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While the general methodology and pressure coefficients given in this standard may be used in other wind climates, it is essential to ensure that the reference wind data are consistent with the assumptions in this standard. The value of the site wind speed Vs should be obtained from the relevant meteorological authority. When the reference wind speed for the site is given as a peak gust, the hourly mean value for the site may be obtained by dividing the peak gust by the factor in Table 4, for the reference terrain and height above ground.
When reference wind speeds apply to locations other than the site, expert advice will generally be needed. It should also be noted that adjustments to partial factors on loading may be necessary depending on: a the probability factors implied in the data given; and b whether or not the site is subject to hurricanes or typhoons. BS was a technical revision of CP3:Chapter V:Part 2 now withdrawn which incorporated the considerable advances made and experience gained in wind engineering since that time.
Changes introduced by Amendment 1 to this part of BS include: closer alignment of the pressure coefficients for pitched roofs in the standard method with those for the directional method; changes to the pressure coefficients for walls including the introduction of net pressure coefficients for estimating overall loads on buildings; reduction factors for free standing walls and parapets depending on their length to height ratios; clearer text for the clause dealing with asymmetry of wind loading.
Opportunity has also been taken to incorporate editorial changes to some clauses for better clarity. The basic wind speed in this British Standard is given as an hourly mean value; this differs from CP3:Chapter V:Part 2 in which it was based on a 3 s gust value. However, the hourly mean basic wind speed is subsequently converted into a gust wind speed for use in design by a gust peak factor which takes account of gust duration time, height of structure above ground and the size of the structure.
The adoption of the hourly mean value for the basic wind speed is for technical reasons. Primarily it allows a more accurate treatment of topography, but it also provides the starting point for serviceability calculations involving fatigue or dynamic response of the structure. Its use is also a move towards harmonization as mean values sometimes 10 min means are often the basis for wind loading calculations in European and International Standards.
Structure factors are used to check whether the response of the structure can be considered to be static, in which case the use of the calculation methods in this standard is appropriate. If the response is found to be mildly dynamic the methods can still be used but the resulting loads will need to be augmented.
Structures which are dynamic will also be identified but their assessment is outside the scope of the standard. Two alternative 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 generally gives a conservative result within its range of applicability. The degree of conservatism can be much larger close to the ground and in towns, but decreases to zero around m above the ground.
Because of this it is anticipated that the standard method will be used for most hand-based calculations and that the directional method will be implemented principally by computer. Procedures are also given to enable the standard effective wind speed to be used with the directional pressure coefficients and for the directional effective wind speeds to be used with the standard pressure coefficients.
CP3:Chapter V:Part 2 allowed for the effect of ground roughness, building size and height above ground by a single factor. This required the calculation of separate wind speeds for every combination of reference height above ground and the size of the loaded area.
However, a simplification has been introduced in the standard method which involves the calculation of only a single wind speed for each reference height. The effect of size is allowed for by a separate factor, Ca. BS also gives values for external pressure coefficients for a greater range of building configurations than did CP3:Chapter V:Part 2.
This new edition introduces Annex G in which empirical equations are provided to enable the topographic location factor s to be calculated.
Also given are tables which have been derived directly from the equations which will be useful as an accuracy check to those wishing to implement the equations into computer software. A British Standard does not purport to include all the necessary provisions of a contract.
Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i to vi, pages 1 to and a back cover.
The BSI copyright notice displayed in this document indicates when the document was last issued. Sidelining in this document indicates the most recent changes by amendment.
Two alternative methods are given: a a standard method which uses a simplified procedure to obtain a standard effective wind speed which is used with standard pressure coefficients to determine the wind loads for orthogonal design cases. Other methods may be used in place of the two methods given in this standard, provided that they can be shown to be equivalent. Such methods include wind tunnel tests which should be taken as equivalent only if they meet the conditions defined in Annex A.
NOTE 2 Wind tunnel tests are recommended when the form of the building is not covered by the data in this standard, when the form of the building can be changed in response to the test results in order to give an optimized design, or when loading data are required in more detail than is given in this standard.
Specialist advice should be sought for building shapes and site locations that are not covered by this standard. The methods given in this Part of BS do not apply to buildings which, by virtue of the structural properties, e. These should be assessed using established dynamic methods or wind tunnel tests. NOTE 3 See references  to  for examples of established dynamic methods.
NOTE 4 If a building is susceptible to excitation by vortex shedding or other aeroelastic instability, the maximum dynamic response may occur at wind speeds lower than the maximum. Editions of these publications current at the time of issue of this standard are listed on the inside back cover, but reference should be made to the latest editions. A Area 2. This shows the stages of the standard method, together with the relevant clause numbers, as the boxes outlined and connected by thick lines.
The stages of the directional method are shown as boxes outlined with double lines and are directly equivalent to the stages of the standard method. Various input data are shown in boxes outlined with single lines. These may be: a the structure as a whole; b parts of the structure, such as walls and roofs; or c individual structural components, including cladding units and their fixings. NOTE Wind load on a partially completed structure may be critical and will be dependent on the method and sequence of construction.
