Modeling of concrete dapped-end connections strengthened with FRP sheets

Abstract

Reinforced concrete beams with dapped-end connections are frequently encountered for bridge beams or in precast structures due to their ease of assembly and statical determinacy. These types of connections are subject to high stress flows at the corner where the cross-section is reduced. Therefore, they exhibit a flexural failure mode along a critical inclined crack that originates at the re-entrant corner. Since they are subjected to high shear forces, FRP sheet reinforcements can be used to improve their resistance. This thesis focuses on the modeling of the behavior of these dapped-end connections externally reinforced with FRP strips/sheets. The aim of this master thesis is to understand and model the effect and effectiveness of strengthening dapped-end reinforced concrete beams using externally bonded fiber-reinforced polymers (FRP). This type of reinforcement has many advantages as such as increasing the shear capacity of the connection, reducing stresses in the steel reinforcing bars, having a better control of the crack or external application as a repair after the damage is observed. This thesis proposes an extension of the kinematic-based model by Rajapakse et al., 2021 in order to predict the peak strength of the connections and to predict the complete flexural behavior of dapped-end connections reinforced with FRP. This model focuses on one failure mode, a flexural failure along a critical inclined crack starting from re-entrant corner. Initially, the model is extended and developed taking into account the behavior of FRP through this critical crack. This allows to add the contribution of FRPs to the kinematic model. Then, this model is compared and validated against a database of 34 experimental tests. This model, predicting encouraging results, is used to study the behavior of the dapped-end connections for all the tests in the database. The results obtained show that FRPs do increase the strength, slightly decrease the stress in steel bars and allow better control of the crack opening. In addition, the model is used to perform a parametric analysis on the parameters influencing the FRPs (presence of anchors, thickness, modulus of elasticity, and compressive strength of concrete). This analysis allows discussing the effect of these parameters on the peak resistance but also on the behavior of the dapped-end connections and the FRP strips/sheets.The inclusion of kinematic data and the good performance of the model allow a good perspective for further developments including even more external data to study more precisely the behavior of structures in real applications.