火灾作用下长期服役与新浇筑混凝土梁爆裂性能比较

对比分析了新浇筑钢筋混凝土梁和长期服役的钢筋混凝土梁火灾破坏特征和力学行为。试验采用恒载升温模式,并使用孔隙压力测量装置和非接触式光学应变采集仪获取了火灾下梁试件的孔隙压力、位移和应变发展等相关数据。试验结果表明,新浇筑钢筋混凝土梁的爆裂程度取决于混凝土含水量。由于环境作用,长期服役的钢筋混凝土梁含水量较低,其爆裂程度远小于新浇筑试件。然而,自然碳化造成长期服役钢筋混凝土梁强度降低,且存在较多微细裂缝,导致内部钢筋在火灾高温下失去隔热保护,从而使受力钢筋高温失效,混凝土梁发生脆性开裂。另外,在火灾高温和拉应力共同作用下,钢筋混凝土梁爆裂时机提前,而孔隙水压力峰值相应降低。

Comparison of Performance Between Long-Term Service and Fresh Concrete Beams Subjected to Fire

In this paper, the failure characteristics and mechanical behavior of newly-casted reinforced concrete beams and long-term service reinforced concrete beams in fire were compared and analyzed by considering the loads and heating mode. Meanwhile, the data such as pore pressure, displacement and strain development of beam specimens in fire were obtained by using the vapor pressure measuring device and a non-contact optical strain collector. The test results show that the spalling degree of newly-casted reinforced specimens depended on the water content. Due to the environmental action, the water content of long-term serviced beams was low, which made the spalling degree much smaller than that of new specimens. However, natural carbonation lead to the decrease in the strength of reinforced concrete beams in long service, and there are many fine cracks. This phenomenon makes the stressed steel bar fail more easily under the action of high temperature, which makes the concrete beam brittle and cracked. In addition, under the combined action of fire and tensile stress, the spalling time of reinforced concrete beam is advanced, while the peak value of vapor pressure decreases.