British Code BS 6399 Part 2 Wind 20loads

BRITISH STANDARD BS 6399:Part 2:1995

Loading forbuildingsPart 2. Code of practice for wind loads

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NO COPYING WITHOUT BS1 PERMISSION EXCEPT AS PERMITTED BY COPYRIGHI LAW—

BS6399:Part2: 1995

This British Standard, havingbee” prepared under thedirection of the Building andChil Engineering %ctor Board,was published tinder theauthority of the StandardsBozwd and comes into effect on15 Ausust 1995

0 BSI 1!295

Nmt published (as CP 4)November 1944First revision (as CP 3:Chapter V) Ausust 1952%rfitd second revision (as CP3:Chapter V : Part 1)Becember 1967Completion of second revision(= CP 3: Chapter V : Part 2)July 1970Published as KS 6399: Fart 2:Au@st 1995

The following 9S1 referencesrelate ro the work on thissta”dati.Committee reference 9/525/ 1Draft for comment 91 I 16625 DC

ISBN06S0 23651 X

Committees responsible for thisBritish Standard

‘rhe preparation of this Britiih Standard was entrusted by ‘lbchnicalCommittee B/525, Buildings and civil engineering structures, to SubcommitteeB/525/1, Actions (loadings) and basis of desigrr, upon which the followingbodies were represented:

British Constructional Steelwork Association Ltd.

British Iron arrd Steel Producem’ Association

British Masonry Society

Concrete SocietyDepartment 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

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

4L

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@sExternal 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

Dcr 0.s33 : - z : 1330

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 dominantopmings

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 ofrectangular-plan buildings

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

28 External pressure coefficients CP, for vertical gable w~k adjacent tOnon-vertical walls and roofs

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

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 roofswith 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 ofhipped 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 recessedbays 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

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

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62

64

65

67

69

71

so

82

Inside back cover

In

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 andincorporates the considerable advances made and experience gained in windengineering since that time. CP3 : Chapter V : M 2 will not be withdrawnimmediately 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 gustvalue. However, the hourly mean basic wind speed is subsequently convertedinto a gust wind speed for use in design (by a gust peak factor wh]ch takesaccount of gust duration time, height of structure above ground and the size ofthe structure). The adoption of the hourly mean value for the basic wind speed isfor technical reasons. Primarily it allows a more accumte treatment oftopography, but it alao provides the starting pohrt for serviceability calculationsinvolving fatigue or dynamic response of the stmcture. Its use is akw a movetowards harmonization as mean values (sometimes 10 min means) are often thebasis for wind loading calculations in European and international standards.

Structure factors are used to check whether the response of the structure can beconsidered to be static, in which caae the use of the calculation methods in thkstandard is appropriate. If the response is found to be mildly dynamic themethods can still be used but the resulting loads will need to be augmented.Structures which are dynamic will alsu be identified but their assessment isoutside 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 standardmethod are around 14 % larger than obtained from the directional method. Thedegee of conservatism can be much larger close to the ground and in towns, butdecreaaes to zero around 100 m above the gruund.

In addition to reduced conservatism, the directional method assesses the loadhgin more detail, but with the penalty of increaaed complexity and compukitionaleffort. Because of this it is anticipated that the standard method will be used formost hand-baaed calculations and that the directional method wifl beimplemented principally by computer

Procedures are alao given to enable the standard effective wind speed to be usedwith the directional pressure coefficients and for the directional effective windspeeds to be used with the standard pressure coefficients.

CP3 : Chapter V : Part 2 allowed for the effect of ground roughness, buildingsize and height above gound by a single factor. This required the calculation ofseparate wind speeds for every combination of reference height above gruundand the size of the loaded area. However, a simp~] cation has been introduced inthe standard method which involves the calculation of only a single wind speedfor each reference height. The effect of size is allowed for by a separatefactor, Cc

BS 6399: Part 2 also gives values for external pressure coefficients for a greatermnge of building configurations than did CP3 : Chapter V : Part 2.

Compliance with a British Standard does not of itseff confer immunity fromlegaf obligations.

iv

BS6399:Part 2:1995

Section 1. General

1.1 Scope‘lidsRut of BS 6399 gives methods for determiningthe gust peak wind loads on buildings andcomponents thereof that should be taken intoaccount in design using equivalent staticprocedures.

Two alternative methods are given:

a) a standard method which uses a sirnpliiledpnxedure to obtain a standard effective windspeed which ix uacd with standard pressurecoefficients to determine the wind loads fororthogonal design cases.NOTE 1. This procedure is virtually the same win CP3 :Chapter V : Parr 2.

b) a directional method in which effective winds~ds ~d Preasurc coefficients arc determinedto derive the wind loads for each wind dtiction.

Other methods may be used in place of the twomethcds given in thix standard, provided that theycan be shown to be equivalent. Such methodsinclude wind tunnel tests which should be taken asequivalent only if they meet the conditions definedin armex A.NUTE2. Wind tunnel tests are recommended when the form ofthe building is not covered by the data i“ this standard, whenthe form of the b.ifdimg cm be changed in response to the testresulf.? in order to give an optimized design, or when loadingdata are required in more derail than is awe” in this standard.

Specialist advice should be sought for buildingshapes and site locations that are not covered bythis standard.

The methods given in this Part of BS 6399 do notapply tO bufldkgs which, by virtue of thestructural properties, e .g, maas, stiffness, naturalfrequency or damping, are particularly susceptibleto dynamic excitation. These should be asaeasedusing established dynamic methods or wind tunneltests.NOTE 3. See references [1] to 14] for examples of establisheddynamic methcds.

NUI’E 4. If a building is susceptible to excitaticm by vortexshedding or other aemelastic instability, tie maximum dynamicrespome may occur at wind speeds lower than the maximum.

1.2 Informative references

Thii British Standard refers to other publicationsthat provide information or guidance. Editions ofthexe publications current at the time of issue ofthis standard am listed on the inaide back cover,but reference should be made to the latesteditions.

1.3 DefiitionxFor the purposes of this British Standard thefollowing definitions apply.

1.3.1 Wind speed

1.3.1.1 basic wind speed

The hourly mean wind speed with an annual risk Qof being exceeded of 0.02, irrespective of winddirection, at a height of 10 m over completely flatterrain at sea Ievei that would occur if theruughneas of the terrabr w uniform everywhere(inclu~l:g urban areas, inland lakes and the sea)and equwalent to typical open country in theUnited Kingdom.

1.3.1.2 site wind speed

The basic wind speed modtiled to account for thealtitude of the site arrd the direction of the windbeing considered (arrd the aeaaon of exposure, ifrequired).NUlll, In the standard metbcd only, effectsof topographicfeaturesareincludedin tbe sitewindspeed.

1.3.1.3 effective wind speed

The site wind speed modfied to a gust speed bytaking account of the effective height, size of thebuilding or structural element Ming considered andof permanent obstmctions upwind,NCII’E. 1“ the direcriomd method only: the effects oftopographic 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 kineticenergy of the effective wind speed.

1.3.2.2 pressrrre coefficient

The ratio of the pressure acting on a surface to thedy-c pKS.SUP2.

1.3.2.3 exterfud pressrrre

The pressure acting on a.frexternal surface of abuilding caused by the dmct action of the wind.

1.3.2.4 intemaf pressure

The preasffrc acting on an internal surface of abuildbrg caused by the action of the externalpressures through porosity and openings in theexternal surfaces of the buildlng.

1.3.2.5 net pressure

The pressure dtiference between opposite faces ofa surface.

1

BS63Y9:Part2:lYY5 Section 1

1.3.3 Height

1.3.3.1 altitude

a) when topography is not si@lcant: the heightabove mean sea level of the ground level of thesite;

b) when topography is significant: the heightabove mean sea level of the base of thetopographic feature,

1.3.3.2 building height

The height of a building or part of a building aboveits base.

1.3.3.3 reference height

The reference height for a part of a structure is thedatum height above Wound for the pressurecoefficients and is defined with the pressurecoefficients for that part.

1.3.3.4 obstruction height

The average height above ground of buildings,structures or other permanent obstmctions to thewind immediately upwind of the site.

1.3.3.5 effective height

The height used in the calculations of the effectivewind speed determined from the reference heightwith slfowance for the obstmction height.

1.3.4 Length

1.3.4.1 buifding length

The longer horizontal dimension of a buildhrg orpart of a building. 1,

1.3.4.2 building width

The shorter horizontal dimension of a building orpart of a building.’)

1.3.4.3 crosswind breadth

The horizontal extent of a buiIding or part of abuilding norrmd to the direction of the wind. l]

1.3.4.4 inwind depth

The horizontal extent of a building or part of abuilding 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 pointson the periphery of the area.

1.3.4.6 scaling length

A reference length determined from theproportions of the building used to define zonesover which the pressure coefficient is Sas”med tobe constant.

1.3.5 Distance

1.3.5.1 fetch

The distance from the site to the upwind edge ofeach category of terrain, used to determine theeffect of termirr roughness changes.

1.4 Main symbolsFor the purposes of this Rut of BS 6399 thefollowing symbols apply.

A

a

B

b

c.Cp

cc:c,D

d

G

9tH

He

H,

Ho

h

Kb

L

LD

L,

Lu

P

P

P,

Area

Largest diagonal dimension of the loaded areaenvelope (figure 5)

Crosswind breadth of building (figure 2b)

Scaling length used to define loaded areas forpressure 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 orheight of inset or lower storey

Effective height (1.7.3)

Reference height (1. 7.3)

Obstruction height (1. 7.3, figure 2), oraverage height of roof tops upwind of thebuilding

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 elementbetween free ends (2.7.3)

Length of downwind slope of topogmphicfeature (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

Section 1 BSS399:Part 2:1995

Pi

Q

9

9.

9i

9s

r

s,

s~

s=

s~

s~

SP

s,sts

T,

Tt

v~v,v,ww

x

z

a

b

AS

AT

Pressure on intemaf surface (2.1.3.2)

Annual risk (pmbabi!lty) of the baaic windspeed being exceeded (2.2.2.4, 2.2.2. 5,)

Dynamic pressure

Dynamic pressure of directional method forexternal pressures (3. 1.2.2)

Dynamic presxure of dkectional method forinternal 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 topographicfeature (2.2.2.2.5, figure 8) or distance inwind direction for buifding spacing ( 1.7.3.3)

Height of crest of topographic feature abovethe upwind baae altitude (figure 8)

Pitch angfe (from horizontal) of roof (2.5) ornon-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 topographicfeature 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 topographicfeature (figure 7)

lkrrgent of upwind slope of topographicfeature (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) orblockage ratio of canopies (2.5.9, figure 24)

Wind direction of degrees from normal tobuilding faces (figure 2) or angle aroundperiphery of circular-plan buildhrg (2.4.6)

1.5 Outline of procedure for calculatingwind loads

1.5.1 The outline of procedure is illustrated in theflow chart given in figfmc 1. This shorn the stagesof the standard method, together with the relevantclause numbem, as the boxes outlined andconnected by thick lines. The stages of thedirectional method are shown as boxes outlinedwith double lines and are directly equivalent to thestages of the standard method. Various input dataare shown in boxes outlined with singfe lines.

1.5.2 The wind loads should be calculated for eachof the loaded areas under consideration, dependingon the dimensions of the building, defined infigure 2. These may be:

a) the structure ax a whole;

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

c) individual stmctural components, includingcladding urrits arrd their ftinga.

Nc71Z. Wind load on a partially completed structure may hecritical and will be dependent on the method and sequence ofconstruction.

3

Wstww:rartz:lxm 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 NoBuilding is dynamic. This Pert

applicability C, < 0.25, does not apply (see references

H <300 m (1.6.2) [1] to [41)

Stage 3: Basic wind speed V, Basic wind speed map [Figure 6)

(2.2.1)

I

Stage 4: Site wind speed V. Altitude factor S,, directional factor

(2.2.2)S~, seaaonal factor S,

■

Stage 5: Terrain categories, Site terrain type, level of upwind

effective height H. (1.7.3) rooftops Ho, separation of buildingsx

9

Stage 6: Choica of method (1 .8)

G

Directional and topographic

9

------’’------=Stage 7: Standard effective wind Directional effective wind speed

--

------’:-----E=Directional pressure coefficients

Stage 10: Wtnd Ioada P (2.1 .3)[

Directional wind loads P (3.1)1

)

I

Figure L Flowchart illustrating outline procedure

4

Section 1 BS63YY:MZ:1YY6

Notes to figure 1

Stage 1 Determines the dynamic augmentation factorfmm the basic geometric and stnctuml pmpenies of thebuilding,

Stage 2 Depending on this value, a check is p+?rformedon the level of dynamic excitatim to determine:

a) whether the methods given in this k%rt of ss 6399aPPIY and the a%ew.ment may proceed; or

b) whether the methcds given in this ~ of ss 6399do not apply and the building should be assessed byone of the methwls for dynmnic buildings (seereferences [1] to [4]) or by wind tunnel tesfs(see annex A).

SW, % Determines the basic hourly mean wind speedfrom the map for the UK.

Sfage 4 Determines a site wind speed, stillcorresponding to the hourly mean wind speeds at aheight of 10 m above ground in the standard exposure,from the basic wind speed by applying corrections for thesite altitude, wind dbwmion and season. Up to this point,no allowance for the exposure of the particular site hasbeen made and the procedure is common (except in ifstreafment of the effectsof topography) to both thesti”dard and dkectional metbd.

NCflE The derivations of the b~ic wind speed map, theadjustments for site altitude, wind direction and seasonare given in annex B.

Stage 6 .ksses.ses the exposure of the site in term of theterrain mugtmes and the effective height. llu?ecategories of terrain roughness are used to define the siteexposure. The effective height depends cm the degee ofshelfer provided by neighbo”ri”g buildings or otherpermanent obstmcfiom.

Stage k Having assessed the exposure of the site, thisSt&3e offersthe choice between the standard nwtbcd a“dthe directional method. The standard method @vesconservative values for standard orthogonal load czses,and a simplified method for buildin@ up to 1C4 m inheight and for signirlcant to fmgmphy. The directionalmethcd gives a more precise value for any given winddirection, particularly for sites in towns, and wheretopography is significant. A simple rule for assessing thesignificance of to fmsraphy is provided.

Stage 7 Determines the effective wind W&&S requiredby either method. The effective wind speed is a gustwind sp+ed appropriate to the site exposure and theheight of the building. h! the scmdard method thiscorrespmds to a datum size of loaded area, while in thedirectional method this cm’resfmnds to the size of theloaded area under consideration.

s~e 8 Converts the effective wind speed into anequwalent dynamic pressure.

Stage 9 Selects pressurecoefficients corresponding tothe form of the building. In the standard method thesecoeffkienb correspond to a number (usually two orthree) of orthogonal load cases, while in the directionalmethcd they correspond to the wind directions beingconsidered (usually twelve).

St-x. 10 Determines the wind loads from the dynamicpressure,pressurecoefficients, dynamic augmentationfactor and, in the standard method, by the size effectfactor, to gtve the characteristic wind load for staticdesign.

5

Bsw99:Partz:lYY5 Section 1

a) Fixed dimensions length, width, height

—.

44~ ‘B k~x

Windrml

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

Section 1 BS 6299: Part 2:1995

1.6 Dynamic classtilcation

1.6.1 Dynamic augmentation factor

The methods of this standard employ equivalentstatic loads to represent the effect of fluctuatingloads which is applicable only to buildings whichare not susceptible to dynamic excitation.

The standard permits equivalent static loads to beused for the design of mildly dynamic structures bythe introduction of a dynamic augmentation factor.The value of this factor depends upon the actualheight H of the building above ground and on abuilding-type factor ~b obtained from table 1, forthe form of construction of the buildlng.

The dynamic augmentation factor C, is given fortypical buildings in figure 3.

‘fhble 1. Building-type fsctor ~b

&p-e of buUdf@

Welded steel unclad frames

Bolted steel and reinforced concreteunclad frames

Fort-d sheds and similar light structureswith few internal walls

Framed buildings with structural wallsaround M- and staim only (e.g. officebuild~ of open plan or withpartitioning)

Framed buildmf@ with structural walkaround lifts and stairs with additionalmasonry subdivision walls (e. g.aptiment buildings), buildings ofma.?arry construction andtimber-framed housing :

f&

?3

4

2

1

0.5

NOTE. The valuesof the facfarsKb and C, have been derivedfor typical building structures with typical frequency anddamping chamcfe!tstics, under typical UK wind speeds, withoutaccounting for topogmphyor tsme.inroughness effects. Moreaccurate values of these factam may be derived using annex Cwhen tbe buifding characteristics am “ot typical, or when theeffectsof topographyand terrain mugtmessneed tobe takeninto account.

1.6.2 Lfndts of applicability

This Part of Ef3 6399 does not apply when thevalue of dynamic augmentation factor exceeds thelimits shown in figure 3. Buildin@ faffing outsidethese !imk? should be assmsed using establisheddynamic methods.NCllll See referemes[1] to [4] for f“rtber information o“analysis of dynamic structures.

1.7 Site exposure

1.7.1 Genersf

The site wind speed V, refers to a standard opencountry exposure at a height of 10 m aboveground. ‘lb obtain the effective wind speed theeffects of varying gruund roughness, the heightand d~tance of obstructions upwind of the site andthe effects of topography should be taken intoaccount.

1.7.2 Ground roughness categories

Three categories of terrain are considered:

a) sea the sea, and inland areas of waterextending more than 1 km in the wind directionwhen closer than 1 km upwind of the site;

b) country: all terrain which is not defined as seaor town;

c) bum: built up aress with an average level ofmof tops at least Ho = 5 m above ground level.NOTE 1. Permanent forest and woodland may be treated 8..stown categmy.

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

1.7.3 Reference height and effective height

L 7.3.1 The reference height H, is defined for thebuilding form in the appropriate pressurecoefficient tables and deftition figures, but canconservatively be taken as the maximum height ofthe building above ground level.

1.7.3.2 For buifdings in country terrain, orconservatively for buildings in town terrain, theeffective height Ife should be taken as thereference height HP

1.7.3.3 For buildings in town terrain, the effectiveheight & depends on the shelter affofied by theavemge level of the height Ho of the roof tops ofthe buildings, or of the height of other permanentobstructions, upwind of the site and their upwindspacing X. These dimensions are defined infigure 2. The effective height He should bedetermined as follows.

a) Ifxs2Ho

then He is the greater of

He = Hr – 0.8H0 or He = 0.4H,;

b) If X > 6H0

tiien He is given by He = Hr;

c) fn the range 2Jfo < X c 6H0

He is the greater of

He = H, - 1.2H0 + 0.2X or He = 0.4HPNOTE. 1. the absence of more accurate information, theobstmction bwgbt Ho may be estimated from the averagenumber of storeys of .pwi”d buildings by raking the typicalstorey height as 3 m. Furrher guidance is given i“ annex E.

7

BsfxfYY: I’artz:lYY5 section 1

@Limits of applicability

Shaded regionoutaidescopeof this Part

0.4

0.3

0.2

0.1

01 10 100 1000

Building height, H (m)

Figure 3. Dynamic augmentation factor C,

1.8 Choice of method

1.8.1 For alf structures less than 100 m in heightand where the wind loading can be represented byequivalent static loads (see 1.6), the wind loadingcan be otained either by the standard methoddescribed in section 2 or by the directional methodgiven in section 3,

1.8.2 The standard method provides values ofeffective wind speed to be used with the standardpressure coefficient (clauses 2.3 to 2.5) todetermine orthogonal load cases, corresponding tothe wind direction notionally normal or parallel tothe faces of the buifding. The standard methoduses a simplilled allowance for signiilcanttopography, as defined in figure 7.

1.8.3 The directional method gives values of theeffective wind s~ed for different wind directions,taking into account the term.in appropriate to thewind dnction behrg considered, to be used withthe directional pressure coefficients. It gives betterestimates of effective wind speeds in towns and forsites affected by topography.

L 8.4 However, m the standard method givesconservative values of both effective wind speed(below 100 m) and pressure coefficient, it maysometimes be appropriate to use a hybridcombination of both methods, either

a) standard effective wind speeds withdirectional pressure coefficients; or

b) directional effective wind speeds withstandard pressure coefficients.

Combination a) k aurxouriate when the form ofthe building is ‘well ‘defied, but the site is not; thecaaes of relocatable buildings or standardmass- pruduced designs are typical examples.Combination b) is appropriate when only thestandmd orthogonal load cases are required, but abetter allowance for site exposure is desiredbecause topogmphy is signifkant and/or the site isin a town. Such hybrid combinations should beapp~ed only in accordance with 3.4.

“-)

8

#BS6399:Part2:lW5

Section 2. Standard method

2.1 Standard wind loads

2.1.1 Wind direction

2.1.1.1 The standard method requires assessmentfor orthogonal load cases for wind dmectionsnormal to the faces of the buifdmg, as shown infigure 2b. When the building is doubly-symmetric,e.g. rectangular-plan with flat, equal- duopitch orhipped roof, the two orthogonal cases shown infigure 2b are sufficient, When the building issingly-symmetric, three orthogonal cases arerequired, e.g. for rectangular-plan monopitchbuildings: wind norrnaf to high eaves; wind normalto low eaves; wind pwallel to eaves. When thebuifdlng is asymmetric, four orthogorwd cases aren?quired.

2.1.1.2 For each orthogonal case, the range ofwind dmctions *45” either side of the directionnormal to the building face should be considered.When symmetry is used to reduce the number oforthogonal load cases, both opposing winddirections, e.g. Q = Oormd O = 180° should beconsidered arrd the more onerous dmction used.

2.1.2 Dynamic prsssure

2.1.2.1 The value of the dynamic pressure q, ofthe standard method is given by

q, = 0.613Ve2 (1)

where

q, is the dynamic pressure (in Pa*);

t’, is the effective wind speed from 2.2.3(in rots).

2.1.2.2 Values of dynamic pressure q~ for variousvalues of Ve are given in table 2.

2.1.3 Wind load

2.1.3.1 Ertemal sueace prssaurw

The pressure acting on the external surface of abuildhg P, is gNen by

where

9s is the dynamic pressure from 2.1. Z

Cw is the extemaf pressure coefficient for thebuifding surface given irr 2.4 and 2.5

c, is the size effect factor for externalpressures defined in 2.1.3.4.

2. L3.2 Internal su~ace prssaurvs

The pressure acting on the internal surface of abuilding, pi, is given by

Pi = q,cplca (3)

where

9, is the dynamic pressure from 2.1. Z

CPi is the internal pressure coefficient for thebuifding given in 2.6

c, is the size effect factor for internalpressures defined in 2.1.3.4.

2.1.3.3 Nst su@ace Preasurw

The net pressure p acting across a surface 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 is the internal pressure given in 2.1.3.2.

b) For free-standing canopies and buildingelements

P = %% G (5)

where

9, is the dynamic pressure from 2.1. Z

Cp is the net pressure coefficient for thecanopy surface or element given in 2.5.9and 2.7

P, - q,cwc, (2) Ca is the size effect factor for externalpressures defined in 2.1.3.4.

uc pressure q~ (in Pa)

+0 + 1.0 + 2.0

61

245

552

981

iCi30

74

270

589

1030

1590

38

297

628

1080

1660

‘Ihble 2. Dyrrs

Y

‘emls

10

20

30

40

50

60 2210 \2280 I 2360

.lPa-l!J/m2

T

I1C4 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

BSfX399: F’art 2:1995 Section 2

2.1.3.4 Sue @ectfactOr

The size effect factor Ca of the standard methodaccounts for the non-simultaneous action of gustsacnmsanextemalsurfaceand for the response ofinternal pressures. Values of size effect factor aregiven in figure4, dependent onthe site exposure(see 1.’7) and the diagonal dnenaion a.

