An investigation into the strength properties of reclaimed timber joists

Smith, Michael J. (2012) An investigation into the strength properties of reclaimed timber joists. Doctoral thesis, Northumbria University.

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Abstract

This research was designed to investigate the mechanical properties of timbers reclaimed from demolition, with the aim of generating a visual grade and model expression to grade these materials for structural reuse. The use of timber, reclaimed from demolition, for new construction or refurbishment has both environmental and economic benefits.

The research developed an appropriate, alternate visual grading method which takes account of the unique problems associated with timber reclaimed from demolition. The research also investigated the loading capacity of timbers where previous structural loading may have affected the strength, and how grading without prior knowledge of the timber species can be utilised. Complimentary research suggested that the number of timber growth rings in a specimen has a direct effect on the mechanical properties, and that this can serve as a predictor of elastic modulus, especially when considered in conjunction with the density of the specimen.

This thesis presents the findings of the research, which involved developing an alternate visual grading methodology, appropriate to the inherent ‘in service’damage sustained by timber, and quantifying the mechanical properties of reclaimed timber joists and comparing these with small clear tests. The visual grade accounted for the lack of species data available, by becoming independent of timber species. The research analysis considered density, specimen age and tree ring frequency as the variables in generating the model expression. In the final instance the analysis rejected the age of the specimen as a variable; this was found to be an anomalous and
inaccurate figure, which could only be estimated and added very little to the accuracy of the model expression. The model expression uses tree ring frequency and specimen density to estimate the modulus of elasticity of the specimen and thus its strength grade.

The contribution to knowledge in this research is through the introduction of an alternate, novel method of investigation and an expression to estimate the modulus of elasticity; the method is aimed specifically towards operatives at the demolition site using simple measuring equipment.

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