经一麻五灰地仗处理的木梁三面受火耐火极限试验研究

传统木结构建筑木构件表面通常采用地仗处理进行保护，而地仗处理对木构件耐火性能的影响规律尚不清晰。为此，通过4组10根三面受火木梁耐火极限的对比试验，研究了截面尺寸、持荷水平、是否地仗处理等因素对木梁耐火极限的影响规律，提出了剩余截面法计算木梁耐火极限，并提出了木梁热力耦合数值分析模型。结果表明，三面受火木梁耐火极限随持荷水平的增加明显降低，当持荷比由30%增加至50%时，木梁耐火极限降低19.6%~31.7%，平均降低17.5min；三面受火木梁耐火极限随截面尺寸增加显著提高，当截面尺寸由100mm×200mm增加至200mm×400mm时，耐火极限提高95.1%~107.8%，平均增加40.0min；木梁表面经一麻五灰地仗处理后，耐火极限提高21.3%~429%，平均提高15.8min。不同持荷水平和截面尺寸木梁内部距离边缘相同位置处的温度变化相近，表面采用一麻五灰地仗处理可显著延缓木梁内部温度的上升速率，木梁两个方向的炭化速度平均值为0.54mm/min，与未作表面处理的木梁相比降低19.4%。基于剩余截面法和数值模拟得到的三面受火木梁耐火极限预测值与试验值的误差在±15%以内，基本满足工程精度要求。

Experimental study on fire endurance of timber beams with treatment of one hemp fiber and five plastering exposed to three-side fire

Timber members in the traditional timber buildings are commonly protected with surface plastering treatment. However, the influence rule of surface plastering treatment on the fire performance of timber members has not been clearly studied. To investigate the influences of cross-sectional dimension, load level, and treatment of one hemp fiber and five plastering on fire endurance, four series in total of ten specimens exposed to three-side fire were experimentally studied. The theory of residual cross section method was developed to calculate the fire endurance of timber beams. A thermo-mechanical numerical simulation model of timber beams was developed. It is found that the fire endurance of timber beams exposed to three side fire decreases greatly with the increasing load level. When the load ratio increases from 30% to 50%, the fire endurance decreases by 19.6%-31.7%, with an average decrease of 17.5 min. The fire endurance increases obviously with the increasing cross sectional dimension. When the cross-sectional dimension increases from 100 mm×200 mm to 200 mm×400 mm, the fire endurance increases by 95.1%-107.8%, with an average decrease of 40.0 min. The fire endurance increases by 21.3% 42.9%, with an average decrease of 15.8 min, when the timber beam surfaces are treated by one hemp fiber and five plastering. Specimens with different load levels and cross sectional dimensions have similar internal temperature development at the same distance to the beam edge, while the treatment of one hemp fiber and five plastering can greatly reduce the temperature increasing rate. The average charring rate of specimens with treatment of one hemp fiber and five plastering along two directions is 0.54 mm/min, which is 19.4% lower than that of the untreated timber beams. The calculated fire endurances based on the theory of residual cross-section method and numerical simulation model agree well with the test results, with errors within ±15%, which meets the requirements of engineering accuracy.