmm table 5.

and cms-wvirrdbreadth B of the windward face.

K

+

Hr=H

A B

c

v

c

I

//////////////////////////////////-

a ) C ut -out dow nw ind: t a ll P ar t long

H,

], ,,,,,,,,,,,,:,,,,,;,,,,,,,,,,),, J

B

t

HI _

c

c

B

H2= H,

b) cut -out upw ind: t a ll pa rt long

K

A

v

,///,,), ,,: ,;,,,,,,B

HI

1’

H,

~ B j ‘+ “ B

-

c

CIB

t

H2= H,

v

77//////////////

.) PUt.OUL d.ymm.i”d t a i l

part

lmrrmv

@ ~.t-..t

.m+.d: ~1

P ~ n~ w

Figure 1 4. Exam ple s of flu sh ir r e gu la r wa lla

23


30/92

BS6299:Part 2:1995

Section 2

2.4.4.2 Waifs

of i n set st or egs

External pres.sum coefficients for the walls of inset

storeya, as illustrated in figure 15, should be

derived se follows.

a)

Ed ge of f a t s i n set f r om ed ge of b.n u w st m w y

(see f i gu r e 1 5a ). l b’ t h e inset walls, provided

that the upwind edge of the wall is inset a

distance of at least 0.2b1 from the upwind edge

of the lower stomy (whers bl is the scaling

length for the upper storey), the loaded zones

are defined from the proportions of the upper

storey, assuming the lower roof to be the ground

plane. However, the reference height H , i s taken

as the actual heidt of the toD of the wall above

ground. -

b)

E d g e offmejlush with edge of lower

sfm-ey

(see figure 15b). Where the upwind edge of the

wall is flush, or inset a distance of less than

0.2b1 from the upwind edge of the lower storey,

the procedure in item a) should bs followed, but

an additional zone E should be included as

defined in figure 15b with an external pressure

coefficient of C ~ –

-

-2.0. The reference height

for zone E shou d be taken as the top of the

lower storey. The greater negative pressure

(suction) determined for zone E or for the

underlying zone A in item a), should be used.

The pressure coefficients for zones A, B and C may

then be obtained from table 5.

> o.2b1

—

E–

B

c

HI

~ ‘L

H,

N(YIX.

b,

isw- lenstb of

“p~~ Stmwy.

a) Edge

of fa ce inset fmm edge of low er st orey

NOfE &

isscaling

bw @h of low er stmey.

b) Edgeof faceflushwithedgeof lowerstorey

Figure

1 5 . Ke ys fo r wa lls

of inset storey

—

24


31/92

Section 2

BS6299:Part2 :1995

I

2.4.5

Fr ic t ion -in du ce d load s on wa lls

F ric t io n fo rc es s h ou ld b e c alc u la t ed for long walls

with D > b when the wind is parallel to the wall.

The frictional drag coefficient should be assumed

to act over all zone C of such walls, with values as

given irrtable 6. The resulting frictional forces

should be added to the normal forces as described

in 2.1.3.8.

‘hide 6. F ric t io n al d ra g c oe ffic ie n t s

‘Nw

OfSUrf=e

FTfctioMfdrag

co emc i e n t

S m oo t h s u rfa ce s wit h o u t

0 . 0 1

c or ru ga t io n s o r r ib s a cr os s t h e

wind direction

Surfaces with corrugations

0.02

ccrma the wind direction

Surfaces with ribs across the

0.04

wind dkection

2.4.6

Cir c u la r -p la n b u fld ir rga

T h e d~t r i bu t i o n

of external pressure coefficient

around the periphery of a circulw-plmr buildlng is

gjven in table 7. These pressure coefficients are

also applicable to silos, tanks, stacks and chimneys.

fhble 7. Ext er n al I

wa lls o f Circrllsr-pl

Positron

m

perfphery

9

>“

10”

20”

30”

40”

50”

60°

70”

80°

90”

100”

120”

140”

160°

180°

NOTE

1.1

;.r fa ce m

mojection

T/d z 10

+1.0

+0.9

+0.7

+0.4

)

-0.5

-0.95

-1.25

-1.2

–1.0

-0.8

-0.5

-0.4

-0.4

-0.4

rpid at ion I

.e s su re coe ffk ie n t s Cm fo r

u r bu i ld i r

-

Hld s 2.6

+1.0

+0.9

+0.7

+ 0.4

0

-0.4

-0.8

-1.1

-1.05

-0.85

-0.65

-0.35

.-0.3

-0.3

-0.3

,ybe used

. .

