Investigation on the residual mechanical properties of glulam after exposure to elevated temperature

Abstract

For structures that experience a fire event without collapse, determination of the residual capacity is required. The objective of this research is to determine the residual properties of glued laminated (glulam) timber after exposure to elevated temperature to enable post-fire structural evaluation. The residual compressive and shear properties of glulam were experimentally measured after exposure to a range of elevated temperatures (50, 100, 150, 200 and 250 ℃), considering also the effect of heating duration (30, 60 and 90 min) and cooling method (air cooling and water cooling). To account for transient temperature gradients, an effective temperature of the specimen was defined based on the dynamic time-temperature profile. For parallel-to-grain compressive strength, the reduction in residual strength remains within 20% of the initial strength as long as the effective temperature has not exceeded 170 ℃, but it drops severely to exceed 50% at 210 ℃. For shear strength, the permanent reduction is also within 20% after exposure to effective temperature lower than 190 ℃ and air cooling. Water-cooling leads to greater permanent reduction of mechanical properties compared with air-cooling. After first temperature exposure, additional cycles of heating-cooling (by air) do not further degrade the properties. Based on the test results, predictive formulae are proposed for the residual mechanical properties of glulam.