AIBS National News

With their potential to cause widespread havoc and destruction, tropical cyclones are one of Earth’s most feared and unpredictable weather systems. On average 13 cyclones form in the Australian region each year, representing a daunting 16% of the global total. While not all of these reach land, with cyclones thought to produce their highest wind pressures within 50 kilometres of the coastline, the potential for damage is still significant for those that remain offshore.

According to figures from the Insurance Council of Australia, losses incurred as a result of cyclones over the last ten years equal more than $587.5 million. If you take into account the 30% of people that aren’t insured, that brings the total damage bill to almost $800 million.

A large amount of these losses are a result of damage to property. When Cyclone Tracy hit Darwin on Christmas Eve in 1974, 50-60% of the city’s houses were classified as destroyed. Only 6% were deemed to be intact with minor damage to cladding and windows; the remainder were regarded as uninhabitable without major repairs. More recently, Cyclone Larry hit northern Queensland in March 2007. On average 30% of homes in regions affected by the cyclone suffered damage while in towns such as Silkwood 99% of homes suffered roof or structural damage and in Innisfail 50% of homes and 25% of government buildings were damaged.



Internal pressure caused by wind allowed into buildings through openings such as broken windows is one of the primary causes of structural damage during cyclones. A report prepared by the Department of Housing and Construction following the devastation of Cyclone Tracy, stated that ‘Failure of windows is a common factor in the initiation of failure in a house’. While this was true at the time, a glass product recently developed by Australian glass manufacturer Viridian has the physical properties to greatly minimise cyclone related property damage.

Viridian StormGuard™ cyclone resistant glass has been specifically designed for buildings in cyclone prone regions. Stormguard is a laminated safety glass incorporating a high tensile strength interlayer to resist penetration from flying debris associated with cyclones. Even if broken, the glass retains its weather-tight ability allowing the building to remain habitable after a cyclone passes.

“Stormguard is suitable for all buildings in strong wind areas including homes, hospitals, hotels and government buildings,” says Viridian’s Paul Cocker. “A recently developed interlayer enables outstanding levels of protection in a thinner and lighter solution than previously available.”

Australian Standard AS1170.2 2002 Structural Design Actions: Wind Actions governs the determination of design wind pressures for buildings. The new cyclone resistant glass has been tested and found to exceed the Standard’s requirements for cyclone regions. Incorporated into a window frame capable of withstanding wind cycles, it can withstand the impact of a 4kg piece of timber at 72 kilometres per hour and, even when broken, can withstand wind pressure of 7.95 kPa for 5000 cycles.

The benefits of investing in cyclone resistant glass are many: building occupants have effective shelter and the building remains habitable after the cyclone without the need for shutters, the need for evacuation or temporary accommodation is avoided and the interior of the building and therefore its contents are protected from wind and rain damage.

"The behaviour of glass and windows is critical to the survival of a building during cyclonic conditions,” says Mr Cocker. “Combined with other correctly specified cladding components, cyclone resistant glazing works to ensure the skin of the building remains intact during the cyclonic onslaught.”