Numerical Analysis of the Flexural Response of CFRP-Strengthened RC Beams Subjected to Low-Velocity Impact

A fiber-reinforced polymer (FRP) sheet bonding method for the flexural strengthening of existing RC members under impact loading has not yet been established because the strengthening effects of the sheet and the impact resistance behavior of the members have not been sufficiently clarified. In this study, a numerical analysis method is proposed to better evaluate the impact resistance behavior, such as sheet debonding and rupturing, of RC beams flexurally strengthened with carbon fiber-reinforced polymer (CFRP) sheets subjected to a low-velocity impact load; moreover, its applicability is investigated, and the results from the experiments, the continuous surface cap (CSC) model and the Karagozian & Case model (KCC model), which were already implemented in a commercial software package as a constitutive model for concrete, were compared. The crack width needs to be sufficiently decreased to follow the actual behavior of the beams and to accurately estimate the strengthening effect of the sheet. In the proposed method, to decrease the element size of the concrete, the tensile stress in the concrete element is assumed to be completely released upon reaching its strength, and an adapted tensile strength of concrete was introduced on the basis of the equivalent tensile fracture energy concept. The results obtained from this study were as follows: (1) the impact resistance behaviors, including sheet debonding and rupturing, were appropriately evaluated by using the proposed method, and the element size of the concrete was set to approximately 6 mm; (2) the CSC model was able to effectively evaluate the behavior of the beams with sheet rupturing but not with sheet debonding; and (3) the KCC model was not able to appropriately evaluate the strengthening effect of the sheet.