For external pressures the diagonal dimension a isthe largest diagonal of the area over which loadsharfng takes place, as illustrated in figure 5. Forinternal pressures an effective diagonal d]menaionis defined in 2.6 which is dependent on theinternal volume.

For all individual stmctural components, claddlngunits and their ftings, the diagonal dimensionshould bc taken as a = 5 m, unless there isadequate load sharing capacity to justify the use ofa diagonal length ~eater than 5 m.

2.1.3.5 Su@ace loads

The net load P on an area of a building surface orelement 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 andshear fomes, at any level in a building should bebaaed on the diagonal dimension of the loaded areaabove the level being considered, as illustrated infigure 5C.

2.1.3.6 Ovemll loads

The ovemfl load P on a building is taken as the sumof the loads on individual surfaces with allowancesfor non-simultaneous action between faces and formildly dynamic response.

The overall horizontal loads are given by

P = 0.85( XPfmnt - EP,,J (1 + C,) (7)

where

,zPfmnt is the horizontal component of surfaceload summed over thewindward-facing walls and roofs;

ZP.W is the horizontal component of surfaceload summed over the leeward-facingwalls and roofs;

c, is the dynamic augmentation factorfmm 1.6.1;

but tafdng the inwind depth of the building, D, asthe smaller of width Wor length L in thedetermination of Pfmntand Prem

NOTE 1. The factor 0.85 accounts for the non-simultaneousaction between faces.

NOTE 2. As the effect of internal pressure on the front andrear faces is eqwd and opposite when they are of equal size,internal presmue can be ignored in the calculation-of overallhorizontal loads on enclosed buildings on level ground.

Where the combination of the orthogonal loads iscritical to the design, for example in derivingstresses in comer columns, the maximum stressescaused by wind in any component may be taken as80 % of the sum of the wind stresses resulting fromeach orthogonal pair of load caaes.

2.1.3.7 .@mmetric loads

Unless specific rules are given for particular formsof buifdlng (e.g. free-standing canopies (2.5.9.1)and signboards (2. 7.6)), an aUowance foraaymmetw of loading should be made, as follows.

For overalf loads on enclosed buildhga, 60 % of theload on each waif or roof pitch should be applied inturn, keeping the loads on the rest of the buildingat the design values.

Where the inffuence function for a structuralcomponent haa regions of negative value, 100 % ofthe design loads to areas contributing to thepositive regions and 60 % of the design loads toareas contributing to the negative regions should beapplied.NIX!%. ‘his procedwe shcmld k used to account for torsionaleffecfs on buildings and is equivalent t. a boriz.ntaldisplacement of the force on each face of 10 % of the facewidth from the cemxe of the face.

2.1.3.8 Fictional dmg component

When deriving overalf forces on the building(see 2.4.5 and 2.5. 10) the contribution of thefrictional forces should be taken to act in thedirection of the wind and should be added to thecontribution of the normal pressure forcesfrom 2.1.3.6 using vectorial summation.

10

ISection 2 BS6299:Part2 :1995

1.m

0.%

0s0

o.m

am

“7”

,! ,,, ,,!0.00

0.%

1 ?0 100 10CO

Diagonal dimensiona (m)

I@ to IInes on figure 4

Effective height Site In county closest distance to sea (km) Site in town: closest distance to seaH, (km)

m Oto<z Zto <10 Iota <1oo 2100 Zto <10 10 to <100 >100

52 A B B B c c c

>2t05 A B B B c c c

>5 to 10 A A B B A c c

>10 to 15 A A B B A B B

>15 to 20 A A B B A B B

>20 to 30 A A A B A A B

>30 to 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

BSS399:Fart2 :1995 Section 2

&a Aa) Diagonals for load on individual b) Diagonal for toti load on combinedfaces faces

aEN

for shear at bsse of shaded parl

A+i2!xf0rc1addC) Diagonals for load on elementi of faces

d) Diagoml for total load on gable e) Diagcmal for total load .“ roof pitch

Figure 5. Deffition of diagonal of losded mess

2.2 Standard wind speeds NUl?3 In considetig the range of wind directions *45”, inacccmdam?e with 2.1.1.2. two amxoa.hes are uossible:

2.2.1 Basic wind speed. .

a) the most onerous value of each factor in equation 8 is

The xeomauhical variation of basic wind sDeed Vb taken, leading to a single conservative value of V,;

shou~d b> ~btained directly from fisure 6.- -NUfE. The method used to derive tbe basic wind speed fmmthe rneteomlwjcal data is descriimd in annex B.

2.2.!2Site wind speed

2.2.2.1 Geneml

The site wind speed V, for any particular directionshould 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 made at inte~ thin@ the ~geof direction and the largest value used.

[n practice, option b) will not produce signincantly lowervalues than a) unless tbe cmnbi”atio” of location, exposureand topography of the site is unusual.

2.2.2.2 Altitude factor

2.2.2.2.1 The altitude factor Sa should be used toadjust the basic wind speed Vb for the altitude ofthe site above sca level. Its calculation in thestandard method depends on whether topographyis considered to be significant, as indicated by thesimple criteria in f~re 7. When topogmphy is notconsidered significant, Sa should be calculatedusing the procedure in 2.2.2.2.2. When topographyis signifhint, S1 should be calculated using theprocedure in 2.2.2.2.3 for the wind direction

-1

yielding the largest value of S=, typically thediection with the steepest slope upwind of the site.

12

ISection 2 BS6299:Part 2:1995

r

63 Crown copyright, Building Research Establishment

Figure 6. Basic wind speed Vb (in rids)

13

BS6399:Fart 2:1995 Section 2

J~. SIOW length

.) Hilland ridge (upwind slope > 0.05; dmvmvind slope > 0.05)

WindP

\d_”ddowyo< 0.05

b) Escarpment (O.3 > upwind slope > 0.05; dmvnwind$lope < 0.05) andcliff(upw’indslope > 0,3; dmvm+inds lope < 0.05)

Figure 7. Defiition of signitlcamt topography

2.2.2.2.2 When topography is not consideredsignificant Sa should be calculated from

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

where

As is the site altitude (in metres above meansea level).

NOTE 1“ this cm the value of S=, based .“ the site altitude,compensates for residual topography effects.

2.2.2.2.3 When topography is consideredsignificant Sa, should be taken as the greater of

Sa= 1 + o.oolzl~ (lo)

where

A ~ is the site altitude (in metres above mean sealevel); or

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

where

AT is the altitude of the upwind baae ofsignificant topography (in metres abovemean sea level);

we is the effective slope of the topographicfeature;

s is a topographic location factor.

2.2.2.2.4 The relevant dmensions of thetopography are defined in figure 8. ‘RVOpararnetem, effective slope we and effective slopelength L, are defined in terms of these dimensionsby the following.

a) For shallow upwind slopes 0,05 < v <0.3:v, = Vu and L, = Lu;

b) For steep upwind slopes v >0.3:

We = 0.3 and L, = Z/O.3.

14


WhdX<o X>o

● ‘~

a) Hilland ridge (Vu >0.05, VD > 0.05)

‘ k—Lu —i

b) Escarpment (0.3 > Vu >0.0.5, WD < 0.05) and cliff (VU >0.3, VD < 0.05)

f@Y

J%

hx

zAs

‘T

v“

w

Length of the downwind slope in the wind dimxtion

Length of the upwind slope in the wind direction

Horizontal disfance of the site from the crest

Effectiveheightof the featureSitealtitudein meows above mean sea level

Altitude of upwind base of topographic feature

Uprnnd SIOW Z{k i. the ~d d~On

Downwind slope ZIL~in the wind direction

Figure 8. Deftition of topographic dimensions

15


2.2.2.2.5 Values of the topographic location b) downwind of thecrest(X > O), the horizontalfactors are given for hills and ridges in figure 9 positiorr ratio is X/LDfor hills and ridges, andand for cliffs and escarpments in figure 10. In XL for cliffs and escarpments.reading the value ofs f-mm these fi&ree., thelocation with respect to the crest of the feature is

In all &ses, the height ab&e ground &-~iois Z/Le.

scaled to the lengths of the upwind Lu orNUI’E. 1. c-s transitionalbetweenhillsandridgesin figw? 8a

downwind LD slopes as follows:andcliffsandexarpmenfsin figure 8b, i.e. when thedownwind slope length ~ is much longer than the upwind

a) upwind of the crest (X < O), the horizontal slopelength ~ it may be difficult to decide which model is the

position ratio is X/Lu for all types of topography;moreappropriate1“ this cm, a value of s may b? derived fromboth figures9 and 10, and the smaller value used.

-1.5 -1.0 -0.5 0 0.5 1.0 1.5 2.0 2.5I

X/Lu <+> x/LD

Horizontalpositionratios

Figure 9. lbpographic location factor s for hills and ridges

16

Section 2i

BS6299:Fart 2:1995

Upwi.d of crest .~,Cfownwindofcreti

4“ 2.0

; 1.50.-@ 1.0uc30~ 0.5a>2m

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 10. ‘lbpographic location factors for cfiffs and escarpments

2.2.2.3 Dirw?ctionfactor ‘Ikble 3. Vfdues of direction factor&

The direction factor Sd maybe used to adjust the Direction v Direction factor S~bssic wind speed to produce wind speeds with thesame risk of being exceeded in any wind direction.

0° North 0.78

Values am given in table 3 for all wind dmtilons in 30° 0.7330” intervals (where the wind direction ix definedin the conventional manner an east wind is a wind

60° 0.73

direction of v = 90° and blows from the east to 90° Esst 0.74

the site). J.fthe orientation of the building is 120” 0.73unknown or ignored, the value of the dim?ctionfactor should be taken ss Sd = 1.00 for all 150°

dmctions.

0.80

180” South 0.85NU1’E. When the direction factor is used with other factom thathave a dbecdonal variadon, values from ‘Ale 3 should be 210” 0.93interpolated for the specific directi.” being consideral, or tielargest tsbulated value in tbe range of wind direction maybe

240° 1.00

selected. 270° West 0.99

300” 0.91

330” 0.82

360° North 0.78

NOTE.Interrelation may be used within this table.

17

BS6299:Part2 :1995 Section 2

2.2.2.4 Seasorralfactor

The seaaonaf factor S, may be used to reduce thebasic wind speed for buildings which are expectedto be exposed to the wind for specific subarmualperiods, in particular for tempmary works andbuildings during construction. Values whichmaintain the risk (probabtity) of being exceeded ofQ -0.02 in the stated period are given inannex D.

For permanent buildlrrgs and buildings exposed tothe wind for a contirrrrous period of more than6 months a value of 1.0 should be used for S,.

2.2.2.5 PrvbabilitfI factorA pmbabiity factor SP may be used to change therisk of the basic wind speed being exceeded fromthe standard value of Q . 0.02 annually, or in thestated subannurd period if S’Sis alao rraed.Equation D.1 gives .SP,together with a number ofvalues for other levefs of risk.

For alf normal design applications, whereadjustments for risk arc made through the partialfactors, the standard value of risk, Q = 0.02, isused and SP = 1.0.

2.2.3 Effective wind speed

2.2.3.1 ‘f’be effective wind speed V, should becalculated from

ve=v, xs~ (12)

where

V, is the site wind speed obtained from 2.2.2,for the range 6 = +45° around thenotiorrrd orthogonal wind directions definedwith the pressure coefficient data for eachform of buifding;

.% is the terrain arrd building factor obtainedfrom 2.2.3.3.

2.2.3.2 For buildings with height ff greater thanthe cmaswind breadth B for the wind dmctionbeing considered, some reduction in later-al loadsmay be obtained by dividhrg the building into anumber of parts m follows

a) buildings with height H leas than or equal to Bshould be considered to be one part, as infigure ha;

b) buildings with height II greater than B but lessthan 2B should be considered to be two parts,comprising a lower part extending upwards fromthe ~ound by a height equal to B and an upperpart which is the remainder, as in figure 1lb;

c) buildings with height H greater than 2B shouldbe considered to be multiple parts, comprising alower part extending upwards fmm the groundby a height equal to B, an upper part extendingdownwards from the top by a height equal to B,and a middle region between upper and lowerparts which may be dMded into a number ofhorizontal parts, as in figure 1lc.

The reference height H, for each part should betaken as the height to the top of that part.

2.2.3.3 The terrain and building factor Sb shouldbe obtained directly from table 4 and takes accountof.

a) the effective height He determined from L 7.3;

b) the closest diatarrce of the site from the sea inthe range of wind direction O = t45° aroundthe notional wind direction for the orthogonalload case, as defiied with the pressurecoefficient data for each form of building

c) whether the site is in country terrain or atleast 2 km irrside town terrain.

NCTE. Forallsites inside towns (except exactly at the upwindedge or at a di.wance of 2 km fmm the upwind edge) thesimp~,cations of the srandard method prcduce a huger value ofSb than the directional methcd. If the loads produced by thesfandard method are critical to the design, the use of tbehyhrid combi”atio” given i“ 3.4.2 should & considered.

18


a) One part when H s B

_FBF _

1 ‘THr=H

HT Hr=B

v////’////////////////////

b) Twoparts when B< Hs 7.,9

~- ~LY–A.

IH, =H

1 Hr=z l;, =

A——H

A

fH=B

vr

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

c) Multipie parts whenfl > ZE

Ngure 11. Division of buildings by parts forlateral loads

H-6

19

BS6399:Fs.rt2 :1995 Section 2

‘fhble 4. I%ctnr .Sbfor standard method

Site in country ] Site in town, extending 22 km .pwInd from the site

Effective height I Closest distance to seaHe

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 1Closest distance to sea

I W I

+2100 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

kkm

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. [nterpaiation may be used within each mble.

N(TE 2. The !iRures in this table have been derived from reference [5]

NOTE 3. Values =.me a diaaon?.1 dimension a = 5 m

NOr2 4. If H, > 100 m use the directional method of section 3.

2.3 Standsrd pressure coefficients 2.3.1.4 Pressure coefficients me given for spec~lc3uIfaces. or uarta of surfaces, of buildings or

2.3.1 General

2.3.1.1 The wind force on a building or elementshould be calculated by the procedure given in2.1.3 using appropriate pressure coefficients thatare dependent on the shape and form of thebuifdmg,NOTE The sfandard pressure coefficients may be used forb.ildi”gs a“d elements of generally similar shape. Where thebuilding or eimnemt shape falls oufside the scow of thetabulated PB.E coefficients in Z.4 to 2.5 or in 3.3, or wheremore detailed data are required, pressure ccefficie”ts may heobfained from wind tunnel tests as defined in 1.1.

2.3.1.2 The standd extemaf pressure coefficientsaet out in 2.4 and 2.5 apply to buifding stmcturesthat me predominantly flat faced, and to walk ofcircular-plan buifd@s. The majority ofconventional buildin~, such as cuboidaf, orcomposed of cuboidal elements, with different roofforms such as flat, monopitcb, duopitch, hippedand mansard, are included.

Where considerable variation of pressure occursover a surface it has been subdivided into zonesand pressure coefficients have been provided foreach zone.

2.3.1.3 When calculating the wind load onindividual structural components and claddingunits and their ftings, it is essential to takeaccount of the pressure difference betweenoPPosite faces of each elements. Extemaf pressurecoefficients are given in 2.4 and 2.5 and internalpressure coefficients in 2.6 for use with proceduresgiven in 2.1,

element& V&en the procedure of 2.1. 3.~ isapplied, they give the wind loads acting in adirection normal to that ptilcular surface,

2.3.1.5 For certain buildhgs a wind load due tofrictional drag should be taken into account (see2.1.3.8, 2.4.5 and 2.5.10).

2.4 External pressure coefficients forwalls

2.4.1 Rectangular-plan buildings

2.4.1.1 External preesure coefficients for verticalwalls of rectangular plan buildings are given intable 5, dependent on the proportions of thebuifdings as shown in figure 12.

2.4.1.2 Vafues of pressure coefficient forwindward and leeward faces are given in tsble 5for buildlngs with D/H s 1 and for buildings withD/H ? 4 where D is the inwind depth of thebuildlng, which varies with the wind directionbeing considered (see figure 2), and His the heightof the wall includkg any parapet.NOTE. Values of pressure coefficient for intermediate D/Hratios may be interpolated.

2.4.1.3 The loaded zones on the side face shouldbe divided into veti]ca.1 strips from the upwindedge of the face with the dimensions shown infigure 12, in terms of the scafing length b given byb = B or b = 2H, whichever is the smaller, whereB is the crosswind breadth of the building, whichdepends on the wind direction being considered(see figure 2b) and H is the height of the wall,including any parapet.

20

Section 2 BS6299:Part2 :1995

Plan PlanW=D

d—h

-n]

L=D

WindL=8

%~~=

a) Load cases wind on long face and wind on short face

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) Keytopressure coefficient mneson side face

Figure 12. Keytowall pressnre data

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 -0.9face Zone C -0.4 -0,9

NUIX. Interpolationmaybe usedin therange1 < D/H <4. See 2.4.1.4 for interpolation Mtween Lwlared and funneling.

2.4.1.4 Where walls of two build@s face eachother and the gap between them is less than b,frmneflirrg will accelerate the flow and make thepressure coefficient more negative. Values ofpressure coefficient for the side faces are given intable 5 for each cf the eases denoted ‘isolated’ and‘funneling’ to be applied aa foUows.

a) Whefe the gap between the buiMin@ is leasthan b/4, or greater than b, the isolated vaIuesshould be used;

b) where the gapbetween the buildings isgreater than b/4 arrd less than b

1) either uae the fumellirrg values,conservatively; or

2) take the furmelling values to apply at a gapwidth of b/2 and the isolated values to apply atgap widths of b/4 and at b, and intefpalatelinearly between these values for the actualgap width in the range from b/4to b/2or therange from b12 to b.

2.4.1.5 The values in table 5 are alao valid fornon-vertical walls within t 15° of the vertical.Values outside this range should be obtainedfrom 3.3.1.4.

21,

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 Buildings with re-entrant comers,recessed bays or internal wefls

2.4.3.1 The external pressure coefficients given intable 5 should be used for the vertical walls ofbuildings containing re-entrant comers or recessedbays, aa shown in figure 13, subject to thefollowing.

a) Where the re-entrant comer or recessed bayresults in one or more upwind wings to thebuilding, shown shaded in figures 13a,13b and 13c, the zones on the side walls aredefined using the crosswind breadth B = B1 andB3 and the height H of the wing.

faces (see figure 13d) where the gap acro~ theweU or bay is smaller than the scaling length b, thefollowing apply.

a) External pressure coefficient for the walls of awell is assumed to be equal to tbe roofcoefficient at the location of the weU given inclause 2.5;

b) External pressure coefficient for the walls ofthe bay is assumed to be equal to the side wallcoefficient at the location of the bay.

Where the well or bay extends acroas more thanone pressure zone, the mea-average of the pressurecoefficients 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 greaterof the building are defined using the crosswind than the scaling length b, the external pressurebreadth B = B2 and the height H of the building. coefficients should be obtained fmm 3.3.1.5.

Wind

d b) c) d)

Figure 13. Typicaf examples of buildings with re-entrant corners andrecessed bays

22


2.4.4 Buildings with irregular or inset faces b) Cut-out upwind, as in fiire 14b and 14d.

2.4.4.1 IrrcgularjfushfacesThe loaded zones on the face are divided into

External pressure coefficients for the flush waifs ofvertical strips immediately downwind of the

buildings with corner cut-outs in elevation, asupwind edges of the upper and lower part of theface 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 determinedbuildings with a lower wing or extension built flush fmm the height HI znd crosswind breadth B1 ofwith the main building, should bs derived as the upper inset windward face. The scalingfollow. length & for the zones of the lower Dart is

a) Cut-out downwind, as in fii 14a and 14c. det&&ed from the height H2 and &osswind

The loaded zones on the face should be divided breadth BZ of the lower windward face. Theinto 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 Cscaling 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 cv c I

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

a) Cut-out downwind: tall Part long

H,

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

B tHI _

cc B H2 = H,

b) cut-out upwind: tall part long

K A

v

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

HI1’

H, ~ B j ‘+ “ B -

c CIB tH2 = H,

v%77//////////////

.) PUt.OUL d.ymm.i”d tail partlmrrmv @ ~.t-..t .m+.d: ~1 P~ n~w

Figure 14. Examples of flush irregular walla

23

BS6299:Part 2:1995 Section 2

2.4.4.2 Waifs of inset storegs

External pres.sum coefficients for the walls of insetstoreya, as illustrated in figure 15, should bederived se follows.

a) Edge offats insetfrom edge of b.nuwstmwy(see figure 15a). lb’ the inset walls, providedthat the upwind edge of the wall is inset adistance of at least 0.2b1 from the upwind edgeof the lower stomy (whers bl is the scalinglength for the upper storey), the loaded zonesare defined from the proportions of the upperstorey, assuming the lower roof to be the groundplane. However, the reference height H, is takenas the actual heidt of the toD of the wall aboveground. -

b) Edge offmejlush with edge of lower sfm-ey(see figure 15b). Where the upwind edge of thewall is flush, or inset a distance of less than0.2b1 from the upwind edge of the lower storey,the procedure in item a) should bs followed, butan additional zone E should be included asdefined in figure 15b with an external pressurecoefficient of C ~ –~- -2.0. The reference heightfor zone E shou d be taken as the top of thelower storey. The greater negative pressure(suction) determined for zone E or for theunderlying zone A in item a), should be used.

The pressure coefficients for zones A, B and C maythen be obtained from table 5.

> o.2b1—

E–

B c HI

~ ‘L

H,

N(YIX. b, isw- lenstb of “p~~ Stmwy.

a) Edgeof face inset fmm edge of lower storey

NOfE & isscaling bw@h of lower stmey.

b) Edgeof faceflushwithedgeof lowerstorey

Figure 15. Keys for walls of inset storey

—

24

Section 2 BS6299:Part2 :1995I

2.4.5 Friction-induced loads on walls

Friction forces should be calculated for long wallswith D > b when the wind is parallel to the wall.The frictional drag coefficient should be assumedto act over all zone C of such walls, with values asgiven irr table 6. The resulting frictional forcesshould be added to the normal forces as describedin 2.1.3.8.

‘hide 6. Frictional drag coefficients

‘Nw OfSUrf=e FTfctioMf dragcoemcient

Smooth surfaces without 0.01corrugations or ribs across thewind direction

Surfaces with corrugations 0.02ccrma the wind direction

Surfaces with ribs across the 0.04wind dkection

2.4.6 Circular-plan bufldirrgaThe d~tribution of external pressure coefficientaround the periphery of a circulw-plmr buildlng isgjven in table 7. These pressure coefficients arealso applicable to silos, tanks, stacks and chimneys.

fhble 7. External Iwalls of Circrllsr-pl

Positron

mperfphery9

>“

10”

20”

30”

40”

50”

60°

70”

80°

90”

100”

120”

140”

160°

180°

NOTE 1.1

;.rface mmojection

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

rpidation I

.essure coeffkients Cm forur buildir

-

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

the range

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 diameters greater that d - 1 m.NUTS 3. T position on the periphery at O - 40” where

% “(! is a region where the pressure will change rapidly

wmh rime, due to fluctuations in wind direction cauwd byatmospheric turbulence, over the range Cw - *0.7. h istherefore the zeaon with the K&est risk of fatigue damage 0cladding fltis.

