Mechanical properties of timber from wind damaged Norway spruce

A storm may subject a tree to such bending stresses that extensive compression damage develops in the lee side. The tree may survive the wind load or it may be thrown. However, the damage is inherent and it may be of a magnitude to influence the mechanical properties of boards sawn from the stem. The paper reports on a investigation of the relation between degree of damage and mechanical proper-ties of sawn timber from wind damaged Norway spruce. The project included about 250 bolts from wind damaged trees. The majority of bolts were cut to deliver a full-diameter plank containing the pith and preferably at the same time representing the windward and the lee sides. The planks were subsequently sawn and planed to deliver approximately 500 specimens of cross sectional dimensions 45x45 mm, 45x95 mm and 45x145 mm. Half of these were cut from the lee side and half from the windward side. They were taken to bending failure and the relations between compression damage and bending strength and stiffness were established. The results showed that significant reductions of bending strength of dry timber are only caused by such wind induced compression damages that are easily recognised at a planed surface of a board.