Tropical cyclone Alessia blew in to the Kimberley coast 12 years ago on November 22 and just as quickly fizzled out. This 2013 flashback report by senior editor Jim Bowden found that although it’s a regular activity in the Brisbane laboratories of the Engineered Wood Products Association of Australasia, wind load testing on plywood sheeting was in full swing.
Fears of another Yasi were allayed. That cyclone, which crossed the Queensland coast on February 3, 2011, brought a Category 5 storm more than 600 km wide with 95 km / hour winds battering towns along a 350-km strip from Cairns to Townsville.
Crews from the cyclone testing station at James Cook University reported very few structural failures in timber buildings built to ‘modern’ building codes and plywood bracings stood their ground against Yasi’s massive wind surge.
‘Tis the season to be merry – and ‘tis the season for cyclone and severe windstorms,” reflected the author.
Australia’s cyclone season runs from November 1 to April 30, with an average of 9 to 11 cyclones forming each year, and the potential for severe cyclones is higher than usual due to warmer ocean temperatures.
On that November day 12 years ago, heavy thuds came down the line as we spoke with EWPAA General Manager Simon Dorries.
“Don’t worry, we’re impact testing for wind loads,” he assured us.
We found laboratory technician Andrew McLaughlin lifting a 20 kg weight into the top end of a tall cylinder positioned by consulting engineer James MacGregor on a plywood panel.
Whoosh, thud … and another plywood product from an EWPAA member passed the impact test for cyclone shelter construction.
The tests simulate the effects of flying debris at different impact speeds in a windstorm.
“Building and construction in cyclone-prone areas requires materials designed to protect against high-wind impact conditions,” MacGregor said.
“EWPAA structural plywood is designed for such conditions and constantly passes flying debris testing with flying colours,” he said.
The plywood for cyclone shelters must resist wind load requirements specified in AS/NZS standard 1170.2, a joint standard for structural design and wind actions.
MacGregor said plywood offered all the inherent advantages of the parent wood plus enhanced properties in its laminated structure.
“Being a wood-based material, plywood has the ability to accommodate the occasional short-term overload at up to twice the design load,” MacGregor continued.
“This is essential in cyclonic winds or seismic activity. This property is also effective when used as construction flooring or as concrete formwork. Plywood’s laminated structure distributes loads from impact over a larger area on the opposite face, which effectively reduces the tensile stress.”
Simon Dorries said timber strength designs and connections were constantly changing, and engineered wood products were continuously tested in EWPAA laboratories.
He said wind and earthquakes continued to impact on low-rise buildings in Australia and New Zealand. Structural plywood provided a reliable means to brace these building frames in accordance with AS1684 (residential timber frame construction), a four-part standard covering design criteria, building practices, tie-downs, bracing and span tables for timber framing members.
EWPAA structural products are third-party audited under a JAS-ANZ accredited product certification scheme, an industry-wide certification based on International Organisation for Standardisation (ISO) requirements.
This system requires that a production facility maintain a documented process control system, conduct in-mill end-product testing and have rigorous internal audit procedures.