2.5 External pressure coefficients forroofs

2.5.1 Flat roofs

2.5.1.1 Scope

The data irr this section should be used for dl roofsof pitch a less than 5°. Pree.sure coefficients aregiven for the orthogonal load cases and are upperbound values to cater for all wind d~ections8 *45° from normal to the eaves being considered.

2.5.1.2 Loaded zones

The roof should be subdkided into zones behindeach upwind eaves(verge as shown in figure 16 fora rectangular roof. The loaded zones, shown infigure 16, are defiied in terms of the scaling lengthb given by b = B or b = 2H, whichever is thesmaller, where B is the cms.swind breadth of thebuilding, which is equal to Wor L, depending onthe wind direction being corwidered, as defined infigure 16a, and His the height of the wall,including any parapet.

2.5.1.3 Ffat m@? with sharp eaues

External pressure coefticienta for each zone of flatroofs with sharp eaves are given in table 8.

2.5.1.4 Ffat majl? with pampcfs

2.5.1.4.1 A parapet along any eaves or edge willreduce the pressure coefficients for the roof in thelocaf edge areaa only. External pressure coefficientsfor flat rcmfs with edge parapeta are given intable 8, dependent upon the ratio of the height h

of the parapet, defined in fwre 17a, to the scalinglength b.

2.5.1.4.2 Loading on the parapet walls, includhrgthe effects of comem where appropriate, should bedeterrrdned as for boundary walls from 2.7.5.

2.5.1.5 FZat roaJ%with curved earxx?

2.5.1.5.1 External pressure coefficients for eachzone are given in table 8 and are dependent on therrrtio of the radius r of the eaves to the scalinglength b, defined in 2.5.1.2, for that eaves. Thezones start fmm the edge of the flat part of themof aa defiied in fii 17b.

2.5.1.5.2 The presmrre on the curved eaves shouldbe linearly interpolated around the arc betweenthe adjacent wall and roof pres.smes.

2.5.1.6 Ffat ro@ with mansard eaves

2.5.1.6.1 External pressure coefficients for eachzone are given in table 8 and arc dependent on thepitch angle a of the mansard eaves. The zones startfrom the edge of the flat part of the roof a-sdefined in fii 17c.

2.5.1.6.2 The pressure on the sloping mansardeaves shordd be aasesed using the procedurein 2.5.4.

—

25


Plan Plan

W=Dd—h

‘o]

L=D

Wind

‘=6 ‘+ ~lp=’

.) Loadcases. wind on long face and wmd on short face

DA

c b12

L ~ ~b/1O

T

T

& ‘x

Wind

b) Key m pressure coefficient zones.. flat roof

Fignre 16. Key for fit roofs

Table 8. External pressure coeffkienta Cw for flat roofs of bnfi~@

FM roof type Zme

A B c D

Shzrp eaves -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 = 0,05 -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 with parapets or curved eaves, i“terpolatio” may be used for intermediate values of hlb and rib.NOTE 2. For rcmfs with mansard eaves, interpolation between a - 30° and a - 60° may be used. For a >60° interpolatebetween the values for m - 60° ad the values for flat roofs with sharp eaves.NOTE 3. 1“ zone D, where both positive and negative values are @ven, both values should be considered.NUTE 4. Values of cc+ fficienfs for other wind directions are @ve” in 3.3.2,NOTE 5. Fbr pitched roofs with curved or nw.”.sard eaves, the values i“ this mble may be compared with the appropriate values infables 9, 10 or 11 and the least negative values used.

26

i

Section 2 BS 6299: Rut 2:1995

Kh

—

Hr

H

a) Parapets

Roof zonas

K

start from here

r

Hr. H

b) Curved eaves

>b/1O—. ~-

+/’’!/”Roof zonesstart from here

a\

‘“HL

c) Mansard eaves

Figure 17. Key to cave details for flat roofs

—5.1.7Flat mqp with inset storwfp

r flat roofs with inset storeys, defined inNre 18, external pressure coefficients for bothe uPPer roofs and lower roofs should be derivedfouows.

a) For the upper roof the appropriate procedureof 2.5.1.3, 2.5.1.4, 2.5.1.5 or 2.5.1.6, dependingon the form of the eaves, should be used, takingthe reference height H, aa the actual height tothe upper eaves, and Has the height of the insetstorey (from the upper eaves to the lower rooflevel) for determining the scaling length b.

b) For the lower roof the appropriate procedureof 2.5.1.3, 2.5.1.4, 2.5.1.5 or 2.5.1.6, dependingon the form of the eaves, should be used, whereH, = H and is the actual height of the lowerstorey, ignoring the effect of the inset atoreys.However, a further zone around the base of theinset storeys extending b/2from each facing waifshould be included, where b is the safingp-eter fmm 2.5.1.2 appropriate to therelevant walls of the inset storey. The pressurecoefficient in this zone should be taken as that ofthe zone in the adjacent wall of the upper stor’ey(as determined from 2.4).

Take prsssure Cnefficienfs on adjacsnt wall in this zone

\

A I ‘rB A I

~

NOTE. b is scaling length of upper storey.

27

BS6399:F%rt 2:1995 Section 2

2.5.2 Monopitch and duopitch roofs

2.5.2.1 General

Monopitch and duopitch rrmfs of buildm aredefined as rvofs with gable ends.NOTE. Hippedroof form aretreatedseparatelyinZ.6.3.

2.5.2.2 Loaded zones

Zones over which the extemaf pressure coefficientis assumed to be constant for both monopitch andduopitch rwfs am shown in figures 19 and 20.These zones are strips parallel to the eaves andverge and are defiied in terms of the walinglengths ~ 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 Monopitch moJ3

External pressure coefficients for monopitch roofsshould be obtained from table 9, using the key infigure 19, Owing to the asymmetry of this roofform, values arc given for three orthogonal loadcases wind normal to the low eaves (0 . 0°),wind normal to the gable [8 = 90°) and windnormaf to the high eaves (6 = 180”).

2.5.2.4 Duopitch roofi

2.5.2.4.1 External pressure coefficients forduopitch roofs should be obtained from table 10,using the key in figure 20. Values arc given for twowind directions: wind normal to the low eaves(d = 0°) and wind normal to the gable (0 - 900).These coefficients are appropriate to duopitchfaces of equal pitch but maybe used withoutmodification provided the upwind and downwindpitch angles are within 5° of each other. Forduopitch roofs of greater disparity in pitch anglessee reference [6].

2.5.2.4.2 When a c 7° and W < bf,, zone C forthe load case .9 = 0° should be considered toextend for a distance bf/2 downwind from thewindward cave (as shown for flat roofs infigure 16), replacing ridge zones E and F and partof zone G.

2.5.3 Hipped roofs

External pressure coefficients for conventionalhipped roofs on cuboidal-plan buildings, where allfaces of the roof have the same pitch angle and arein the range a = -45° to +75°, are given intable 11. The definitions of loaded zones and pitchaf@eS are given in tigurc 21. The data in table 11may be applied to hipped roofs where main facesand hipped faces have dtiferent pitch angles,provided the pitch angle of the upwind face is usedfor each wind direction, as indicated in f~re 21.Negative pitch angles occur when the roof is ahipped-tmugh form. For pressure coefficients forskew- bipped roofs and other hipped rcmf forms seereference [6].

2.5.4 Mansard roofs

External pressure coefficients for mansard roofsand other multi-pitch roofs should be derived foreach plane face by the procedure given in 2.5.2 forroofs with gable ver%es or the procedure givenin 2.5.3 for roofs with hipped verges, using thepitch angle for each plane face. The key infigure 22 indicates where edge zones should beomitted.

28

!Section 2 BS6W9:M 2:1995

a) Geneml

Plan

Ib) Zones for wind directions O - 0° and 8- 180°

IbJ70 Highcave

F-1 “xPlan

T

w/2 B

r -

Wind,. c D

I

w

w/2 A

Y-

I c) Zones for wind direction O = 900 IFignre 19. Key for monopitch roofs

, 29

BS6399:RIrt2 :1995 Section 2

fliim!!m,’a) General

~–- L

4Plan

G

E F E ~b’,111

c

A B A ~b,,lo

,<bL/2

J fk >Wind bL12

b) Zones for wind direction 8 - 0°

‘k Ab$

c) Zones for wind direction O . 90°

Figure 20. Key for duopitch roofs

~>!.

30

H

Section 2 BS 6399: Fart 2:1995

‘Ihble 9. External pressure coefficients Cmfor monopitch rOOfs Of bnild~gs

Fffch aI@e a Zone for 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 +0.4

45” -1.1 -0.3 +0.7 -1,5 -1.2 -1.0 -0.9 -1.3 -1.0 -0.8

+0.8 +0.6

60° +0,8 +0,8 +0,8 -1.2 -1.2 -0,4 -0.4 -1.0 -0.7 -0.7

+0.4

75” +0.8 +0.8 +0.8 -1.2 -1.2 -0.4 -0.2 -1.1 -0.7 -0.7

+0.5 +0.4

NOTE1.At 0 = 0° thepressurechangesrapidlybetweenpmitiveandnegativevaluesin therangeof pitchangle1so < m<30°, w both positive and negative values are given. At 8 . 90° with ha roof pitches, the press”= changes between positiveand negative with fluctuations of wind direction, so both !-mitive and negative values are again given.NUTE 2. Intemlatio” for intermediate ~itch a“des mav be wed between val”w of the same sire.

Table 10. External pressure coefficients Cw for duopitch r~fs Of buildings

Pffrh @e a zone for R = 0° zone for e . 90~A B c E F G A B c D

-45” -1.3 -1.0 -0.8 -1.0 -0.7 -0.7 -1.5 –1.3 -1.0 -0.2

-30° -2.3 -1.2 -0.8 -0.9 –0.7 -0.7 -1.7 –1.3 –1.0 -0.2

– 15° -2.6 -1.0 -0.9 -0.7 -0.5 -0.5 -2.7 -1.4 -0.8 -0.3

- 5“ -2.3 -1.2 –0.8 -0.8 -0.3 -0.3 -2.2 –1.5 -0.7 -0.4

+ 5“ -1.8 -1.2 -0.6 -0.5 -0.3 -0.3 -2.0 -1.1 -0.6 -0.4

+ 15° -1.3 -0.8 -0.3 -1.1 -0.9 -0.5 –1.6 -1.5 -0.6 -0.3

+0.2 +0.2 +0.2

+ 30° -1.1 -0.5 -0,2 –0.7 -0.4 -0.4 -1.2 -1.1 -0.6 -0.2

+0.8 +0.5 + 0.4

+ 45” -1.1 -0.3 +0.7 -0.4 -0.3 -0.3 -1.2 -1.2 -0.6 -0.2

+0.8 +0.6

+ 60” +0.8 +0.8 +0.8 -0.4 -0.3 -0.3 -1.2 –1.2 -0.7 -0,2

+ 75” +0.8 +0,8 +0.8 -0.4 -0.3 -0.3 -1.2 -1.2 -0.7 -0.2

NOlY31.At9 - 0° the pmsa”re changes rapidly between positive and negative values i“ the range of pitch angle + 15° < a< .30-, so ‘both pmit!ve znd “egztivc values are given.NU1’E 2. Interpolation for intermediate pitch angles of the same sign may be wed between values of the same sigm (Do notinterpolate between a - + 5° and a - – 5°; uw the data for flat roofs in 2.6. 1.)

31

BS6299:Rwt 2:1995 Section 2

Table 11. Exte&d pressure coefficients Cp, for Mpped rOOfs Of buil~gs

Pitch angle a Zone for O - 0“ and 8- 90”. I . I . I m F G fi I J

7 I -0.7 I -0.7 I -0.8 I -0.8 I -0.2

“

-45” -1.3 -0.6 -0.8 -0.7

-30” -2.3 -0.8 –0.8 -0.7 I -0.7 I -0.7 ] -0.8 I -0.8 -0.2

– 15” -2.6 -1.0 -

– 5“ -2.3 –1.2 -0,8 -0.3 -0.3 -0.3 -0.6 -0.6 -0,4

+ 5“ -1.8 -1.2 -0.6 -0.6 -0.6 -0.3 -1.2 -0.6 -0.4

+ 15” -1.3 -0.8 -0,3 -1.0 –1.2 -0.5 -1.4 -0.6 -0.3

-0.9 I -0.5 I -0.5 I -0.5 I -0.6 I -0.6 I -0.3 I

I I +0.2 I +0.2 I +02 Ill+ 30° -1.1 -0.5

.“ ~.,-~.y I -0.7 I -05 ,-0.4 I -1.4 I -08 ]-0.2 I

I ‘“’5 ‘“”” I ‘U*+45” -1.1 -0.3 +0.7 -0.6 -0.3 -0.3 -1.3 -0.8 -0.2

+0.8 +0.6

+ 60° +0.8 +0.8 +0.8 -0.6 -0.3 -0.3 –1.2 -0.4 -0.2

+ 75” +0.8 +0.8 +0.8 -0.6 -0.3 -0.3 -1.2 -0.4 –0.2

,.-. —...... . . .+ 15° < a < +30 o, so both positive &d n&at{ve vNO1’2 2. Interpolation for intermediate pitch anglesinterpolate between a - +5° a“d a - –5°; use the data for flat %ofs ~n 2. S.l. ) I

NIWF 1. AL O . 0° the mess.re changes rmidlv hetwee” positive and negative values in the range of pitch angle.alues are given.sof thesame simmaybe used between tiue$ofthe=mesi!?m (Do not I

32

Section 2 BS6399:Part 2:1995

->0.

,:+ r=”,;+//,//////////////////1//////////////////////// /

,=”o:~///////////////////////////////////////////////

a) General

Plani+

G

I F

c

B A

sbLIZ

4 +L ,. >Wind L

b) Zones for wind direction O - 0° using q

Plan

J%

c) Zones for wind direction 0 - 90° using am

Figure 21. Key for ldpped roofs

33

BS 6299: Part 2:1995 Section 2

1///////,,///////, ,,/, /,,,/

a) Decreasing pitch multipitch (mansard)

b) Increasing pitch muldpitch

Figure 22. Key for ma.rraardandmrrltipitch roofs

2.5.5 Multi-bay roofs

External pressure coefficients on downwind bays ofmulti-bay monopitch and duopitch roofs as definedin figure 23 may conservatively be taken to be thesame as for a single-bay roof.

However, reduced values of external pressurecoefficients may be derived from table 9 ortable 10, as appropriate, using the reductionfactom given in table 12, as follows.

a) For monopitch roofs, on second andsubsequent downwind bays, any positivepressure coefficient obtained from table 9 shouldbe replaced by Cw = -0.4.

b) Fbr duopitch roofs, all roof slopes downwindof the fmt ridge should be treated as beingtroughed (negative pitch angle), even when theupwind slope is ridged as shown in figure 23c,thus enaurirrg that the pressure coefficients onthe second and subsequent downwind bays arealways negative in value.

c) For the wind directions 6 = 0° and 180°, asshown in figure 23d, the pressure coef flcients onthe second and downwind bays may bemultiplied by the reduction factor given intable 12.

34

ISection 2 BS6399:Psrt2 :1995

7////// /////.///////////////////////////////////

a) Multi-bay monop,tcb

H,

7//,///, /,,/////,,,,,,,//////,////////////////, /,,

b) MuIt]-bay trougbed duopitch

,//////////.\ \

Treat as monopitch Treat as troughed duopitch

c) Multi-bayridged d“opitch

Wind

I II

) I I

L A

I

$

I I

I Iuc

3 ~All u~secuerIt bays :.-3 I

II

I, 1.!

E IIq $

IL

d) Key to reduction zones

Figure 23. Key formulti-bay roofs

35


2.5.6 Fitched roofs with inset storcys

The procedure given for inset storeys on flat roofsin 2.5.1.7 should be followed, but using theappropriate zones for pitched roofs as derived from2.5.2 to 2.5.5.

2.5.7 Effect of parapets on pitched roofs

Parapets reduce the high suction in the edge zonesaround the periphefy of the roof and neglectingthese effects will give a conservative result for mofpitches less than a = 30°. For steeper roofs, theeffects of pampets should be taken hrto account byusing the procedure given in 3.3.3.7.

2.5.8 Roof overhangs

2.5.8.1 General

Where the roof overhangs the walls by an amountleas than b/10, pressure coefficients should beassessed using the procedure given in 2.5.8.2.

Ikble 13. Net ,ressure coefficients

Pitch angle Q

1“

j.

10”

15”

20”

25°

30”

Load case

Maximum, zdf c

Minimum C = O

Minimum C = 1

M-urn, all c

Mirrimum ( = O

Minimum c = 1

Maximum, all (

Minimum C = O

Mlnirnum ~ = 1

Maximum, all C

Minimum C = O

Minimum ( = 1

Maximum, all (

Minimum C = O

Minimum [ = 1

Maximum, all (

Mhdmum ( = O

Minimum c = 1

Maximum, all (

Minimum ~ = O

Minimum C = 1

Larger overhangs should be treated as open-sidedbuildings, with internal pressure coefficientsdetenwirred using the provi.+oms of 2.6.3.

2.5.8.2 Small overhangs ..

The net pressure across a small roof overhangshould be calculated taking the pressure coefficienton the upper surface from 2.5.2 to 2.5.5, asappropriate, and the preasurc coeffkient on thelower surface as that on the adjacent wall fmm 2.4

2.6.9 Canopies, grandstands and open-sidedbuildings

2.5.9.1 Fkce-standing canopies

2.5.9.1.1 Net pressure coefficients CP forfree-standing canopy roofs are given in tables 13,14 and 15, which take account of the Eombmedeffect of the wind on both upper and lowersurfaces of the canopy for all wind directions.

~ for free-standiru? mOnODitCh canODY roofs

-

+0,2

-0.5

-1.2

+0.4

-0.7

-1.4(-1.2)

+0.5

-0.9

-1.4(-1.1)

+0,7

–1.1

-1.5(-1.0)

+0,8

-1.3

-1.5(-0.9)

+1.0

-1.6

-1.4(-0.8)

+1.2

-1.8

-1.4(-0.8)

LOmfcoefficients4 1

+0.5

-0.6

– 1.3

+0,8

-1.1

-1.4(-1.2)

+1.2

-1,5

-1.4(-1.1)

+1.4

-1.8

-1.5(-1.0)

+1.7

-2.2

-1.5(-0.9)

+2.0

–2.6

-1.4(-0.8)

+2.2

-3.0

-1.4 (-0.8)

: < 1 a“d for i“term

B

+1,8

–1.3

-1.8

+2.1

-1.7

-2.6

+2.4

-2.0

-2.6

+2,7

-2.4

-2.9

+2.9

-2.8

-2.9

+3.1

-3.2

-2.5

+3.2

-3.8

-2.0

irate pitxh angNfYfT 1. [nterpd i.. may be usd for solidity ratio in the range O <NUCE 2. Where two values are given for C - 1, the first value is for I ocka.se to the low downwind eaves:(in parentheses) is for blockage w the K&b do~rn.d eaves.NOTE 3. Load cases cover all wxsible wind direction% When “si”x directional effective wind speeds, use:

al these values of C. with ihe lamest value of V. found: or -b) directional value; of C, from ;ference [6] -

+1.1

-1.4

-2.2

+1.3

-1.8

-2.6(-2.1)

+1.6

-2.1

-2.7(-1.8)

+1.8

-2.5

-2.8(-1.6)

+2.1

-2.9

-2.7(-1.5)

+2.3

-3.2

-2.5 (-1.4)

+2.4

-3.6

-2.3 (-1.2)

the second value

.

36

i


lhble 14. Net nressure coefficients C. for free-standimf duouit.ch canonv roofs

=-15” Maximum, all ~

Mtimum ( = O

Minimuml=l

+

-10” M-urn, all ~

Minimum 1 = O

Minimum c = 1

-5” M-urn, all (

Miniium 1 = O

Mbdmum L . 1

-1---+5” Maximum, fl c

Minimum ~ = O

Mfnimum c = 1

+ 10” M-urn, all (

Minimum [ = O

Mbdmum ~ = 1

m+ 20” Maximum, all C

Minimum ~ = O

IMtim”nl [ = 1

+ 25° Maximum, all c

---Ei3i

F

1

)verall coefficients

+0.7

-0.7

-1.5

1

+0.5

-0.6

–1.5

+0,4

-0.6

-1.4

+0.3

-0.5

-1.4

+0.3

-0.6

-1.2

+0.4

-0.7

–1.2

+0.4

-0.8

-1.2

+0.6

-0.9

-1.2

+0,7

–1.0

-1.2

+0.9

-1.0

Minimum ~ = 1 -1.2

NOTE1.hwerpolacionformlidityratioIMY be u.wtiin therange(NOTE2. l“terpolati.” for intermediatepitch angles maybe used INCllT 3. Load casa cover all possible wind directic.”s. When using

a) tfww values of Cp with the largest value of V, found; orb) directional values of Cr from reference [6]

‘Ihble 16. Reduction factors for free-standingmulti-bay canopy roofs

Location Factors for au solidity ratio cOn maxim.. On mhdumm

End bay 1.00 0.81

8econd bay 0.87 0.64

Third and subsequent 0.68 0.63bays

Local coefficients——

3k

+0,8

-0.9

-1.5

+0.6

-0.8

-1.5

+0.6

-0.8

-1.4

+0,5

-0.7

-1.4

+0.6

-0.6

-1.2

+0,7

-0.7

-1.2

+0.9

-0.9

–1.2

+1.1

–1.2

-1.2

+1,2

–1.4

-1.2

+1.3

-1.4

+1,6

-1.3

-2.4

+1.5

-1.3

-2.7

+1.4

-1.3

-2.5

+1.5

-1.3

-2.3

+1.8

-1.4

-2.0

+1.8

-1.5

–1.8

+1.9

-1.7

-1.6

+1.9

–1.8

-1.5

+1.9

-1.9

-1.4

+1.9

-1.9

–1.3

c+0.6

-1.6

-2.4

+0,7

–1.6

-2.6

+0.8

-1.5

-2.5

+0.8

-1.6

-2.4

+1.3

-1.4

-1.8

+1,4

–1.4

–1.6

+1.4

-1.4

–1.3

+1.5

–1.4

-1.2

+1,6

-1.4

–1.1

+1.6

-1.4

-1.1-1.2

<; <1.,tween values of the same sign.directional effective wind speeds, use:

D

+1.7

-0.6

-1,2

+1,4

-0.6

-1.2

+1,1

-0.6

-1.2

+0.8

-0.6

–1.2

+0.4

-1.1

-1.5

+0.4

-1.4

–1.6

+0.4

-1.8

-1.7

+0.4

-2.0

-1.7

+0,5

-2.0

-1.6

+0,7

–2.0

-1.6

37


2.5.9.1.2 Canopies should beableto resist themaximum (kgestpositive) and the minimum(largest negative) net pressures, the latterdepending on the degree of blockage under thecanopy. The blockage ratio (at anycross section isequal to the height of obstructions under thecanopy divided by the height to the downwindeaves of the canopy, both areas normal to the winddnction. The value ( = O repreeenta a canopywith no obstructions underneath. The value c = 1represents the canopy fully blocked with contentsto the downwind eaves. Values of CP for

---

intermediate blockages may be linearly interpolatedbetween these two extremes, and app!ied upwindof the position of maximum blockage only.Downwind of the position of maximum blockagethe coefficients for L = O may be used.

