A Cohesive Interface Model for the Pullout of Inclined Steel Fibers in Cementitious Matrixes

The nonlinear behavior of fractured quasi-brittle materials is conventionally modeled with a fictitious crack model, which relates stresses on the crack surfaces to the corresponding crack widths. Its definition for fiber reinforced concrete is only possible by introducing a cohesive model for the matrix, and by modeling the pullout of randomly oriented fibers. To this aim, a new cohesive interface model, able to predict effectively the pullout response of inclined fiber, is presented in this paper. Based on the nonlinear behavior of steel fibers and cementitious matrixes, the proposed approach also takes into account the bond-slip relationship between the materials. By means of an iterative procedure, numerical results similar to experimental data can be obtained. In particular, maximum pullout forces at given inclination angles, as well as the complete pullout load vs. displacement diagrams, can be correctly predicted. Moreover, according to test results, the proposed approach shows, from the first pullout stage, the dependence of the response both on crushing of cementitious matrix and on yield strength of steel fibers.