Modeling of Onset of Spalling of Concrete during Fire by Pore Pressure Rise

通过孔隙压力上升模拟火灾期间混凝土剥落的发生

• 批准号: 12450235
• 负责人: HARADA Kazunori
• 金额: $ 5.95万
• 依托单位: KYOTO UNIVERSITY
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 2000
• 资助国家: 日本
• 起止时间: 2000 至 2002
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-12450235/
• 关键词: Concrete; Spalling; Vapor Pressure; Thermal Stress; Heat and Mass Transfer; Stress Analysis; 空隙圧力; 火災; 高強度コンクリート; 含水率

This work is concerned with; 1) Sensitivity analysis of thermal stress and pore vapor pressure upon the onset of spalling of concrete during fire, 2) experimental analysis by using small scale specimens and 3) development of computer code for simultaneous transfer of heat, mass (water vapor) and stress within concrete material. 1) As to the sensitivity analysis, a simple two-dimensional model for heat and mass transfer program was developed. Simulations were carried out for cylinders heated by standard time- temperature curve. The resulting thermal stress was calculated under the assumption of plane strain. It was found that the thermal stress is increased as the strength of concrete is increased. Comparing with thermal stress and pore pressure, thermal stress is dominant in magnitude. The effect of pore pressure may have certain effect, however pore pressure alone cannot be a main cause of spalling. Following the findings of sensitivity analysis. 2) experiments were conducted for cylindrical specimens of three different strength (40, 110 and 150 MPa). Axial loading and non-uniformity of heating were selected as parameters to be examined. The results showed at least qualitatively that frequency and degree of spalling is increased as strength is increased, that non-uniform heating cause the degree of spalling considerably and that existence of axial compression and end-restraint changes the depth of spalling to shallow layer. By summarizing above, it was suggested to analyze stress and pore pressure in the early stage of heating in three- dimensional field. Thus the simple model used in sensitivity analysis was extended into three dimensional model. In addition, the effect of pore pressure was explicitly taken into account by using the concept of uplift coefficient. The analytical results showed that the effect of non-uniform heating may cause large thermal stress in the early stage of heating.

这项工作涉及：1)混凝土在火灾过程中开始剥落时温度应力和孔隙蒸汽压力的敏感性分析，2)用小尺寸试件进行实验分析，3)开发用于混凝土材料内热、质量(水蒸气)和应力同时传递的计算机程序。1)在敏感性分析方面，建立了简单的二维传热传质模型。对标准时间-温度曲线加热的圆柱体进行了数值模拟。在平面应变假设下计算了由此产生的热应力。结果表明，混凝土的温度应力随混凝土强度的增加而增大。与温度应力和孔压相比，温度应力在大小上占主导地位。孔压的影响可能会有一定的影响，但孔压本身并不是剥落的主要原因。根据敏感性分析的结果。2)对三种不同强度(40、110和150 Mpa)的圆柱形试件进行了试验。选择轴向载荷和加热不均匀作为考察参数。结果至少定性地表明，剥落的频率和程度随着强度的增加而增加，不均匀加热导致剥落程度显著增加，轴向压缩和端部约束的存在使剥落深度向浅层改变。在此基础上，提出了在三维场中进行加热初期的应力和孔压分析。从而将用于灵敏度分析的简单模型推广到三维模型。此外，还引入了上拔系数的概念，明确考虑了孔压的影响。分析结果表明，不均匀加热的影响可能在加热初期产生较大的热应力。