Strength grading of narrow dimension Norway spruce side boards in the wet state using first axial resonance frequency

Strength grading of Norway spruce [Picea abies (L.) Karst.] side boards in the wet state was investigated. For a sample of 58 boards, density and dynamic modulus of elasticity in the axial direction (MOE_dyn) were determined in the wet state. The boards were then split into two parts and the procedure of determining MOE_dyn was repeated both before and after the boards were dried to a target moisture content of 12%. Finally, tensile strength of the split boards was measured and its relationship to MOE_dyn for both wet and dried split boards was determined. The investigation also included an evaluation of a so called reversed lamination effect on the stiffness caused by the splitting of boards into two parts. The results show that strength grading of split boards in the wet state can give just as good results as grading performed after drying. The reversed lamination effect on the stiffness of split boards was found to be of lower order.