Cracked Membrane Model for Strain-Softening Fiber-Reinforced Concrete

This paper presents the extension of the cracked membrane model, developed originally for predicting the behavior of conventionally reinforced concrete members subjected to in-plane loading, to include the effect of fiber reinforcement. This mechanically sound model combines the tension chord model with appropriate compatibility conditions for membrane elements, and thus expresses equilibrium at the cracks and yields explicit information on the crack spacings and kinematics. The model can readily be extended by incorporating well-established constitutive models for the crack-bridging fiber stresses. In its general formulation with fixed cracks, the extended model accounts for the interaction of crack-bridging fiber stresses and aggregate interlock and can capture crack sliding failure mechanisms as observed in experiments on fiber-reinforced concrete members with anisotropic or uniaxial bar reinforcement. The response predictions were validated against the experimental data of all shear panel tests available within the existing literature that contain fiber reinforcement. The model predictions correlate very well with the load-deformation behavior of the panels, including shear strength, corresponding deformation and failure modes, confirming the general applicability of the general model for a wide range of fiber contents and concrete strengths. Additionally, a simplified version of the model considering rotating, aggregate interlock-free cracks was derived, yielding reliable response predictions for members with low amounts of fibers. While the global response is accurately predicted by the general model, experiments with direct and detailed measurements of the crack and kinematics and stresses at the cracks are scarce. Future studies should thus focus on validating the postulated stress transfer mechanism across cracks in membrane elements by relying on more tests with direct and detailed measurements of the kinematics and stresses at the crack.