Creep of Wood I-Joists Exposed to Abnormally High Moisture Conditions

Abstract

Wood I-joists have taken a large share of the wood floor framing market and have distinct advantages over solid-sawn joists. Like other wood products, I-joists are intended for dry-use environments. However, in the unusual event that I-joists are exposed to abnormally high or rapidly changing moisture environments, such as occur in certain disaster situations, research shows that the I-joists can undergo greater creep deflection than solid-sawn members exposed to similar environments. Field experience of the writer indicates that creep of I-joists in abnormally high moisture situations can render them unserviceable due to excessive deflection, even though the strength of the I-joists may not have been significantly reduced. Structural engineers and insurance investigators who are involved in natural disasters where I-joists are exposed to water, such as in floods or fires, should take measures to prevent damage to the I-joists from moisture-related creep deflection. Owners and designers of buildings with wood I-joists should also be aware of and take into account this unique performance characteristic of wood I-joists. A brief review of the literature on moisture-related creep deflection of I-joists is provided. Then field observations are discussed to illustrate practical situations in which I-joists can be exposed to abnormally high moisture conditions and experience problems due to excessive creep deflection. These situations include buildings that are waterlogged by fire-fighting operations, are flooded, or have very moist or wet crawl spaces.