Wind Actions to AS/NZS 1170.2:2002

by Engineers' Compendium

The procedures and formulas processed by the forms on this site are based on the Joint Australian/New Zealand Standard AS/NZS 1170.2:2002 Structural design actions, Part 2: Wind actions. To view a Digest of the standard, click here (opens in new window). The Digest includes cue cards for processing the formulas with MATHSERV.

The Digest or this Online Program should NOT be referenced without having access to the code. They are NOT a substitute for the code but are my personal interpretation of the code. Clause and Table numbers refer to AS/NZS 1170.2:2002 unless otherwise noted.

Procedure For Determining Wind Actions

• Step 1 (you are here): determine the design wind speeds from Section 3 - Regional Wind Speeds, and Section 4 - Site Exposure Multipliers;
   
• Step 2: determine design wind pressures from Section 5 - Aerodynamic Shape Factors, and Section 6 - Dynamic Response Factors;
   
• Step 3: calculate wind actions from Section 2 - Calculation of Wind Actions, being the vector sum of the forces calculated from the design pressures applied to surface areas or structural elements.

Simply *Tab* through all the input fields and change as appropriate for your given situation:

Regional wind speeds, VR (Clause 3.2)

These are 3-second gust wind speeds appropriate to the region in which the structure is to be constructed, where R (average recurrence interval) is the inverse of the annual probability of exceedance...

Please note that this form allows you to insert any equation based on RS and RU simply by selecting "CUS" and typing your equations for VR in the appropriate boxes. You may also overwrite any calculated or default values (in yellow boxes) with your own custom values.

Wind direction multiplier, MD (Clause 3.3)

Regions B, C and D:

Multipliers for regions A and W are shown in Table 3.2. Permission to reproduce the copyright table has not been sought. You may overwrite the above default values with your own custom values.

Terrain and height multiplier, MZC (Clause 4.2)

To understand the input and output of this form, please refer to the standard or read my digest of AS/NZS 1170.2:2002.

You will note that the output is single comma-separated values if the region is non-cyclonic and double slash-separated values if it is cyclonic. The reason is that cyclonic regions usually have separate formulas for serviceability and ultimate limit state. It may have something to do with "progress in extreme value theory, notably the development of 'peaks over threshold' methods" (see OMAE98-1218).

Shielding multiplier, MS (Clause 4.3)

See the digest of AS/NZS 1170.2:2002 for the formulas used by this form.

Topographic multiplier, MT (Clause 4.4)

See the digest of AS/NZS 1170.2:2002 for the formulas used by this form.

Summary of Step 1 - design wind speeds in m/sec

"Summary" looks at the required input fields and calculates site wind speed
VSB = VR*MD*(MZC*MS*MT) and sets this equal to the design wind speed (Clauses 2.2 and 2.3). If design level, Z, is an array, the output is a corresponding array.
"Report" produces a printable summary of your input and output data.
"Pass results and goto Step 2" saves the data to a cookie and changes this page so that one of five types of structure may be selected for further processing.