AS/NZS 1170.2 Site Wind Speed Calculator

Calculate site wind speed V_sit,β from regional wind speed and site exposure multipliers

V_sit,β = V_R × M_d × M_z,cat × M_s × M_t

1 — Regional Wind Speed, V_R

AS/NZS 1170.2:2011 — Clause 3.2

Regional wind speed V_R (m/s) Enter the regional gust wind speed determined from Section 3.

Wind Region Required for determining M_d.

2 — Climate Change Multiplier

Edition check

Climate multiplier used in attached 2011 basis M_c = 1.000

Important: The attached AS/NZS 1170.2:2011 edition does not include a climate-change multiplier in Equation 2.2. Therefore this calculator does not multiply the 2011 site-wind-speed equation by a climate factor. AS/NZS 1170.2:2021 introduced a climate-change multiplier.

3 — Wind Direction Multiplier, M_d

Clause 3.3 — Table 3.2

Wind Direction β

Regions B, C & D — Application

Wind direction multiplier M_d = 1.000

M_d is determined from the selected wind region, wind direction and structural application.

4 — Terrain / Height Multiplier, M_z,cat

Clauses 4.2.1 & 4.2.2 — Table 4.1

Terrain Category

Reference height z (m) Generally the average roof height is used, subject to the applicable structural provisions.

Terrain / height multiplier M_z,cat = 0.830

Table 4.1 values are linearly interpolated for intermediate heights and intermediate terrain categories TC1.5 and TC2.5.

5 — Shielding Multiplier, M_s

Clause 4.3 — Table 4.3

Shielding assessment

Subject building height h (m)

Average shielding building height h_s (m)

Average shielding breadth b_s (m)

Number of shielding buildings n_s

Average upwind ground gradient

Only qualifying upwind buildings within the applicable shielding sector should be counted. Trees and vegetation are not used as shielding under the attached 2011 Standard.

Shielding multiplier M_s = 1.000

Shielding is currently ignored, therefore M_s = 1.0.

6 — Topographic Multiplier, M_t

Clause 4.4

Topographic condition

Topographic height H (m)

Upwind half-height distance L_u (m)

Distance from crest |x| (m)

Reference height z (m)

Site position

Manual M_t

Topographic multiplier M_t = 1.000

Flat or insignificant topography selected.

7 — Site Wind Speed, V_sit,β

AS/NZS 1170.2:2011 — Clause 2.2

M_d 1.000

M_z,cat 0.830

M_s 1.000

M_t 1.000

V_R 45.0

SITE WIND SPEED V_sit,β = — m/s AS/NZS 1170.2:2011 — Equation 2.2

Enter the project parameters and select “Calculate Site Wind Speed”.

This engineering tool assists with calculation only. Terrain, shielding, topography, wind region and wind direction must be selected using engineering judgement and the complete requirements of AS/NZS 1170.2.

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