Fire Safety Science Digital Archive

The design of wood-he structural systems to withstand exposure to fire depends on knowledge of the fire endurance (time to failure) of the wood members in these systems. In fires, wood looses part of its load-carrying capacity to charring and part to strength degradation. The design must also consider factors such as loads in the system, heat transfer, wood quality and member size. All these variables interact to affect the time to failure. This paper summarizes the results of a Forintek study on the strength behavior of structural wood members stressed in tension and exposed to elevated temperatures. Approximately 1200 pieces of lodge pole pine Machine-Stress Rated (MSR) lumber were tested in tension under various temperature and load-rate histories. Results indicate that strength losses are significant. A model developed to predict the time to failure has been applied to predict the mean short-term strength as a function of temperature of exposure and duration of exposure.