Assessment of the behavior of FRP-strengthened RC slabs using a discrete crack model

This paper presents a new discrete crack model that can simulate the complex behavior of fiber-reinforced polymer (FRP)-strengthened reinforced concrete (RC) slabs. The model approximates the kinematics of crack openings by a rigid body movement that can be easily embedded in regular finite elements. As such, concrete cracking and its interaction with the FRP can be automatically accounted for in finite element simulations. The proposed technique includes all relevant material nonlinearities related with concrete, steel, and FRP, as well the debonding at interfaces. The model is validated against experimental results on one-way simply supported slabs before assessing in detail the relevance of the discrete simulation of cracks for the analysis of the behavior of the strengthened structure. The numerical model provides important insights on the bond mechanism that cannot be easily determined otherwise. For example, the debond failure is shown to be composed of a critical local stable debonding length that is then followed by global debonding which triggers a rapid loss of strength provided by the FRP. The model also provides the stable bond length from parametric analysis of the optimal strengthening layout. Overall, the model correctly predicts the composite behavior and strength of the FRP-strengthened structure, confirming experimental observations, and expanding the current capabilities of existing analytical and numerical models.