Is graded South African pine the best structural wood in the world ?
By Brand Wessels
But , in general , they will be wrong . There is a very good argument for calling structural wood that has been graded according to the latest SANS 1783 specifications as “ the best ”. Below I will set out the reasons why South African sawmillers can , from this year , lay a credible claim to this title .
TALKING TIMBER
This question might elicit a condescending smile from our northern hemisphere colleagues who might believe the wood of their slow-growing pines and spruces are far superior to structural timber from that of southern hemisphere plantations .
ALL IMAGES SUPPLIED BY BRAND WESSELS
Firstly , how can the performance of structural wood be quantified ? In other words , when is structural timber good and when is it poor ? This is an easy question and is largely based on safety . The smaller the chance of failure of timber in a structure , the better the timber . It is important to notice that stronger timber does not necessarily mean better timber . Timber can be very strong but will still fail if the engineer uses a design value higher than the strength of the timber . Safety of structural timber therefore depends on having a predictable strength rather than a high strength . Deformation also plays a role since structural elements often have a limitation in how much it is allowed to deform under load .
To ensure that timber has predictable mechanical performance , it is stress graded – in most countries this is a legal requirement for structural timber . Grading can be performed by human operators based on visual characteristics such as knots and density or by
A bending test machine at a sawmill used for continuous quality control testing .
Some of the role players responsible for developing the new SANS 1873-5 standards – from left : George Dowse , Abe Stears , Roy Southey , and Peter Muller . machines using various types of sensors or mechanical devices . Through large scale testing the non-destructively measured properties of timber is related to its strength and stiffness characteristics . Most grading systems therefore depend on a consistent relationship between the measured properties and the mechanical performance of the timber . The biggest risk for users of structural graded timber is that the relationship between wood properties measured during grading and the mechanical properties of wood change over time . This might happen due to changes in plantation management regimes , rotation ages , new genetic material or even climate change . In most cases large scale destructive testing takes place very rarely . The grade properties of South African structural grades were , for instance , determined in large scale testing in the 1980s .
In order to minimise the risk of substandard structural timber entering the market , the South African sawmilling industry , through SawmillingSA , decided a few years ago to develop two quality control standards for structural timber graders ( SANS 1783-5-1
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