2.5.9.1.3 The values in the columns with themulti-column heading sLocal coefficients’,corresponding to the loaded areas defined infigure 24, should be used for the design of therespective areas of the canopy. Where the localcoefficient areas overlap the greater of the twogjven values should be taken,

a > 0“ for ridged a < 0“ for tmughed

0.CT v

~ >~-?—fi-~– ~~Hr Cp,0 downwards

PlHr C,, Odownwards

!

a) General

b) Blockage ratio

LI

w

LI

c) Keyto zones o. nmnopitch and duopitch canopy roofs

Figure 24. Key for free-standing canopy roofs

w

38

,


2.5.9.1.4 The values br the columns headed‘Overall coefficients’ should be wed for the designof the members supporting the canopy. Formonopitch canopies the centre of pressure shouldbe taken to act at 0.3W fmm the windward edge.For duopitch canopies the centre of pressure shouldbe taken to act at the centre of each slope.Additionally, duopitch canopies should k able tosupport forces with one slope at the m-urn orminimum snd the other slope unloaded.

2.5.9.1.5 In addition to the pressure normal to thecamopy, there will be horizontal loads on thecanopy due to the wind pressure on any fascia atthe eaves or on any gable between eaves mrd ridgeon duopitch canopies. Fascia loads should becalculated on the area of the surface facing thewind using a net pressure coefficient of Cp - 1.3on the windward faacitigable and Cp - 0.6 on theleeward faacialgable acting in the direction of thewind.

2.5.9.2 Canopies attached to buildings

Pressures on canopies attached to buildings dependon the shape and size of the building, the locationof the canopy and on the surrounding buildings.Advice is given in reference [6].

2.5.9.3 Grandstands and open-sided buildings

Buildings with permanent walls and one or moreopen sides should be treated as conventionalbuildings, with external pressure coefficientsdetermined from 2.4 and 2.5 and the internalpressure coefficients determined from 2.6.3.

2.5.10 Priction induced loads on roofs

2.5.10.1 ROOD of buildings

Frictional forces should be considered on long roofsaway frum the upwind edges. The resultingfrictional drag coefficient should be a.smrned to actover zone D on flat roofs (see fiire 16) for allwind directions; and over zone D for monopitch orduopitch roofs (see figures 19 and 20 and zone Jfor hipped roofs in figure 21) only when the windis parallel to the ridge. Values of frictional dragcoefficient should be obtained from table 6 and theresulting frictional forces combmed with theno.rnralpressure forces us desmired in 2.1.3.8.

2.5.10.2 Frre-starrding canopy m@

FYictionzd forces should be assumed to act over thewhole of the top and bottom sufaces of an emptycanopy or the whole of the top surface only for afully blocked canopy. Wdues of frictiousl drsgcoefficient should be obtained from table 6 and theresulting frictional forces combhed with thenormal forces as described in 2.1.3.8NGTE.[f there are fascias at the eaves or verges (we 2.5.9.1.5)only the greater of the fascia or friction forces need to be takeninto account.

2.6 Internal pressure coefficients

2.6.1 Enclosed buildings

2.6.1.1 fn enclosed buildings, containing externaldoors and windows which may be kept closed, andwhere any internal doom are generally open or amat least three ties more permeable than theexternal doom mrd windows, the internal pressurecmr be taken as uniform; appropriate intemafpressure coefficients are given in table 16. Therelevant diagonal dmension a for the internalpressure may be tiken as

a= lox 3internal volume of storey (13)

‘lkble 16. Internal pressure coefficients CP1forenclosed buildings

‘&p .f walls ‘piTWOopposite walls equally permeable;other faces impermeable

- Wind normal to permeable face +0.2

- Wmd normal to impermeable face -0.3

Four walls equally permeable; mof -0.3impermeable

2.6.1.2 When? an enclosed buildhrg is subdividedinto moms with internal doom which are not atleast three times more permeable than the externaldoors, the internal pressure may differ betweenrooms. This will result in net wind loads oninternal waifs. A method for calculating theinternal pressures in multi-room buildings is givenin reference [6], For external walk, provided thereme no dominant openings, the intemsl preesurecoefficient CPi should be taken as either – 0.3 or+ 0.2, whichever gives the larger net pressurecoefficient across the wall. The m-urn netpressure coefficient Cp across internal walls shouldbe taken as 0.5. The relevant diagonal dmen.sion afor the intemsl pressure may be taken as

a= lox ainternal volume of room (14)

2.6.1.3 Where an external opening, such as a door,would be dominant when open but is considered tobe closed in the ultimate limit st&e, the conditionwith door open should be considered ~ aserviceabilityy limit state, and the loads assessedusing the appropriate partial load factom forserviceabfity.

2.6.2 Buildings with dominant openings

An opening will be dominant, and control theinternal pressure coefficients, when its area isequal to, or greater than, twice the sum of theopenings in other faces which contribute porosityto the internal volume containing the opening. z)

21TWOor ~o,e oprdns in theme fwe will contribute to one ef fmive dominat ope”i.g qua) to the combined area ad adwonal dimension a equal to Mat of the Iarg@t ope”i~.

!m


Internal preamre coefficients Cp] arc given irrtable 17 as a fraction of the avemge externalpressure CY at the dominant opening obtainedfrom 2.4 or 2.5 aa appropriate. The relevantdiagonal dimension a depends on the size of thedominant opening rvlative to the internal volumeand may be taken as the greater of

a = diagonal dimension of dominant opening or

a= O.2x ‘ internal volume (15)

where the internal volume is the volume of thestorcy or room containhrg the dominant opening.

‘lhble 17. fnternal pressure coefficients CPi forbuildings with dominant openings

Ilatioof dominantqe~ c,!area to sum of remablhlgopetigs and distributedporosities

2 0.75 x (&

3 0.9 x Cw

2.6.3 Open-sided buildings

2.6.3.1 Internal pressure coefficients 6’ i forfopen-sided buildings are given in table 8 accorrhng

to the form of the buildhg. The relevant diagonaldimension a for use with these coefficients is thediagonal dmension of the open face. In table 18 awind direction of O = O“ corresponds to windnormal and blowing into the open face, or thelonger face in the case of two open faces, andnormal to the wall in the c&se of three open faces.

2.6.3.2 For buildings with two opposite openfaces, wind skewed at about # = 45° to the axis ofthe building increases the overall side force. Thisload case should be allowed for by using a netpressure coefficient of 2.2, divided equallybetween each side wall. More details are given inreference [6].

2.6.4 Open-topped cylinder%The internal pressure coefficient for anopen-topped vertical cylinder, such aa a tank, siloor stack, is given in table 19.

.-

lkble 18. Internal pressrrre coefficients Cpi for open-sided buildings

Wind direction O One open face lWo adjacent open Three adjacent open

Shorter Longer faces’] faces~]

*O” \+0.85 I +0.68 +0.77 + 0.60

*9W -0.60 – 0.40 +0.77, -0.38 0

k 180° –0.16 -0.16 -0.30 -0.39

+270° -0,60 -0.40 +0.77 0’1)~. ~ue~ ~ sjvenfor o . W., the p,itlve ~uw co~spond t. the short face downwind; the negative values correspond

to the shorf face upwind.2)Apply,due~ to “nde=ide .f ~f ~nIy. For the single wall, use pressure coefficients for walls siven in table 5.

~

‘fkble 19. Intemaf pressure coefficients CPi for

H/d <0.3 ] -0.5

40


2.7 Pressure coefficients for elements

2.7.1 General

This section deals with the pressure coefficients ofelements of small crosswind breadth, typicalfy200 mm, attsched to buildings. For sharp-edgedshapes the pressure coefficients remainaPPmximately constant over the whole mnge ofwind speeds likely to be encountered. However, forcircular sections the pressure ccefficienta vary withwind speed and dkuneter. For circular elementswhose diameter is greater than about 200 nun thevalues in this section are conservative.

2.7.2 Individual aectiona

2.7.2.1 Net pressure coefficients for long circularand sharp-edged sections, such as rolled steelsections, plate girdem, bux sections, beams andcimular tubes with the long axis normal to thewind are given in table 20. These net pressurecoefficients should be taken to act on the projectedarea normal to the wind.

ITable 20. Net pressure coeffkienta CDfor longelements

Elementtype Cp

Ckmdar sections I 1.2

Sharp-edged sections 2.0

2.7.2.2 For horizontal sections, the referenceheight ffr should be taken aa the height aboveground of the axis of the section. Vertical orinclined sections may be taken as being divided

into parts of length at leaat twice the crosswindbreadth, L z 2B, and the reference height H,should be taken as the height above ground of thetop of each part.

2.7.3 Effect of length

The net pressure coefficient for individual sectionsreduces when length L between free ends is leasthan 20 dkmeters. A reduction factor K to beapplied to the net pressure coefficient in thesecases is given by figure 25 in terms of the ratioLIB. In the case of sections cantilevered fmm theground or another plane surface, such as a roof,the length L should be taken as twice theprotruding length. For sections spanning betweentwo planes L should be taken as infbrite (K = 1).

2.7.4 Lattices and unclsd building franrea

2.7.4.1 Conaer’vativeestimates of the loading onopen lattices can be determined by summing theloads on individual members using 2.7.1 to 2.7.3.The length L between free ends should be taken asthe length of each element, i.e. the length betweennodes of the lattice. When the lattice is dense orshielded, as with multiple lattices frames, thedegee of conservatism can be large.

2.7.4.2 I.mads on unclad building frames camrotexceed the loads on the fully clad building, exceptwhen the building is very long and the wind isskewed about O - 30° to the long axis. Asimplified method of calculating the wind loads onunclad building frames which accounts properly forthe shielding effects is given in reference [71, basedon the full method give; in reference [6].

Y

1.1

1

0.9

0.8

0.7

0.6

0.5

0.4

,lx ! , 1 1 1 1,: > [ , ,&tlarp-efl!yd/\/ * I

I , ! [ ,L-,’ , , . , , !,

t

,, )(,1,,!, !’1 ,,, ,,!I , ,,1 , I \ , I ,

, ) [ , , I \ [ , I ,1 [ ,, 1 1 ,, I , ! , I

1 1 1 1 , 1 I 1{1 t , I , , ,, 1 I 1 I , I , J0.1 1 10 10C

Ratio of length and breadth, L/B

I Figure 25. Reduction factor for length of elements

41

BS6399:RU%2 :1995 Section 2

2.7.5 Free-standing wafls and parapets

2.7.5.1 Values of net pressure coefficients C for“\free-standing walls and parapets, with or wlt out

return comers, are given irr table 21 appropriate tothe zones shown irr figure 26 for two values ofsolidity. Solidity ( = 1 refers to solid walk, while( = 0.8 refers to walls which are 80 % solid and20 % open.

2.7.5.2 The high values near the free end orreturn comers of solid walls (zones A and B) occurwhen the wind is blowing at 0 = 45° onto thatend. Moderate porosity in this region, i.e. solidlty0:eOD8, reduces these high loads to the vafues in

2.7.5.3 Interpolation for solidity may be used inthe range 0.8 < ~ < 1. For porous walls and fenceswith solidity less than 0.8, coefficients shoufd bederived as for plane lattice frames (ace 2.7.4).

2.7.5.4 When there are other walls or fencesupwind that are equal in height or taller than thewall or fence height h an additional shelter factorcan be used with the net pressure coefficierrta forboundary walk and lattice fences. The degree ofthe shelter depends on the spacing between thewalls or fences and the solidity < of the upwind(sheltering) wall or fence. Values of shelter factorto reduce the net pressure coefficient are plottedin f@ure 27. Shelter remains sigrr~lcant up tospacin& of 20 wall beighta. At very close spacingsthe net pressure coefficient on the downwind(sheltered) wall can be zero or can rcveme in sigrr.A mirrirrrumlimit to the shelter factor of 0.3 hasbeen set to cover this caae safely.

Table 21. Net pressure coefficients Cp for free-standing WdfS

aoudity Wrdrs ZOn.sA B c D

(=1 Without return comers 3.4 2.1 1,7 1.2

With return comers 2.1 1.8 1.4 1.2

c = 0.8 AU 1.2 1.2 1.2 1.2

Wind

+ 1<-o.3h l<- 2h 1<-4h I

B c DjJ,

h=Hr

7// ///////////////// ///////////////////

Comer or fraa and

a) Key to zones

-x

Plan> hi3

8 8 I_

Plan

L

AB C D AS C D

Without returncorner With returncornerb) Key to return comers

Ngure 26. Key for free-standing wafls

—

42

I


0.200.5 1 2 5 10 20 5(

Spacing X/h (log scale)

Figure 27. Shelter factor for fences

I

h

B14

* : ‘1

.—. .

Hr

I Figure 2S. Key for signboards

2.7.6 .%@bonrds the board, then it should be treated as a

The net prcs.sure coefficient Cp fOr si@bO~ds,free-standing waif in accordance with 2.7.5. The

separated from the ground by at least half theirnormal fome should be taken to act at the height

height as defined in figure 28, should be taken aaof the centre of the board, but the horizontal

Cp- 1.8. If the gap is lee-sthan half the height ofposition should be taken to vary between *0.25Bfrom the centre of the board.

43

1BS6399:Part 2:1995

Section 3. Directional method

3.1 Directional wind loads

3.1.1 Wind direction

3.1.1.1 The directional wind load method requiresknowledge of the wind dkection in two forms:

a) in degrees east of north, represented by p,used to determine wind speeds and dynamicpressure;

b) in degrees relative to normal to each buildingface (or around the periphery of a circular-planbuilding), represented by 8, used to determinethe pressure coefficients.

NC1l’E. In practice, it is usually most convenient to relate trothq and the various values of e for each face, 01,ez, 83,et., to asrandard value of O, mmqxmdimg m a primipal axis orreferemx face of the building. TM is illustrated in figure 29 forthe case of a rectangulaqian building.

3.1.2 Dynamic pressure

3.1.2.1 The value of the dynamic pressure q(in F@ of the directional method is given by

Q = 0.613Ve2 (16)

where

V, is the effective wind speed (in m/s) from3.2.3.1.

3.1.2.2 The reference value of dynamic pressurefor deriving pressure on external surfaces isdenoted by g, and the reference value for derivinginternal pressures by qi.

3.1.2.3 Values of dynamic pressure for variousvalues of wind speed are given in table 2.

3.1.3 Wind load

3.1.3.1 Directional suflace pressures..

3.1.3.1.1 The pressure acting on the externalsurface of a building, p,, is given by

Pe = %Cpe (17)

where

is the dynamic pressure (3. 1.2.2) from theeffective wind speed in wind direction p forthe external surface defined in 3. 1.2;

is the external pressure coefficient for thebuildhg surface in wind direction .9given in3.3.

3.1.3.1.2 The pressure acting on the internalsurface of a building, pi, is given by

pi =

where

qi

Cpl

qicpi (18)

is the dynamic pressure (3.1.2.2) from theeffective wind speed in wind direction p forthe intemaJ surface defined in 3. 1.2;

is the internal pressure coefficient for thebuilding in wind direction Ogiven in 3.3.5.

3.1.3.1.3 The net pressure acting across a surfacep is given by the foUowing.

a) For enclosed build@s

P= P,– P, (19)

where

Ae3=li30”-e

Ar702=90 ”-0

e4=90”+e

d

I Figure 29. Wind directiom for a rectangular-plan buifding

*m,

■Section 3 BS6399:Part 2:1995

p, is the external pressure given in 3.1.3. L 1;

P, is the internal pressure given in 3.1.3.1.2.

b) For canopies or building elements

P = %CP (20)

where

%

co

is the dynmrric pressure from theeffective wind speed for the canopysurface or element defined in 3.1.2;

is the net pressure coefficient for theelement given in 2.7.

3.1.3.2 Directional suflace bad-s

The net wind load P on a building surface orelement is given by

P=PA (21)

where

P is the net pressure across the surface;

A is the loaded mea.

3.1.3.3 Dinxtional ouemll lads

3.1.3.3.1 The overall load P on a building maybetaken as the vectorial sum of the loads onindividual surfaces, multiplied by (1 + Cr) toaccount for mildly dynamic response. However,since peak loads on each face of buildings do notact simultaneously, the resulting summation wouldbe conservative.

3.1.3.3.2 Accordk@y, the ovendl load on abuilding of arbkrary shape may be represented bythe csaes shown in figure 30 hr which allwindward-facing walls or mof faces are categorizedas ‘front’ and all leewan-facing walls or roof facesas ‘rear’, when the overall load in the winddifection, ~ may be taken as

P -0.85 [X(Pfmnt C0Sr9) -

z(Pmm CoSe)] (1 + c,) (22)

where

P~mnt is the norizontai component of netwind load acting on windward-facingWSk and roofs;

Prear is the horizontal component of netwind load acting on leewami-fachgwaifs and roof%

e is the angfe of the wind frum normalto the WSU or to the roof in thehorizontal plane;

c, is the dynamic augmentation factorfrom 1.6.1.

NOTE 1. The factor 0.85 accounts for the non-simultaneousactionof wind pressures.

N(YI!3 2. The horizontal component of the net wind load foreach loaded area k resolved into the wind dkction bymultiplying with the appropriate value of cm 6 before beingsummed

For buildings with flat roofs, or where thecontribution to the horizontal loads from the roof isinsi~lcant, the oversll load in the wind directionP may be taken, without siwlcant loss ofaccuracy, as

P = 0.85 q, [Z(cw,fm”t ACOS20-

~(cw,-ear A cOs@] (1 + G) (23)

where

Cw, fm”t

cpe,rear

is the pressure coefficient forwindward walls in the standardmethod from table 5;

is the pressure coefficient for leewardwalls in the standard method fmmtable 5;

NOTE 3. Equation 23 implies that the pmiti.e pressure actingo“ each windward-facing wail reduces with wind angle normalto tie wall in proportion m cm 0, whereas the negativepressure acting 0. leeward-facing walls is taken as consfamwith wind angle. Face loads are then resolved vecbmially to3ive the OVeI’dl load in the wind direction. Walls ali~ed exactlyparallel to the wind give no resolved component in the winddir.xtion. fn the case of rectangular buildings, the Pmedure@v= the exact result of the orthogonal cases in 2.1.3.6 of thesfandard methcd at the wind directions O - O” and 8 - 90”and very close to the combination of orthogonal loads case in2.1.3.6 of the sfandard metkd at the wind direction 8 - 45”.

3.1.3.3.3 In the case of re-entrant comem andrecessed bays, (see 3.3.1.5 and 3.3. 1.6), theboundary of the ‘wedge’ should be taken as a solidsurface normsl to the flow (cosz@ = 1) as indicatedin figure 30b.

3.1.3.4 Directional jkictional dmg component

Itisrecommended in 3.3.1.9, 3.3.2.8, 3.3.3.9 and3.3.4.3 that frictional forces on long walls androofs are determined in addition to the forcesgenerated by normal preesures. When determiningoverall forws on the building, the contribution offrictional fomes should be taken to act in the windd~ction and added to the norrnsl pressure loadgiven by R

3.1.3.5 Directional cladding loada

3.1.3.5.1 A simp~lcation of the full dkectionalmethud which leads to fewer calculations may beused to determine directional cladding loads. Thebasis of the simplification is to calculate allexternal surface pressures corresponding to anominal diagonal dimension a = 5 m, and then toadjust these pressures for the actual diagonal sizeof cladding element using the size effect factor ofthe standard method C= gNen in figure 4.


w

(3A

Smallaatenclosing/7 wind direction

rectangle

a) Generalcasefor arbitrary shaped b.ddmg

b) Building with re-entmnt corner (see figure 33)

Figure 30. Ksy to overall load P

3.1.3.5.2 For this method the expression for the 3.2 Directional wind speedsdirectional external surface pressure Pe givenbv 3.1.4.1.1 becomes 3.2.1 Baaic wind speed

P. = 93cpefZ (24)

where

% is directly equivalent to the dynamicpressure of the standard method but isdetermined from the equivalent effectivewind speed V_ of the directional method for

a Wst peak factor (see 3.2.3.3) of9t = 3.44, corresponding to the nominaldiagonal dimension a = 5 m,

The expression for the directional internal surfacepressure p, given in 3.1.3.1.2 remains unchanged.

The geogmphlcal variation of basic wind speed Vbshould be obtained directly fmm figure 6.NIYCE. ‘l’be method used to derive the basic wind speed fromtbe meteomlo@cal data is desm’ibed in annex B,

3.2.2 Site wind speed

The site wind speed V, should be calculated fmmequation 8, following the procedure given in 2.2.2,except for the determination of the altitudefactor Sa.NU1’E. 1. tbe directional method, topographic effects aredetermined separately from altitude effects

.

mSection 3 BS6399:Part2:l!W5

When topography is not to be considered, thealtitude factor S= should be determined from

sa = 1 + O.oolzts (25)

where

As is the site altitude (in metres above meansea level).

When topo@aphy is to be considered, the altitudefactor Sa should be determined from

s. = 1 + &@)lLtT (26)

where

ztT k the altitude of the base of the topography(in metres above mean sea level).

3.2.3 ~ectiue wind speed

3.2.3.1 The effective wind speed V. for each winddirection for a building on a particular site shouldbe determined from

v, = v, x s~ (27)

where

v, is the site wind speed for each winddmction given by 3.2.2;

s~ is the terrain and buifdhg factoraPPMPfiate to the wind direction kingconsdered, determined from 3.2.3.2.2 forsites in country terrain and from 3.2.3.2.3for sites in town te-.

The effective wind speed should be crdculated atthe effective height He, determined from thereference height Hr in accordance with 1.7.3.Reference heighta H, are defined with the pressurecoefficient data for each form of buifdirrg.

For brdldm& whose height His greater than thecmsawind breadth B in the wind direction kingconsidered, some reduction in lateral loads may beobtained by dlvidmg the building into a number ofparts in accordance with 2.2.3.

3.2.3.2 Terrain and building factor

3.2.3.2.1 General

The terrain and building factor & should be usedto modtiy the site wind speed to take account ofthe effective height He of the boildhrg or part, thedimensions of the building, the local topographyand the terrain upwind of the site. It also modifiesthe hourly mean site wind speed to an effectivegust wind speed.

The te- and building factor Sb should bedetermined from 3.2.3.2.2 for sites in countryterrain and from 3.2.3.2.3 for sites in town terrain,taking the following into account:

a) the effective height He determined inaccordance with 1.7.3 from the reference heightH, defined for the form of the building or part(see 2.2.3.2).

b) the distance of the site from the sea in thewind direction being considered;

c) for sites in town terrain, the distance of thesite fmm the edge of the town in the winddirection being considered;

d) the largest diagonal a of the area over whichload sharing takes place as defined in figure 5.

Load effects, e.g. bending moments and shearforces, at any level in a building should be basedon the diagonal dlmerrsion of the loaded area abovethe level being considered, as illustrated inf~re 5C.

3.2.3.2.2 Sites in counlry terrain

In country terrain Sb should be determined from

& = S.(1 + @t X SJ + Sh] (28)

where

SC is the fetch factor obtained from table 22;

s~ is the turbulence factor obtained fromtable 22;

9t is the gust peak factor (see 3.2.3.3);

Sh is the topographic increment (see 3.2.3.4).