@

kf.ce smooth

Y/d z

10

+1.0

+0.9

+0.7

+0.35

D

–0.7

–1.2

-1.4

– 1.45

-1.4

-1.1

-0.6

-0.35

-0.35

-0.35

t he ra nge

fld z 2.5

+1.0

+0.9

+0.7

+ 0.35

)

-0.5

-1.05

-1.25

-1.3

–1.2

-0,85

-0.4

-0.25

-0.25

-0.25

2.5<

Hld

1’3.

NOl?32. V d for dia m et ers grea t er t ha t d - 1 m .

NUTS 3. T posit ion on t h e per iph er y a t O - 40” w her e

% “

( is a region w here t he pressure w ill ch an ge ra pidly

w mh rim e, due t o fluct ua tion s in w in d direct ion ca uw d by

a tm ospher ic t urbulence, over t he ra n ge C w - *0.7. h is

t h erefore t he zea on w it h t h e K &est r isk of fa t igue da ma ge 0

cl a d di ng f lt is .

2.5 External pressure coefficients for

roofs

2.5.1 Flat roofs

2.5.1.1 Scope

T h e

data irrthis section should be used for dl roofs

of pitch a less than 5°. Pree.sure coefficients are

given for the orthogonal load cases and are upper

bound values to cater for all wind d~ections

8 *45° from normal to the eaves being considered.

2.5.1.2 Loa d ed zon es

T h e

roof should be subdkided into zones behind

each upwind eaves(verge as shown in figure 16 for

a rectangular roof. The loaded zones, shown in

figure 16, are defiied in terms of the scaling length

b given by b = B or b = 2 H , whichever is the

smaller, where B is the cms.swind breadth of the

building, which is equal to Wor L, depending on

the wind direction being corwidered, as defined in

figure 16a, and

H i s t h e

height of the wall,

including any parapet.

2.5.1.3

Ff a t m @? w i t h sh a r p ea u es

External

pressure

coefticienta for each zone of flat

roofs with sharp eaves are given in table 8.

2.5.1.4 Ff a t m a jl ? w i th p a m p cf s

2 . 5 . 1 . 4 . 1

A parapet along any eaves or edge will

reduce the pressure coefficients for the roof in the

locaf edge areaa only. External pressure coefficients

for flat rcmfs with edge parapeta are given in

table 8, dependent upon the ratio of the height h

of the parapet, defined in fwre 17a, to the scaling

length b.

2.5.1.4.2 Loading on the parapet walls, includhrg

the effects of comem where appropriate, should be

deterrrdned as for boundary walls from 2.7.5.

2.5.1.5 F Za t r oa J %w i t h c ur ve d e ar xx?

2 .5 . 1 . 5 . 1 External pressure coefficients for each

zone are given in table 8 and are dependent on the

rrrtioof the radius r of the eaves to the scaling

length

b,

defined in 2.5.1.2, for that eaves. The

zones start fmm the edge of the flat part of the

mof aa defiied in fii 17b.

2.5.1.5.2 The presmrre on the curved eaves should

be linearly interpolated around the arc between

the adjacent wall and roof pres.smes.

2.5.1.6

Ff a t r o@ w i t h m a n sa r d ea ves

2 .5 . 1 . 6 . 1

External pressure coefficients for each

zone are given in table 8 and arc dependent on the

pitch angle a of the mansard eaves. The zones start

from the edge of the flat part of the roof a-s

defined in fii 17c.

2.5.1.6.2 The pressure on the sloping mansard

eaves shordd be aasesed using the procedure

in 2.5.4.

—

25


32/92

BS6399:Fart 2:1995

Section 2

P la n P la n

W =D

d —h

‘o]

L =D

Wind

‘=6 ‘+ ~lp=’

.) Loada ses. w ind on long fa ce a nd w md on short fa ce

D

A

c

b12

L ~ ~

b/1O

T

T

& ‘x

Wind

b) Key m pressure coefficient zones.. fla t r oof

Fignre 16. K ey for fit r oofs

Table 8.

