PERFORMANCE OF SOLID TIMBER EXTERNAL WALLS UNDER SIMULATED BUSHFIRE ATTACK

T. Wakefield and Y. He
University of Western Sydney, Australia
Y. Liu and V. Dowling
CSIRO, Australia

INTRODUCTION
With the current focus on global climate change and the increasing focus 代写澳大利亚论文on cataclysmic bushfires in Australia, the use of a renewable resource such as timber as a building material creates a quandary. Timber is an environmentally advantageous building material; timber has low embodied energy, it contributes to the carbon balance, it reduces CO2 emissions when replacing other energy intensive building materials and it is a renewable resource. Timber is also a combustible material, and current and proposed Australian standards for building in bushfire prone areas discriminate heavily against the use of timber.
The fire performance of solid timber wall construction in Australian bushfires is an area with very limited research. Current Australian standards for the construction of homes in bushfire prone areas do not consider the use of timber as a suitable material in high to extreme bushfire risk areas unless it is rated as fire-retardant (treated or naturally) timber. This form of construction refers to timber cladding (15 􀀐 20 mm) on timber stud walls. There is some consideration of solid timber wall construction, such as tongue and groove logs, which is mentioned in the Australian Standard AS 3959-19991, however it appears that the standard is referring to the treated pine log construction commonly referred to as “log homes” found in Australia. Current proposed changes to the standard (DR 050602) limit the use of timber entirely in the category of extreme bushfire attack, and preclude the use of timber log construction (even if a fire retardant timber is used) for very high bushfire attack category.
In North America there has been a surge in popularity of machined timber log homes referred to as “engineered log” homes over the past twenty-five years. These homes use various profiles of log. Presented in FIGURE 1 are two profiles which have a tongue-and-grove (T&G) configuration. These logs vary in thickness from 90 mm to 200 mm and are usually sealed http:// /australia/in the tongue and groove with compressible PVC closed cell foam sealant tape. Timber species also vary from softwoods such as Western Red Cedar or Pine through to hardwoods such as Oak. This form of building has been growing in popularity in Australia, using 90 mm thick logs of Australian White Cypress, over the past eighteen years.
In Australia the “log homes” most people are familiar with are Copper Chrome Arsenic (CCA) treated round log panels which are considerably different than the North American counterpart. The main differences are that the round log panels do not have a tongue-and-groove (T&G) joins as shown in FIGURE 1, have minimal surface contact between logs, are not load bearing, and are of a timber that develops heavy checks (cracks) up to 10 mm. The wall system studied in this research has a wide contact surface between the logs, has through-bolts (threaded rod) from the top to the bottom log, which are tensioned progressively, and therefore has load-bearing capacity.
REFERENCES
1. AS 3959-1999, Construction of Buildings in Bushfire-Prone Areas, Standards Australia, 1999.
2. DR-05060 Draft for Public Comme

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