Bending and compression properties of small diameter round timber

Objective of the completed European project was to find new uses for small diameter round timber harvested in forest thinning. The project included a wide range of studies: economy of harvesting, drying technology, development of structures and connections, and demonstration of feasible use of round small diameter wood. The mechanical properties are of special interest because the material includes a large portion of juvenile wood. This paper reports on the bending and compression test results and gives a suggestion for visual strength grading. The material includes Scots pine, Norway spruce, Sitka spruce and larch. Results show that strength of small diameter round timber is high corresponding to the highest quality sawn timber. There are however limits in growth rate and knot dimensions which have to be respected when used in load bearing structures. The effect of juvenile wood is observed only on compression behaviour in part of the material. The project has demonstrated that small diameter timber can be used in load bearing structures, and it is in fact a strong material. Simple visual rules are adequate for strength grading. The results give a basis to start an international standardisation for structural use of small diameter round timber.