Ext e rn a l p re ss u re

coeffkienta Cw for flat roofs of bnfi~@

FM roof type

Zme

A

B

c D

S hzrp ea ves

-2.0

-1.4

-0.7

*0.2

With parapets I h/b = 0.05 -1. s –1.25 -0.7 *0.2

h/b = 0.10 –1.75

–1.2 -0.7

*0.2

h)b = 0.20 -1.4

-1.0

-0.7

*0.2

Curved eaves

rib = 0 , 0 5

-1.0

-1.2

-0.4

*0 ,2

r / b = 0.10 -0.75 -0.8

-0.3

*0.2

r/b = 0,20

-0.55

-0.55

-0.3

*0.2

Mamad eaves a = 30° -0.95

-1.0

-0.3

*0.2

@ = 45.

-1.2 -1.3

-0.4

*0,2

a = 60° -1.3

– 1.25 -0.6

*0.2

NOTE 1. For roofs w it h pa ra pet s or cur ved ea ves, i“t erpola tio” ma y be used for in t erm edia te va lues of

hlb

a nd

rib.

NOTE 2. For

rcmfs w it h ma nsa rd ea ves, in t erpola t ion bet w een a - 30° a nd a - 60° ma y be used. F or a >60° in t erpola t e

bet w een t he va lues for m - 60° a d t he va lues for fla t r oofs w it h sha rp ea ves.

NOTE 3. 1“ zone D , w her e bot h posit ive a nd nega tive va lues a re @ven, bot h va lues should be considered.

NU TE 4. Va lues of cc+ fficien fs for ot her w in d direct ion s a re @ve” in 3.3.2,

NOTE 5. Fbr pit ched roofs w it h curved or nw .”.sa rd ea ves, t he va lues i“ t his mble ma y be com pa red w it h t he a ppropria te va lues in

fa bles 9, 10 or 11 a nd t he lea st nega tive va lues used.

26


33/92

i

Section 2

BS 6299: Rut 2:1995

K

—

H

r

H

a) Parapets

R oof z on a s

K

st a rt f rom h er e

r

Hr. H

b) C ur ved ea ves

>b/1O

—. ~-

+/’’ /”

oof z on es

st a rt f rom h er e

a\

‘“H

c) Mansard

eaves

Figu r e 1 7 . Key t o cave de t ails fo r fla t r oofs

—

5 .1 .7 F l a t m qp

with inset storwfp

r flat roofs with inset storeys, defined in

Nre 18, external pressure coefficients for both

e uPPer roofs and lower roofs should be derived

fouows.

a) For the upper roof the appropriate procedure

of 2.5.1.3, 2.5.1.4, 2.5.1.5 or 2.5.1.6, depending

on the form of the eaves, should be used, taking

the reference height H, aa the actual height to

the upper eaves, and Has the height of the inset

storey (from the upper eaves to the lower roof

level) for determining the scaling length b.

b) For the lower roof the appropriate procedure

of 2.5.1.3, 2.5.1.4, 2.5.1.5 or 2.5.1.6, depending

on the form of the eaves, should be used, where

H, = H and is the actual height of the lower

storey, ignoring the effect of the inset atoreys.

However, a further zone around the base of the

inset storeys extending b/2from each facing waif

should be included, where b is the safing

p-eter fmm 2.5.1.2 appropriate to the

relevant walls of the inset storey. The pressure

coefficient in this zone should be taken as that of

the zone in the adjacent wall of the upper stor’ey

(as determined from 2.4).

Ta ke pr sssu re C nefficien fs on a dja csn t w a ll in t his z on e

\

A I ‘rB

A

I

~

NOTE.

b is scaling

lengt h of upper st or ey.

27


34/92

BS6399:F%rt 2:1995

Section 2

2.5.2 Mon op it ch an d d uop it ch roofs

2 .5 .2 .1

Genera l

Monopitch and duopitch rrmfs of buildm are

defined as rvofs with gable ends.

NOTE. Hippedroofform aretreatedseparatelynZ.6.3.

2.5.2.2

L oa d ed zon es

Zones over which the extemaf

pressure

coefficient

is assumed to be constant for both monopitch and

duopitch rwfs am shown in figures 19 and 20.

