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AS/NZS 1170.2:2011 - 4.4.2 Hill-shape multiplier

AS/NZS 1170.2:2011 - 4.4.2 Hill-shape multiplier

AS/NZS 1170.2:2011 - 4.4.2 Hill-shape multiplier

The hill-shape multiplier has the greatest effect on site wind speed of all the site exposure multipliers (up to x1.71), yet the standard does not offer much guidance on how to calculate the value. I would appreciate finding out how others arrive at calculating this multiplier.

1. How do you decide the height (H) of the hill, ridge or escarpment when the terrain is complex (i.e. foothills or multiple peaks)?

2. How do you select the "most adverse topographic cross-section within the range of directions within 22.5 degrees on either side of the cardinal direction being considered" (See clause 4.4.2), given that there are theoretically infinite cross-sections within the sector. Any methods?

RE: AS/NZS 1170.2:2011 - 4.4.2 Hill-shape multiplier

1. Refer to the commentary, there is a procedure recommend in CL C4.4.2 that could be applied.

2. Look at the values you need in the formulas and calculate it out. It should become apparent what drives the result (generally its the steepness of the top slope height of H/2, so relationship of Lu and H matter as this flows through into L1 and L2 values). Search for the worst case of this condition within your sector.

RE: AS/NZS 1170.2:2011 - 4.4.2 Hill-shape multiplier

Thanks for the response Agent666, however:
1. "AS/NZS 1170.2 Supplement 1:2002" is now withdrawn, and AS/NZS 1170.2:2011 has no commentary.

2. I fully agree, however this may be a time consuming process when H is redetermined for each cross-section, by a method like you referred to from the old supplement (As mentioned in 1.).

RE: AS/NZS 1170.2:2011 - 4.4.2 Hill-shape multiplier

There is software that can help make these easier checkwind is one such software.

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

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