Impact Response in Flexural Strengthening of Reinforced Concrete Beams with CFRP Grid and PCM

This paper presents an analytical investigation of the impact response and failure mechanisms of reinforced concrete (RC) beams—including both bending- and shear-type beams reinforced with carbon fiber-reinforced polymer (CFRP) grids and polymer cement mortar (PCM)—under single and repeated impact loads. A simplified smoothed particle hydrodynamics (SPH) method was used for the simulation, incorporating a virtual particle concept to model the debonding of the strengthening layers. Compared to the experimental results, the simulation method accurately predicted the response of the bending-failure-type beams with an average error margin of 7%. However, concerning shear failure beams, the simulation accuracy is significantly influenced by the adhesion model between the concrete and steel bars. The findings indicate that different impact velocities alter the crack propagation under repeated impact conditions, with two distinct failure modes observed: CFRP rupture in the high-flexibility grids and debonding in the low-flexibility grids. Nonetheless, if no debonding occurred, the strengthening layer reduced the displacement and crack development in bending-failure beams by 20% while having no effect on shear-failure beams. A parametric study conducted to assess the key parameters affecting strengthening effectiveness, emphasizing the importance of optimizing the PCM layer to enhance reinforcement while minimizing debonding risks, revealed that an excessively high PCM strength and thickness did not yield significant improvements and increased the risk of debonding. Additionally, lower-flexibility CFRP grids increased the occurrence of debonding, particularly in thicker grid layers, whereas thinner grids provided a more effective strengthening solution, highlighting the influence of grid flexibility on failure mechanisms.