Abstract： The fracture mechanism and tension constitutive relationship of the steel fiber reinforced concrete (SFRC) play the most important role in its engineering applications. However, there is not a constitutive model that can explore the evolutions of energy dissipations for the matrix cracking and fiber pull-out. A uniaxial tensile elastic-plastic damage constitutive model was proposed for SFRC based on the principles of the damage mechanics and the results of the three-point bending tests of the notched SFRC beams. Acoustic Emission (AE) technique was used to detect the evolutions of energy dissipations of different micro-crack modes. A total of 36 specimens with three matrix concrete mix proportions and four volume fractions of steel fibers (0, 0.5%, 1.0% and 1.5%) were tested and analyzed. Based on the experimental results, four damage stages and the corresponding limit state criterions were proposed. Furthermore, the relationships between the fracture energy, the characteristic axial tension strength and the steel fiber volume fraction were obtained. A new method was proposed to verify the tension crack mode and shear crack mode by analyzing the peak frequencies of AE signals. The mathematical expressions of the matrix concrete cracking damage index and steel fiber bridging damage index were respectively obtained by fitting the monitored AE energy evolutions corresponding to the tensile crack mode and shear crack mode. Thus, the uniaxial tensile elastic-plastic damage constitutive model of SFRC was built up. The stress-strain curve from the proposed model matches closely to the RILEM model. The stress-strain curve from the proposed model appears the softening and hardening characteristics in the post-peak regime when the steel fiber volume fraction is below 0.5% and over 1.0%, respectively. The steel fiber bridging stresses during the whole fracture process can be calculated by the proposed model, which could provide reference for the design and nonlinear analysis of SFRC structure. The research methodology adopted in this paper could also be referred for the constitutive relationship study of similar materials.
