British Code BS 6399 Part 2 Wind 20loads

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Text of 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 thisstadati.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 Ic 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) 137 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 arbMary 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

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    56

    57

    58

    59

    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