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The near surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) strengthening technique, combined with gradually anchored prestressed technique, is utilized to delay the occurrence of concrete cover separation (CCS) and enhance the ductility of reinforced concrete beams. The load-carrying capacity of fully prestressed beams and gradually prestressed beams are investigated under both static and fatigue loading conditions. The study focused on the effect of gradient prestress on flexural behavior of strengthened beams, analyzed the failure mode, characteristic load, ductility, and stress distribution at CFRP-concrete interface under both prestress and load conditions. Results indicate that gradually prestressed beams outperform fully prestressed ones in restraining crack development, delaying yield of tensile reinforcement, improving bearing capacity and avoiding CCS failure. Bearing capacity was significantly increased by up to 35.48%, while ductility was greatly improved by 100.33% with ultimate deflection for gradually prestressed beams compared to fully prestressed ones. The fatigue life of gradually prestressed beams, which experienced a transition from CCS failure mode to fatigue fracture of tensile reinforcement, was significantly extended. Additionally, their ductility at failure was also greatly enhanced, thus confirming the effectiveness of gradually prestressed NSM CFRP strengthening technique. [ABSTRACT FROM AUTHOR]

This study investigates the effect of strengthening self-compacted concrete (SCC) beams using CFRP sheets on flexural behaviour subjected to repeated loads. During the experiment, six rectangular reinforced SCC beams were evaluated; two were reference beams without strengthening, while the remaining four were strengthened with CFRP sheets. The beam's length, depth, and width are 2100 mm, 300 mm, and 200 mm, respectively. A monotonic load was applied to one of the reference beams, while repeated loads were applied to the remaining (compression cyclic loads). The main parameters studied in this experimental work were the type of loading (monotonic and repeated), the positions of strengthening and the dimensions of CFRP sheets. The flexural behaviour of these beams was investigated through experimental examination by recording the ultimate load and maximum deflection. Meanwhile, the cracks' pattern and failure modes were observed. The findings of the present study demonstrated that the limited cycles of repeated loads have marginal effect on the flexural behaviour of the beams. This results in an ultimate load reduction of no more than 11%. It was also noted that SCC beams strengthened using CFRP sheets subjected to repeated loads significantly affected the flexural behaviour of these beams. Consequently, the ultimate load of the strengthened beams was improved by up to 18%. Besides, the maximum deflection of the strengthened SCC beams was reduced by 45% compared to those without strengthening. Using strengthening throughout the beams' entire width and length that are subjected to repeated loads improved their ultimate load to surpass that of non-strengthened beams under monotonic loads by as much as 7%. [ABSTRACT FROM AUTHOR]

This study investigates the flexural performance of reinforced concrete (RC) beams strengthened by FRP-reinforced geopolymer matrix (FRGM) through a comprehensive numerical analysis. A two-dimensional (2D) finite element (FE) model is developed to simulate the behavior of the FRGM-strengthened RC beams, including the failure modes, load-deflection curves, and interfacial slips. The settings of the FE model, such as material properties, boundary conditions and interfacial bond properties between the FRGM and RC beams, are firstly validated by comparing the predicted results with the existing experimental data from previous publication. Subsequently, a parametric analysis involving 200 specimens is conducted to evaluate the effects of FRGM thickness, sectional area, location and type of the FRP rebar. The results indicate that the uniaxial compressive behaviors of geopolymer mortar and interfacial properties can be accurately described by the parabolic curve and bilinear traction-separation curve, respectively. The failure mode and load-carrying capacity of the specimens are primarily influenced by the axial strength of the reinforced FRP rebar. Additionally, the interfacial slip distributions transform from an inverse tangential shape to a sawtooth shape depending on the cracking pattern of the specimen. [ABSTRACT FROM AUTHOR]