Measurement of Wood Stiffness in Standing Trees and Logs: Implications for End-Product Quality

At present, mills producing structural timber generally undertake strength grading at the end of the production process, i.e., after buying the material and sawing it into timber which is then dried. This means that any variation in wood stiffness between forest stands and between trees is unknown and unaccounted for until the end of the manufacturing process. Portable stress-wavebased tools provide a cost effective means for predicting the stiffness of the resource, either in standing tree or in log form. Better knowledge of the properties of the available forest resource will allow manufacturers to optimise production capability. By knowing the average properties of their raw material stocks mills will be better able to predict the grade outturn of structural products. They will also be able to segregate out low stiffness stands or logs and use this material to create non-structural products, such as fencing, pallets, etc. Finally, knowledge about the average stiffness of individual logs, could potentially allow a mill to change the cutting pattern in order to maximise the value of each log. In this paper, the application of stress-wave-based tools to the Sitka spruce supply chain in the UK is discussed along with the implications of raw material segregation on timber mechanical properties.