Modeling the Reliability of Wood Tension Members Exposed to Elevated Temperatures

Peter W. Lau, J. Dave Barrett

Abstract


The merit of approaching fire safety design from the standpoint of reliability is the impetus of this paper. Reliability, a direct function of time to failure, is a measure of performance that falls naturally under a performance-based code. The objectives of this study focus on advancing our understanding of the structural behavior of light-frame wood members subject to tension and elevated temperatures, and on the time to failure under a given stress and temperature history. A model based on linear damage accumulation theory was developed to predict the time to failure. This model is based on a kinetic theory for strength as a function of temperature and stress, coupled with a kinetic term, to express the pyrolytic process as a form of damage. The model, which requires the short-term strength as an input, fits well to experimental data on nominal 2X4 structural lumber tested at three different rates of tension loading, and at 150, 200, and 250°C, and room temperature. The model also predicts, with reasonable accuracy, the behavior of lumber under constant-load at 250°C. It predicts that lower-grade material generally has a lower reliability index; however, those differences are insignificant as far as current design practices are concerned. The reliability is sensitive to variability in temperature but not to variability in stress.

Keywords


Modeling;reliability;wood;lumber;tension member;elevated temperature;fire

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