BS 6399: Fart 2:1995 Section 3

‘lhble 22. Factors SCand St

Effective height Factor Upwind distance from sea to siteHe

km

m so. 1 0.3 1.0 3.0 10 30 2Km

52 SC 0.873 0.840 0.812 0.792 0.774 0.761 0.723

St 0,203 0.215 0.215 0.215 0.215 0.215 0.215

5 SC 1.06 1.02 0.990 0.966 0.944 0.928 0.882

st 0.161 0.179 0.192 0.192 0,192 0.192 0.192

10 SC 1.21 1.17 1.13 1.10 1.07 1.06 1.00

St 0.137 0.154 0.169 0.175 0.178 0.178 0.178

15 s, 1.28 1.25 1.21 1.18 1.15 1.13 1.08

s~ 0.131 0.141 0.156 0.167 0.171 0.171 “- 0.171

20 s. 1.32 1.31 1.27 1.23 1.21 1.19 1,13

s~ 0.127 0.132 0.145 0.157 0.163 0.164 0.166

30 SC 1.39 1.39 1.35 1.31 1.28 1.26 1.20

St 0.120 0,122 0.132 0.145 0.155 0.159 0.159

50 s= 1.47 1.47 1.46 1.42 1.39 1.36 1.30

St 0.112 0.113 0.117 0.125 0.135 0.145 0.149

100 s. 1.59 1.59 1.59 1.57 1.54 1.51 1.43

St 0.097 0.100 0.100 0.100 0.110 0.120 0.132

200 SC 1.74 1.74 1,74 1.73 1.70 1.67 1.59

s~ 0.75 0.75 0.75 0.078 0.083 0.093 0.111

300 SC 1.84 1.64 1.84 1.83 1.82 1.78 “-” 1.70

St 0.065 0.065 0.065 0.067 0.068 0.80 0.098

NUI’E1. Interpolation may tm used.NOTE 2. The fmres in this table have been derived from reference [8].

“o

mSection 3 BS6399:Part 2:1995

3.2.3 .2.3 Sites in town tarain

In town terrain Sb should be determined from

s~ = SCT. [1+ @~ X St X TJ + Sh] (29)

where

Sc

T,

s~

Tt

9t

s~

is the fetch factor obtained from table 22;

is the fetch adjustment factor obtained fromtable 23;

is the turbulence factor obtained fromtable 22;

is the turbulence a@ustment factorobtained fmm table 23;

is the gust peak factor (see 3.2.3.3);

is the topographic increment (see 3.2.3.4).

3.2.3.3 Gust peak factor

3.2.3.3.1 The gust IY?ak factor gt used in thecalculation of the terrain and building factor Sballows for the influence of the dnenaioms of thebuilding on the maximum gust speed. Thedimension of the building which determines thevalue of the gust peak factor is the length of thedlWOnd a of the loaded area over which Ioadsharing takes place (see figure 5). Separate valuesshould be used depending upon whether windloads are being calculated for the whole buifdlng,portions of the buifding or individual components

3.2.3.3.2 For external pressures on wholebuildings and portions of buildings, the values of gtshould be obtained from table 24 using theeffective height He of the top of the building andthe diagonal of the loaded area, a,

lhble 23. .4r@stment factors TCarrd Tt for sites in town terrain

Effective height He FhctOr Upwind disfance from edge of row. to site 1

km

m o.I 0.3 1.0 3.0 10 230

=2 T. 0.695 0.653 0.619 0.596 0.576 0.562

Tt 1.92 1.93 1.93 1.93 1.93 1.93

5 TC 0.846 0.795 0.754 0.725 0.701 0.684

Tt 1.41 1.60 1.63 1.63 1.63 1.63

10 T. 0,929 0.873 0.828 0.796 0.770 0.751

Tt 1.16 1.34 1.50 1.52 1.52 1.52

15 T. 0.969 0.911 0.863 0.831 0.803 0.783

Tt 1.04 1.22 1.38 1.47 1.47 1.47

20 T, 0.984 0.935 0.886 0,853 0.824 0.804

Tt 1.00 1.17 1.35 1.44 1.45 1.45

30 T, 0.984 0.965 0.915 0.880 0.851 0.830

T, 1.00 1.06 1.21 1.33 1.43 1.43

50 T. 0.96’4 0.984 0.947 0.912 0.881 0.859

Tt 1.00 1.00 1.12 1.24 1.38 1.42

100 TC 0.984 0.984 0.984 0.948 0.917 0.894

Tt ‘ 1.00 1.00 1.00 1.14 1.28 1.38

200 Tc 0.984 0.984 0.984 0.980 0.947 0.924

Tt 1.00 1.00 100 1.07 1,19 1.31

300 T= 0.984 0.984 0.984 0.984 0.964 0.940

Tt 1.00 l.oil 1.IXI 1.04 1.14 1.24

NUTE 1. Interpolation may be wed,NOI’E 2. For sites in towns less than 0.1 km from the edge in the upwind direction the site should be assumed to be in openc@u~tv re~n (=. 3.~.3.2.2).NCllT ?. ‘The figures i“ this table have been derived from reference [8].


‘Ikble 24. Gust neak factor a.

Effective height Diagonaf dimension a.

Hem

m <5 10 20 40 100 Zwl am

510 3.44 3.19 2.90 2.62 2.23 1.97 1.77

20 3.44 3.24 2.98 2.69 2,27 2.04 1.83

50 3.44 3.30 3.02 2.75 2.36 2.10 1.89

100 3.44 3.33 3.07 2.79 2.40 2.14 1.95

200 3.44 3.40 3.13 2.84 2.47 2.18 2.01

300 3.44 3.44 3.17 2.86 2.49 2.21 2.04

NCTE Interpolationmaybe used.

3.2.3.3.3 When asseasing the loads on individual 3.2.3.4.3 Depending on whether the topographicstmctural components, cladding unita and their increment S~ is uacd, care should be taken toftings a vafue of gt = 3.44 should be taken, unless ensure that the altitude factor S=, used tothere is adequate load sharing capacity to justify determine the site wind speed V,, is derived fromthe use of a lower value (i.e. a diagonal length a the appropriate definition of altitude A ~ or A~greater than 5 m) in which caae table 24 should be in 3.2.2.used to obtain the appropriate value for the gustpeak factor gt. ‘f’his value of gt = 3.44 should alsobe taken when using the previsions of 3.1.3.5.2 or3.4.2 in conjunction with the size effect factor C.of the standad method.

3.2.3.3.4 For internal pressures, the values of g~should be obtained from table 24 using theeffective height He of the top of the building orpart of the building containing the relevant storey,and the diagonal of the loaded area a is determinedfrom the volume of the building, storey or room asdefined in 2.6.Nf7fE The derivation of the gust peak factor is described inannex F, which also includes mathematical equations to derive9,. Note that the size effect factor of the sfandard method C.,@ven in fitwe 4, W= dete~ined fmm g, - 3.44 hy themethod give” in 3.2.3. Z and 3. Z.3.3 for a “umber of typical siteexposures.

3.2.3.4 lbpogmphic increment

3.2.3.4.1 The topographic increment S’hshould beused to modify the terrain and building factor toallow for local topo~phical features such as KI1ls,valleys, cliffs, escarpments or ridges which cansignificantly affect the wind speed in their vicinity.Values of Sh should be derived for each winddirection cofraidercd and used in conjunction withthe corresponding direction factor Sd.

3.2.3.4.2 Where the average slope of the grounddoes not exceed 0.05 within a kilometre radius ofthe site the terrain should be taken as level and thetopographic increment Sh should be taken as zero.When tbe topography is defined as not significantby the simple criteria in figure 7, the terrain maybe taken as level and the topographic increment Shmay be taken as zero, but implementation of thetopogmphlc increment will produce a moreaccurate assessment.

3.2.3.4.4 In the vicinity of local topographicfeatures the topographic increment .9his a functionof the upwind slope and the position of the siterelative to the summit or crest. It should be notedthat Sh will vary with height above ground level,from maximum near to the ground reducing to zeroat higher levels, and with position from the crest,from m-urn near the crest reducing to zerodktant from the crest.

3.2.3.4.5 Values of topographic increment arecotilned to the range O < Sh < 0.6 and apply onlyto the simple topographic features defined infigure 8. fn situations of multiple Km or ridges,th~ procedure is appropriate when applied to thesingle bill or ridge on which the site is situated.

3.2.3.4.6 In certain steep-sided enclosed valleyswind speeds may be leas than in level terrain.Before any reduction in wind speeds is consideredspecialist advice should be sought. For sites incomplex topography speciahst advice should besought (see references [5] to [8]) or a maximumvalue of Sh = 0.6 used.NUIE Values of Sh may be derived from model-scale orfull. scale measurements or from numerical simulations.

3.2.3.4.7 In undulating terrain it is often notpossible to decide whether the local topography ofthe site is significant in terms of wind flow. Insuch cases the average level of the terrain upwindof the site for a distance of 2 km should be takenas the baae level from which to as-seasthe height Zand the upwind slope Vu of the feature.

3.2.3.4.8 Values of the topographic increment Shshould be obtained from table 25 using theappropriate values for the upwind slope Vu, theeffective length Le and the factors which shouldbe determined from figure 9 for hills and ridges orfigure 10 for cliffs and escarpments.

!=.n

mSection 3 BS6399:E%Z %2:1995

I‘fkble 25. Values of L, snd .Sh

slope Shfdrow steep(W = Z/Lu) (0.05< vu > 0.3) ( 1#~> 0.3)

Effective I L. = LIT IL. = ZIO.3length

‘f@graphic s~ = 2.ol/@ .5&= 0.6sincrement

3.2.3.4.9 In cases transitional between hills andridges in figurY 8a and cliffs and escarpments infigure 8b, i.e. when the downwind slope length LD

is much longer than the upwind slope length Lu, itmay be difficult to decide which model is the moreaPPmPf’iate. In this case, a value ofs may bederived from both figures 9 and 10 and the smallervalue used.

3.2.3.4.10 At some distance from a topographicfeature the effect of local topography is replacedby the general effect of altitude. In many cases, itwill not be clear whether topogmphy or altitudedominates. As each is assessed differently by thedirectional method, it is necessary to calcufate theeffective wind speed Ve twice, as follows, and totake the larger value of V, obtained:

with topo.gaphy, using Sa for the terrainbase altitude and the appropriate valueof Sh; and

without topography, using Sa for the sitealtitude and Sh = O.

‘f’hii procedure is recommended to determine thelimit of topographic influence downwind of a cliffor escarpment.

3.2.3.4.11 Where the downwind slope of a hfl orridge is greater than wfI = 0.3 there will be largeregions of reduced acceleration or even shelter andit is not possible to give precise design roles forthese circumstances. Values ofs from figure 9should be used as upper bound values.

3.3 Directional pressure coefficients

3.3.1 External pressure coeffkients Cm forWttfk of buildings

3.3.1.1 Vertical waifs of rectangular-planbrfildi..rgs

3.3.1.1.1 Pressure coefficients for walls ofrectangular-plan buildin~ are given in table 26 forthe zones as defined in figure 31. Zones A and Bshould be defined, measuring their width from theupwind edge of the wall. If zones A and B do notoccupy the whole of the wslf, zone D should bedefined from the downwind edge of the wall. Ifzone D does not occupy the remainder of the face,zone C is then defined as the remainder of the facebetween zones B and D.

3.3.1.1.2 The wind direction Ois defined as theangle of the wind from normal to the wall beingconsidered (see 3.1. 1). The reference height If, isthe height above ground of the top of the wall,including any parapet, or the top of the Part if thebuilding has been divided into parts in accordancewith 2.2.3. The crosswind breadth B and inwinddepth D are defined in figure 2. The scaling lengthb for defining the zones is given by b = B orb = 2H, whichever is the smaller.

3.3.1.1.3 Where walls of two buildin@ face eachother and the gap between them is less than b andgreater than b/4some funneling of the flow willoccur between the build@s. The maximum effectoccurs at a spacing of b/2 and is maintained over arange of wind angles *45° from normal to the axisof the gap. In this circumstance, the followingapply.

a) Over the range of wind angle– 45° < b’ < + 45° the windward-facing wall issheltered by the leeward-facing wall of the otherbuilding. The positive pressures in table 26 applywhere the wafl is directly exposed to the windbut gjve conservative values for the whole wall.

b) Over the ranges of wind angle-135° < @ < –45° and +45° c 6’ c +135°funneling occurs. Vshres for zone A at 6’ = * 90°should be multiplied by 1.2. Values for zones Bate= *90° should be multiplied by 1.1 andapplied to aU Parts of zones B to D which facethe other building over these mnges of windangfe. These ‘ funnellhrg factors’ give themaximum effect which corresponds to a gapwidth of b/2 and interpolation is permitted in the~ge of gaP widths from b14 to b (see 2.4.1.4).c) Over the ranges of wind angfe-180 °<@< –1350and +1350 <tr <+1800the values of pressure coefficient remain thesame as given in table 26.

3.3.1.2 Vertical waifs qfpol~gonal-planbuildings

3.3.1.2.1 The pressure coefficients given intable 26 should also be used for the vertical wallsof po! ygonal-plan buildings, In such cases therema~ be any number of faces (greater than or equalto 3). The wind dkection, principal dimensions andscaling length remain as defined in 3.3. L 1.2.NUTE.:nstead of calculating the crosswind breadtb B midinwind depth D for the complex building plan, these dimensionsmay be determined from the smallest recta”gJe or circle whichencloses the plan shape of the building.

3.3.1.2.2 Provided the length of the adjacentupwind face is gzeater than b/5 the peak suctioncoefficients for zone A given in table 26 can bereduced by multiplying them by the reductionfactor appropriate to the adjacent corner angle Bgiven in table 27.NCflT A recta”@w comer b - 90° gjves th, highest locals“ctio” in zone A.

BS6399:l%rt 2:1995 Section 3

Ibble 26. External PIWfnd direction O

1“

*15°

*300

*45°

*60°

*75°

*90°

i 105°

* 1200

*135°

* 150”

* 165°

* 180°

NOTE 1. Interpolation mqNc71z 2. When the result

ssure coefficients CP, for vertictd wa

D/H s 1

k

+0.70

+0.77

+ 0,80

+0.79

+ 0.24

-1.10

-1,30

-0.80

-0.63

-0.50

-0.34

-0.30

-0.34

B

+ 0,83

+0.88

+0.80

+0.69

+0.51

-0.73

-0.80

-0.73

-0.63

-0.50

-0.34

-0.30

-0.24

c

+0.86

+0.80

+0.71

+ 0.54

+0.40

+0.23

-0.42

-0.48

-0.45

-0.40

-0.26

-0.23

–0.24

D

+ 0.83

+0.68

+0,49

+ 0.34

+ 0.26

+0.08

*0.20

-0.26

-0.29

-0.33

-0.32

-0.28

-0.24

Jof rectangular-plan buildings

r)/H> 4

A

+0.50

+ 0.55

+0.57

+ 0.56

*0.20

-1.10

– 1.30

-0.80

-0.63

-0.50

-0.34

-0.20

-0.17

B

+ 0.59

+ 0.62

+0.57

+0.49

+0.36

–0.73

-0.80

-0.73

-0.63

-0.50

-0.34

-0.17

-0.15

l< D/H<? used between @ven W d directions and for D/fl n the rangenterpolatiw between positive a“d negative values s in the range – 0.2 <

wefficient should b+ taken as Cp . i 0.2 and both possible values used.

c

+0.61

+0.57

+0,51

+ 0.38

+ 0.29

+ 0.23

-0.42

-0.48

-0.45

-0.40:.

-0.26 ~~

-0.15

-0.15

>

+0.59

+0.49

+0,35

+0.24

*0.20

*0.20

*0.20

-0.26

-0.29

-0.33

-0.32

-0.18

-0.15

, < +0.2, the

-TJ51‘&” I

IFigure 31. Key for vertical walls of buildings

~

lhble 27. Reduction factors for zone A onvertical WSIIS of polygonal-plan buildings

“ANQTE. Interpolation is allowed m the range 60° <8 < 150°.

..3

=Section 3 BS6399:Part 2:1995

3.3.1.2.3 Whenever the value of pressurecoefficient for peak suction in zones B and C aremore negative than the reduced pressurecoefficient in zone A, the reduced zone A valuesshould be applied to these zones alao.

3.3.1.3 %angular gable rods

3.3.1.3.1 Preaaure coefficients for the triangulargable wdl.s formed by steep duopitch roofs ornon-vertical walls (A-frame buildinga) in therange 30° s a s 75° are given in table 28 forzones H to K as defined in figure 32. For gablewalls formed by duopitch roofs of pitches less thana = 30° or by non-vertical walk of pitches greatertham a = 75° (nearly vertical) the general methodgiven in 3.3. L 1 should be used.

3.3.1.3.2 The wirrd direction 6 is defined as theangle of the wind from normal to the wall beingconsidered (see 3.1. 1). The reference height H, isthe height of the peak of the gable.

3.3.1.3.3 Where gables of two buildhrgs face eachother and the gap between them is leas than bsome funneling of the flow will occur between thebuildings. The maximum effect occum at a spacingof b/2and is maintained over a range of windangl~ *45° frum psrallel to the axis of the gap. Inthis crmumstance, the folfowing apply.

a) Over the range of wind angle-45° <8 < + 45° the windward-facing gable issheltered by the leeward-facing gable of theouter buifding. The positive pressures in table 28applY where the gable is dhectly exposed to thewind but give conservative values for the wholegable.

b) Over the ranges of wind angle-135” < e < -45° and +45”< e < +135”funneling occurs. Values for zone H at 8 = *90°should be multiplied by 1.2. Values for zone I ate= +90° should be multiplied by 1.1 and

applied to all ParW of zones I to K which facethe other building over these rsnges of windangle. These furmelling factors give themaximum effect which corresponds to a gap

width of b/2snd interpolation is permitted in themge of gap Widtk from b/4 to b (see 2.4.1.4).c) Over the ranges of wind angle-180” < e < – 135”and + 135° < .9 < + 180° the vrdues of pressurecoefficient remain the asme as given in table 28.

3.3.1.4 Non-uertical wrdf.s

3.3.1.4.1 Pressure coefficients forwindward-facing non-vertical wslls irr the rangeb’= *90° are given in table 29 for zones A to Ddefined in figure 31. Fur all other wind angles,pressures on non-vertical wallx should be taken asthe same as for vertical walls

3.3.1.4.2 The wind direction # is defined as thea@e Of the wind from normal to the wall beingconsidered (ace 3.1. 1) and is lirrdted here to therange O = *90°. The pitch angle a is defined asthe angle fmm horizontal, hence a = 90° forvertical walls. The reference height If, is the heightabove ground of the top of the wall.NUIX. The pressure coefficients for non-vetiical walls intable 29 are essentially identical to the pressure cc.efficients forsteep pitched mfs in 3.3.3, allowing for the differences inde ftition of mne% therefore at large pitch angles (a > 454)the distinction between wall’ and rc@ is largely irrelevant.However, stee~ pitched surfaces which meet along the top edgeto form a ridge, e.g. A-frame’huildin.gs,arebetterinterpretedas.duopifchrwfs’, fallingundertheprovisionsof 3.3.3.

3.3.1.5 Buildings with re-entmnt comers

3.3.1.5.1 The prucedure given in 3.3.1.1 should beused for vertical walls of buildhgs containingre-entrarrt comers, such as L, T, X and Y shapedbuildings in plan. Iterns a) to e) define the zones,using figure 33 aa reference.

a) For the faces of the upwirrd wing, thecruaswind breadth and the height of the wingshould be used to determine the scalingp-eter b. For all other wings the overallcrosswind breadth of the building should beused.

NOTE. h!stead of calculating the crosswind breadth B andimvtnd depth D for the complex building plan, these dimensionsmay be detemd”ed from the smallest rectangle or circle whichencloses the plan shape of the upwind wingor of the wholeb“ild~, respectively.

b) For faces with two external comers, zones A,B, C arrd D are defined in accordance with3.3.1.1.

c) For faces with one upwind (external) comersrrd one downwind re-entrant comer, zones A, Band C are defined (zone D does not apply).

d) For faces with one upwind m-entrant comerand one downwind external comer, zones Cand D arc defined (zones A and B do not apply).

e) In reentrant comers that face directly intothe wind a wedge that extends from the internalcomer with the face of the wedge normal to thewind direction is defined. The width of thewedge w should bs taken as w = b or w = thewidth of the wedge Iirrrited by an extemaf comer(marked limit of wedge), wh]chever is thesmafler.

3.3.1.5.2 The pressure coefficients for zonesdefined in 3.3.1.5.1 should be obtained fromtable 26 appropriate to the wind angle f?measuredfrum normal to each wsll.

The pressure coefficients for the zones that liewithin the defined wedge should be taken forzone C at O = 0° from table 26.


Wind

-+? AI

HJ

K

H,

A B c D

I

+//// //. ////,, ,/////,, ///////,//////,///H

@ Duopitch roof

,,:tijm+al

b) Monopitcb roof

Figure 32. Keytovertical gable wzdls

Ihble 28. Extetipressure coefficients Cwforvetiicd gable wdlsa~acent tenon-verticalwallsmd roofs

W,nd direction o Pitch of adjacent mdlorroof 31Y s a s 75e

D/H s 1 DIH z 4

H I J K H 1 J K

1“ +0,25 + 0.80 + 0.80 +0.25 +0. 18 +0.57 + 0.57 +0.18

*30” +0.70 + 0.75 +0.50 +0.2 + 0.50 +0,54 + 0.36 *0.20

f60° + 0.50 + 0.40 *0.2 -0.25 + 0.36 + 0.29 *0.20 *0.20

*90° -1.10 -0.80 -0.70 -0.60 -1.10 -0.80 -0.70 -0.60

*lZoo -1.30 -0.75 -0.60 -0.50 – 1.30 -0.75 -0.60 -0.50

* 1500 -0.30 -0.25 -0.25 -0.25 –0.21 -0.18 -0.18 -0.18

i180° -0.25 -0.25 -0.25 -0.25 -0.18 -0.18 -0.18 -0.18

NOIT 1.lnte~latio”mayku~d~twwn givenwi”d directiom.mdforD/lfintbera”ge 1 < D/f{ <4.NUI’E2, Wbe"rhe msultof intemlating ktween~sitive andnegative values isintbemnge -0.2 < Cm < +(),2, thecoefficient should be take” as Cy . iO.2a.d Lwjtbpossiblevalues”$ed.

❑Section 3 BS 6399: Part 2:1995

m

BS6399:Fart2 :1995 Section 3

ABCD

61

i

AUpwind :

WindB

wing for

wind

Limkof wedgec direction c

.-.~--”=b-”-

Shown

~ y~) (01< ‘o)~.-if”- ....-:,.:-,-.=,.,..,,,.., CD,..

