Critical vapour pressure for explosive spalling of high-strength concretebased on Mohr-Coulomb criterion
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摘要: 高强度混凝土高温爆裂概率随含水率的增大而增大，表明蒸汽压力是诱发爆裂的重要因素之一，该压力通过改变有效应力影响了强度。为定量研究蒸汽压力对强度的影响，基于莫尔-库仑准则和有效应力原理，推导了临界爆裂蒸汽压力的求解公式，并从数理角度证明了其严密性，结果表明：(1)公式物理意义明确，并与现有的研究成果和实际工程灾害一致性好；(2)理论分析尚不能完全考虑材料物理特征对爆裂的影响，还需结合模型实验开展极端高温环境下理论模型中相关系数的测定；(3)应结合火灾后建筑物不同部位构件的破坏形态，从受力状态与破坏特征两方面去分析和反馈其中的机理，完善理论分析中的不足。Abstract: The explosive spalling probability of high-strength concrete will increase with the increase of water content, which shows that the vapour pressure is one of the main factors causing the explosive spalling, and this pressure affects the strength through changing the effective stress. To determine the effect of vapour pressure on strength quantitatively, a formula of critical vapour pressure was obtained on the basis of the principle of effective stress and Mohr-Coulomb criterion, and its logical rigor was proved from the aspect of mathematics. The main conclusions are as follows. (1) The theoretical formula has a clear physical meaning, and has a good consistency with the existing research results and the practical engineering disaster. (2) The influences of material physical properties on the crack cannot be fully considered in theoretical analyses, so the mechanical tests of concrete at extreme high temperature are the bases for determining the relevant coefficients of theory analysis. (3) Fire accidents should be investigated on the spot. Meanwhile, the destruction form and characteristics of different parts of the building should be analyzed after the fire. On the basis of these, the mechanism is clarified from the two aspects of the stress state and the ultimate failure characteristic of the component. Finally, the deficiencies were improved in theoretical analysis.
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图 2 混凝土不受外力时的高温爆裂
Figure 2. High temperature burst of concrete subjected to free state
图 4 轴压约束共同作用下桩体中一点的应力状态
Figure 4. Stress state at a point subjected to axial compression and lateral restraint in the cylinder
图 5 莫尔-库仑准则中的主应力关系
Figure 5. Relationship between the principal stress in the Mohr-coulomb criterion
图 6 带有抗拉强度切割的莫尔-库仑包络线
Figure 6. Mohr-coulomb criterion envelope with cross line of tensile strength
图 7 空间应力状态下压剪破坏时的受力图
Figure 7. Force diagram subjected to compression and shear failure in three-dimensional stress state
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