Graduate Thesis Or Dissertation
 

Moisture effects on properties of wood-composite assemblies

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/6395w973w

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  • Engineered wood composites are used in many structural applications and are intended for dry use. However, these materials may encounter significant amounts of wetting while in service, which can lead to structural failures. This study combined aspects of wood science, mechanics, structural engineering, and mycology to assess changes in material properties of I-joists and small-scale, wood-composite shear walls over extended periods of wetting. Exposure time, total rainfall, and rain days were used to develop predictive models of ultimate flexural failure for I-joists subjected to long-term external exposure. I-joists were experimentally evaluated with a full-scale, six-point bending test followed by a web-flange seam tension test. Bending test failure modes progressed from pure shear to web buckling with prolonged exposure time. Variance in flexural strength nearly doubled after 27 days of exposure. Decreases in flexural strength became significant after 65 days of exposure, reducing capacity by 9%. I-joist flexural strength reduced to 18% after 138 days of exposure. The results illustrate the detrimental effects of exposure to wetting during construction, and support improved efforts to limit wetting. Properties of small-scale shear walls were evaluated in a similar study monitoring the effects of moisture exposure and fungal inoculating over time. Shear wall capacity was tested using a lateral point load at various exposure intervals. Initial shear wall capacity increased by 37% as the fasteners corroded, producing better withdrawal resistance. Shear wall assemblies with visual decay experienced losses in capacity ranging from 13 to 61%. Comparisons of moisture and density distributions showed that wetting had an effect on panel properties. Visual evidence of decay in the uplift corner of a shear wall suggests considerable reductions in capacity and should require immediate repair.
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