Graduate Thesis Or Dissertation
 

Modeling changes in flexural properties of softwood beams during fungal decomposition

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  • Moisture intrusion in residential structures can lead to substantial fungal decay and this damage costs billions in repair/replacement costs. The extent of damage and the rate at which it occurs are primarily dependent on the wood moisture content and temperature in the structure. Determining the risk of decay for various building materials would help designers identify the most suitable materials and schedule maintenance/replacement; however, attempts to model decay have been constrained by the lack of data on decay rates under varying environmental conditions. In this project, the rates of decay, as measured by loss in flexural and strength properties, were assessed on three wood species under varying temperature and moisture conditions for three fungi that commonly attack building components. The results were used to develop nine models to predict fungal decomposition rates in wood at moisture contents above fiber saturation point. The models incorporate relationships between temperature, and fungal species for three species of wood (Douglas- fir, western hemlock and southern pine) at various moisture content regimes. The models rely on empirical data obtained from flexural and strength testing of four thousand beams and were validated against previously published data. Fungal decomposition was found to cause considerable flexural losses (~50-60%) after only 6 weeks of fungal exposure in all wood species at 25 and 35°C. MOE losses at 15°C were not evident until week 12. Decay was generally associated with strength losses in the range of 20-40% for wood incubated at 25 and 35°C for 6 weeks, losses were lower at 15°C. Flexural results obtained from non-inoculated control beams showed a progressive increase in loss, which could not be explained by chemical analyses of the wood. Chemical analyses performed on decayed samples were consistent with the tendency for brown rot fungi to increase alkali solubility with time, as well as with the tendency for white rot fungi to consume nearly all breakdown materials as they are produced. The results provided the basis for continued study to further refine the model. Eventually the model could be used to predict fungal effects based upon time of wetting, wood species and temperature.
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