Damage Behavior Of SFRC Under Unidimensional Stress State

Steel fiber reinforced concrete(SFRC)is a kind of multiphase composite material mixed with random distribution of short steel fibers in the concrete matrix.SFRC has excellent physical and mechanical properties such as tensile strength,iMPact resistance,bending resistance and wear resistance.Due to its excellent performance,steel fiber reinforced concrete has been widely applied in various engineering fields.The damage behavior of steel fiber reinforced concrete under uniaxial compression loading is studied with the aid of acoustic emission(AE)technique.The main research works and results are as follows:(1)The mechanical behaviors of SFRC under monotonic loading and cyclic loading were studied.The influence of steel fiber on its mechanical properties and the failure process are analyzed.The failure patterns of steel fiber reinforced concrete were also discussed.An expression for generating the stress-strain curve of SFRC under cyclic loading was proposed.The results show that the failure modes of steel fiber reinforced concrete show obviously ductility characteristics.The addition of steel fiber significantly improves many of the engineering properties of concrete,notably peak strength,post-peak ductility and hysteretic energy dissipation ability.Particular emphasis has been paid to the description of residual strain and stress deterioration produced by the load cycling in compression.The influence of steel fiber is taken into account by defined the relationship between residual stain and unloading strain,and the residual strain decreases with the increase of volume fraction.The addition of steel fiber can significantly delay the degradation rate of concrete stiffness and stress,and the degradation rate gradually decreases with the increase of volume fraction.(2)The relationship between AE characteristic parameters of SFRC under uniaxial compression and the damage process of SFRC were studied.The damage mechanism of SFRC is analyzed by the AE characteristic parameters.A damage evolution equation of SFRC was proposed based on acoustic emission characteristic parameters.The results show that the variation of AE characteristic parameters of SFRC corresponds to the damage state of concrete under different stress levels.The AE location technology can be used to describe the initial damage location and damage process of SFRC.The failure pattern of SFRC under uniaxial compression loading can be classified by AE characteristic parameters,and the damage mechanism of SFRC at different stress stages can be determined.The RA value of SFRC is obviously larger than plain concrete.The failure pattern of concrete changes from tensile failure pattern to shear failure pattern after adding the steel fibers.(3)The variation rule of damage index of SFRC under uniaxial loading is analyzed based on the above analysis and test results.A damage evolution equation is established based on Code for design of concrete structures(GB50010-2010).In addition,an elasto-plastic damage constitutive model of SFRC is developed.The research shows that the damage index of SFRC is smaller than that of plain concrete at the same strain.Damage evolution of SFRC tends to flat with the increase in fiber volume fraction and aspect ratio.The proposed model is proved to be valid to predict the stress-strain relation and damage revolution of SFRC under unidimensional stress state,which could be served as a reference for the engineering application of SFRC and the revision of relevant standards.Finally,some suggestions for further research was put forward based on the whole thesis.