The application of fiber-reinforced polymer (FRP) jacketing for confinement may not always be feasible, particularly in cases where adjacent elements obstruct the structural member and prevent wrapping. To address this issue, the utilization of FRP laminate and spike anchors has been proven as an alternative solution. This study focuses on proposing a design methodology for this particular application. A stress-strain model was developed to assess the behavior of concrete prisms confined with FRP laminates and spike anchors under axial compression. The model adopts a bi-parabola stress-strain curve, with the coefficients derived from previously published experimental data on concrete prisms confined using this solution. The comparison between the analytical and tested stress-strain curves yielded a coefficient of determination (R2) averaging at 0.96, demonstrating the effectiveness of the bi-parabola model in describing the tested stress-strain responses.

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.

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.

Fiber reinforced polymers (FRP) are commonly used to seismically retrofit concrete structural walls. Limited design guidance for the seismic application of FRP strengthening is currently available to designers in guidelines such as ACI PRC-440.2-17 or standards like ASCE/SEI 41-17. This paper presents the description and results of an experimental effort to investigate the effectiveness of FRP retrofitted concrete walls. The specimen wall thickness was either 6 in or 12 in, which represents a typical range of wall thickness seen in older buildings. To better reflect the most common applications seen in the industry, the walls were retrofitted with FRP, and anchored with fiber anchors only on one side of the wall. The study demonstrates that the effectiveness of FRP is reduced as the wall thickness increases and that the FRP must be anchored to the wall for any tangible benefit. The results are used to assess the current provisions in ACI PRC-440.2-17 and ASCE/SEI 41-17. It is apparent that additional testing is required to better understand the complexities involved in the FRP strengthening of shear walls and such testing is scheduled for the near future.

Mehdi Khorasani, Giovanni Muciaccia, and Davood Mostofinejad Synopsis: The externally bonded reinforcement on grooves (EBROG) technique has been recently shown to outperform its rival techniques of surface preparation (such as externally bonded reinforcement, EBR) employed to delay the undesirably premature debonding of fiber reinforced polymer (FRP) from the concrete substrate in retrofitted structure. However, the behavior of EBROG method under fatigue loading has not been assessed yet, and the present study is the first attempt to achieve the above aim. For this purpose, an experimental program is conducted in which 16 CFRP-to-concrete bonded joints on the concrete slab prepared through the EBROG and EBR techniques are subjected to the single lap-shear test and fatigue cyclic loading. Furthermore, the bond behavior of CFRP strips-to-concrete substrate is investigated in this research in terms of the load capacity, slip, debonding mechanism, and fatigue life. The results showed that the grooving method improved the bond properties of CFRP-to-concrete joints under fatigue loading. By using this alternative technique, the number of cycles until failure (fatigue life) increases incredibly under the same fatigue cycle loading and the service life of strengthened members could be improved under fatigue loading. Furthermore, the effects of different loading levels on the behavior of CFRP-concrete joints installed by EBROG method are evaluated. The results showed that fatigue life of strengthened specimens decreases by increasing fatigue upper load limit. Finally, a new predictive equation was developed based on plotting the maximum applied fatigue load versus fatigue life curves for CFRP-to-concrete bonded joints for the EBROG method.