木柱四面受火后力学性能的试验研究

木柱受火后截面演化为三个区域:外侧为漆黑的炭化层,承载力完全丧失;中间为深灰的高温分解层,承载力明显劣化;内部为颜色不变的正常层,承载力无变化。通过5组24根木柱四面受火后力学性能的对比试验研究,了解不同受火时间后木柱剩余承载力、延性、破坏形态和炭化速度的变化过程。研究结果表明,受火后木柱剩余承载力显著降低,受火木柱的初始刚度均明显低于对比试件,部分截面较小的受火木柱发生偏压破坏。四面受火后木柱承载力下降原因主要包括:受火使木柱表面炭化,木柱有效面积减小;受火后靠近炭化层的高温分解层木材强度明显劣化;随着受火时间增加,木柱截面长细比增加导致其稳定系数降低;部分木柱由于局部裂缝使炭化不均,使受火后木柱的破坏形态由轴压转变为偏压破坏。受火木柱表面有裂缝处及角部的炭化速度加大;随着含水率降低,炭化速度有所增加;随着受火时间增加,炭化速度有所降低。

Experimental study on the mechanical behavior of timber columns after exposure to fire on four sides

The cross-section of fire-exposed timber columns are divided into three parts: the dark black char layer with no strength,the dark gray pyrolysis zone with decreasing strength,and the normal zone.To learn about the fire performance,such as residual bearing capacity,ductility,failure mode and charing rate,of timber columns exposed to fire on four sides,5 series and a total of 24 specimens were experimentally studied.It was found that the residual bearing capacity and initial stiffness of exposed specimens obviously decreased,and the failure mode of three exposed timber columns with small cross-section changed from central axial compression to eccentric compression.The reasons of decreasing of ultimate strength include: decrease of effective cross-section,reduction of strength of pyrolysis zone,increase of slenderness ratio and change of failure mode.The charring rate increases in the corner area and near the cracks,with decreasing exposed time and decreasing moisture content.