The serviceability and ultimate limit states of a concrete member are reliant upon the bond of reinforcement. The performance of glass fiber reinforced polymer (GFRP) reinforced concrete structures is influenced by multiple parameters and one of these parameters is the bond length of GFRP rebars. The scope of the present research is to experimentally study the effects of fully and partially bonded rebars on the load-bearing capacity and cracking of GFRP-reinforced concrete beams. The beams with partially bonded reinforcement show reduced capacities compared with those with fully bonded reinforcement, and the former reveals localized cracks. The partially bonded beams fail as a result of concrete splitting, while their fully bonded counterparts fail by concrete crushing.

This paper presents an experimental study that investigated the physical and mechanical properties of the helical wrap glass fiber-reinforced polymer (GFRP) bars. The physical tests are conducted to check the feasibility and quality of the production process through the cross-sectional area and evaluation of the fiber content, moisture absorption, and glass transition temperature of the specimens. While the mechanical tests in this study included testing of the GFRP specimens to determine their tensile properties, transverse shear, and bond strength. Four bar sizes (#3, #4, #5, and #6), representing the range of GFRP reinforcing bars used in practice as longitudinal reinforcement in concrete members subjected to bending, are selected in this investigation. The GFRP bars had a helical wrap surface. The tensile failure of the GFRP bars started with rupture of glass fibers followed by interlaminar delamination and bar crushing. The bond strength of the GFRP bars satisfied the limits in ASTM D7957/D7957M. The test results reveal that the helical wrap GFRP bars had physical and mechanical properties within the standard limits.

In the last decades, the devastating effects of earthquake events in seismic prone regions increased the attention on the vulnerability of existing constructions. Masonry walls especially experienced severe damage, both considering out-of-plane and in-plane mechanisms. To increase their resistance to horizontal forces, different strengthening systems can be applied. The objective of the present work is to study the efficiency of an innovative strengthening solution, involving the use of fiber reinforced polymer (FRP) pultruded bars. An experimental campaign is presented, in which clay-brick single-leaf masonry panels are retrofitted by carbon FRP rebars, inserted into grooves cut within the masonry panel with a cementitious mortar, and CFRP sheets applied on the panel external surfaces. A total of seven direct shear tests (ST) and four diagonal compression tests (DC) were performed on unreinforced and strengthened samples. The results of the tests showed that the strengthening technique can be effective for the improvement of the shear sliding and diagonal cracking resistances, also allowing to deepen the knowledge of the principal failure mechanisms characterizing the FRP-retrofitted masonry elements.

Corrosion of reinforcement steel is a major issue for many structural concrete components, because it leads to strength reduction and may significantly reduce the service life. For this reason, fiber-reinforced polymer rebars (FRP rebars) have been developed, as they represent a viable alternative that may replace reinforcing steel for structures that are particularly susceptible to corrosion issues. However, structural design philosophies for these new materials are still in development and further research is needed to implement FRP rebars properly and safely in design codes but also to ensure that design calculations properly predict the actual behavior and performance of FRP reinforced structures.

This study was conducted to evaluate the strength and structural deformation behavior of flexural beams that were designed according to Eurocode 2 and, for comparison, according to different design methods pro-posed for FRP reinforced structures. With regard to the development of a uniform design concept for alternative reinforcement materials existing in Germany/Europe, different bending design concepts includ-ing the serviceability limit state were evaluated. In addition, the theoretically calculated and predicted strength/deformation were compared to the experimentally obtained measurements. A total of 15 flexu-ral beams, with ans overall length of 4.5 m (177 in.), a width of 200 mm (7.8 in.), and a height of 400 mm (15.8 in.), were cast; three of these beams (designed according to Eurocode 2) featured traditional steel rein-forcement, to serve as control group. The remaining 12 flexural beams were evenly allocated to capture the two alternative reinforcement materials, while generating three different reinforcement distribution patterns with comparable reinforcement ratios (equivalent cross-sectional areas). Thus, a total of six subgroups –three with GFRP and three with BFRP – each with two specimens, were analized. To test all beam in pure bending and to eliminate the influence from shear forces, two equally increasing loads were applied at the (longitudinal) third-points of the beams. Both deflections and loads were measured at several points to evaluate the structural performance of the FRP reinforced structural members.

The results showed that the deflection of the glass fiber reinforced bars at the design load capacity measured twice as much as the deflection of the control group. Almost three times as much deflection (at the same load) was observed for the concrete beams reinforced with basalt fiber rebars. In addition, it was observed that the concrete beams with glass and basalt fiber reinforcement bars showed a nearly elastic-elastic behavior up to the point of failure, whereas the steel-reinforced concrete beams showed an elastic-plastic behavior. However, the deformational behavior differed between the various beam types. While the prevailing equations properly captured the post-cracking performance of traditionally reinforced concrete beams, they do not adequately predict the deflections of FRP reinforced concrete beams. From the measurements and analyses, it was concluded that the serviceability limit state (SST) is more critical than the ultimate limit state (LTS) for the design of concrete flexural beams reinforced with FRP rebars.

The durability of the bond between carbon fiber reinforced polymer (CFRP) and concrete surface under freeze-thaw (FT) cycles is a very significant issue in the application of external CFRP strengthening of reinforced concrete structures. This paper presents an experimental and analytical study on the bond behavior between CFRP and concrete under FT cycles. In this study, the samples were exposed to freeze-thaw cycles in accordance with ASTM C666 where the temperature range varies between -18 °C to +4 °C. Moreover, the bond properties between CFRP and concrete were experimentally evaluated through single lap shear tests and compared with the analytical prediction models proposed in the literature. The failure modes of the control samples as well as the samples exposed to freeze-thaw cycles were presented in this research. In addition, the load-slip behavior was discussed. A non-linear bond-slip relationship between the CFRP-concrete interface was presented at 0, 100, 200, and 300 of freeze-thaw cycles. The results show that the cohesive failure of concrete substrate was observed for the control samples. On the other hand, the mode of the interface failure was changed after exposure to freeze-thaw cycles. In addition, the bond strength of the CFRP-concrete interface increases with increasing freeze-thaw cycles.