火灾下钢筋混凝土平面框架结构受力机理分析

为研究火灾下钢筋混凝土框架结构的受力机理,采用梁单元建立了钢筋混凝土框架结构耐火性能有限元计算模型,考虑火灾位置、柱轴压比和梁配筋率等参数的影响,对火灾下钢筋混凝土框架结构的变形、内力重分布、破坏形态以及耐火极限进行了参数分析。分析结果表明,火灾下框架结构出现了整体破坏形态和局部破坏形态两种典型的破坏形态:当柱轴压比较小时,框架出现受火梁破坏导致的框架局部破坏形态;当柱轴压比和梁配筋率均较大时,框架出现受火中柱和受火边柱破坏导致的框架整体破坏形态,整体破坏形态为连续性倒塌破坏。在框架局部破坏形态条件下,三面受火梁在框架竖向分布位置不同,受约束作用不同,框架的耐火极限亦不同;而在框架整体破坏条件下,柱轴压比越大,耐火极限越小。

Mechanical principle of reinforced concrete planar frame structures in fire

In order to analyze the mechanical principle of reinforced concrete frame structures in fire, a finite element (FE) model for the fire performance of reinforced concrete frame structures based on beam elements was proposed in this paper. The deformation, failure mode, redistribution of the internal forces and the fire resistance of the typical reinforced concrete frame structures were studied by using the FE model on condition that such parameters as fire location, axial compression ratio of columns and reinforcement ratio of beams were considered. The results show that there are two typical failure modes when the reinforced concrete frame structure fails in fire, which are whole failure mode and local failure mode. When the axial compression ratio of columns is small, the local failure mode induced by the failure of frame beams occurs. When the axial compression ratio of columns and the reinforcement ratio of frame beams are both large, the whole failure mode induced by the frame column collapse occurs, and the whole failure mode can thus lead to a progressive collapse of the whole frame structure. In the local failure mode, the fire resistance of frame structure relates to the location of the fire floor because the fire resistance of the failed three-face heated frame beams relates to their restrained stiffness which is different for the heated beams at different fire floors. In the whole failure mode, the fire resistance decreases with the increase of the axial compression ratio of the heated columns.