Wind tunnel testing key to development

Wind engineers say developers need to give greater consideration to wind conditions and the comfort of ground-level pedestrians when designing new buildings.

While in some overseas jurisdictions, such as Canada and a host of European countries, developers are required to conduct pedestrian wind studies before building, that is not the case in Australia.

According to Global Wind Technology Services consultant Craig Skipsey, while there is strict safety criteria in place when it comes to the height of a development, rules governing ground level wind speeds were not being enforced.

“The safety criteria is pretty well-known and that’s the minimum – which is an average wind speed both mean and gust, so that’s pretty straight forward,” he said.

“There is a further set of criteria, which defines what the pedestrian area is being used for, and that is walking, standing and sitting.”

“Different wind engineers use variations of these criteria but generally they’re all on the same principle and that is what is the area going to be used for?”

When it comes to built-form, current safety standards render a building unsafe if any aspect of the development is susceptible to an average gust speed of more than 82 kmh (measured over three seconds) or 54 kmh over an hour.

According to Mr Skipsey, ground level wind speeds are an issue of comfort rather than safety and become a concern when developers incorporate space for retail or cafes.

Wind engineer and director of JDH Consulting Dr John Holmes said under the current system, developers could choose to ignore wind tunnel findings if the recommended changes weren’t financially viable.  

“It may be the case that, even though wind tunnel tests were done, they didn’t really follow the results of the test,” he said.

“They accepted them and got the planning approval but didn’t implement what was recommended.”

However, Dr Holmes noted that in certain planning jurisdictions, such as Southbank and Fishermans Bend, the requirements are more stringent.

“In Southbank and Fishermans Bend they’ve actually designated wind speeds in numerical units,” he said. “That is different to other parts of Melbourne, which tend to just have more general criteria.”

“But in this area, for the first time, they’ve actually designated certain comfort levels of wind speed that mustn’t occur more than a certain percentage of the time.”

The City of Melbourne’s design and development overlay policy states that developments in Southbank are expected to be acceptable for stationary long-term wind exposure “where the peak gust speed must not exceed 10 m/s.”

Dr Holmes said he believed such guidelines had been implemented by the City of Melbourne due to lessons learned from planning failures in Docklands.

“I think there has been a lot of problems in Docklands,” he said. “I think there have been cases where people have set up outdoor coffee shops and they can’t use them and the businesses are suffering as a result,” he said.

Wind tunnel testing typically models a development and its surrounding area in either 1:200 or 1:400 scales, in order to assess a building’s impact on adjacent air conditions.

Small sensors are scattered in various locations across the model area, which provides a range of statistical data that is subsequently correlated back to the meteorological data collected from surrounding weather stations.

While all developments will go through wind tunnel testing, Mr Skipsey said developers should undertake a wind analysis before the design phase.

“There is definitely value in getting wind advice early rather than creating a design and then dealing with wind as a problem to solve later,” he said.

Dr Holmes said the matter was a national issue and that the Australasian Wind Engineering Society was seeking more consistency on the criteria.

He said the group had put forward a proposal to the City of Melbourne to conduct a comprehensive temperature and wind-speed study.

If given the green light, it is hoped that findings from the study will assist Australian planning authorities to implement a blanket criteria for all developers to adhere to.