Cantilever Roofs - AS/NZS 1170 - change proposed as wind loading may be underestimated

This article is to advise structural designers that, as a result of recent research, a change to wind loading requirements for cantilevered roofs is being proposed. Any structural designer analysing roofs of this type (eg, grandstands of rectangular plan form) should be aware that current requirements may significantly underestimate bending moments on the cantilever.

An amendment to Appendix D5 of AS/NZS 1170.2:2002 is being proposed and public comment will be invited by Standards Australia and Standards New Zealand shortly.

To ensure you are notifed when public comment is invited on this draft amendment, please contact Standards New Zealand to be added to the mailing list.

The Department recommends, pending approval of the amendment by the Standards New Zealand Council and citation by the Department, that either the proposed changes be applied to this type of roof or, as a minimum, the implications of the revised loading be examined.

The proposed change follows a comprehensive study of equivalent static wind loads on typical cantilevered stadium roofs of rectangular plan form. Reasons for the higher loads include:

• inclusion of shielding from other structures in past tests
• use of dynamic displacements rather than pressure measurements to derive wind loading from tests
• inconsistencies in the conversion from hourly mean wind speed to 3-second gusts, and
• d use of a more realistic pressure distribution on the roof.

The Department is grateful for information provided by Dr John D Holmes of Melbourne, Chair of the BD006-02 Committee of Standards Australia and Standards New Zealand.