Description

This commentary provides background material to the requirements of AS/NZS 1170.2, Wind actions. Clause by clause, it gives the origins of requirements, departures from previous practice and explanations with examples to illustrate their application.

Scope

This Commentary is intended to be read in conjunction with AS/NZS 1170.2:2002. The Commentary includes explanations of the provisions and in some cases suggests approaches that may satisfy the intent of the Standard. Commentary Clauses are not mandatory. Lists of references are also given at the end of each Section for further reading. The principles for determining wind actions given in the Standard are generally applicable to wind loads on any structure. The specific data given for the cases outlined (e.g., aerodynamic shape factors) are based on research involving wind tunnel testing, measurements in the field and calculation using established principles of fluid mechanics. They are generally relevant for simplified situations; however, the values derived are applied to real design cases using methods that account for such uncertainties (see also Clause C1.4).

The Standard does not attempt to predict the effects of possible future climatic changes, as the evidence for changes in wind speeds is inconclusive. For the effects of tornadoes, wind speeds can be significantly higher than those given in the Standard. The effect of debris is also significant. Such wind events are not covered due to their small nature and low occurrence in populated areas of Australia and New Zealand. Structures that extend over considerable distances, such as powerlines or pipelines, may be affected by tornadoes if the usual path of such events is across the structure.

The methods given in the Standard are not sufficient for some structures such as electricity transmission structures, bridges, lattice towers, cranes and similar, as specific details necessary to perform calculations are not given. In these cases, the Standard may be used to determine site wind speeds or design wind speeds, but other Standards should be referenced for detailed factors.