Strength and deformation modification factors of wood based composites for engineering design

Abstract

This paper summarizes some of the findings from a comprehensive study concerning the performance of wood based composites in building construction. The presentation only focuses on the strength and deformation modification factors for engineering design of wood based composites, that is, i) to determine whether the strength and deformation modification factors (kmod and kdef ) in Eurocode 5 for formaldehyde based boards are applicable to boards manufactured using new alternative binders such as isocyanate and cement, ii) to evaluate the effect of long-term concentrated loading by a full scale component test and small-scale indicative test, and iii) to examine the effect of long-term shear loading (panel and planar shears) on the performance of wood based composites for structural uses in comparison with long term bending loading in Eurocodes 1 and 5. Numerous results and important findings showed that i) the kc and kd values of isocyanate bonded particleboard (PB) under bending loads were lower than those of formaldehyde based PB, the former being 70-80% the latter; ii) the kc of cement bonded particleboard (CBPB) were similar to that of formaldehyde based particleboards, but with the deflection of the former being about 1/5 the latter, the CBPB test pieces lasted much longer than MUFPB under duration of load tests; iii) stress modes had a significant effect on long term performance: The extrapolated kc values under concentrated load were generally higher than those under bending load and in EC5, depending on the type of materials and joint profiles, the extrapolated kd were very similar between concentrated and bending loads and in EC5, the extrapolated kd values under shear load were higher than those in EC5, however, the kc values varied considerably with the type of oriented strand boards (OSB) and medium density boards (MDF) under shear loading tests. The results clearly showed that there is a need for developing strength and deformation modification factors for new materials and materials under various stress modes for engineering designs.