使用损伤与高温耦合作用下钢筋混凝土梁火灾试验研究与数值分析

为研究不同裂缝宽度对钢筋混凝土梁抗火性能的影响,以混凝土裂缝最大宽度wmax为损伤指标,制作7个钢筋混凝土梁试件,加静载使其产生最大宽度为0.05 mm、0.10 mm、0.15 mm、0.20 mm、0.25 mm、0.30 mm的裂缝,模拟其正常使用时受力状态,并对其进行火灾试验。试验结果表明:不同试件相同位置测点升温大致相同,但截面历经最高温度相差较大,最大温差达到150℃;裂缝宽度越大,试件最终破坏时历经最高温度越小,挠度增长越快。采用ANSYS有限元软件分析梁截面的温度场分布,结果表明:由于初始损伤的存在,相同截面高度处,不同截面沿跨度方向的温度曲线出现波动,裂缝处尤为明显;同一截面,沿截面高度方向的温度曲线出现平台,且裂缝越宽,平台越长,使得截面高温承载力显著退化。提出了考虑裂缝影响的高温作用下混凝土梁承载力简化计算模型,较未考虑裂缝影响的高温作用下混凝土梁承载力的计算精度提高显著。

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

In order to study the effects of crack width on fire resistance of RC beams, the widest concrete crack was defined as damage index. Seven RC members were designed to develop different crack widths ranging from 0.05 mm to 0.3 mm, which were caused by service loading. Then RC beams with different initial damages were set on fire until they lost load carrying capacity. The results show that the temperature rising trend of different members in the same location is roughly similar, but the temperature values have great difference. Different initial states have great effects on the deflection of members in elevated temperature. A nephogram of temperature distribution at different time and sections was drawn with ANSYS software. Because of the initial damage, a fluctuation appears in the temperature curve along the span in the same height, especially the cracks. A platform is taken in the temperature curve along the height in the same section, and the more serious the initial damage is, the longer the platform is, which will weaken the bearing capacity of RC beams in high temperature. A simplified computational model of RC beam is adopted, which improves the accuracy significantly.