Abstract:
Service life prediction models for light-framed wood structures require an extensive quantity of empirical data on deterioration pathologies for the numerous structural components, as well as mechanistic approaches to determine their capacity at various levels of deterioration. The data and
models presented in this study satisfy a portion of the information intensive
requirements of service life prediction models and will be used for continued
development of these models. This study investigated single-shear mechanical properties of three nailed connection geometries of biodeteriorated aspen oriented strand board (OSB) sheathing and Douglas-fir framing members, typical in light-framed
lateral force resisting systems. Mechanical properties of the nailed connections including ultimate and yield strength, stiffness, and energy dissipation were evaluated at increasing levels of deterioration caused by the brown rot fungus, Postia placenta, through monotonic and quasi-static fully-reversed cyclic testing. The OSB sheathing specific gravity was the strongest explanatory variable for the mechanical properties examined and
controlled the behavior of the connections at increasing levels of fungal damage. The data suggested that nailed connections in light-framed lateral force resisting systems can tolerate a moderate amount of fungal attack prior to significant loss of connection capacity. The connection yield mode transitioned from nail bending (mode IIIs) to side member crushing (mode Is) as the weight loss of the OSB sheathing approached 30 percent. Nominal design capacity and yield mode of nailed sheathing to framing member connections with fungal deterioration can be estimated using existing yield models for dowel-type connections through evaluation of the dowel bearing strength of the decay-damaged wood materials. Various physical, mechanical, and chemical properties of the OSB sheathing were monitored in a parallel study at increasing levels of fungal deterioration including dowel bearing strength, shear strength, weight loss, and solubility in an aqueous solution of sodium hydroxide (NaOH). These properties were strongly correlated with the OSB sheathing specific gravity. Near infrared (NIR) spectroscopy, in combination with multivariate statistical
methods, was used to develop predictive models for weight loss, shear strength, dowel bearing strength, and solubility. The NIR methods showed considerable promise as a field inspection tool based on the accuracy of models developed in this study.
