Effects of Outdoor Exposure on Properties of I-joists

Wood I-joists are often left uncovered and exposed to the weather during construction, allowing the oriented strandboard and laminated veneer lumber in these systems to be adversely affected by water absorption. Manufacturers typically specify that these materials be protected from wetting, but this can be difficult in wetter climates. There are few studies examining the potential effects of wetting on these building elements. In this study, flexural properties and ultimate tensile strength of I-joists exposed for extended periods of time during the rainy winter months in the Willamette Valley of western Oregon were evaluated. I-joists were removed from the field each month, dried, and then tested in static bending (flexure) using a six-point bending test. I-joist strength decreased as a function of exposure time and rainfall. Twenty-seven da of external exposure was associated with a significant increase in flexural variability. Further exposure was associated with significant decreases in I-joist strength (modulus of rupture). Although most I-joists never experience this degree of wetting, they can when construction is delayed. The results illustrate the detrimental effects of exposure to wetting during construction and support improved efforts to limit wetting.