EXAMINATION OF PROPER SPAN/DEPTH RATIO RANGE IN MEASURING THE BENDING STRENGTH OF WOOD BASED ON THE ELEMENTARY BENDING THEORY
In this paper, the method of measuring the bending properties of wood using spruce (Picea abies Karsten) by elementary bending theory has been examined. Three-point bending tests (EN 310) were conducted under various span/depth (L/h) ratios. Load-deflection diagram was simultaneously measured. Modulus of rapture MOR, bending strength in proportional limits SPL and Modulus of elasticity in bending MOE, were conducted under 3.4 to 30 span/depth ratios. The results suggest that for testing solid wood spruce the ratio should be L/h ≥ 20. This principle can be used as an aid to engineering purposes, particularly in controlling the production process. 1. BACKGRAUND Application of wood and composite materials based on wood are treated as unloaded elements in most of the wood industry. In accordance with that and with the European standard EN 310 [2], bending strength and modulus of elasticity in bending are tested by method of three point.The adopted method for flexural strength test ignores the effect of transverse forces or shear stresses caused by loading and reduces the calculation of bending strength of the Euler-Bernoulli theory to pure bending. Many factors influence the mechanical properties of wood, as non-homogeneous and orthotropic material: moisture contents, slope of grain, temperature, annual ring width, density, etc. Given the adopted method of testing, bending depends on the specimen, span/depth ratio, load, loading speed etc.