Progressive failure and size effect in fiber-reinforced cementitious composites: A coupled elastoplastic-gradient damage approach

This work is devoted to numerical analysis of progressive failure process and structural size effect of fiber-reinforced cementitious composites. A new approach is proposed in the framework of coupled elastoplastic - gradient damage method. The composite is modeled within a phenomenological framework that integrates an ordinary concrete matrix with an equivalent fiber phase. Their coupling through elastic-brittle damage and plastic hardening captures progressive failure, while structural size effects emerge from the macroscopic competition between hardening and damage evolution. The proposed model is verified against uniaxial tension data, where the ductility and strain-hardening regime with 4.88 MPa peak strength are reproduced. It accurately captures the experimentally observed deformation, damage evolution, and failure load in beams of varying sizes under both mode I and mixed-mode I/II cracking. With increasing beam depth, the computed nominal strength decreases from 4.17 to 2.27 MPa for mode I and from 5.73 to 3.48 MPa for mixed-mode failure. In particular, the structural size effect in fiber-reinforced cementitious composites is well described by the proposed model, without introducing any additional size-dependent parameters.