使用损伤钢筋混凝土柱高温作用下受力性能试验研究与有限元分析

为研究裂缝对火灾下钢筋混凝土结构性能的影响，设计4个足尺寸钢筋混凝土偏压柱试件，以裂缝宽度ω作为损伤指标，加载使其产生ω分别为0.05、0.10、0.15、0.20mm的裂缝，继而对不同使用损伤的柱试件进行四面受火试验。试验研究表明：受火后裂缝宽度发展约为受火前10倍，深度约为受火前3倍；使用损伤愈大，柱极限耐火时间愈短。假定火灾下裂缝宽度、深度开展与受火试验升温时间成正比，采用ANSYS软件对偏压柱截面进行温度场有限元分析。结果表明：有限元分析得出的截面温度与试验实测温度有较好的拟合性；沿柱截面高度方向温度分布存在一个温度畸变平台且使用损伤越大平台越长，导致截面高温下承载力显著退化；沿柱计算长度方向各截面温度分布发生变化，有限元分析中假设沿柱计算长度方向各截面温度分布相同的结论不再适用。提出考虑损伤平台的高温下混凝土柱承载力简化计算模型，显著提高了计算精度，证明了该方法的正确性和可靠性。

Experimental research and numerical simulation analysis on fire resistance performance of RC columns with damages caused by service loading

In order to study the influence of cracks on performance of RC structures under fire, four full-scale RC columns under eccentric compressive loading were designed and fire tests were carried out on four specimens with concrete crack widths of 0.05, 0.10, 0.15 and 0.20mm respectively which were taken as the damage index caused by service loading. The experimental results show that the crack width is ten times larger and the crack depth is about three times larger than before fire. With the damage increased, the fire endurance time is decreased. Computer simulation was done by using the finite element analysis software ANSYS on the assumption that the development of crack width and depth was proportional to time. The numerical results agree well with test data. There is a platform named temperature distortion on the section temperature distribution along the section depth direction which can be increased with the larger damage caused by service loading and significantly affects the bearing capacity of RC columns. The section temperature distribution along the length direction of column is also changed and the assumption that the column section temperature distributions along the length direction of column is all same in ANSYS analysis is no longer correct. A simplified calculation formula taking into account the damage for RC columns’ bearing capacity under fire was put forward in order to refine the calculation accuracy significantly, which is proved correct and reliable.