Static And Dynamic Mechanical Properties Of Fiber Reinforced Concrete And Analysis Of Fiber Effect

In the process of using concrete materials,problems such as dry shrinkage cracking,brittle fracture and lack of impact resistance always exist,which restrict the development of modern architectural structure.The method of improving concrete performance by adding fiber has been proved to be stable and effective,and has been widely used in engineering.Steel fiber,glass fiber,carbon fiber and plant fiber can be used as reinforcing materials of concrete,but the difference of different fiber effects and the factors affecting the effects of fiber are still in need of further study.In this paper,the dynamic splitting test of plain concrete,steel fiber concrete and palm fiber concrete specimens is firstly carried out to compare and analyze the effect of different elastic modulus fibers on the dynamic mechanical properties of concrete.Then,the damage theory and fiber reinforcement theory are used to analyze and explain the effect and mechanism of fiber,and the experimental results are compared to verify the calculation formula of fiber concrete tensile strength.Finally,the application effect and prospect of fiber reinforced concrete on cracked beam are discussed by finite element simulation.Main research contents and results of this paper:1.The static and dynamic mechanical properties of different kinds of fiber concrete were compared and analyzed through experiments.Impact tests were carried out on plain concrete,steel fiber concrete(high elastic modulus)and palm fiber concrete(low elastic modulus).The loading equipment was separated Hopkinson bar,and the loading method was disc splitting.The entire damage process was recorded and analyzed by high-speed camera,strain gauge and DIC software.Firstly,the effect of the fiber is analyzed from the impact failure form of the specimen.Through the test data,the strengthening and toughening effect of fiber is verified,and the relationship between the main mechanical parameters of fiber concrete(tensile strength,peak strain,elastic modulus,strain rate,fracture toughness,etc.)and the elastic modulus of fiber is discussed.2.Analyze the effect of the fiber based on the damage theory.By using the model of a micro cracks round pie,by mesoscopic analysis method,analysis of representative volume unit circle pie the size of the micro cracks on macroscopic deformation and density change parameters and the influence of damage variable,then by means of the macroscopic fracture cohesion crack model,will damage the unit into the macroscopic fracture process zone of the crack tip,formed from the mesoscopic damage to the macroscopic damage of multi-scale mechanics research.It can be found from the damage calculation formula that the damage degree of the representative volume element is directly proportional to the equivalent microcrack density,and is also related to the equivalent crack radius,and the addition of fiber can significantly reduce the damage amount of the structure so as to enhance the toughening effect.3.Based on the composite material theory and fiber spacing theory to explain the effect of fiber,the tensile strength calculation formula of fiber concrete was obtained.It was found that in addition to the content of fiber,the length-diameter ratio of fiber and the strength of matrix,the factors affecting the overall strength of composite materials also included the interface bond performance between fiber and matrix.The theoretical value of tensile strength was obtained by substituting the bond stress of a single fiber into the strength calculation formula.4.The influence of crack location,crack length,crack number and fiber bridging force on the inherent mode of the cracked beam was studied by finite element simulation analysis,and the application prospect of fiber concrete on the beam was discussed based on the simulation results.By analyzing the simulation data,it is found that the sensitivity of the natural mode of the cantilever beam to the change of crack depth is greater than the change of crack position,and the closer the crack is to the fixed end,the greater the influence is.The bridging force on the crack surface has little effect on the mode.The crack resistance of fiber reinforced concrete can significantly reduce the modal change of trabeculae and increase the service life of the beam.