A A

B B

c c

D D

AB c c cc D

D D

ABCD

Figure 33. Key for walls of buildings with re-entrantcomers

3.3.1.6 Buildings with recessed ba~s 3.3.1.6.2 Where the recessed bay is limited in

3.3.1.6.1 Buildings where there are recessedheight byafloororasoffit, thepres.sure in the

openings, such as porches arrdbalconies orrecess should be taken to act on the floor and soff]t

between thewinmo fabuildln~, should retreatedin addition to the walls.

as follows, using &ure 34 as relerence.

a) The p-eter b should be determined inaccordance with 3.3.1.1.2

NOTE.Inste&of&culating thecm=rnnd b~adthBandinwind depth Dforthe cmnplex building plan, these dimensionsmay bedetemdned from the smallest recfangle m’ circle whichenclosed the relevant plan shaw defined in itemsb) ore).

b) IfG < b/2therecesa iscategorized aa narrow.The wall in which the recess should be assessedas if the recess d]d not exist, as shown infigure 34a. ‘fhepressur ecoefficientcorresponding to the position of the recessshould be applied to all the walls inside therecess. Forpeak cladding loads at the mouth ofthe narrow recess, additional locti zones A at theexternal edge of the walls of the recess should bedefined aaindkatedinfigurc 34a. The relevantpku-shape for calculating b is that of the wholebuilding.

c) If G > b/2 the recess is categorized as wide,The procedure in 3.3.1.5 for buildings withre-entfant cornem should be applied as indicatedin figure 34b. The relevant plan-shape forcalculating b is that of any upwind wing, or ofthe whole building, respectively.

3.3.1.7 Buildings with internal welfs

3.3.1.7.1 For buildlngs with internal wells, thepressure coefficient for the external walls areunaffected by the well and should be derived as ifthe well d]d not exist.

3.3. L 7.2 Pressure within the well is dominated byflow over the roof and should be derived asfollows.

a) When the gap across the well G is smaller thanb/2 the pressure in the well is taken aa uniformand equal to the pressure on the roof containingthe well.

b) When G > b12the procedure for re-entmntcomem in 3.3.1.5 should be used.

3.3.1.8 Irrvgularfaccs and inset waifs

‘lb determine pressure coefficients for the irregularfaces of buildings with re-entrarrt comers inelevation (i. e. walls formed by more than onerectangle) the procedure given for the standardmethod in 2.4 should be used with dkectionalpressure coefficients obtained from table 26appropriate to the wind angle # from normal toeach face.

*Co

.

■Section 3 BS6399:Part 2:1995

D A c BA

< >

G < b12

\

%-

ev

a) Narrow recess

b) Wide recess

Figure 34. Key for wafls of buildings with recessedbays

3.3.1.9 FHction induced loads on uxdfaFriction forces should be determined for long wallswith D > b when the wind is parallel to the wall.The frictional drag coefficient should be assumedto act over all zone C and D of such walls, withvalues as given in table 6. The resulting frictionalforces should be applied in acconhwewith 3.1.3.4.

3.3.2 Extemaf pressure coefficients for flatroofs nf build@s

3.3.2. i Choice of method

3.3.2.! 1 A geneml methcd for deterrninhg thewind pressures on flat, or nearly flat roofs ofbuifdings with any arbitrary plan shape is given inthe fodowing section. l’hii general method alsoaccounts for the variations in high local suction

around the periphery of the roof caused by variouscommon forms of eaves detail.

3.3.2.1.2 A simpler method, restricted torectangular-plan buildings only, is given in 3.3.3.3,assuming the flat roof to be a monopitch roof withzero pitch angle. The general method should beused for afl roofs of pitch less than u = 50 onnon-rectangular plan buildings.

3.3.2.2 General method

3.3.2.2.1 The roof should be subdivided intosections by lines drawn in the wind directionthrough each upwind-facing comer.Zones of pressure coefficient are defined for eachsection from the upwind comer as given infigure 35. The shape of the roof in figure 35represents a typical arbitrary roof plan.

BS6399:I%rt 2:1995 Section 3

t eFigure 35. Keytogeneral method for ffat roofs

3.3.2.2.2 Thewind direction 8.isdefined as theangle of the wind from nornmlto the eaves of thesection of roof Ming considered, as defined infigure 35. Thereference height Hris the heightabove ground of the top of the roof. The crosswindbreadth B znd inwind depth D are defined infigure 2.NUTE.insteadofcalc.latingthecmsswindbreadthBandinwinddepthDfor thecomplexbuildingplanat every windangle, thedimensions may bedetemnined from thewnallestrectandeorcimle which encloses the pbin shape of thebuild,ng.

The scaling length b for defining the zones is givenby b= Borb= 2H, whichever is the smaller.

3.3.2.2.3 Application of the zones as defined infigure 35 should be repeated for every section ofthe mof until pressure coefficients for all zonesover the whole roof have been defined. Figure 36ashows the completed assignment for the arbitraryshape and wind direction used in figure 35.Figure 36b shows the zones for the same shapedroof but a different wind direction. The examplesin figure 36 cover most conditions likely to beencountered.

3.3.2.3 Ffat roofi with sharp eaves

External pressure coefficients for each zone of flatroofs with sharp eaves are given in table 30. Sharpeaves represent the most onerous loading condition(highest suction). Pressure coefficients for othercommon types of eaves are given in 3.3.2.4to 3.3.2.6.

3.3.2.4 Ffat roo~ with parapets

3.3.2.4.1 A pampet along any eaves or edge w’ilfreduce the pressure coefficients in zones A and Dimmediately adjacent to that eaves but thepressures in zones E, F and G will be unaffected.tie external pressure coefficients given in table 30for zones A to D for flat roofs with sharp eavesshould be multiplied by the appropriate reductionfactors given in table 31, dependent on the heightof the parapet h, az defined for the standardmethod in figure 17, and the eaves height H orcrosswind width B.

Nf7113. The reference height H, isthe height above ground ofthe top of the parapet.

3.3.2.4.2 I.aadlng of the parapet walls should bedetermined fmm 2.7.5.1 for free-standing parapetsand from 2.7.5.4 for downwind parapets

3.3.2.5 Ffat roo~ with curved eaves

For flat roofs with curved eaves, as defined for thestandard method in figure 17, the zones start fromthe edge of the flat part of the roof. Externalpressure coefficients for each zone are given intable 32 dependent on the mtio of the cornerradius r of the eaves to the scaling length b.

3.3.2.6 Ffat mop with mansard eaves

For flat roofs with mansard eaves, as defined forthe standard method in figure 17, the zones startfrom the edge of the flat part of the roof. Externalpressure coefficients for each zone are given intable 33 dependent on the pitch of the mansardeaves a.

❑Section 3 BS6399:l%t2 :1995

/’6a) Assignment of zones for arbitrary shape according to wind direction of figure 35

b) As.signme”t of zones for arbitrary shape accotilng to a different wind direction

Figure 36. Examples of zones of flat roof of arbitrary planshape

‘lhble 30. External pressure coefficients Cw for flat roofs with Sk eaves

~ial wind Zonedirection e A B c D E F G

o“ -1.47 -1.25 -1.15 -1.15 -0.69 –0.71 *0.20

+15° –1.68 – 1,47 -1.24 -1.14 -0.61 -0.70 *0,20

*30° -2.00 -1.70 -1.38 -1.03 -0.66 -0.67 *0,20

*450 -1.90 -1.49 -1.18 -0.86 -0.59

*60°

-0.54 *0.20

– 1.70 -1.24 –1.10 -0.64 -0.61 -0.42 *0,20

i75” -1.45 -0.85 -CI.69 -G.35 –0.61 -0.21 *0,20

t90° - i,43 -0.75 -0.52 -0.24 -0.62 *0.20 *0.20

NOTE1.IMerpdatio. mayheused.NOTE2. W!tereboil, positive and negative values are given buth values should be considered.

BS6299:Paxt 2:1995 Section 3

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

kwd wind FamPetheightratiohlbdirection O 0 0.05 0.10 20.20

0“ 1.00 I 0.76 I 0.67 I 0.56

hble 32. Extetivresswe coefficients CP, for flat roofs with cu~ed eaves

,aves radiusttie ./b

.05

1.10

,MO

LOCal winddirection .9

o“*15°

f30°

*450

i60°

*750

*90”

o“

*15°

*30”

*450

*60°

*75°

i90”

o“

* 15”

+30°

*45”

*60°

*75”

i-90°

brie

i

-0.81

-0.79

-0.66

-0.61

-0.66

-0.79

-0.81

-0.77

-0.64

-0.56

-0.49

-0.56

-0.64

–0.77

–0.51

-0.46

-0.40

-0.38

-0.40

-0.46

-0.51

B

-1.00

– 1.06

-0.97

-0.80

-0.64

-0.48

-0.48

-0.73

-0.65

-0.60

-0.51

-0.40

-0.39

-0.43

-0.54

-0.49

-0.43

-0.41

-0.38

-0.35

-0.40

-1.15

-1.16

-1.07

-0.92

-0.69

-0.53

-0.39

-0.79

-0.70

-0.62

–0.56

-0.43

-0.36

-0.37

–0.54

-0.52

-0.47

-0.43

-0.40

-0.31

–0.36

D

-1.26

-1.09

-1.06

-0.35

-0.62

-0.48

-0.29

-0.79

–0.69

-0.63

-0.58

-0.46

-0.36

-0.37

-0.56

–0.53

-0.51

-0.43

-0.38

-0.28

-0.23

-0.39

-0.37

-0.35

-0.35

-0.35

-0.37

-0.39

–0.30

-0.29

-0.29

–0.28

-0.29

-0.29

-0.30

-0.30

~0.28

-0.26

-0.26

-0.26

–0.28

-0,30

NOTE 1. Interpolation maybe usedNCITE2. Where bvthpmitive and negative val.es.aI? given botbval.es sho.ld reconsidered.

F

*0.20

-0.22

-0.29

-0.35

-0,38

-0.40

-0.43

-0.21

-0.22

-0.25

-0.28

-0.30

-0.30

–0.30

-0.21

-0.22

–0.25

-0.27

-0.29

-0.29

-0.30

:

*0.20

*0.20

*0.20

*0.20

*0.20

*0.20

*0.20

*0.20

*0.20

*0.20

*0,20

*0.20

*0,20

*0.20

*0.20

*0,20

*0.20

*0.20

*0.20

io.20

*0,20

*m*

■Section 3 BS6399:Fart 2:1995

hble 33. Externaf messure coefficients C.. for flat roofs with —d eaves

fansard pitch@e a

100

15”

;0”

{(JTE 1.InterpolariarE2. Fbra>fWrE 3. where b+

Local winddirection O

o“*150

*30”

i45°

+ 60°

*75°

*90Q

o“

*150

*30”

+45°

+60°

*75”

+90°00

*15°

*30”

i45°

*60°

k75”

*90°

tine

&

-0.93

-0.76

-0.66

-0,60

-0.66

-0.76

-0.93

-1.19

-1.10

-0.98

-0.87

-0.98

-1.10

–1.10

-1.27

-1.37

-1.32

-1.21

– 1.32

-1.37

-1.27

ud a-60

-0.98

-0.85

-0.73

-0.59

-0.40

-0.34

-0.39

-1.24

-1.22

-1.06

-0.89

-0.62

-0.50

–0,56

-1.27

-1.25

-1.22

–1.11

–0.81

-0.70

-0.69

may be usm a - 60’

=---

=J---0.75

-0.63

-0.42

-0.30

-0.30

– 1.29

-1.22

-1.05

–0.88

-0.64

-0.45

-0.41

-1,27

-1.27

-1.08

-0.97

-0.73

-0.54

-0.48

D

-0.98

-0.94

-0.88

-0.66

-0.36

-0.23

-0.22

– 1.34

-1.24

–1.05

-0.80

-0.34

-0.24

-0.21

-1.23

-1.17

-1.02

-0.77

-0.35

-0.23

-0.21

-0.27

-0.22

-0.20

-0.21

-0.20

-0.22

-0.27

-0.44-0.39

-0.35

-0.35

-0.35

-0.39

-0.44

-0.59

-0.54

-0.49

-0.45

-0.49

-0.54

-0.59

F

*0.20*0.20*0.20*0.25

-0.30-0.30-0.26

*0,20*0.20+0.24*0,36

-0.46-0.48-0.46

*0.20*0.20

-0.26-0.45-0.60-0.66-0.66

:

*0.20*0.20*0.20*0,20*0.20*0.20*0.20

*0,20*0.20*0.20*0.20*0,20*0.20*0.20

*0,20*0.20*0.20*0.20*0,20*0.20*0.20

m between a - 30°,0 interpolate between the value k table 33 and the values give” i“ table 30.I positive and negative values are given, both values should be considered.

3.3.2.7 Flat r@b with inset storc~

For flat roofs with inset storeys, pressurecoefficients for both the upper and lower roofshould bc derived as foffows.

a) For the upper roof 3.3.2.3 to 3.3.2.6,depending on the form of the eaves, should beused, taking the reference height H, as theactual height to the upper eaves but taking H asthe height of the inset storey (from the uppereaves to the lower roof level) for determining thescafing length b.

b) For the lower roof 3.3.2.3 to 3.3.2.6,dependhrg on the form of the eaves, should beused, where H, - H, the actual height of thelower storey, ignoring the effect of the insetstoreys. In addkion, two further zones, X and Y,around the base of the inset storeys are definedin figure 37, where the scaling parameter b isbawd on the dimensions of the upper, irrsctStorey.

c) In zones X and Y the pressures shalf be takenas the pressure appropriate to the waif zones Ato D on each adjacent inset stcmcywall from 3.3. L

3.3.2.8 Friction induced loads on flat roqfkFriction forces should be determined for long flatroofs with D > b/2 in alfwind directions. Thefrictional drag coefficient should be assumed to actover alf of zone G of such roofs, with values asgiven in table 6. The resulting frictional forcesshould be applied in accordance with 3.1.3.4.

3.3.3 External pressure coefficients for pitchedroofs of buffdfngs

3.3.3.1 GcnerdThe pressure coefficients for windward-facing steeppitched roofs (a > 45°) given irr th~ section areeasentiafly identical to the pressure coefficients forwindward-facing non-vertical waifs in 3.3. L4 andtable 29, affowing for the differences in definitionof zones. ‘f’hereforc at large pitch angles (a > 45°)the dutinction between wall and mof is largelyirrelevant Steep-pitched surfaces attached to thetop of vertical walls are better interpreted 6spitched roofs, fafling under the provisions of 3.3.3,Steep-pitched surfaces springing directly from theground which meet along the top edge to form aridge, e.g. A-frame buildirr@, are also betterinterpreted as duopitch roofs, frdfing under thepmtilons of 3.3.3

BS6399:Paxt 2:1995 Section 3

Plan

b

L<Y

x Upper storeyY

/2~ x,1k-J yb/2

Lower storey

/’Wind

e

Figure 37. Additional zones around inset storey

3.3.3.2 Scaling length and tyference height

3.3.3.2.1 TWOvalues are needed for the scalinglength b: ~ = L or bL = 2H, whichever is thesmaller, and LW= W or tW = 2H, whichever is thesmaller.

3.3.3.2.2 The reference height H, is the heightabove ground of the h@est point on the roof, thehigh eaves in the case of monopitch and troughedduopitched roofs, and the ridge in the case ridgedduopitch and hipped roofs.

3.3.3.3 Monopitch roofi

3.3.3.3.1 External pressure coefficients CP, formonopitch roofs are given in table 34 for zonesA to J defined in fieure 38. These zones are

3.3.3.3.2 When all wind directions are considered,smmetv leads to four possible patterns of zonesfor each form of roof, as shown in figure 39a. Windnornmf to either the eaves (6 = 0° ) or the verge(6 = 90°) provides special cases where either oftwo patterns in figure 39a could apply. Because ofthe fluctuations of wind direction found in practiceand in order to give the expected range ofasymmetric loading, both patterns should beconsidered. In the special case O = 0° the two loadcases have symmetrically identical values, whereasin the special case O = 90° the two load casesdiffer one with the pitch angle positive and theedge zones along the low eaves; the other with thepitch angle negative and the edge zones along thehigh eaves.

defined from the upwind comer,NOTE The pitch angle a is taken as positive when the loweaves is upwind and negative when the high eaves is upwind.

Section 3❑

BS6399:M2:1995

Wchanglea

hble 34. External pressure coefficients Cp, fOr pitched rOOf zOnes A tO Jactiwind ZoneUrectione A r

-45.

-30”

-15°

-5.

+ 5.

+ 150

+ 60.

+o.75~

,. -0.61k30. -0.53k60° -1.11 I

E----R2---I-R

%

k so. -1.66* go. -1.30

P -1.47*30. -2.00&60. -1.70* ew -1.43). -1.39+30. -1.78+60° -1.67*90° \ -1.21P I -0.91

5+0.20

+30° -0.84+0.20

* 60. -1.27+0,20

*WY -1.20

W -0.38+0,50

*30. -0.60+ 0.75

i 6W -0.14+0.50

* eo~ -1.130’= +0,52t30° I+0.80* 60. +0.60

=

J!90° -1.17

00 +0.57+30. +0.80

* 60° + 0.70* !30. -0.440. +0.81

Tc

0.58 -0.56

.0.50 -0.49

.1.29 -1.36

.0.81 -0.62

0.68 -0.60

1.02 –0.89

-i

-2.33 -2.17

-0,94 -0,70

-1.05 -0.97

-2.37 -1.71

.2.15 -1.85

*-2.21 -1.63

-1.57 -1.28

*-1.70 -1.38

-1.24 –1.10

%-t-%%

=

-1.64 -1.34

-1.33 -1.12

-0.83 -0.55

-0.33 -0.78+0.20 +0.20

-0.88 -0,82+ 0.20 + 0.20

-0.86 -0.70+0.20 +0.20

-0.84 -0.58

-0.50 -0.50+0.50 +0.50

-0.50 -0.50+ 0.55 +0.40

-0.50 -0.45+0.43 +0.30

-0.94 -0.77

+ 0.50 + 0.50

-4-+0.78 + 0.48

+0.45 +0.35

-0.76 -0.86

+0.57 +0.57

-i-

+0.79 +0.59

+ 0.47 +0.37

-0.44 -0.44

+ 0.81 +0.81

t 0.83 +0.3s

+ 0.55 +0.55

-0.43 -0.43

0.41

0.56

0.96

0.42

0.50

0.79

1.22-0,37

.0.92

-1.00-1,02

-0.31

-1.12

-1.04

-0.77-0.27

-1.15-1.03

-0.64-0.24

-1.19

-1.09

-0.71

-0.25

-0.81+0.20

-0.83+0.20

-0.61+ 0.20

-0.27

-0.50+0.50

-0.50+0.45

-0.40+0.26

-0.19+0.60

+0.55

+ 0.30-0.33

+0.80

+ 0.62+0.35*0. !20

+ 0.81+0.73

+0.41

-0.55 -0.81

-0,97 -0.91

-0.84-1.03

-0.70

-0.88

-0.93

-0.76

-0.60

-0.83

-0.82

-0.66-0.59

-0.69

-0.66

-0.61-0.62

-0.56

-0.62

-0.64

-0.61

-0.21+0.20

-0.21+ 0.20

-0.54+0.20

-0.64

-0.20+0.39

-0,20+ 0.41

–0.30+0.20

–0.60

+ 0.49

+0.45

+0.28-0.55

+ 0.57

+0.59

I

+0.37

-0.44

+0.81

I :::+0.20 \ -0.43

0.76

0.80:0.20

0.82

.0,85

-0.72

-0.20

-0.82

-0.77

-0.54

-0.20

-0.71

-0.67-0.42to.20

-0.59-0.60

-0.42ko. zo

-0.31+0.20

-0.37+0,20

-0.33+0.20*0,20

-0.25+0.40

-0.20+ 0.26

-0.20+0.20

-0.20

+ 0.70,+0.45

+0.21

-0.28+0.80

+ 0.62

+0.35*0.20

+0.81+().73

+ 0,41

~-0.62 I -0.79

-0.52 -0.58

-1.05 -0.97

+%--&%-1.17 -0,87

-1.69 -1.18-1.54

-1.10-2.75-2.44-1.51-1.47-2.24-2.10-1.65-1,43-1.70-2.00-1.47-1.39-1.75-2.05-1.48-0.90+0.20-0.63+0.20– 1.57+0.20-1.42-0.60+0.20-0.40

3+0.40-1.25+0,42+IJ.65+0.50-1.25+0,50+0.77

k

+().59-1.21+0.58+0.85+0.78

*(),20I-1.21

1.10.0.961.661.60

1.15-0.91-1.30-1.67.1.15.0.75-1.24-1.70-1.25-0.69-1.02-1.51-1.15-0.36+0.20-().35+0.20-1.21+().20-1.15-0.30+(1.20-0.30+0.,50-0.89+0.40-1.15+0.40+{1.60+0.50–1,15+0.50+[).77+().59-1.21+().58+!1.85

J

-0.94–0.58

-1.17

-0,97

-0.90-0.73

-1.21

–1.01

-0.83

–1,11

-1.07

-1.10

-().67

-0.91

-1.09–1.lU

–0.52

-1.10–1,38

-1.16-0.43-0.76-1,05-1.10-0.30+0,20-0.32+0.20-0.93+0.20-1.10-0.25+0.20-0.25+0.47-0.83+0.33-1.10+0.35+().55+0.50-1.15+0.5,(1+(),77+0.59-1.21

r+0.58+0.85

+ [1.78 + 0.7$– 1.21 -1.21

NOTE 1. Interpolation may be betwem values of the same sign.NUTE r!. P,essure chamze rmidlv from nemtive to wsitive with inm=imz pitch between a - 15” and a - 30” ~d v~ues forboth signs are @en. - “ - -NCITE 3. When imerpdating hetwee” a - 15° and a - 30°, interpolate between negative values to give I“ad case for upwardload and between paitive values to @ve load c= for dmvmvard load.


“2iz2E‘E”Pitch angle positive Pitch angle negative

a) General

b)Keyto zones

Figure 3S. Key for monopitch roofs

3.3.3.3.3 Loading of rectangular-plan flat ornearly-flat roofs in the range – 50 < a < 5“ maybe assessed as monopitch roofs as a simpleralternative to the general method for flat roofsin 3.3.2. In this case, when the roof is long in thewind direction, i.e. D > b/2, a downwind zoneequivalent to zone G in figure 35 may be definedfor which Cw = +0.2,

3.3.3.4 Duopitch mor

3.3.3.4.1 External pressure coefficients Cp, forduopitch roofs are given in table 34 for zones Ato J and table 35 for zones K to S defined infigure 40. These zones are defined from theupwind comer of each face.NUIE The pitch angle a is taken as positive when the rcmf hasa central ridge and negative when the roof has a centraltrough.

3.3.3.4.2 When all wind directions are considered,symmetry leads to four possible patterns of zonesfor each form of roof, as shown in figure 39b.Wind normal to either the eaves (0 = 00, or theverge (0 = 90° ) provides special cases where eitherof two patterns in figure 39b could apply. Becauseof the fluctuations of wind direction found inpractice and in order to give the expected range ofWmmetric loading, both patterns should beconsidered.

3.3.3.4.3 When a < 10” and W < B, zones Eand F should be considered to extend for a distanceB/2 downwind from the windward cave, replacingzones L, M and N and part of zones O and P. Thisload caae should be compared with the standardload case defined in figure 40 and the moreonerous condition should be used.

“.

