Integrated fracture-based model formulation for RC crack analysis

There is an opportunity to revisit and generalise classical theories for concrete cracking in light of increased interest in the use of non-conventional reinforcing materials and material efficiency. Fracture-based models to describe concrete cracking have potential but a limitation has been that many variables and different phenomena have to be incorporated to produce realistic material models. In this paper, an integrated fracture-based model (IFBM) is developed to predict the behaviour of lightly reinforced concrete beams. The proposed model is a closed-form solution that integrates different local phenomena to more precisely describe the onset of cracking, crack propagation and crack rotation. The IFBM incorporates post-cracking tensile stresses in the concrete, the bond-slip behaviour between the reinforcement and concrete, and compression softening in the concrete compressive zone. The model can predict parameters such as the crack length development and crack mouth opening displacement in Mode I lightly reinforced concrete flexural specimens subjected to three-point bending. The predictions show a fairly good agreement with experimental results for small-scale reinforced concrete beams with low reinforcement ratios (0.15-0.5%). The ability of the IFBM to identify specific failure modes and to capture the crack propagation and crack rotation stages of behaviour in lightly reinforced concrete beams are particular advantages. Such an approach provides a powerful tool to study the problem of minimum reinforcement requirements.