The properties of timber vary depending on the direction of the grain, with parallel to grain timber elements tending to be stronger than their perpendicular to grain counterparts.
A more accurate method of predicting the deformation of timber loaded perpendicular to grain has now been developed, with the goal of instilling more confidence amongst designers exploring the specification of wood for their projects.
For one and two storey structures, where load is relatively low, the differences in strength and performance between these two types of wood has minimal impact. However, as wood is increasingly used as a primary material in the construction of mid-rise structures, the load bearing capacity of the timber needs to be better understood to prevent problematic levels of compression and deformation.
The research team from the Timber Development Association of NSW noted that existing available data has been around for many years and is derived from timber not commonly used or available today. In addition, existing methods of calculation are based on low-rise structures. Therefore, the researchers set out to understand the performance of timbers commonly used in construction today, developing and testing a new approach to calculating load impact on perpendicular to grain timber in various scenarios.
Andrew Dunn, CEO of the Timber Development Association of NSW, said to increase market acceptance of timber we need to improve the knowledge and data available to the construction industry, to supports their designs.
“The existing data, which has been around for more than half a century, is not reliable enough to help accurately calculate how much compression perpendicular to grain wood might experience in any given scenario,” Mr Dunn said.
“Having access to this kind of information will support designers within the construction industry when considering what types of material to use in their structures, and for what purpose.”
The research team used rigorous testing to determine the characteristic perpendicular to grain bearing values for 15 separate timber species, from Australia and overseas, that are used in construction. This included an investigation into different stress grades and locations of supply.
When comparing their results against the characteristic design values currently contained in the Australian Standard 1720.1, the team found significant variations across many species. In particular, they noted perpendicular to grain performance was directly correlated with wood density, rather than strength grade or stress group, as the previous data had assumed.
This work has resulted in a new and more reliable method of calculating the deformation of perpendicular to grain timber, allowing more accurate anticipation of likely compression and deformation.
This new approach will be published as part of the updated WoodSolutions mid-rise timber building structure engineering guide, which will inform future calculations relating to the use of wood in lightweight, mid-rise timber-framed buildings.
The findings have also been made available to those responsible for the relevant Australian standard, to help inform any potential amendments in the future.
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