Performance of edgewise loaded wood based panels and their I-beam components

Abstract

A method has been developed and evaluated for determining the edgewise bending strength and modulus of elasticity of wood based panels by using semi-size test pieces without laminating the test pieces. The method has been employed to evaluate the edgewise bending performance of commercial particleboard (PB), oriented strand boards (OSBs), medium density fibreboards (MDFs) and plywood (PW). The results showed that the developed method was able to generate correct bending failure modes, consistent and repeatable results. Both the strength and modulus of elasticity were dependent on the depth of test pieces: the modulus of elasticity polynomially increased by about 44%, 56%, 50% and 31% for MDF, OSB, PB and PW respectively over the depth increasing from 50 to 250mm, and the strength by about 8% for PB and 14% for OSB over the depth increasing from 50 to 200mm while the strength linearly decreased by about 18% for MDF and 22% for PW over the whole range of the depths tested. The optimum (reference) depth of 200mm has been derived accompanying with corresponding depth factors for calibrating both the strength and modulus of elasticity tested with other depths between 50 and 250mm.Three types of I-beams have been webbed with the OSB, together with type A of PW and hardboard webbed I-beam for comparison. Wood based panel webbed I-beams showed three main failure modes: shear/bending failure, delamination between flange and web, and buckling, depending on the types of I-beam configurations and web materials. The strength and stiffness were closely related to both I-beam types and web materials, with the type C being about 1.5 times that of type A for strength and about 1.2 times for stiffness, and the strength of HB:OSB:PW being 1.95:1.12:1.00 and the stiffness about 4.67:3.39:1.00.Excellent correlations between semi- and small-size edgewise bending tests have been established for both the strength and modulus of elasticity, with the edgewise bending strength from semi-size being about 25% lower than that from small-size tests while the modulus of elasticity 17% higher. Both strength and stiffness of large scale edgewise loaded OSB is higher than that tested as the web of I-beam components, although the strength showed the same trend of changes while the stiffness had an opposite trend of changes between edgewise loaded and I-beam tests. These have showed significant over- or under-estimations of material and component (e.g. I-beam) performance and inaccuracy of the replaced test methodologies (EN 789, EN 13879 [9,10]) for edgewise bending properties of wood based panels.