In light-frame residential construction wood-based composite panels used externally or
internally are exposed to relative humidity and/or temperature changes. The subsequent moisture
content change of the panels will result in two types of deformations as follows: 1. elastic
deformation of the panel due to the constraint, 2. warpage of the panel due to the unbalanced
expansion of the layers. Such deformations can cause unacceptable serviceability problems in
light-frame wood construction.
A model was developed to predict quantitatively the global deflection of wood-based
composite panels exposed to relative humidity changes. The model was based on the constitutive
relationship of the Classical Lamination Theory and the thermal stress analogy in composites. As
an alternative solution, the applicability of the eccentrically loaded column formula was evaluated.
The developed models were experimentally validated for OSB and plywood sheathing.
Test variables included the panel type, exposure (symmetric and non-symmetric MC gradient)
and specimen configuration (single span, multiple span). The comparison of measured and
predicted deflections are presented. The important elastic and hygroscopic material properties
were acquired through testing. Statistical analyses of test results are discussed.
The uncertainty analysis was used to make statistical inference comparing the means of
measured deflection to the uncertainty interval of predictions. Good agreement between predicted
and measured deflections was found for single span test structures. Also, for double span
structures the models predicted the experimental response fairly veil. Uncertainties in Me
measurements made the prediction less reliable when symmetric moisture content gradient
developed during the exposure. Due to its lower variability in material properties, the response
of OSB sheathing to moisture content changes is more predictable.
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