Abstract
The correct characterisation of wood properties is fundamental for the best utilisation of resources. In Europe, grading is defined by strength classes that are determined based on either bending or tension tests. The European standards give equations to estimate characteristic strength in tension from characteristic strength in bending, and vice versa depending on which was tested. These equations are applied to all softwoods. The aim of this paper is to empirically determine the relationship between bending and tension strength properties using two conifer species grown in Ireland and the UK. The results show that the relationships change with species. The standard conversion underestimates, importantly, the performance of spruce for tension loads calculated for the most common bending strength class for Ireland and the UK, C16. The opposite occurs on the reverse conversion. Additionally, the study includes published data from continental Europe, to establish a new conversion that uses timber from a broader range of grades, and that adjusts the tension performance of Irish and UK spruce obtained from bending strength classes, ensuring safe values for design.
Highlights
Sawn timber needs to be strength graded prior to its use for structural applications
The aim of this study is to investigate the relationships between bending and tension characteristic strength of lower-grade timber
The whole population achieved a T11 strength class, and more than 90% a T12
Summary
Sawn timber needs to be strength graded prior to its use for structural applications. In Europe, grading is based on the allocation of timber to groups called strength classes. These classes are defined by sets of statistical “characteristic values” of key properties, that allow safe design with timber by specifying minimum requirements for those values, allowing them to be used for structural calculations. The characteristic values for stiffness (Em,0,mean) are based on the mean, whereas for strength (fm,k) and density (ρk) it is based on the lower 5th percentiles. It is the collective properties within a grade that matter, and not the properties of individual pieces of timber
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