Thermal Effects On Load-Duration Behavior Of Lumber. Part I. Effect Of Constant Temperature

The effect of constant thermal loadings on the load-duration relationships for structural lumber in bending is presented. Select Structural and No. 2 grade Douglas-fir nominal 2 by 4 (38.1 mm by 88.9 mm) beams were tested in bending under constant load. Constant temperature environments of 73 F, 100 F, and 130 F (22.8 C, 37.8 C, and 54.4 C) were used in the investigation. A constant 50% relative humidity (RH) was maintained for each temperature. The applied bending loads were based on the 15th percentile of the assumed static strength distributions for each grade at 73 F and 50% RH. An exponential damage accumulation model modified to account for temperature effects is used to define the load-duration response. The results indicate shorter times-to-failure with corresponding higher probabilities of failure for equal levels of mechanical stress as the temperature is increased