An experimental and numerical study on the charring rate of timber beams exposed to three-side fire

To investigate the charring rate of timber beams exposed to three-side fire, a total of fifteen new and used Douglas-Fir timber beams in four groups exposed to three-side fire were experimentally studied, together with the finite element analyses of the temperature distribution in the beam section. The durations of fire exposure were 0 (on a test piece), 10, 15, 20 and 30 min, according to the ISO 834 standard fire curve. The charring depth of each timber beam was calculated by averaging the values at one-third and two-thirds along each cross section to give the charring rate of timber beams. It was found that the timber beam's charring rate reduces as the duration of fire exposure increases and the vertical charring rate is slightly higher than the horizontal one. The areas of beam sections reduce due to charring and the strength and stiffness of the pyrolysis layer near the charring edge decrease owing to the high-temperature. The average horizontal and vertical charring rates are 0.98 and 1.08 mm/min, respectively. To take into account the difference between the test furnace temperature curve and the ISO 834 stand- ard fire curve, some corrections were made for these data to yield the solution for charring rate. With the help of the finite element software ANSYS, the temperature distribution of the wood's cross-section was analyzed. The longer the exposure time is, the greater the effect of density will impose on the distribution of temperature, but the moisture content has no effect.

基于无损检测与木材力学性能相关性的既有木构件剩余抗弯承载力研究（英文）

目的:利用无损检测的方法,定量评估经腐朽和虫蛀后的既有木构件的剩余抗弯承载力。方法:1.通过对木材小试件进行阻抗仪检测试验和材性试验,建立木材阻力值与抗压/抗拉强度之间的线性回归方程;2.对大段木梁试件进行阻抗仪检测试验,基于木材阻力值与抗压/抗拉强度之间的关系,计算得到大段木梁各部分的强度值;3.在Abaqus中对既有木梁的初始缺陷进行模拟并将木梁的计算强度值赋予木梁的各个部分,综合分析木梁的剩余抗弯承载力。结论:1.木材小试件的阻力值与抗压/抗拉强度值之间呈现出显著的相关性,各测点处的木材强度值可通过阻力值计算得到;2.虫蛀、木节和裂缝等初始缺陷对试件的破坏形式和极限荷载影响显著;3.非线性仿真分析所得的结果与试验结果基本吻合。