A rationalized model for calculating the fire endurance of wood beams

This paper summarizes previously unpublished research conducted by the National Forest Products Association in 1982 to 1983 to develop a rationalized comprehensive model for predicting the fire endurance of wood beams subjected to a standard ASTM E 119 (1) fire exposure. A rationalized fire endurance model was developed to characterize the structural fire performance of exposed wood members. The mathematical model is based upon elastic transformed section analysis. The model differs from others described in the literature by recognizing two zones of reduced strength between the char or zero strength layer and the core of normal temperature wood in the center of the beam; and by assuming a faster rate of char in the first 15 minutes of fire exposure than the steady-state char rate. Comparison of model predictions with actual fire test data indicates a high degree of correlation over a range of lumber sizes. The complexity of the model, requiring computer computation, results in the model being most appropriate for research and development purposes rather than as a handy design tool.

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