I'm wondering whether there is any documentation relating to stress grade of timber rounds? AS 1684 has round substitutes for square post sizes however I am unable to find any information in relation to the stress grade or structural properties for various timber rounds. Is the expectation that a structural engineer would be involved where timber rounds are used for verandahs/dwellings etc.
The design of timber rounds is covered in AS 1720.1-2010, Timber structures, Part 1: Design methods. Table 6.1 in Section 6 gives the relationship between the Strength Group of a species and its Stress Grade. For example, radiata pine falls into Strength Group S6 (unseasoned) and the related stress grade is F11. If not from a 'mature' tree the designer would apply a reduction factor. It is assumed that the round material complies with AS 3818.11, which deals primarily with allowable splits and straightness. The reason why rounds are not graded in the same way as sawn timber is because the grain is not interrupted as it is in sawn timber, unless rounds are shaved to achieve a cylindrical form, in which case a further reduction factor applies.
The life span of H3 treated pine compared to various hardwoods can be estimated by reference to our Technical Design Guide no. 5 titled Timber Service Life Design. A copy can be downloaded free of charge from our website via this link https://www.woodsolutions.com.au/publications, or a hard copy can be purchased here https://www.intertekinform.com/en-au/search/standard/?searchTerm=WS05&productFamily=STANDARD&q=WS05. Regarding hardwoods, durability will vary according to the Durability Class of the species concerned, Class 1 being the highest level of durability and Class 4 the lowest.
We can now advise that Regulatory Information Report 41117.11 has been extended to 30 April 2025 by Warringtonfire Australia - refer Letter of Extension LOE 1.2 available on our website here: https://www.woodsolutions.com.au/resources/standards-codes/fire-test-reports.
