Guide To Wind Classification PDF

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GUIDE TO WIND CLASSIFICATION

MONIER – GUIDE TO WIND CLASSIFICATION

GUIDE TO WIND CLASSIFICATION Introduction An accurate wind classification is essential input to determining the installation standard to ensure that the performance of a tiled roof is not compromised by environmental conditions.

It is important to categorize each building on a case-by-case basis. Each site should be assessed individually for its wind classification. Each building must be assessed for compliance with geometry and for evaluation of pressures.

It is normal practice that the advice of a suitably qualified building engineer be sort to accurately determine the Wind Classification for a site.

Therefore, Monier Roofing does not accept liability for any loss or damage suffered as a result of any errors in the interpretation or application of this design guide. Monier Roofing recommends that the advice of a suitably qualified building engineer is sort in assessing the wind classification of a particular site.

The information provided in this guide has been created to assist the designer or the main contractor in their responsibility in determining the appropriate wind classification (or design wind velocity (m/s)) for a site. Also note that the process used in the guide is an approximate method for estimating wind classifications for residential structures only. For full analysis refer to Australian/NZ Standards; • AS/NZS 1170.2:2011 and by its Amendment 2 (2012); Definition of Terrain category • AS1170.2-2002 - Structural design actions, Part 2: Wind actions; This Standard is generally applicable to determining the wind loads on any structure. • AS 4055-2002: Wind loads for housing”. In NZ, the relevant standard is NZS 4203.

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MONIER – GUIDE TO WIND CLASSIFICATION

What is wind classification

Step 1. Geographic wind speed region

The wind classification relates to gust wind speeds (m/s) that affecting a given site. The determination of a wind classification is critical in ensuring that a building is designed and constructed to the level appropriate to withstand the wind forces it will be subjected to. The wind classifications defined in the standards are summarised in the Table 1 below:

FIGURE 1: Wind Speed Region

MORETON

BORROLOOLA KUNUNURRA

TABLE 1 – WIND CLASSICATION CONVERSION TABLE

AT HERTON BURKETOWN

WIND CLASSIFICATION Regions A and B

Regions C and D

Gust Wind Speed (m/s)

N1 (Non-Cyclonic)

N/A

W28

N2 (Non-Cyclonic)

N/A

W33

N3 (Non-Cyclonic)

C1 (Cyclonic)

W41

N4 (Non-Cyclonic)

C2 (Cyclonic)

W50

N5 (Non-Cyclonic)

C3 (Cyclonic)

W60

N6 (Non-Cyclonic)

C4 (Cyclonic)

W70

20ϒ

PORT HEDLAND

20ϒ

COLLINSVILLE

MARBLE BAR MILLST REAM BILOELA

BUNDABERG 25ϒ

CARNARVON 25ϒ

30ϒ

BOURKE 30ϒ

GREEN HEAD

Determining a wind speed classification The selection of wind speed classification for a house depends on the conditions at the site of the house. The classification shall be determined from Table 2 on Page 8 using the following site conditions: STEP 1 The region where the site is located as defined in Figure 1 (Region A B C or D as given in AS/NZS 1170.2).

50km 100km

45ϒ

150km

STEP 2 The terrain that surrounds or is likely to surround the site within the next 5 years, as defined in Figure 2 on Page 4

NON-CYCLONIC CLASSIFICATION

Region A

Region B

CYCLONIC CLASSIFICATION

Region C

Region D

STEP 3 The topography of the site, as defined in Figure 3 on Page 5

Please note: Specific design wind speed recommendations are available for some regions via government recommended websites. Refer to the links below for specific regionally information;

STEP 4 The shielding that a structure is subjected to, as defined in Figure 4 on Page 6 FS PS or NS

> SOUTH AUSTRALIA http://tinyurl.com/mns36yv

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MONIER – GUIDE TO WIND CLASSIFICATION

Step 2. Selection of terrain category Terrain categories are used for determining a structure’s exposure to wind as a result of terrain that surrounds it. The terrain category for a housing site is a measure of the lowest effective surface roughness from any radial direction within a distance of 500 m of the proposed housing site.

It shall be based on the likely terrain five years after design. The terrain category for a housing site shall be identified by the notation TC1, TC1.5, TC2, TC2.5 or TC3 and shall be determined as follows:

Supporting Notes: Well established trees may be considered as obstructions for evaluation of terrain category. In selecting a terrain category due regard to the permanence of the obstructions should be made.