The standard method gives conservative level of dynamic excitation to determine: values for standard orthogonal load cases, and a simplified a whether the methods given in this Part of BS apply method for buildings up to m in height and for significant and the assessment may proceed; or topography. The directional method gives a more precise value b whether the methods given in this Part of BS do not for any given wind direction, particularly for sites in towns, and apply and the building should be assessed by one of the where topography is significant.
A simple rule for assessing the methods for dynamic buildings see references  to  or significance of topography is provided. Stage 7: Determines the effective wind speeds required by Stage 3: Determines the basic hourly mean wind speed from either method.
The effective wind speed is a gust wind speed the map for the UK. In the standard method this corresponds to a datum size of Stage 4: Determines a site wind speed, still corresponding to the hourly mean wind speeds at a height of 10 m above ground loaded area, while in the directional method this corresponds to in the standard exposure, from the basic wind speed by the size of the loaded area under consideration. Up to this point, no allowance for the exposure of the dynamic pressure.
In the standard method these coefficients standard and directional method. Stage Determines the wind loads from the dynamic Stage 5: Assesses the exposure of the site in terms of the pressure, pressure coefficients, dynamic augmentation factor terrain roughness and the effective height. Three categories of and, in the standard method, by the size effect factor, to give terrain roughness are used to define the site exposure.
The the characteristic wind load for static design. The standard permits equivalent static loads to be used for the design of mildly dynamic structures by the introduction of a dynamic augmentation factor. The value of this factor depends upon the actual height H of the building above ground and on a building-type factor Kb obtained from Table 1, for the form of construction of the building.
The dynamic augmentation factor Cr is given for typical buildings in Figure 3. Table 1 — Building-type factor Kb Type of building Kb Welded steel unclad flames 8 Bolted steel and reinforced concrete unclad frames 4 Portal sheds and similar light structures with few internal walls 2 Framed buildings with structural walls around lifts and stairs only 1 e. More accurate values of these factors may be derived using Annex C when the building characteristics are not typical, or when the effects of topography and terrain roughness need to be taken into account.
Buildings falling outside these limits should be assessed using established dynamic methods. NOTE See references  to  for further information on analysis of dynamic structures. To obtain the effective wind speed the effects of varying ground roughness, the height and distance of obstructions upwind of the site and the effects of topography should be taken into account. NOTE 1 Permanent forest and woodland may be treated as town category.
NOTE 1 In the absence of more accurate information, the obstruction height Ho may be estimated from the average number of storeys of upwind buildings by taking the typical storey height as 3 m. Further guidance is given in Annex E. When considering low rise buildings which are close to other tall buildings the rules for effective height will not necessarily lead to conservative values and specialist advice should be sought.
The standard method uses a simplified allowance for significant topography, as defined in Figure 7. It gives better estimates of effective wind speeds in towns and for sites affected by topography. Combination a is appropriate when the form of the building is well defined, but the site is not; the cases of relocatable buildings or standard mass-produced designs are typical examples.
Such hybrid combinations should be applied only in accordance with 3. When the building is doubly-symmetric, e. When the building is singly-symmetric, three orthogonal cases are required, e. When the building is asymmetric, four orthogonal cases are required. When symmetry is used to reduce the number of orthogonal load cases, both opposing wind directions, e.
Values of size effect factor are given in Figure 4, dependent on the site exposure see 1. For external pressures the diagonal dimension a is the largest diagonal of the area over which load sharing takes place, as illustrated in Figure 5. For internal pressures an effective diagonal dimension is defined in 2. Load effects, for example bending moments and shear forces, at any level in a building should be based on the diagonal dimension of the loaded area above the level being considered, as illustrated in Figure 5c.
NOTE 2 As the effect of internal pressure on the front and rear faces is equal and opposite when they are of equal size, internal pressure can be ignored in the calculation of overall horizontal loads on enclosed buildings on level ground. In practice, option b will not produce significantly lower values than a unless the combination of location, exposure and topography of the site is unusual.
Its calculation in the standard method depends on whether topography is considered to be significant, as indicated by the simple criteria in Figure 7.
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BS-6399-2 Wind Code Options - CAESAR II - Help
Specifies the design value of the wind speed. These vary according to geographical location and according to company or vendor standards. Here are a few typical wind speeds in miles per hour. Typical wind speeds are shown in Figure 6 of BS The wind speeds are only relevant to the United Kingdom.
Caution Newer versions. Code of practice for wind loads. Gives methods for determining the gust peak wind loads on buildings and components thereof that should be taken into account in design using equivalent static procedures. Not applicable to buildings which, by virtue of the structural properties, e. Only applicable to sites in the UK. Superseded by BS EN Amendment dated 27 March - Indicated by a sideline in the margin.
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