Laboratory and Outdoor Weathering of Wood-Composite I-Joists

Abstract

Wood-composite I-joists are commonly used in residential and light commercial construction. I-joists are intended for use in dry-service environments, but rare situations exist in which I-joists may be subjected to environments that promote elevated moisture content levels. For example, flooding, poor construction practices or disaster situations leading to unprotected exposure, or abnormally long construction delays may arise. In these extreme situations it becomes necessary to characterize I-joist performance to determine if replacement is needed. This research subjects wood-composite I-joists (32 mm deep by 1.32 m long) to two extreme environments intended to assess moisture durability: laboratory-accelerated weathering and unprotected outdoor exposure. Joists are tested in short-span bending to assess shear capacity after conditioning back to the dry state. Shear capacity decreases as a result of exposure to high moisture conditions. All outdoor exposure intervals lead to greater losses in shear capacity than do any of the laboratory-accelerated weathering periods evaluated. In addition, the failure mode of I-joists changes with exposure type and duration.