Section 3m

BS6399:Part2 :1995

Wind

‘m

IE F

J

EiLiElWind

Aa) Symmetries for monopitch roofs

4Wind

w

I

E FJ

Ro P

s

Hs

o PR

JE F

I

Wind

AW,Symmetries for duopitch roofs

Figure S9. Symmetries for pitched roofs

Wmdm’m

FWind

%

I

F EJ

RP o

s

asP o

R

JF E

I

windR

Bs6399:Part 2:1995 Section 3

kible 35. Extem

T

1

-45”

-30”

-15”

- 5“

+5°

+ 15”

+ 30°

+45”

+ 60°

+75°

1 pressure coei

Loc.sfwindiirection8

)“

*300*60°*900

1“*30°*60°+90°

3“*30°t60°*90°

1)”*30”*60°*90°0“*30°*60°*90°

0“+30°+60°*90°

o“*30°*60°*90°

o“*30’3*60°+90°

o“+30”+60°*90°

o“*30°*60°*90°

NOTE 1, Interpdatir mmaybe.sed, excelNOTE2. When theresult of interpolating

:ients CPefor pitched roof zones K to S

Cone

TK L

-0.92 -0.92-1.12 -1.12

–1.04 -1.04

-1.17 -0.96

-0.78 -0.78

-0.44 -0,44-0.74 -0.74

–1.13 -0.94

T

-0.69 -0.69*0.20 *0.20

-0.67 -0.67

-1.20 -0.84

-0.34 -0.34*0,20 *0.20

-0.69 -0.69

-1.21 –0.83

-0.32 -0.27’-0.70 -0.46

-1.04 -0.90

-0.90 -0.83

T

-0.8 –0.81

–1.32 -1.14

-1.31 -0.92

-0.81 -0.74

T

-0.29 *0.26

-0.74 -0.63

-1.04 -1.05

-0.661-0.61

~-0.21 -0.20–0.54 –0.54-0.55 -0.46

i

-0.49 -0.49–0.63 -0.62-1.00 -1.OC-0.72 -0.72

-0.54 -0.54

-0.71 -0.71

–1.13 –1.1:

-0.79 –0.7s

1! N o P Q E s

-0.92 -0.75 -0.75 -0.75 -0.63 -0.63 -0.63

-1.12 -0.52 *0.20 -0,52 -0.32 -0.32 -0.32

-1.04 -0.24 -0.73 -0.24 -1.05 -1,05 -1.05

-0.86 -0.33 -0.88 -0.28 -1.25 -1.08 -1.36

-0.78 -0.66 -0.47 -0.66 -0.40 -0.40 -0.40-0.44 -0,52 *0,20 –0,52 *0.20 *0.20 *0.20

-0.74 -0.27 -0.62 -0.27 -1.01 -1,01 -1.01

-0.77 -0.19 *0.20 -0.19 -1.25 -1.06 -1.36

-0.69 -0.52 -0.26 -0.52 -0.21 -0.21 -0.21*0.20 *0,20 *0,20 *0.20 -0.55 –0.55 –0.55

-0.67 *0.20 -0.65 *0.20 -1.03 -1.03 -1.03

-0.58 -0.27 -0.64 *0.20 -1.42 -1.10 -1.30

-0.34 -0.25 -0.25 -0.25 -0.28 -0,28 -0.28*0.20 *0.20 –0.26 *0,20 – 0,48 -0.48 –0.48

–0.69 *0.20 –0,66 *0,20 -0.88 -0.88 –0.88

-0.55 -0.25 -0.61 *0.20 -1.48 -1.12 -1.30

-0.28 -0.28 *0.20 *0.20 -0,36 -0.30 -0.24

-0.30 -0.23 –0.31 *0.20 –0.71 -0.59 -0.46

-0.52 *0.20 -0.56 *0.20 -0.97 -0.83 -0.73

-0.58 *0.20 -0.60 *0.20 -0.89 -0.89 -1.09

-0.80 -0.78 -0.39 -0.40 -0.85 -0:55 -0.39

-1.11 -0.88 -0.46 –0.34 -0.47 -1:25 -0.81

-0.72 -0.58 -0.57 -0.23 -1.45 -1,08 -0.75

-0.54 *0.20 -0.58 *0.20 -0.83 -0.77 -0.92

–0.25 -0.30 -0.30 -0.30 -0.31 -0.32 -0.33

-0.52 -0.43 -0.39 -0.43 -0.76 -0.51 -0.40

-0.90 -0.64 –0.58 -0.47 -1.02 -0.67 –0.64

-0.491-0.21 I -0.49 *0.20 -0.671-0.581-0.69

-0.211-0.201-0.231-0.231 -0.211-0.241-0.26

-0.20 –0.27 –0.23 -0.26 -0.20 –0.21 -0.22-0.51 -0.41 -0.44 –0.38 –0.55 –0.47 –0.50-0.38 -0.20 -0.40 *0.20 -0.60 -0.45 -0.47

-0.40 -0.40 -0.30 -0.30 -0.57 -0.57 -0.57-0.71 -0,69 -0.40 -0.40 -0.67 -0.67 -0.67-0.60 -0.42 -0.74 -0.63 -0.91 -0.91 -0.91-0.241 *0.201 -O.60 *0.201 -1.21 -1.211-1.21

-0.431 –0.431 –0.301 –0.301 -0.581 –0.581 -0.58

-0.64 -0.63 -0.40 -0.40 -0.70 -0.70 -0.70

-0.67 -0.31 -1.15 -0,61 -0.97 –0.97 –0,97

-0.42 -0.21 -0.80 *0.20 -1.21 -1.21 -1.21

etween.z - +5 °anda - –5°.wee” positive and mgative values is in the range – 0.2 < C= < + 0.2, the I

ccefiicient should be taken as Cm - + 0.2 and both Pssible values used. I

mSection 3 BS6399:Pmt 2:1995

‘+ ‘+. <0”

“’0= =’I%dged, pitch angle positiie Troughed, pitch angle negative

Plan

bwti

bJl O L M NA

J

bJ4~E F

BIC D@lo 1$4 l@

Wind

7 e

o) Key t. zones

Figure 40. Key for duopitch roofs

)L/l o

t

w


3.3.3.5 Hipped roo~

3.3.3.5.1 TheprOvisiOns in3.3.3.5.2 t03.3.3.5.4aPPIY tO conventionalKlpped roofs onrectarrgulw-plarr buildings, where the pitch of themain ridged faces have pitch angle al and thetriangular side faces have pitch arrglea2. Zones ofexternal pressure coefficient are defined infigare 41. Local wind dmctions O1and f12aredefined from normal to the longer and shortereaves, respectively, where 6’z = 90° – 01.

3.3.3.5.2 Thas, forthemain ridged faces the pitchis al, the wind dwection is 61 and the zones are AItoY1, arrdfor thetriangular side faces the pitch isCX2,the wind diretilonis62 and the zones are A2 toY2. Therefererrce height Hristhe height aboveground of the ridge.

3.3.3.5.3 External preasure coefficients forzones A to E on the upwind faces are given irrtable 34. External pressure coefficient.s forzones Oand Ponthedownwind faces sregiven in table 35.The size of each of these zones is given infigure 40.

3.3.3.5.4 Extema.l pressure coefficients for theadditional zones T to Walong the hip ridges and forzones Xarrd Yalong the main ridge arc given intable 36. The width of each of these additionalzonesin plan isshowrrin figare 41b. The boundarybetween each pair ofadditional zones, T-U, V-Wand X-Y, is the mid-point of the respective hip ormain ridge.

3.3.3.6 Mired gables and hipped roofi

Roofs with a standard gable at one end and a hlpat the other are a frequent occurrence. In suchcases, the governing criterion is the form of theupwind comer for the wind dlrectirm beingconsidered.

3.3.3.7 Effect of parapets on pitched m@

3.3.3.7.1 The effects of parapets should be takeninto account to determine external pressurecoefficients on pitched roofs. Owing to the waythat parapets around roofs change the positivepressures expected on upwind pitches with largepositive pitch angles to suction, neglecting theiref feet is not always conservative. Pressures on theparapet walls should be determined using theprocedure in 2.7.5.1 for free-standing parapets andfrom 2.7.5.4 for downwind parapets.

3.3.3.7.2 Morrqitch mqfs

a) Lurueat.%’with pampet upwind. For the partof the roof below the top of the parapet,external prwssure coefficients should bedeterrrrirred in accordance with 3.3.2.4, i.e. theroof should be treated as a flat mof withparapets, irrespective of actual roof pitch. For

anY Part of the roof that is above the top os theparapet, i.e. if the top of the parapet is belowthe level of the h@fr eaves, external pressurecoefficients should be determined in accordancewith 3.3.3.3 as if the parapet did not exist.

b) High eaves upwind. External pressurecoefficients should be determined in accordancewith 3.3.3.3, The reduction factors of table 31should be used for upwind eaves and vergezones A to D and H to J, with the parapet heighth determined at the upwind comer of eachrespective zone. Thus, for parapets level with thehigh eaves the parapet height should be taken ash = O for zones A to D and H, so that thereduction factor is less than unity only for zonesfor zones I and J.

3.3.3.7.3 Daopitch roofs

a) Upwind fbxe. For the part of the roof belowthe top of the parapet, exterrmf pressurecoefficients should be determined in accordancewith 3.3.2.4, i.e. the roof should be treated as aflat roof with parapets, irrespective of actualroof pitch. For any part of the roof that is abovethe top of the parapet, i.e. if the top of theparapet is below the level of the ridge, externalpressure coefficients should be determined inaccordance with 3.3.3.4 as if the parapet did notexist.

b) Drrrmnuindfbce. External pressure coefficientsshould be deterrrrined in accordance with 3.3.3.4for the downwind pitch of duopitch roofs. Thereduction factorx of table 31 should be used onlyfor the verge zones Q to S with the parapetheight h deterrrrined at the upwirrd comer ofeach respective zone.

3.3.3.7.4 Hipped roofs

a) Upwind main arui hip fwes. For the part ofthe roof below the top of the parapet, externalpressure coefficients shorrfd be determined inaccordance with 3.3.2.4, i.e. the roof should betreated as a flat roof with parapets, irrespectiveof actual rcmf pitch. For any part of the mof thatis above the top of the parapet, i.e. if the top ofthe parapet is below the level of the ridge,external pressure coefficients shoald bedetermined trraccordance with 3.3.3.5 as if theparapet did not exist.

b) Downwind main and hip fax%. Externalpressure coefficients should be determined inaccordance with 3.3.3.5 as if the parapet did notexist. The reduction factors of table 31 shouldnot be applied to any zone.

3.3.3.8 Pitched ra@ with irrset ston?vs

External pressure coefficients should bedetermined in accordance with 3.3.2.7, using theaPPmPriate zones for the pitched roofs as derivedfrom 3.3.3.3 to 3.3.3.5.

mSection 3 BS6399:Part 2:1995

—— %>0.a.>c-J7-

,:+ (“’,J,,,,,,,,,,,,L,,,,/,>,H,,:+-

//

‘A—

,:+ H, ,!>

7//,////,,//,//////// ,,, /,,,/,,,/,,/,/,,,,, ,,

a) Oeneml

Plan

b /2“~

bL/l O

Q

.-

W

—

b) Key to zones

Ngure 41. Key foridppedmofs


Oible 36. External uressure coefficients C- For additional zones T to Y of hiDDed roofs I?ttchangle a

+ 5°

+ 15°

+30”

+ 45°

Local winddirection .9

0“f30”*60°*90”

o“+30°

*60”*!900

0“*30°

*60°

*90°

0“t30”*60°

I *90”WTCE. Interpolation may be used.

T

-0.56

-0.62

-1.13

-1.19

-0.31

-0.37

-0.94

-1.09

-0.40

-0.26

-0.99

-1.10

-0.74

–0.55

–1.11

-1.22

u

-0.56

-0.62

-0.63

-0.76

-0.31

-0.37

-0.52

-0.77

-0.40-0.26–0.47– 1.01

–0.74

-0.55

-0.33

-0.71

v

-0.31

-0.60

-0.76

-0.89

–0.44

-1.00

-1.43

-0.97

-0.53

-0.74

– 1.25

-1.40

-0.65

-0.52

-0.67

-1.35

w

-0.45-0.46-0.51-0.50

–0.83-0,99-0.71-0.59

-0.33-0.55–0.82-0.62

–0.24-0.22-0,35-0.43

x Y

-0.58 -0.58

-0.47 -0.54

-0.38 -0.36

-0.61 *0,20

-1.17 -1.17

-1.31 -1.13

-0.78 -0.80

-0.64 *0.20

-0.28 ~0.28

-0.51 ;0.50

-0.77 -0.49

-0.78 *0.20

-0.20 -0.20

-0.22 -0.28

-0.32 -0.41

-0.88 -0.28

3.3.3.9 fiction induced loads on pitched roo~

Friction forces should be determined for longpitched roofs when the wind is parallel to theeaves or ridge, i.e. 8 = 90°. The frictional dragcoefficient should be assumed to act over zones Fand P only of such roofs, with the values as gjvenin table 6. The resulting frictional forces should beapplied in accodance with 3.1.3.4.

3.3.4 Multipitch and multi-bay roofs

3.3.4.1 Multipitch roofi

3.3.4.L 1 Multipitch roofs are defined as roofs inwhich each span is made up of pitches of two ormore pitch angles, as shown in figure 22 for thestandard method. The form in figure 22a iscommonly known as a mansard roof.NCJTE Flat roofs with mansard eaves are dealt with in 3.3.2.6.

3.3.4.1.2 External pressure coefficients for eachpitch should be derived in accordance with 3.3.3.4or 3.3.3.5, according to the form of the verges, butomitting the eaves edge zones along the change inslope where indicated in figure 22.NOTE The letters designating the zones in figure 22 whichcm’respmd to the standard method should be ignored.

a) The eaves edge zones A to D on the bottomedge Of df windward faces should be includedwhen the pitch angle of that face is less thanthat of the pitch below, including the lowest faceforming the actual eaves of the windward side,as shown in figure 22a. The eaves zones A to Dshould be excluded when the pitch angle isgreater than that of the pitch below, as shown infigure 22b.

b) The ridge zones K to N for gabled roofs orridge zones X and Y for hipped roofs should beincluded only on the highest downwind facealong the actual ridge, as shown in figures 22aand 22b. Ridge zones on all other downwindfaces should be excluded.

c) Verge zones H to J on gabled roofs or hipzones U to W on hipped roofs should be includedfor all faces.

mSection 3 BS6399:Part. 2:1995

3.3.4.2 Multi-bag rooJ%

3.3.4.2.1 Multi-bay roofs are defiied as roofsmade up of a series of monopitch, duopitch, hlppedor similar spans as shown in fwres 23a to 23c.

3.3.4.2.2 pressure coefficients on the fmt span,i.e. the upwind pitch of multi-bay monopitch roofsand the upwind pair of pitches of duopitch roofs,may be taken to be the same as for single spanmof, However, these preasurss w.? reduced in valuefor the downwind spans.

3.3.4.2.3 Account may be taken of th~ reductionby following the procedure in 2.5.5 of the standardmethod, but using the key in figure 42 to defineregions of shelter at any given wind direction.

NUI’E. When the wind direction is normal ta the eaves, i.e.8- 0°, tllre 42 becomes identical to the standard methodcase of fwre 23d. When the wind is normal to the gables, i.e.e . 90°, there are no regkms of shelte~

3.3.4.3 Friction induced luarfs on multipitchand multi-bag mojk

Friction forces should be determined for longpitched roofs when the wind is parallel to the

eaves or ridge, i.e. 6 = 90°. The frictiorvd dragcoefficient should be assumed to act over onlyzones F and P of such roofs, with values as given intable 6. The resulting frictional forces should beadded to the normal pressure forces in accordancewith 3.1.3.4.

3.3.5 fnternal pressure coefficients

3.3.5.1 It is recommended that the procedures forinternal pressure coefficients given in 2.6 for thestandard method are used. When necessary,interpolation should be used between theorthogonal wind directions to obtain values for theother wind directions.

3.3.5.2 Table 18, giving internal pressurecoefficients for open-sided buildin&, has beenexpanded in table 37 to give values for 30°increments of wind direction.NCTE. If more accurate values are required, internal PIWSUreSin .mclwed buildins or buildings with dominant openin@ mayalso be determined fmm the distribution of external pressuresby calculating the balance of internal flow (W refermce [6]).

\Linsa in wind difWlon through upwind comer of bay

mA Upwind bay

B Second bay

C AU subsequent bays

Figure 42. Key tu multi-bay roofs


Eable 37. fnternslpressu

7

Wfnd dkection 8 One open fa!

(

T*o. +0.85

* 30~ +0.71

*600 +0.32

* 600 -0.60

* 120~ -0.46

* 150~ -0,31

e coefficients Cpi for open-side

Longer

Upwindthfrd

+0.68

+0.54

+0.38

-0.40

-0.46

-0.40

-0.16

Middlethird

+ 0.68

+0.70

+ 0.44

-0.40

-0.46

-0.40

-0.16

third

+ 0.66

+ 0.80

+ 0.54

-0.40

-0.46

-0.40

–0.16

buildings

IWOm more adjacent OP.

~w= and one shorter’]

+ 0.77

+0.77

+0.77

+0.77, –0.38

-0.53

-0.60

-0.33

P: the positive values cm’reymnd to the short face dmvmvhd; the m

faces

I.mwer and both,horte$]

+0.60

+0.50

+ 0.30

0

-0.63

-0.49

i 180° -0.16

‘) TWOvalues are gWen f.. @ - !to the short face upwind.2)APP,Y dues ~0 “ndemide Of m~f OIIIY.FOr the single wall, use pressure coefficients for wails @en in table 26. .:

3.4 Hybrid combinations of standardsnd directional methods

3.4.1Standsrd effective wind speeds withdirectiomd pressure coeftlcients

3.4.L 1 ApplicabilityStandsrd effective wind speeds should becombmed with directional prcasure coefficients incsaes where the form of the building is welldefined but the exposure of the site is not welldefined.NM’E. &@cal examples are relocatable Or patable buildings,or m-produced designs

3.4.1.2 ApplicationAs the standsrd effective wind speeds apply to the

~ge o = *45° either side of the rmtionalorthogonal wind directions, the appropriatestandsni effective wind speed to be used with eachof the directiorwd pressure coefficients should beselected from this range. This results in a load casefor each wind direction for which pressurecoefficients are given, usually tweive.

3.4.2 Dfrectionsf effective wind speeds withstsndsrd pressure coefficients

3.4.2.1 ApplicabilityDirectional effective wind speed should becombined with standmd pressure coefficients if amore precise estimate of site exposure is required,particularly when there is significant topography orwhen the site is in a town. In the standard methodthe method for significant topography (2. 2.2. 2) wasderived assuming the turbulence characteristics foropen country terrain and some advantage may begained by using the actual site characteristics. Thestandard method for effective wind speeds sssumesthat the site is 2 km from the edge of a town, withsites closer to the edge treated as being in countryterrain snd sites further into the town treated asbeing at 2 km, thus, the potential benefits ofshelter from the town exposure are not exploitedfor any locations except those at exactly 2 km fromthe edge.

-0.39

,tive values correspond

,,: ,.,3.4.2.2. Application

3.4.2.2.1 The directional effective wind speedsshould be determined in each of the twelve winddirections using the value of gust fsctor m = 3.44,for the datum diagonsl dlme&ion a = 5-m asfollows:

a) from p = O“ to p = 330° in 30° intervals,aligned from north, for which values ofdirectional factor are given in table 3; or

b) from @ = 0° to d = 330° in 30° intervals,alied with respect to the building axes,interpolating corresponding values of directionalfactor from table 3; or

c) in 30° intervxls from normal to the steepestslope of the signtilcant topographic feature,interpolating corresponding values of directionalfactor from table 3.

Option a) is the simplest to implement whentopography is not si~”tilcant; option b) ensuresthat estimates will correspond exactly with thebuilding axes; option c) ensures that the mostonerous topographic effects are included.

3.4.2.2.2 For each orthogonal load case the largestvalue in the range O = *45° either side of thenotional wind direction should be selected from thedirectional wind speeds. ‘llreae vslues may be takento be equivalent to the stsndard effective windspeeds and used in the standard method.

Annex A BS6399:Part 2:1995

Amexes

Annex A (normative)

Necessary provisions for wind tunneltesting

A. 1 Static structures

Tests for the determination of wind loads on staticstructures should not be considered to have beenproperly conducted unless

a) the natural wind has been modelfed toaccount for

1) the variation of mean wind speed withheight above ground appropriate to the terrainof the site; and

2) the intensity and scale of the turbulence

aPPmPriate to the terrain of the site at adeterrrrined geometric wile;

b) the brdldhg has been modelled at a geometricscale not more than the following mrdtiples ofthe geometric scale of the simulated naturalwind, with appropriate corrections applied toaccount for any geometric scale discrepancieswithin this range:

3 for overall loads; and

2 for cladding loads;

c) the response characteristics of the wind tunnelinstrumentation are consistent with themeasurements to be made;

d) the testa enable the peak wind loads with therequired annual risk of being exceeded to bepredicted.

A.2 Dynamic structures

‘l%stsfor the determination of the respmse ofdynamic structures should not be considered tohave been properly conducted unless the previsionsfor static stmctures in items a) to d) of A. 1 aresatisfied, together with the additional provisionthat:

the structural model is represented (physically ormathematically) in maw distribution, stiffnessand damping in accordance with the establishedlaw of dimensional scaling.

NOTE. Information to enable desigmem t.o make a consideredjudgment of the facilities offered when commkioning windtunnel tests is available in reference (9]. Mvice may also besought from the Buildina Research Advisory Service, BuildingResearch Establishment, Gamtmn, W.tfmd, Hats WD2 7JR.lkl 01923 ~S46&!.

Annex B (informative)

Derivation of extreme wind information

B. 1 Introduction

The wind data archived by the MeteorologicalOffice are derived from continuously recordinganemographs, normally exposed at a height of10 m above ground in open, level terrain or, inother terrains, at a height equivalent to thestandard exposure. Currently, the networknumbers about 130 stations and the main archivecomprises hourly mean wind speeds and winddirections, together with details of the maximumgust each hour. Many of these stations have pastrvcords spanning several decades, although thecomputer-held ones generally begin in about 1970,

Conventionally, estimation of the extreme windclinratc in temperate regions has involved theanalysis of a series of annual maximum windspeeds, for example using the method proposed byGumbel [8]. The main dffiadvantage of methodsusing only annual maxbnum values is that manyother useful data within each year are discarded.For the preparation of the basic wind speed mapgiven in f= 6, a superior technique involvingthe m-urn wind speed during every period ofwindy weather (or storm) was used. This approach.gmatly incnmaed the amount of data available foranrdy%.sand enabled the directional and seasonalcharacteristics of the UK wind climate to beexamined.

A storm was defined as a period of at lea.%10 consecutive hours with ruroverall mean windspeed greater than 5 tis. Such periods wereidentified for 50 anemogr-aph stations, evenlydtiributed over the United Kingdom and mostlyhaving standard exposures, using their recordsduring the period 1970 to 19S0. At the majority ofthese stations, the average number of storms eachyear was about 140. The maximum hourly meanwind speed blowing from each of twelve 300 winddirection sectors (centred on 0°, 30°, 60°, etc.)was calculated for each storm.

Three types of new extreme wind information wereneeded: an improved map of basic wind speeds Vb;dmction factors Sd; and seasonal factors S~.

Analyses of extreme wind speeds are performed interms of their probability of occurrence. Thestandard measure of probability is the cumulativedistribution function (CDF), conventionally giventhe symbol P (used elsewhere in this standard forwind load), and corresponding to the annual risk ofnot being exceeded.

