超500MPa高强约束钢柱受火后剩余承载性能和评定方法研究

The degradation of steel strength after fire exposure is more serious for high strength steel than for conventional mild carbon steel. Therefore, it is necessary to evaluate if high strength steel members has enough post-fire residual resistance to ensure the structure safety. In practice, steel columns are generally restrained. The constraint condition influences the residual bending deformation and residual stress of the steel columns after fire, which will further influence the post-fire residual resistance of the columns. However, the investigations of the effect of the restraint on the post-fire residual resistance of high strength steel columns are very limited. This project aims to develop a mathematical model to predict the relationship between the experienced highest temperature and the post-fire mechanical properties of high strength steel with yield strength over 500 MPa under different cooling processes based on the statistical analysis of previous test data. The fire induced deformation and internal force of restrained high strength steel columns during the full process of heating and cooling will be experimentally and theoretically investigated. The post-fire residual resistance of restrained high strength steel columns will be investigated by systemic tests, theoretical analysis and numerical simulation. The formula with consideration of the effects of restraint stiffness, load ratio, column slenderness ratio and the experienced highest temperature on the residual bending deformation, residual stress and post-fire resistance after the heating and cooling process will be established. A practical assessment method for the residual resistance of restrained high strength steel columns after fire will be proposed.

高强钢材受火高温后强度退化比普通钢材严重，因此，受火后高强钢构件是否仍具有足够的承载力保证结构继续使用的安全，显得更为重要。实际建筑中的钢柱大多受约束，而约束会影响过火钢柱的残余弯曲变形和残余应力，进而影响钢柱的剩余承载性能，但目前国内外缺乏考虑约束效应对钢构件受火后承载性能影响的研究。本项目拟在前期已开展试验数据统计分析的基础上，建立超500MPa高强钢材在不同冷却方式下的力学性能参数与过火温度间的数学关系模型；通过升降温试验、理论和数值模拟方法，研究约束高强钢柱在火灾升降温全过程中变形和内力随温度的变化规律，建立其经历火灾升降温全过程后的残余弯曲变形和残余应力与约束刚度、荷载比、长细比及过火温度间的关系与计算公式；通过受火后极限承载力试验、理论和数值模拟方法，研究约束高强钢柱的剩余承载力与约束刚度、荷载比、长细比及过火温度间的定量关系，建立约束高强钢柱受火后剩余承载力的实用评定方法。

高强钢应用于建筑结构中从安全性、经济性与环保性等方面而言都比普通钢有更大的优势。对于钢结构建筑，钢柱是重要的承载构件，且通常受相邻构件的约束。在火灾升降温的过程中，约束使钢柱产生热应力与变形，同时钢材的力学性能可能折减，尤其是高强钢的材性折减程度比普通钢更严重，这两方面将进一步影响钢柱受火后的剩余承载力。因此，研究受火后的约束高强钢柱是否仍具有足够的承载力以保证结构能继续安全使用十分重要。目前国内外缺乏考虑约束效应对高强钢构件受火后承载性能影响的研究。本项目从高强钢高温力学性能入手，以高强钢柱为对象，考虑在结构中约束效应的影响，研究高强钢约束柱受火后剩余承载力的主要影响因素及变化规律，提出其实用评定方法。本项目进行了TMCP型Q550、Q690高强钢高温下与高温后的力学性能试验并给出相关力学性能参数与过火温度间的数学关系模型，同时与前期已开展的QT型Q550、Q690高强钢的材性试验数据进行对比，得到交货状态对高强钢高温力学性能的影响；进行了QT型Q550、Q690高强钢约束柱的升降温试验与受火后的极限承载力试验，并通过数值模拟研究约束高强钢柱在火灾升降温全过程后的残余弯曲变形、残余应力和受火后剩余承载力与过火温度、轴向约束刚度比、转动约束刚度比、荷载比、偏心率、长细比及钢材牌号与交货状态间的关系，建立约束高强钢柱受火后剩余承载力的实用评定方法。