These zones are strips parallel to the eaves and

verge and are defiied in terms of the waling

lengths ~ and bW where bf, = L or bf, = 2ff,

whichever is the smaller, and bW = W or bW = 21f,

whichever is the smaller.

2.5.2.3

Mon op i t ch m oJ 3

External pressure coefficients for monopitch roofs

should be obtained from table 9, using the key in

figure 19, Owing to the asymmetry of this roof

form, values arc given for three orthogonal load

cases wind normal to the low eaves (0 . 0°),

wind normal to the gable [8 = 90°) and wind

normaf to the high eaves (6 = 180”).

2.5.2.4

Du op i t ch r oof i

2 . 5 . 2 . 4 . 1 External pressure coefficients for

duopitch roofs should be obtained from table 10,

using the key in figure 20. Values arc given for two

wind directions: wind normal to the low eaves

(d = 0°) and wind normal to the gable (0 - 900).

These coefficients are appropriate to duopitch

faces of equal pitch but maybe used without

modification provided the upwind and downwind

pitch angles are within 5° of each other. For

duopitch roofs of greater disparity in pitch angles

see reference [6].

2 .5 .2 . 4 . 2 When a c 7 °and W < bf,, zone C for

the load case .9= 0° should be considered to

extend for a distance bf/2 downwind from the

windward cave (as shown for flat roofs in

figure 16), replacing ridge zones E and F and part

of zone G.

2.5.3 Hipped roofs

External pressure coefficients for conventional

hipped roofs on cuboidal-plan buildings, where all

faces of the roof have the same pitch angle and are

in the range a =

-45° t o +75°, are given in

table 11. The definitions of loaded zones and pitch

af@eS are

given in tigurc 21. The data in table 11

may be applied to hipped roofs where main faces

and hipped faces have dtiferent pitch angles,

provided the pitch angle of the upwind face is used

for each wind direction, as indicated in f~re 21.

Negative pitch angles occur when the roof is a

hipped-tmugh form. For pressure coefficients for

skew- bipped roofs and other hipped rcmf forms see

reference [6].

2.5.4 Mansard roofs

External pressure coefficients for mansard roofs

and other multi-pitch roofs should be derived for

each plane face by the procedure given in 2.5.2 for

roofs with gable ver%es or the procedure given

in

2 .5 .3

for roofs with hipped verges, using the

pitch angle for each plane face. The key in

figure 22 indicates

where

edge zones should be

omitted.

28


35/92

Section 2

BS6W9:M 2:1995

a ) G e nem l

Plan

I

b) Zones for w ind direct ions O - 0° a nd 8- 180°

I

bJ 70

Highcave

F-1

“x

Plan

T

w/2 B

r -

Wind,.

c D

I

w

w/2 A

Y-

I

c) Z on es

for

w ind dir ect ion O = 900

I

Fign re 1 9 . Key for m on op it ch roofs

, 29


36/92

BS6399:RIrt2 :1995

Section 2

fliim m,’

G ener a l

~–-

L

4

Plan

G

E

F E

~b’,111

c

A

B

A

~b, , lo

,<

bL /2

J

f k >

Wind

bL12

b) Zones for w ind direct ion 8 - 0°

‘k

A

b

c) Z on es

for

w ind dir ect ion O . 90°

Figu re 2 0. Key fo r du op it ch roofs

~>

.

30


37/92

Section 2 BS 6399: Fart 2:1995

‘Ih ble 9 . Ext e rn a l p re ss ur e c oe ffic ie n t s Cmfo r m o no pit ch r OOfs Of bn ild ~gs

Fffch a I@e a Zon e f or O . 0° Zone for %= 90° Zonefor O- 180°

A

B c

A B c D A B

c

5“

-1.8

-1,2 -0.6

-2.2 –1.1 -0.6 -0.5 -2.3

-1.2 -0.8

15” -1.3 -0.8 -0,3 -2.8 -1.1 -0.8 -0.7 -2.6 –1.0

-0.9

+0,2

+0.2 +0.2

30” -1.1

-0.5 -0.2 -1.7 -1.2 -1,0 -0.8 -2.3 –1.2 -0.8

+0.8 +0.5 +0