四面受火胶合木中长柱耐火极限试验研究

通过4组10根胶合木中长柱四面受火的耐火极限试验，研究截面尺寸、持荷水平、阻燃涂料等对胶合木中长柱耐火极限的影响规律。通过理论分析提出了胶合木中长柱基于炭化速度的耐火极限计算方法，并采用有限元软件建立了胶合木柱热力耦合数值分析模型。结果表明，随着持荷水平增加，四面受火胶合木柱耐火极限明显降低，当持荷比由30%增加至50%时，耐火极限平均降低24.5min；随着截面尺寸增加，四面受火胶合木柱耐火极限显著提高，当截面尺寸由200mm×200mm增加至300mm×300mm时，耐火极限平均增加28.0min；当胶合木柱表面采用阻燃涂料涂刷后，耐火极限平均增加4.0min。胶层、持荷水平和截面尺寸对试件内部距离边缘相同位置处的温度变化无明显影响，表面涂抹阻燃涂料可稍降低试件内部温度的上升速度。垂直胶层方向和平行胶层方向的炭化速度无明显差异，有阻燃涂料处理的木柱炭化速度略小于无阻燃涂料处理的木柱炭化速度。基于剩余截面法计算的四面受火胶合木中长柱耐火极限计算值与试验值的相对误差绝对值的平均值为6.5%，基本满足工程精度要求。有限元模拟得到的耐火极限与试验值的平均相对误差为8.6%，也满足工程精度要求。

Experimental research on fire endurance of moderately long glulam columns exposed to four-side fire

To investigate the influence of cross-section geometry, load level, and fire retardant coating on the fire endurance of moderately long glulam columns, 4 series in total of 10 specimens exposed to four-side fire were experimentally studied. The charring rate based calculation method for fire endurance of moderately long glulam columns was developed through theoretical analysis. A thermal-mechanical coupled numerical simulation model was proposed to simulate the glulam columns. It is found that the fire endurance of moderately long glulam columns exposed to four-side fire decreases greatly with the increasing load level. When the load ratio increases from 30% to 50%, the fire endurance decreases 24.5min in average. The fire endurance increases obviously with the increasing cross-section geometry. When the cross-section geometry increases from 200mm×200mm to 300mm×300mm, the fire endurance increases 28.0min in average. The fire endurance increases 4.0min in average, while painted with fire retardant coating over the column surfaces. Glue layer, load level and cross-section geometry have slight influence on the internal temperature development at the points with the same distance to the column surface, while fire retardant coating can slightly reduce the temperature increasing rate. The charring rate is similar in the parallel and perpendicular directions to the glue-line, while the fire retardant coating treated columns have slightly lower charring rate than untreated columns. Based on the theory of residual cross-section, the fire endurance is calculated, and the calculated results agree well with the test results, with an average error of 6.5%, which can meet the engineering accuracy requirements.The average error between the simulated and measured fire endurance is 8.6%,which also meets the engineering accuracy requirements.