Monotonic and Fatigue Response of RC Beams Strengthened with Near-End Enhanced Embedment Prestressed CFRP Strips

This paper presents a new prestressing reinforcement technique based on prestressed near-end enhanced embedment (NEEE) carbon fiber–reinforced polymer (CFRP) strips for concrete beams. This technique offers significant economic and performance advantages over existing methods by using prestressed externally bonded (EB) or near-surface mounted (NSM) CFRP strips, thus reducing the cost of permanent mechanical anchors required and avoiding the heavy labor of cutting grooves in the concrete cover. Fourteen concrete beams strengthened with prestressed EB, NSM, and NEEE CFRP strips were tested under monotonic and fatigue loading. The test results showed that the prestressed NEEE CFRP-strengthened specimens exhibited better static and fatigue performances than the others. This was because of the unique nature of the NEEE technique, which can effectively anchor the prestressed CFRP reinforcement. Additionally, the bending CFRP strips within the NEEE section can restrain the transitive behavior of the CFRP tensile stress from the midspan to the beam end, inhibit concrete cover separation, and fully utilize the strength of the material. The restraining effect can be further enhanced by increasing the bending angle of the CFRP strips, e.g., by reducing the length of the inclined embedment section. However, if this length becomes too short (e.g., 150 mm in this study), the bonding performance of the surface-bonding sectional CFRP–concrete interface, which is positively correlated with the static and fatigue performances of the reinforced beam, is weakened. The use of a shallow embedment construction in the surface-bonding section can improve the bonding performance significantly, thereby increasing the structural stiffness, reducing the stress amplitudes of the tensile steel bars, and improving the load-carrying capacity and fatigue life of the strengthened beams.