73

BS6399:Part 2:1995 Annex B

‘)

Desigm to fesist extreme winds is based on theannual risk (probability) Q of the hourly meamwind speed being exceeded given by Q = 1 – F?The reciprocal of the annual risk is sometimesreferred to as the return period and is bestinterpreted as the mean interval betweenrecurrences when averaged over a very longperiod. The definition of return period rapidlybecomes invafid for periods less than about10 years The period between individualrecurrences varies considerably fmm this meanvafue, so the concept of return period is not veryuseful and is open to misinterpretation. Theconcept of annual risk is less open tomisinterpretation and should be viewed as the riskof exceeding the design wind speed in each yeafthe building is exposed to the wind.

B.2 Baaic wind apeed

B.2. 1 Storm mczrima

The baaic wind speed Vb is estimated to have a riskof Q = 0.02 of being exceeded in any year lbobtain this speed for each station, all the maximumwind speeds in storms v, were first abstracted,irrespective of direction. The cumulatived~tribution function P representing the risk of aparticukw value not being exceeded wasdetermined by the method of order statistics. Inthis method, the m-a were sorted intoascending order of value and assigned a rank mwhere rn = 1 for the lowest value and m = N forthe highest value, then P was estimated for thestorm maxima v~by F(v,) = m/(N + 1).

B.2.2 Annual ma”ma

Maxima from different storms can be regarded asstatistically independent, m the CDF Hv) of annualmaximum wind speeds v was found fromflu) = V(U,), where r is the average annual rateof storms.’ This CDF of annual maxima was fitted toa Fisher-Tippett Type 1 (FTl ) distribution, definedby

F(v) = exp[ - exp( - y)] (B.1)

where

Y =a(v-fl);

U is the mode;

I/a is the dispersion

Hence

“ -1” [-’”[[fin (B.2)

and a plot of y vemus v~ led to estimates of theannual mode and dispemion. The wind speed Vassociated with a certain annual cumulative risk Pof not being exceeded may be found from:

v= U+*][ (B.3)

N~: Equation B. 3 follows from equation B.2 because thea!wmximati.n - ln( 1 – P) = P holds well for small values of P

B.2.3 Best extreme model

When the maximum wind speed in each storm v, isreplaced by its square v~z and thk is multiplied byhalf the density of air, the dynamic pressure q isobtained. Extreme-value theory predicts that theETl distribution should be a better fit to dynamicpressure than to wind speed. The above, e,tiremevalue analysis method was repeated for~eachstation using g as the variable. It was found thatthe rate of convergence of storm maxima to theFTl model was faster for the g model than the v,model. The wind speed corresponding to thedynamic pressure having a risk of Q = 0.02 ofbeing exceeded at least once per year was used toderive the value at each station. Corrections werethen made to the individual station estimates toensure that when all the values were plotted on amap, they represented a height of 10 m aboveground in open, level termin at mean sea level.Isotachs were then drawn to be a best fit to thewind speeds plotted.

Fkting the dynamic pressure g to the FTl modelhas been standard practice in most of Europe formany yeas, whereas the practice in the UK hadpreviously been to fit the wind speed V. Thedtiference between the two models at the designriak Q= 0.02 is small, about 4 %. At very smallrisks, for example at Q = 10-4 used for nucleafinstallations, the q model predicts smaller windspeeds than before. Whereas at higher risks, forexample for frequent service conditions, the qmodel predicts higher wind speeds than before.While adoption of the better q model brings the UKinto line with European practice, it fdao impliesthat previous practice at small risks wasoverconservative, but that service conditions mayhave been unconservative. Tlese changes are alaoreflected in the expression for probabtity factor SPin annex D.

B.2.4 Extension to Northern Ireland

There were insufficient anemograph stations todefine the isotachs for Northern Ireland, so it wasnecessary to incorporate addkionzd data from Eirein order to allow interpolation up to the nationalborder. This was done by comparing results fromthe storms analysis for Northern Ireland with amap, prepared by the Irish Meteorological Service,showing isotach.sof gust speeds having an annuafrisk of being exceeded of Q = 0.02.

Annex B BS6299:Part 2:1995

B.3 Direction factor

The same analyais was performed on the series ofmaximum wind speeds from each 30° winddirection sector, to yield ratios of the sectorialextreme to the al-direction extreme for windspeed and dynamic pressure. After correction forsite exposure, the directional characteristics ofextreme winds showed no significant variation withlocation anywhere in the United Kingdom, withthe strongest winds blowing from dmctions south-west to west. This enabled one set of directionfactom to be proposed. The ratios calculated referto a given risk in each sector. However, due tocontributions from other sectom, the overall riskwiIl be greater than the required value. Thedirection factor Sd has been derived by adjustingsectorial ratios to ensure an evenly distributedoverall risk.

B. 4 &aaonaf factor

The overall storm maxima (irrespective of winddirection) were arralysed for each month, using atechnique similar to that used for the annualarralyaes. Given the risk of a value being exceededby month, the risk in any longer period is the sumof the monthly risks. The seasonal characteristicsof strong winds also show no significant variationacross the UK so, again, one set of factors could beproposed .S,. The strongest winds usually occur inmid-winter and the leaat windy period is betweenJune and August.

B.5 Verification of the data

Since this analysis was performed, a further10 years of data has become available whichdoubles the data record and includes the severestorms of October 1987 and of JanuaIY andFebruary 1990. A more recent anaiyais of the full21-year records for ten of the original 50 sitesshowed an improved analysis accuracy but thevalues were not signfilcantly different from theoriginal analysis. This gives further cotildence thatthe 1l-year period of the original analysis wasrepresentative.

B. 6 Further information

References [8] and [ 10] to [14] give furtherinformation on the derivation of extreme windinformation.

Advice can also be obtained from theMeteorological Office at the following addresses.

England and Wales Meteorological Office, AdvisoryService, London Road, Bracknell, Berkshire RG122S2. lkl: 01344856856 or 01344856207

Scotland: Meteorological Office, Saughton House,Broomhouse Drive, Edinburgh EH11 3XQ. Tel:01312448362 or 0131 2448363

Annex C (informative)

Dynamic augmentation

C. 1 Dy-c augmentation factor

C. 1.1 General

The dynamic displacement of a structure in itslowest-frequency mode can be related to thecomespondlng quaai-static displacement by theproduct of two parametem: the buildlng heightfactor Kh and the buifding type factor Ifb. The fullanalysis of the governing relationships leads toequations which are too complex for codificationpurposes. A numerical evaluation and curve-fittingexercise carried out for practical prismaticbuildings, including portd-fmme structures,showed that simplifications could be made to thealgebraic relationships with only marginal loss ofaccuracy within a range of mildly dynamicstructures.

C. 1.2 Full equation

The peak deflection (and hence peak stresses) canbe obtained by applying a factor to the staticdeflection, where this factor is the ratio of theactual peak deflection to the static peak deflection.This ratio is defined here as (1 + C,) in terms ofthe dynamic augmentation factor Cr given by

,- .>

(Cl)

sg is the gust factor appropriate tothe size of the structure andterrain and is given bySg = 1 + gt.$ for country terrain;and Sg = 1 + g$t Z’t for towntermin;

St> Tt, gt are obtained from tables 22,23 and 24, respectively.

Kh and I& are parameters depending on thebuilding height and location andon the form of constmction of thebuilding (see C.2). VahIeS of ffbarc given in table 1.

Northern Ireland: Meteorological Office,Pmgrssive House, 1 College Square Eaat,Belfast ml 6BQ. Tel: O123? 328457

75

BS6399:Rtrt2 :1995 Annex C

C. 1.3 Range of ualiditff

As long as the dynamic augmentation factorremains in the mnge O s C, s 0.25 the methodworks weU, and this range can be used as thedefinition of mildly dynamic buifdings. With fullydynamic buildings, which give values of Cr >0.25,the method becomes leas accurate and generallymore conservative. The limits of C, < 0.25 andIf< 300 m in figure 3 serve to exclude these fuUydynamic structures from the protilons of this Partof BS 6399.

C. 1.4 Simple equation

Using the curve-fitted expressions for the buildlngheight factor F& and the buildhg type factor&enables presentation of the values of C, to a goodaPPmximation by the family of curves presented infigure 3. The equation for this family of curves is

&(~/&, )075

Cr = 800 log (If/ho)(C.2)

where

ho is a dimensional const&t with valueho = O.lm.

C.2 Building height factor and building typefactor

C.2. 1 Derivation of values

The product Ifh x & given in equation (C. 1) isgiven with ordy marginal 10SSof accuracy by

Kh X

where

Kb =[b x 632’31x [al ‘C3)

is the terrain arrd building factor for meanvalues given in 3.2.2, so thatSo = Sc (1 + S~) for country termin;and SO = & T.(1 + ~h) fOr tOWn tet’r’ain(from tables 22 and 23);

is the natural frequency of thefundamental mode of vibmtion (in Hz);

is the diagonal size of the buildlng (in m);

is the stmctural damping of the buildingas a fraction of critical;

is the basic hourly mean wind speed(in m/s);

is a terrain correction factor such thatKt = 1.33 at the sea coaat; and Kt = 0.75at least 2 km inside town terrain.

C.2.2 Default values of parameters

In figure 3 and equation (C. 2) standard @ues ofp-eters have been assumed tn be given’ by thefouowing,

‘“-E(C.4)

Vb = 24 (C.5)

Kh - &2/3 ~ ~/3 ~ & (C.6)

Kb=& (C.7)

The building height factor Kh defined byequation (C. 6) varies only weakly with change ofterrain roughness, so that a simpleterrain-independent form given by

Kh = (0.8H)075 SC.8)

where His the buUding height in metres, can beused without sitilcarrt loss of accuracy. Thissirnp~lcation is used in figure 3 andequation (C.2).

Values of the building type factor Kb given intable 1, have been derived from data obtainedfrom a large number of completed buildings andother structures.

C.3 More accurate assessment of dynamicaugmentation

If the assumptions used to derive the value ofdynamic augmentation factor C, are inappropriatefor the patilcular building, or if a more accurateassessment is required, then the expression for theproduct & x ffb @Ven by eqUatiOn (C.3) can beused in conjunction with relevant values of theparameters In particul=, values of Vb, & and K~can be derived for the actual location and exposureof the building, and values of no and ~ obtainedfrom measurements or predictions for thestmcture.

NOTE Intermediate values of Kt could lx? obtained byinterpolation, taking the variation of SO = a guide.

Annex D BS6399:Part2 :1995

Annex D (normative)

Probability factor and seasonal factor

D. 1 Probability factor

The basic wind speed as defined in clause 2.2.1 hasarr annual risk of being exceeded of Q = 0.02. ‘lbvary the basic wind speed for other such annualprobabilities the basic wind speed should bemultiplied by the probability factor SP @ven by

‘p‘Ex%iY (D. 1)

where Q is the snnusl probability required. Thisexpression corresponds to a Fisher-Tippett type 1(FTl) model for dynamic pressurs that has acharacteristic product (mode/dLspemion ratio) valueof 5, which is vslid for the UK climate ordy.

A number of vslues of Sp for standard values of Qsre relevant:

‘p -0.749 for Q = 0.632 (see note 1);

S, = 0.S45 for Q = 0.227 (see note 2);

‘p - 1.000 for Q = 0.02 (see note 3);

‘p = 1.048 for Q = 0.0083 (see note 4);

‘p -~1.4f0r Q= 5.7 x 10-4 (see note 5);

‘p = 1.263 for Q = 10-4 (see note 6).

NIJTE 1. The annual mcde, corresponding to the most likelyannual maximum value.

NCfl’E 2. fir the serviceability limit, assuming tbe partial factorfor loads for the ultimate limit is y~ - 1.4 and for theserviceability limit is Yf - 1.0, gtving

s, - m - o~sNUIT 3. The standard desigm value, corresponding ta a meanrecurrence interval of 50 yearn.

NOTE 4. The design risk for bridges, corresponding t. a meanrecunwnce interval of 120 yearn.

NUTE 5. The annual risk comqm.ding to the standard partialfrwror for loads, corresponding m a mean recurrence interval of1754 yeas. Eack-calculated awnning the partial factor load forthe ultimate limit is YC- 1.4 and all risk is ascribed to tberecurrence of wind.

NIJTE 6. The design risk for nuclear installations, correspondingto a mean recurrence interval of 10 COOyew.

D.2 Seaaomd factor

The seasonal factor S, maybe used for buildingswhich are expected to be exposed to the wind forspecific subamrual periods, reducing the basic windspeeds while maintaining the risk Q of Lr.ingexceeded at a value 0.02 in the stated period. Theseasonal factor S~ may also be used in conjunctionwith the probabfity factor Sp for other risks Q ofbebrg exceeded in the stated period. If values of S,are used they should be taken fmm table D. 1.

77

BS6399:RUt 2:1995 Annex D

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Annex E BS6399:Fart 2:1995

Annex E (infomtive)

‘lkrra.in categories and effective height

E. 1 Terrain categories

E. 1.1 Geneml

The roughness of the ground surface controls boththe mean wind speed and its turbulentcharacteristics and is described by an effectiveaemdynrunic roughness length Zo. Over a smoothsurface such as open country the wind sp+ed ishigher near the ground than over a rougher surfacesuch as a town. By deftig three basic terraincategories wind speeds can be derived for anyinterrnediate category or to account for theinfluence of differing upwind categories to that ofthe site. The three basic categories defined in 1.7are as foffows.

a) Sea. This applies to the sea, but also to infmrdlakes which are large enough and close enoughto affect the wind speed at the site. Althoughthis standard dots not cover offshore structures,it is necessary to define such a category so thatthe gradual deceleration of the wind speed fromthe coast inland can be quantitled and the windspeed for any land-baaed site can be determined.The aerodynamic rmrgbnesa length for sca istaken as 20 = 0.003 m.

b) Cuutiry. This covers a wide range of terrain,from the flat open level, or nearly level countrywith no shelter, such as fens, airt3elds, moorlandor farmfand with no hedges or walls, toundulating countryside with obstmctions such asoccasional buildings and windbreaks of trees,hedges and walls. Examples are farmlands andcountry estates and, in reality, all terrain notothe- defined or sea or town. Theaerodynamic r’oughnesa length for country istaken as% = 0.03 m.

c) Tbwn. This terrain includes suburban rcgiomsin which the general level of ruof tops is about5 m above @und level, encompassing all twostorey domestic housing, provided that suchbuildings are at least as dense as normalsuburban developments for at least 100 mupwind of the site. Whilst it is not easy toquantify it is expected that the plan area of thebuifriings is at least 8 % of the total area within a30° sector centred on the wind direction beiigconsidered. The aerodynamic roughness lengthfor town is taken as% = 0.3 m.NOTE.The aerodynamic mugbn- of foresk3 and maturevmdand is similar to town terrain (z. - 0.3 m). It isinadvkable to take advan-age of the shelter providrn bywoodland unless it is permanent (not likely to be clearfd.+.

E. 1.2 Variation qffetch

Fetch refers to the terrain directly upwind of thesite. The ar@tment of wind speed characteristicsas the wind flows from one terrain to another isnot inatantr.neuus. At a change frum a smoother toa rougher surface the mean wind speed is graduallyslowed down near the ground and the turbulencein the wind increases.

This adjustment requires time to work up throughthe wind prufde and at any site downwind of achange in terrain the wind speed is at someintermediate flow between that for the smoothterrain and that for the fufly developed roughterrain. The resulting gradual deceleration of themean speed and increase in turbulence has beenaccounted for in tables 22 and 23 by defining thesite by ita distance downwind from the coast and,in addition if it is in a town, by its distance fromthe edge of the town.

Shelter of a site from a town upwind of the site hasnot been allowed for, other than if the site is in atown itself. lb do su would introduce too muchcomplexity with only a marginal saving irr theresulting wind loads. However, [8] and [15] giveinformation on how to take such effects intoaccount.

It is important, if directional effects need to beconsidered, to take full account of the effects ofte- upwind of the site in conjunction with thedirection factor. This becomes even more importantif the effects of topography also need to beconsidered, as the topographic increment Sh can belarge.

E.2 Effective height

E.2. 1 In rough te-, such as towns and cities,the wind tends to behave as if the ground level wasraised to a height just below the average roofheight, leaving an indeterrninate rc@on belowwhich is often sheltered. This displacement heightffd is a fUIICtiOXI of the plan area density andgeneral height of the buildings or obstructions. Theeffective height, He of any build~ that is higherthan its surroundings in such terrain is thus thereference height H, less the d~placement heightHd. Thus He = H, – Hd.

E.2.2 The d~pfacement height has beendetermined by ESDU [16] from available referencesfor urban and wcedlzwd terrain. Ehacd on thiswork the normal practical range of duplacementheights has been found to be0.75H0 < Hd < 0.90H0. A value of Hd = 0.8H0 hasbeen adcpted in 1.7.3.

79

BS6399:14U%2 :1995 Annex E

E. 2.3 This does not apply where the buildlng to be E. 2.5 Accelerated wind speeds occur close to thedesigned is a similar height or lower than its baae of buildings which are si@lcantly taller thansurmundhigs, A minimum effective height of the displacement height. When considering low-riseHe . 0.47, has been adopted. buildings which are close to other tall buildinm the

E.2.4 The displacement height reduces withrules for effective height wilf not necessarily ~ead

separation distance X between buildin&to conservative values and specialist advice shouldbe sought,

particularly across open spaces within, or at theedge of, a built up area, as described in 1.7.3.3 andillustrated in figure E. 1.

6 Ho

Wind

f“-”,, T - ,],,]/,,,>

2HO>

~Hd”

JK He Hr

--

~

>- .-0.8 Ho A “-. -N

//,,//

k 4x

Figure E. 1 Effective heights in towns I

Annex F BS6299:Fart 2:1995

Amex F (informative)

Gust peak factor

A simplified formula [8] for gt given by9t = 0.42 in (3600/t), where t is the gust durationtime in seconds, has been shown to be within afew percent of more complex formulations asproposed by Gm?enway [17] and ESDU [18]. For thepurposes of these procedures the simplifkd formulawas thus considered adequate. However, the valueof the gust factor in terms of the gust period t isnot of direct application to design. The problem israther to determine, for static structures, theappropriate gust speed which will envelop thestmcture or component to produce the maximumloading thereon.

Fortunately for bluff type structures, such asbuildings, which can be designed statically, there isa simple empirical relationship between the periodt and the characteristic size of the structurs orelement a given by

t= 4.5a/VO (F.1)

where

V. isthe relevant mean wind speed at heightH, given by V. = V& for country terrain;and V. = V& T= for town terrain

NOTE. Acceleration of the wind speed by tqwgmphy dws notsignifkantiy affect the size of the gusts, w that topographicincrement Sk is not included in the equatiow for Vw

By combining these two equations, a gmph can beplotted of height against a/V, for town te- togive values of the gust peak factor gt. Thii isshown in f~rc F.1. For design purposes it is likelythat V~ will lie within the range20 m/s < V, <30 m/s so that for a size of, forexample, 20 m, a/V, lies in the range0.67s < aJV, < 1s. For a height of 20 m abovegrrmnd, gt wind speed would be within * 1.8 %over this range of site mean speed. Simifarpercentage changes would apply for different sizesand heights. Comequently for these purposes thevrdues of gt adopted have been based on a singlevalue of V, - 24 m/s, representative of the wholeof the UK. The resulting values of size a are thenshown as the abscissa on the graph of figure F.1which enables gt to be read directly for givenheights and sizes. Factor gt is given in table 24 forvarious heights and building sizes.

81

BS6299:Pert 2:1995 Annex F

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BS6399:Part2 :1995

List of references (see clause 2)

Informative references

[1] ENGINEERING SCIENCES DATA UNIT (ESDU). Wind Engineering. London: ESDU InterrrationaL~l

(2] CONSTRUCITON INDUSTRY RESEARCH AND INFORMATION ASSOCIATION (CIRIA). WindEngineering in thsEighties. London: CIRfA, 1981.4)

[3] SIMIU, E., and SCANLAN, R.H. Wind Effects on .StWturws. New York: John Wiley and Sons, 1978.

[4] NATIONAL COUNCIL OF CANADA. Suppfernent totAsNational Building COCI%of Canada, 1980. NRCCNo. 17724, Ottawa: National Council of Canada, 19S0.

[5] COOK, N.J. Tlwasawmmi of dssign wind spsed data: manual works~ets with ready-reckoner tabfes.(Supplement 1 to The &signer’s guids to wind foad of building struzturws [6,S] ). Gamton: BuildingResearch Establishment, 1985 (Reprinted with amendment 1991).

[6] COOK, N.J. The &?.signer’s gaide to wind foading of building structures. Rmt 2: Static structures.London: Butterworth Scientific, 1985.

[7] WILLFORD, bf.R., and ALLSOP, A.C. Dssign guids fb-r wirui loads on urrzfadfranwd buildingstructures during construction (Supplement 3 to W dssigrum’s guide to wind faadirrg of buildinystructures [6, 81). Gamton: Building Research Establishment, 1990.

[8] COOK, NJ, The de-signer’s guirk to wind foading of imilding structures. F&t 1: Background, damageSWTS?Y,WirJ-ddata ad St?%cturaL cfa.sst~ication. London: Butterwor’th Scientific, 1985.

[9] REINHOLD, T.A., ed. Wind Tunnel ModAlirrg fm Civil EWirreering Applications. Cambridge:Cambridge Unive~ity Press, 1982.

[ 10] COLLINGBOURNE, R.H. Wind data available in the Meteorolo~cal Office. .Juur_nulof hrdu.sttia~Aervdwwmics. 1978, 3, 145-155.

[11] COOK, N.J. lbwards better estimation of extreme winds. Jo-urnal of Wind Errginsering and IndustrialAerudynnmics. 19S2, 9, 295-323.

[12] COOK, N.J. Note on directional and seaaonal assessment of extreme winds for design. Jvurrzd of WindEngineering and Industrial Aerodynamics 1983, 12, 365-372.

[13] COOK, NJ,, and PRIOR, M.J. Extreme wind climate of the United Kingdom. Journal of WindEngineering and Industrial Aervdy?ramirs. 1987, 26, 371-3S9.

[14] MAYNE J R. The estimation of extreme winds. Journal of Industrial Aerodynamics. 1979, 5, 109-137.

[15] COOK, N. J., SMfTH, B.W., arrd HUBAND, M.V. BREprvgram STRONGBLOU?’ user’s manual(Supplement 2 to The dssignerk guids to w“rrd foadirrg of &uildirrg structures [6,S]). BRE Microcomputerpackage, Garston: Building Research Establishment, 1985.

[16] ENGINEERING SCIENCES DATA UNIT. Strong winds i. thx atmospheric bouruiarg faym Ftzrt 1:Mean hourly wirrd speeds. Engineering Sciences Data Item S2026. London: ESDU International, 1990.

[17] GREENWAY, M.A. An smdytical approach to wind velocity gust factors. Journal of IndustrialAerodynamics. 1979, 6, 61-91.

[ 1S] ENGINEERING SCIENCES DATA UNIT. Strung winds i. tfrz atmospheric bwundary kzym F&t 2:Disc-r%% gust speeds Engineering Wiences Data Item S3045. London: ESDU International, 19S3.

3) Available from: ESD~ Intemati.nal, 27 C“mham street, L.ordoc, N1 6UA. Tel. 0171 4905161.

4) Available from: CIRIA, 6 Storeys Gate, London, sWIP :3AU. Tel. {1171 222 S891.

BS 6399 :Part 2:1995

B81389 Chiswick H@ RoadLondonW44AL

9508– 10

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British Code BS 6399 Part 2 Wind 20loads