Mesoscopic Models Of FiberReinforced Concrete And Their Applications

Fiber reinforced concrete materials (FRC) are increasingly used in civil engineering. The incorporation of steel or other fibers in concrete can significantly improve the performance of cementitious materials, such as tensile strength, toughness, and ductility as well as resistance to crack and fatigue.The current researches on the reinforced mechanism of fiber reinforced concrete are mainly concentrated on macro experiments and qualitative analyses, mature mesoscopic models are absent. The quantitative analyses of the relationship between the meso-structural and macroscopic response are even fewer. Such drawbacks will dampen the improvement of FRC's performance, also its development and application. Hence, the study on the models and the relationship is of great importance.In order to provide more understanding to the reinforcement mechanism of FRC, a series of mesoscopic models for fiber pullout are developed in this dissertation, the analysis results are shown, and some suggestions for further research are given.The major works in this dissertation include four models of three aspects. They are: 1) a 3D elastic model based on Love Displacement Function to analyze the stress transference mechanism of a smooth straight fiber from a cement matrix; 2) a mesoscopic model for hooked steel fiber to forecast the tensile curve of steel fiber reinforced concrete under uniaxial tension; 3) and two mesoscopic models for synthetic fiber to forecast the tensile curve of synthetic fiber reinforced concrete under uniaxial tension. The 3D elastic model is developed as the first approach. An exact and more general solution of stress field in the entire bonding region is directly obtained by avoiding some inexact assumptions in the existed method. This model can be used in the complete analysis of fiber pullout while combined with model for fiber debonding.Based on some experimental curves, a mesoscopic model for hooked steel fiber is developed to describe the load-displacement relationship of inclined steel fiber pullout. Several mathematical simplifications and approximate assumptions are employed to attain the model. The predicted curve of SFRC material under uniaxial tension based on the model is in good agreement with the experimental result.Then, two mesoscopic models for synthetic fiber are formulated by employing the experimental results of previous researches. Good predicted results can be achieved from these models. The models can be used in the analysis of bridging stress or prediction of tensile curve under uniaxial tension.The models proposed in this dissertation have clear physical concept, simple mathematical form and good inlet for use, and therefore can be used as a guide for the theoretical analysis or engineering application of FRC.