## 1 Introduction
Various modifications of thin RC jacketing have been examined in the literature. The jacket usually comprises a very thin layer of fine-aggregate concrete, generally not exceeding 25 mm in thickness. This jacket is applied to the external surfaces of existing RC members and encases small-diameter longitudinal and transverse steel reinforcement. Using SCC, mortar, or grout simplifies the casting process. This approach contrasts with conventional RC jacketing, which often employs shotcrete application, resulting in much thicker shell layers of 50-70 mm, significantly changing the geometry of the retrofitted element [51]. A critical aspect in the success of any jacketing method is the degree of bonding and interaction between the original member and the new jacket. This interaction largely depends on frictional forces between the old and new concrete, which can be enhanced through dowels [2; 52] or steel connectors [53]. Recent techniques also involve shear connectors formed by welding corner bars and bending down reinforcing bars to link the jacket and the core [54]. The efficacy of any jacketing scheme can be assessed based on its ability to alter the failure mode and improve the monolithic performance of the retrofitted element. Thus, the shear transfer mechanism between the initial RC core and the applied jacket at the interface is a key aspect [55]. Recently, several researchers have studied the bond strength between old and new concrete to enhance the connection at the interface zone, which depends on factors, such as the surface roughness, jacket design, material strength, cleanliness of the surface, deterioration of the substrate, moisture content, curing conditions, interface orientation, and the type of load applied. Concrete substrates can suffer damage from various factors, which are generally classified into two types: sudden damage (from events, like natural disasters, wars, or accidents) and progressive damage (due to misuse, neglect, or harmful environmental factors, like carbonation, sulfate and chloride attacks, or alkali-silica reactions). Some of these factors may even improve the bond strength between the old and new concrete [56]. In practice, the direction in which the new concrete is poured is crucial for strengthening beams, as the interface orientation highly influences bond strength between SCC and conventional concrete. Research has shown that top bonding surfaces offer the highest bond strength, followed by side and bottom surfaces. The success of the jacketing process largely depends on achieving a solid bond between the two materials. SCC is particularly effective for this purpose due to its excellent workability, flowability, and ability to fill spaces without additional vibration, preventing issues like agglomerates or voids in the RC element or at the interface between old and new concrete. The latter makes SCC a highly reliable material for strengthening concrete members, especially RC beams. In this context, U-shaped mortar jackets were employed to strengthen three shear-critical beams that had primarily failed due to shear cracking under monotonic loading. These beams were retrofitted with three-sided jacketing and then reloaded to failure. The experimental results demonstrated U-shaped jackets' significant potential to improve the shear strength and deformation capacity. Although shear failure persisted due to the beams' predisposed design and span-to-depth ratio, the U-shaped jackets made of cement-based grout, small-diameter mild steel bars, and open stirrups provided considerable strengthening effects. Additionally, the performance of these U-shaped jackets was assessed through the implementation of Structural Health Monitoring (SHM). In the emerging field of advancing SHM technology, considerable research has focused on damage identification, localization, and assessment of RC structures [57; 58; 59].