To blow over the Sky Tower?
When high-rise buildings are close to each other they can increase and channel wind causing more powerful gusts, which could suck windows out of their frames.
While there is a theoretical limit to any building, Locke said the level of storm that could blow down a high-rise building in Auckland was ‘‘pretty hard to imagine’’, even if not impossible.
‘‘The typical office building would be built for a one-in500-year storm, which is very unlikely to be experienced by any person.
‘‘While it’s easy to conceive of thanks to Hollywood movies, the
reality is that they probably wouldn’t fall down. But they might not be operational afterwards.’’
The Harbour Bridge, he added, was built to withstand wind, although ‘‘it has been closed due to wind damage before’’.
It’s patio furniture that keeps Locke up at night. He said in his view the scariest potential for damage in Auckland was things left outside of high-rise penthouse apartments.
‘‘Even at ground levels trampolines can fly.
‘‘Up there, the wind speed would be much higher, and it’s not well understood how a pot
plant or a table on an apartment deck would interact with those winds and what damage that might cause.’’
Experts look at wind data from New Zealand to predict what a worst-case scenario might look like in a 500 or 1000-year timeframe. But meteorologists haven’t been recording data for 500 years, and Locke admits these predictions are based on computer modelling, and experts never had 100% certainty.
‘‘We can’t say what’s going to happen with the weather tomorrow, and there’s no doubt that wind speeds can increase very rapidly. We work to a low level of risk, but it’s not no level of risk. It’s up to society to decide what the acceptable level is.’’
Dr Ahmad Zaki is a senior technician from the aerodynamics lab at the University of Auckland’s Newmarket campus.
Along with a team of researchers, he uses a 20m wind tunnel to measure how much pressure wind creates on scale models of cities. The buildings made from foam blocks are cut to resemble the real thing – most recently Auckland and London. The model is around 3.5m wide, representing several kilometres, Zaki said.
The target building for testing sits in the centre. Small holes in the model are connected to tubes which run beneath the model through to a computer sensor which measures pressure.
The researchers use a fog machine aptly named ‘‘The Hurricane’’ to help visualise how the wind interacts with the models.
‘‘We see if the building will hold or not, and may suggest a modification of the design.’’
Sometimes the polystyrene buildings get sent flying but Dr Zaki emphasises that is a failure of craft glue and not an indication that skyscrapers are about to crumble.
These models are also used to test how buildings themselves change wind speeds and what street-level pedestrians might experience in the event of a storm.
Doctoral candidate Muizz Shah has been doing just that, using 2017’s Cyclone Cook as a reference. He’s been blasting wind at a model of the PwC Tower to determine whether ‘‘wind tunnels’’ would form.
The research is part of a major collaboration between MBIE, Niwa, the University of Auckland and WSP.
High-rise buildings can deflect wind to the ground and then channel it around the base. These effects can be mitigated with concrete buffers or by planting trees.
Sure enough, Shah found that if 165kph winds hit Auckland CBD, wind tunnels would form on streets that intersect with Queen St. ‘‘It would definitely be advisable to stay inside, because it’s not going to be comfortable. Signage and poles will be bending, and Coca-Cola cans will be flying.’’