FIGURE 2: Terrain Category

TERRAIN CATEGORY 1 Very exposed open terrain with few or no obstructions and enclosed limited sized water surfaces at serviceability and ultimate wind speeds in all wind regions, e.g. flat, treeless, poorly grassed plains, or river, canals, lakes and enclosed bays, extending less than 10 km in the wind direction.

1

TC

TERRAIN CATEGORY 1.5 Open water surfaces subjected to shoaling waves at serviceability and ultimate wind speeds in all wind regions, e.g. nearshore water, large unenclosed bays on seas and oceans, lakes and enclosed bays extending greater than 10 km in the wind direction. TERRAIN CATEGORY 2 Open terrain including grassland with well-scattered obstructions having heights generally from 1.5 m to 5 m with no more than two obstructions per hectare, e.g. farmland and cleared subdivisions with isolated trees and uncut grass. TERRAIN CATEGORY 2.5 Terrain with a few trees and/or isolated obstructions. This category is intermediate between TC2 and TC3 and represents the terrain in developing outer urban areas with scattered houses, or large acreage developments with fewer than 10 buildings per hectare.

1.5

TC

2

TC

2.5

TC

TERRAIN CATEGORY 3 Terrain with numerous closely spaced obstructions having heights, generally from 3 m to 10 m. The minimum density of obstructions shall be at least the equivalent of 10 house-size obstructions per hectare, e.g. suburban housing or light industrial estates.

3

TC

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MONIER – GUIDE TO WIND CLASSIFICATION

Supporting Notes: In urban situations, roads, rivers, small lakes or canals less than 200 m wide shall be considered to form part of normal ‘Terrain Category 3’ terrain. Parks and other open spaces less than 250 000 m2 in area shall also be considered to form part of normal ‘Terrain Category 3’ terrain provided they are not within 500 m of each other, or not within 500 m of open country. Housing sites less than 200 m from the boundaries of open areas larger than 250 000 m2, e.g. golf courses, that are completely surrounded by urban terrain, shall be considered to have the terrain category applicable to the open area itself Shielding provisions may still apply to these sites. Housing sites less than 500 m from the edge of a development shall be classified as the applicable terrain that adjoins the development, i.e. TC1, TC1.5, TC2, TC2.5 or TC3, as applicable.

Where the water body is large (i.e. the wind has been blowing over the water for more than 10 km), then wind has the chance to develop long wavelength waves that will shoal on reaching the shore irrespective of the wind. Hence: (a) Water bodies less than 200 m wide in the direction that the wind is blowing to affect a site do not affect the terrain category. (b) Water bodies greater than 200 m wide, but less than 10 km wide in the direction that the wind is blowing to affect a site are deemed to be Terrain Category 1. (c) Only water bodies greater than 10 km wide in the direction that the wind is blowing to affect a site are deemed to be Terrain Category 1.5.

(i)

Fewer than 2 large trees per hectare can be categorized as TC2.

(ii)

Between 2 and 10 large trees per hectare can be categorized as TC2.5.

(iii)

More than 10 large trees per hectare can be categorized as TC3.

In some cases, the 500 m radius circle may contain combinations of smooth features. For example, a small lake with diameter less than 200 m may be adjoined by a park also with width less than 200 m. However, the combine width of smooth features is greater than 200 m and the lake should be considered as part of the park, giving limiting terrain category for the building at the centre of the 500 m radius circle as Terrain Category 2.

Terrain Category 2.5 addresses acreage subdivisions where the house density is less than 10 per hectare. Where trees are large and robust (similar size to houses) then wooded areas with:

Step 3. Selection of topography The topographic classification determines the effect of wind on a structure due to its location on a hill, ridge or escarpment relative to the height and slope of a hill, ridge or escarpment. A hill, ridge or escarpment is a natural feature that rises in height by more than 3° from the surrounding area. The slope of a hill, ridge or escarpment is measured by measuring the slope throughout the top half of the hill, ridge or escarpment at its steepest point. The second consideration is to determine whether the structure is located in the bottom, middle or top third of the hill, ridge or escarpment in terms of height. With the slope and the position of the structure known, the adjacent diagrams may be used to determine the topographic classification i.e T0, T1,T2, and T3.

FIGURE 3: Topographic Class

HILL WIND DIRECTION

Lower 1/3 Middle 1/3 1:20(2.9º) to...