Extensive consideration should be given by developers to the impact of new buildings on wind conditions within their immediate vicinity and the comfort of ground-level pedestrians.
In certain overseas jurisdictions, such as Toronto, Canada, pedestrian wind studies are now required before new building developments proceed, given the impact of tall structures in particular on ground-level wind conditions.
According to wind engineer Dr. John Holmes, director of JDH Consulting, the major cities of Australia already impose similar requirements for certain building developments.
“While no Australian jurisdiction explicitly requires wind tunnel tests for any new project as Toronto apparently does, the capital cities and the Gold Coast in Australia do require a wind environment report for projects above certain height limits in order to get planning approval,” he said. “These have varying degrees of detail. In some cases ‘desktop’ assessments are accepted instead of wind-tunnel test reports – usually for building heights of 60 metres or lower."
Holmes noted that in certain jurisdictions the requirements are more stringent, entailing more sophisticated and costly assessment methods.
“Melbourne has specific criteria for Southbank and Fishermen’s Bend, placing limits on gust speeds at ground level with a defined probability of exceeding various activities, which new projects must meet prior to approval," he said. “To demonstrate this would generally require wind tunnel tests.”
A case in point is the assessment of a development situated at 545 Station Street in the Melbourne suburb of Box Hill by wind engineering company Windtech, based on architectural and landscape drawings of the proposed project submitted in the first half of 2013.
The proposed development consists of a seven-storey podium topped by an L-shaped tower, rising to a height of 118.3 metres above Station Street.
Testing of the impact of the building on surrounding wind conditions was of particular importance given the nature of the adjacent ground-level areas and the specific features of the project itself.
Pedestrian footpaths are situated along Station Street to the east as well as Carrington Street to the south, while the southern side of Carrington Street is also host to café seating areas.
In order to assess the buiding’s impact on adjacent air conditions, a boundary layer wind tunnel was used to test a 1:400 detailed scale model of the development. The tunnel itself possesses a 2.6-metre wide working section, and a fetch length of 14 metres.
Proximity models were also employed to represent adjacent buildings and land topography to a radius of roughly 500 metres from the development site.
The wind tunnel testing enabled engineers to measure peak gust and mean wind speeds at various study point locations both within and around the development.
This information was then combined with the relevant meteorological data for the Box Hill area to determine equivalent full-scale wind speeds, and then measured against a range of criteria for pedestrian wind comfort and safety.
In the case of the Box Hill development, the study concluded that no treatment would be required as the surrounding patches of dense foliage would help it satisfy pedestrian comfort requirements for the relevant outdoor areas.
Buildings in other parts of Australia may soon become subject to similar wind tunnel testing requirements, however, with the Australasian Wind Engineering Society currently producing recommended criteria similar to those imposed in Melbourne’s Southbank area.
Holmes pointed out that regulatory requirements are of particular importance for new development zones, given their increased susceptibility to ground-level wind comfort issues.
“New areas without any specific regulatory requirements are more likely to have pedestrian-level wind problems than developed areas, as an isolated tall building without surrounding buildings of similar height to provide shielding is more likely to bring higher winds down to ground levels,” he said.