Strategies for improving thermal and mechanical properties of wood-strand composites

Nathan Bryce White

Wood-strand sandwich panel development over recent years found a sustainable means to use undervalued small-diameter timber to create a building envelope material with similar bending stiffness as typical sheathing [oriented strand board (OSB) and plywood]. Changing resources and demand for reduced energy dependency have led to consideration of combining energy and structural performance codes for construction of sustainable buildings and reduced operational energy (residential and commercial buildings account for 39% of total U.S. energy consumption and 38% of U.S. carbon dioxide emissions). This research is aimed toward replacing OSB sheathing with this energy efficient sandwich panel for “green” building construction. Thermal properties of sandwich panels were evaluated to determine effectiveness of their use in reducing operational energy. By replacing 12.7 mm OSB with 32 mm sandwich panels (half the density yet stiffer panels compared to OSB), thermal resistance (R-value) of a wall cross-section increased by 6%. Incorporation of insulating type materials (foam or radiant barrier) within the sandwich panel cavities improved thermal performance more significantly, creating a more desirable building envelope material. Rigid foam insulation within panel cavities increased wall cross-section R-value by 20% while incorporation of radiant barrier increased R-value by 10% compared to 12.7 mm OSB. Improvements in energy efficiency by addition of materials may affect structural integrity of a material, thus mechanical properties were also analyzed. Sandwich panels with foam yielded bending stiffness 41% greater than OSB of similar thickness and 16% stiffer than sandwich panels without foam. Similar to wood-strand sandwich panels, the more energy efficient sandwich panel with foam still utilized 40% less strand and resin material than OSB of equal thickness while only increasing density of the sandwich panels about 10%. A finite element model was developed to predict standard beam flexure tests of sandwich panels. This aids in understanding material behavior and allows for future alterations to panel geometry without a need to fabricate a costly mold to produce the corrugated core. Analysis discovered that Young’s modulus in the strong direction for thin ply material, along with experimental deformation occurring at support bars, drastically affect accuracy of the model compared to experimental results.

Strategies for improving thermal and mechanical properties of wood-strand composites

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