Hours before Cyclone Alfred makes a “direct hit” with the Brisbane CBD—the first cyclone in decades to hit Australia’s third largest city—millions of people are bunkered down and preparing for impact. “This is a very rare event,” said David Crisafulli, Queensland’s Premier, whilst Chris Minns – NSW Premier – warned that northern New South Wales residents, who are also in the firing line, should make preparations for devastating winds (up to 155km on the coasts) and flash flooding.
As it stands, more than 1.8 million dwellings—many of them timber-framed Queenslander’s—are in the direct path of the category two system, with the latest forecast from the Bureau of Meteorology warning that Brisbane and Gold Coast residents should brace for 130km per hour wind gusts.
Today, Wood Central spoke exclusively to Andrew Dunn, CEO of the Australian Timber Development Association (TDA) and structural engineer. Dunn said that the key was not just the high winds—as reported in the media—but the housing capacity to withstand peak speeds.
“For example, in Brisbane, houses are usually designed to withstand peak speeds of 185km per hour winds – which was the highest recorded speed (for the city of Brisbane) during a severe storm in 1985.”
Andrew Dunn – co-author of Resilient Timber Homes – a technical design guide published by Forest and Wood Products Australia last year.
Referencing Resilient Timber Homes, a technical design guide that he, along with Clive Ba-Pe, James Davison, James McIntosh and Professor Keith Crews, helped co-author, Mr Dunn stressed that understanding wind speed designs could help determine the capacity for well-designed timber-framed buildings to withstand weather events like Alfred.
“For perception, a 108 km per hour gust can sweep an average-weight adult off their feet. In comparison, 145km per hour winds wield enough power to dislodge stationary vehicles, with the latter being the design wind speed assumed for most non-cyclonic regions of Australia.”
According to the guide, “the maximum wind speed experienced in each region (for example 185km per hour in Brisbane) aligns with the expected average design wind speed category (C1 in Brisbane),” noting that estimates are conservative: “Because weather stations measure wind speed 10m from the ground, whilst house levels is usually 6m or below.”
“Strong winds can damage cladding and overload connections within the building structure – resulting in the loss of all, or part of a roof, or damage to windows, doors or other-wall cladding elements.” At the same time, “damage from wind-borne debris can destroy vegetation and lift elements such as trampolines, outdoor furniture, unsecured sheds and caravans and stored building materials.”
Please Note: Wood Central will have further coverage of Cyclone Alfred in the coming days.
