A new 2021 edition of AS/NZS 1170.2 Structural design actions - Wind actions has been included for adoption in the 2022 edition of the National Construction Code (NCC).
The new edition of AS/NZS 1170.2 has many improvements, however it includes a reduction in design wind speeds for wind Region D.
Wind Region D is unique to Western Australia. It is a 50km wide band stretching along the northwest coast from approximately Port Hedland to Carnarvon in the Pilbara region.
Building and Energy and the Cyclone Testing Station (James Cook University) have identified that the reduction in design wind speeds will lead to significant social and economic implications for Western Australia.
Mining activity in the Pilbara underpins the State's economy and is a significant contributor to the national economy. If housing stock in this region was damaged, it would be difficult to accommodate the essential workforce and local communities.
The potential impact of a wind event would be such an event will be far wider than just the local communities, and the widespread damage associated with a cyclone event with winds near the design wind speed level in the Pilbara region would have a larger effect on the State of WA as a whole.
Dr Geoff Boughton AM, Senior Research Engineer, James Cook University Cyclone Testing Station was commissioned by Building and Energy to provide an expert report on the matter. This report has led to a Western Australian State variation to NCC 2022, which aims to retain similar design wind speeds for wind Region D as the 2011 edition of AS/NZS 1170.2 (referenced in NCC 2019).
The State variation for wind Region D will only apply to those parts of Region D - being north of the Tropic of Capricorn. The State variation is not contained in the NCC 2022 Stage 1 Preview, however it will be in the final version for adoption of NCC 2022 on 1 September 2022.
What will the variation look like in NCC 2022?
The NCC clauses regarding the determination of individual actions under structural provisions refer to a table for the annual probability of exceedance when considering design for wind action. Changes shall be made to the clauses and relevant tables in both Volumes One and Volume Two of the NCC.
An additional column shall be inserted in the 'Design events for safety' table for cyclonic wind in wind Region D north of the Tropic of Capricorn similar to the example below.
Furthermore for wind actions using AS 4055, site wind classification is to be determined with a table similar to the one below to replace Table 2.2 in AS 4055.
