Description

Provides background material to the requirements of AS/NZS 1170.3, Snow and ice actions. Clause by clause, it gives the origins of requirements, departures from previous practice and explanations with examples to illustrate their applications. Common problems for design are also discussed.

Scope

This Commentary is intended to be read in conjunction with AS/NZS 1170.3:2003. The Commentary includes explanations of the provisions of AS/NZS 1170.3 and, in some cases, suggests approaches that may satisfy the intent of the Standard. Commentary Clauses are not mandatory.

Appendices contain additional information on design and worked examples as follows:

• Appendix CA - background to the loading equations and format of the Standard, including extracts from ISO 4355,
• Appendix CB - common problems and their avoidance,
• Appendix CC - methods for determining terrain classification, and'
• Appendix CD - worked examples.

For assessment of snow action, the Standard considers the uniform snow that accumulates under calm air conditions, the shape of the roof and the snow pattern on the roof caused by windy conditions. For vertical loads on roofs, these influences are described in terms of shape coefficients (µi).

Methods are given for use in alpine areas where snow may accumulate for 3 or 4 months and for sub-alpine areas where it only lasts for a few days. Sub-alpine areas are where wind speeds are high and weather conditions are such that all the snow normally melts and clears between individual weather systems.

A load case corresponding to severe imbalances resulting from snow removal, redistribution, sliding, melting, etc. (e.g., zero snow load on specific parts of the roof) should always be considered. Such considerations are important for structures that are sensitive to the form of the load distribution (e.g., curved roofs, arches, domes or other structures).