AS/NZS 1170 Wind Code Options - CAESAR II - Help

CAESAR II Users Guide

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CAESAR II Version
13

Specifies options for the AS/NZS 1170.2 wind code.

Design Wind Speed

Typical units (depending on your unit system):

  • ft/sec

  • m/sec

  • mm/sec

Design Wind Speed Vr. This is the regional wind speed described in section 3.2 of the code.

Wind Region

Wind region. The wind region is determined from the geographic locations for Australia and New Zealand. The maps of these locations are in Figure 3.1 of the code.

Terrain Category

Value discussed in section 4.2.1 of the code. These categories are defined as:

Category 1 - Exposed open terrain with few or no obstructions and water surfaces at serviceable wind speeds

Category 2 - Water surfaces, open terrain, grassland with few, well-scattered obstructions having heights generally from 1.5 m to 10 m.

Category 3 - Terrain with numerous closely spaced obstructions 3 m to 5 m high such as areas of suburban housing

Category 4 - Terrain with numerous large, high (10 m to 30 m high) and closely spaced obstructions such as large city centers and well-developed industrial complexes

Choose the terrain category with due regard to the permanence of the obstructions that constitute the surface roughness. Vegetation in tropical cyclonic regions cannot be relied upon to maintain surface roughness during wind events.

Lee Effect Multiplier (Mlee)

Specifies the Lee Effect Multiplier. The default value is 1.0. Paragraph 4.4.3 discusses the issue of the lee effect multiplier. In the case of New Zealand, reference is made to the New Zealand site map. For all other sites, it shall be taken as 1.0.

Hill Shape Factor (Mh)

Specifies the appropriate hill shape factor, which can be obtained from Table 4.4 of the code. Please refer to paragraph 4.4.2 which gives precise details for the derivation of the hill shape factor.

Upwind Slope

(H/2Lu)

Mh

< 0.05

1.00

0.05

1.8

0.10

1.16

0.20

1.32

0.30

1.48

>= 0.45

1.71

Wind Direction Multiplier (Md)

Specifies the wind direction multiplier. The default value is 1.0.

The wind direction multiplier is detailed in paragraph 3.4 of the code, specifically Table 3.2. As the wind multiplier is determined from the cardinal wind directions (N, NE, E, SE, S SW, W and NW), the value for any direction is specified in the table as 1.0. We recommend this value be used for all cases.

Convert to Permissible Stress Gust Wind Speed

In the standard AS/NZS 1170.2 Supp 1:2002 Section C3, there is a discussion regarding the division of the wind speed given in the standard by the square root of 1.5. Checking the box converts the wind speed given to a permissible stress basis. Doing this lowers the wind loads on the vessel.

Surface Roughness Height (hr)

Typical units (depending on your unit system):

  • in

  • mm

  • cm

This value is used to compute the ratio hr/d which is then used to compute the drag force coefficient (Cd) for rounded cylindrical shapes per Table E3. For pressure vessels, this value ranges from 0.003 mm for painted metal surfaces to 15 mm for heavily rusted surfaces. Light rust has a value of 2.5 mm while galvanized steel has a value of 0.15 mm.

The ratio hr/d is taken to be unitless (mm/mm).

Site Elevation (E)

Specify the height of the site above the mean sea level, E.

Average Spacing of Shielding Buildings

Typical units (depending on your unit system):

  • ft

  • m

  • mm

Specifies the average spacing of the shielding buildings. This is discussed in paragraph 4.3.3 of the code.

Average Breadth of Shielding Buildings (bs)

Typical units (depending on your unit system):

  • ft

  • m

  • mm

Specifies the average breadth of the buildings that shield the piping.

Average Height of Shielding Buildings (hs)

Typical units (depending on your unit system):

  • ft

  • m

  • mm

Specifies the average height of the buildings that shield the piping.

Number of Upwind Bldgs at 45 degs

Specifies the number of upwind buildings within a 45 degree arc. The upwind buildings are the ones shielding the piping.