混杂纤维自密实混凝土隧道管片火灾高温爆裂机制与力学性能退化规律研究

Fire is one of the major disasters to tunnel structures, which usually leads to spalling and degradation of mechanical performance of concrete tunnel segment, thus reduces the safety of structures. Hybrid use of steel fiber and PP fiber can improve the spalling resistance and mechanical performance of tunnel segment. But the reinforcement of tunnel segment is dense and complex, which leads to a big difficulty in the preparation of tunnel segment by using hybrid fiber reinforced concrete. The use of hybrid fiber reinforced self-consolidating concrete (HyFRSCC) is an effective way to settle the above problem. However, the mechanism of fire spalling and mechanical performance degradation of HyFRSCC segment is not clearly understood now, which becomes the bottleneck restricting the application of HyFRSCC tunnel segment. In this project, the effect mechanism of hybrid fibers on the spalling and mechanical behaviors of HyFRSCC segment will be studied experimentally and theoretically. The contents include the design of mix proportion for HyFRSCC, the mechanical properties of HyFRSCC at elevated temperature, the spalling behavior of HyFRSCC segment and the mechanical performance of HyFRSCC segment during fire exposure. It aims at setting up the design method of mix proportion for HyFRSCC, the mechanical constitutive models of HyFRSCC during elevated temperature, the spalling prediction model, bearing capacity model, cracking and deformation model of HyFRSCC segment during exposing to fire. This project will serve as a reference for the study of fire resistance of tunnel concrete materials and structures.

火灾是隧道结构面临的重大灾害之一，通常会导致混凝土管片的高温爆裂和力学性能退化，降低其安全性。混杂使用钢纤维与PP纤维可以改善管片的高温爆裂行为与力学性能，但管片密集且复杂的配筋使混杂纤维混凝土管片存在制备上的难题，而配制混杂纤维自密实混凝土（HyFRSCC）是解决上述问题的有效途径。但是，目前对于HyFRSCC管片的火灾高温爆裂机制与力学性能退化规律尚不明确，成为制约HyFRSCC管片应用的瓶颈。本项目拟针对HyFRSCC管片的火灾高温爆裂和力学性能退化问题，通过试验与理论方法研究混杂纤维的影响规律和作用机制。具体包括：HyFRSCC的配合比、材料高温力学性能、管片高温爆裂行为以及管片高温力学性能研究。拟完成HyFRSCC的配合比设计、建立材料的高温力学本构模型、管片的火灾高温爆裂行为预测模型以及承载力、裂缝和变形性能的计算模型。研究成果可为隧道混凝土材料与结构的抗火研究提供参考。

混杂纤维自密实混凝土隧道管片已在工程中得到了越来越广泛的应用，但是目前其火灾高温爆裂机制与力学性能退化规律尚不明确。本项目针对上述问题，开展了以下四方面内容的研究，具体包括：（1）研究了混杂纤维自密实混凝土材料的高温性能，探明了纤维对自密实混凝土高温作用前后压缩性能、拉伸性能和弯曲性能的影响规律；（2）研究了混杂纤维自密实混凝土的高温爆裂行为，探明了蒸汽压力-时间-温度之间的关系，建立了考虑混杂纤维作用的自密实混凝土火灾高温蒸汽压力预测模型和数值模拟方法；（3）研究了混杂纤维自密实混凝土火灾高温作用下的内部温度场，分析了纤维对于温度场和温度梯度的影响规律；（4）采用对称倾角梁简化模拟隧道管片受力特点，对比研究了火灾高温作用前后混杂纤维自密实混凝土管片在轴力-弯矩-剪力复合作用下的弯曲性能，分析了纤维对管片高温作用前后力学性能的影响，提出了可以考虑混杂纤维作用的隧道管片高温作用前后受弯承载力计算模型与方法。