经历不同燃烧模式的火灾后钢筋混凝土短柱轴压力学性能试验研究

EXPERIMENTAL STUDY ON MECHANICAL PROPERTIES OF REINFORCED CONCRETE STUB COLUMNS IN AXIAL COMPRESSION EXPOSED TO FIRES WITH DIFFERENT COMBUSTION MODES

  • 摘要: 为研究火灾燃烧模式与轴压比对火灾后钢筋混凝土柱轴压力学性能的影响,选取商场、住宅两类典型火灾场景,完成14根足尺钢筋混凝土短柱的火灾全过程试验与火灾后轴压试验,系统分析火灾燃烧模式与轴压比对试件破坏形态、荷载-变形曲线、剩余承载力及轴压刚度的影响规律,对比等面积法与等能量法两种等效曝火时间方法的适用性,并采用现行规范对火灾后构件剩余承载力进行计算与评估。结果表明:试件破坏形态集中于柱中,在本文选取的实际火灾场景中,商场类试件比住宅类试件高温损伤更严重,相同轴压比下,商场类试件剩余承载力退化幅度高出20%~40%,轴压刚度退化幅度高出9%~13%;随轴压比增大,试件剩余承载力呈先增大后减小趋势,剩余轴压刚度则持续增大;使用等能量法得到的试验结果与实际火灾试验结果吻合较好,剩余承载力和刚度偏差仅1%~24%和2%~13%,而等面积法相对应的偏差达5%~40%和8%~20%;通过试验与规范计算结果对比,现行规范计算火灾后剩余承载力偏保守,建议后续规范修订时,考虑火灾燃烧模式与轴压比的影响,完善基于等能量等效曝火时间的计算方法,以提升火灾后钢筋混凝土柱力学性能评估精度。

     

    Abstract: Two typical fire scenarios of shopping mall and residential building are selected to investigate the influences of fire combustion modes and of axial load ratios on the mechanical behavior of post-fire reinforced concrete (RC) columns in axial compression. Full-scale fire exposure tests and subsequent post-fire axial compression tests are performed on 14 RC stub columns. The effects of fire combustion modes and of axial load ratios on failure modes, on load-deformation curves, on the residual bearing capacity and, on the axial stiffness of specimens are systematically analyzed. The paper compares the practicality of two calculation methods for equivalent fire duration, i.e., equal-area method and equal-energy method. The current design codes are used to predict and to evaluate the residual bearing capacity of post-fire components. Test results indicate that failure mainly occurs at the mid-section region. For the adopted practical fire scenarios, specimens exposed to shopping mall fire suffer severer high-temperature damage than those exposed to residential fire. With identical axial load ratios, the degradations of residual bearing capacity and stiffness of specimens exposed to mall-fire are 20%–40% and 9%–13% higher than those of the counterparts. As axial load ratio increases, the residual bearing capacity rises first and then drops, while the residual axial stiffness increases continuously. The equal-energy method can be used to predict the test results with a good agreement and the relative errors of 1%–24% for residual bearing capacity and 2%–13% for axial stiffness. While the equal-area method produces the errors of 5%–40% and of 8%–20%, respectively. The comparisons between test data and code calculations show that the current codes give conservative evaluations of post-fire residual bearing capacity. It is suggested that the design codes should be revised in the future to consider the effects of fire combustion modes and axial load ratios, and should optimize the calculation formula based on equal-energy equivalent fire duration to improve the evaluation precision of mechanical properties of post-fire RC columns.

     

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