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Externally Bonded Reinforcement (EBR) is the most common technique used to strengthen the RC members with carbon fiber reinforced polymer (CFRP) sheets. Recently, a new proposed technique was named Externally Bonded Reinforcement on Grooves (EBROG) has been presented as an alternative method to avoid or eliminate the undesirable de-bonging failure mode that is accompanying to EBR method. This paper is devoted to investigating the effect of the strengthening techniques on the flexural behavior of RC continuous beams externally strengthened with CFRP sheets in both hogging and sagging zones, by testing twelve beam specimens. All beams have the same cross-section (200×130) mm and 2300 mm length. The parameters of this study include strengthening methods, length and layers number of CFRP sheet and number, length and direction of grooves, in addition to the effect of presence of steel fiber in the hogging zone. The results are introduced in terms of ultimate load, ultimate deflection, ductility index and mode of failure. The test results showed that the EBROG strengthening method has highly effective in improving the ultimate load of strengthened beams. The specimens strengthened by one and two layers of CFRP using EBROG with three longitudinal grooves have a rising in the ultimate load by about (24.4 and 52.6) % respectively, in comparison with the same beams but strengthened by EBR. Also, the mode of failure was changed from CFRP debonding in case of EBR beams to CFRP rupture, or to concrete cover separation in EBROG beams. Finally, the strengthened beams with CFRP sheets presented a more brittle behavior at failure than the unstrengthening specimen.

Abstract Externally bonded reinforcement on groove (EBROG) is a significant reinforcement technology proposed by researchers to enhance the bond properties of reinforced concrete structural members. To understand the influence of groove size on concrete specimens of different strength, a total of 60 concrete specimens with 4 different strengths were cast with the single shear test in this paper, among which 48 EBROG specimens and 12 specimens with externally bonded reinforcement method (EBR) were used as the control group. The failure modes and failure mechanisms of specimens with various sizes and reinforcement methods were analyzed. Additionally, the test results of ultimate load, load–displacement curves, and bond-slip curves for specimens with different groove sizes were compared. The effectiveness of EBROG method in enhancing the ultimate load capacity at the bond interface of the specimens is proved. Furthermore, in situations where the volume of the groove was kept constant, the specimens with lower concrete strength and deeper groove exhibited superior bond properties. Also, the influence of groove width on bond properties was better than that of groove depth. Finally, the test results in this paper were compared with the prediction of the existing EBR and EBROG models to evaluate the performance of different models, and based on the original model, a prediction model for EBROG method in the groove region with higher accuracy was proposed.

In recent years, CFRP is the most popular material in strengthening RC members (columns, beams, slabs…etc.) as well as the textile-reinforced mortar (TRM) was also used as an alternative method for strengthening RC columns. The present study includes fifteen circular RC columns: One control column, ten columns strengthened by one or two layers of CFRP using EBR or EBROG methods, two columns was strengthened by textile-reinforced epoxy on grooves and last two columns were strengthened by textile reinforced mortar without grooves. The parameters of this investigation are type of strengthening technique (EBR, EBROG and TRM), number of CFRP layers, and the grooves configuration. The results showed that the columns strengthened longitudinally with one or two layers of CFRP strips using EBR technique enhanced the load-carrying capacity by 2 and 7.13%, respectively, when compared with control column. However, the load carrying capacity of RC columns strengthened by EBROG increased by the range of 11.65% to 71.4%. in comparison with control column. Finally, TRM strengthening method enhanced the load carrying capacity by about 21% to 58.5%. Also, the results showed that the EBROG and TRM approaches were improved the stiffness and ductility of the columns in comparison with EBR method.

Recently, a new proposed technique named; Externally Bonded Reinforcement on Grooves (EBROG) has been presented as a strengthening method to postpone or eliminate the undesirable debonding failure mode that is accompanying to Externally Bonded Reinforcement (EBR) method. This paper introduces an experimental and analytical study to evaluate the validity and accuracy of the formulas that were introduced by the standard codes and researchers, in estimating the ultimate load of RC continuous beams strengthened with carbon fiber reinforced polymer (CFRP) sheets in flexure. The experimental program includes testing of ten RC beams with cross section of (200×130) mm and two equal spans, each span has a 1050 mm length. The comparison between the ultimate load collected from the test results and that predicted using ten different analytical models is conducted. It is found that the ACI 440.2R-17 and most of other analytical models well predicted the ultimate load of RC beams strengthening with one layer of CFRP sheets using EBR, but most of these models significantly underestimate the ultimate load of tested beams that were strengthened using EBROG method. ACI, Shehata el. al., and Teng et al. models give close predicted load to the experimental results in case of EBR beams strengthened with two layers.

Externally bonded reinforcement on groove (EBROG) is a significant reinforcement technology proposed by researchers to enhance the bond properties of reinforced concrete structural members. To understand the influence of groove size on concrete specimens of different strength, a total of 60 concrete specimens with 4 different strengths were cast with the single shear test in this paper, among which 48 EBROG specimens and 12 specimens with externally bonded reinforcement method (EBR) were used as the control group. The failure modes and failure mechanisms of specimens with various sizes and reinforcement methods were analyzed. Additionally, the test results of ultimate load, load–displacement curves, and bond-slip curves for specimens with different groove sizes were compared. The effectiveness of EBROG method in enhancing the ultimate load capacity at the bond interface of the specimens is proved. Furthermore, in situations where the volume of the groove was kept constant, the specimens with lower concrete strength and deeper groove exhibited superior bond properties. Also, the influence of groove width on bond properties was better than that of groove depth. Finally, the test results in this paper were compared with the prediction of the existing EBR and EBROG models to evaluate the performance of different models, and based on the original model, a prediction model for EBROG method in the groove region with higher accuracy was proposed. [ABSTRACT FROM AUTHOR]

The present study aims to fill a gap in the literature on the estimation of the bond strength of fiber reinforced polymer sheets bonded to concrete, via the externally bonded reinforcement on grooves (EBROG) technique, employing the curve-fitting on existing datasets in the literature and the methodology of Artificial Neural Networks (ANNs). Therefore, a dataset of 39 experimental results derived from EBROG technique is collected from the literature. A mathematical equation for the bond strength of FRP sheets applied on concrete via the EBROG technique was suggested using curve-fitting and general regression. The proposed mathematical equation is compared and validated with experimental results. The developed ANN model was constructed after testing diverse hidden layers and neurons to find the optimal predictions. The validation of the model is carried out using the experimental results and a statistical analysis is applied to assess the proposed mathematical equation and the proposed ANN model. Furthermore, a parametric study using the ANN model was also performed to investigate the influence of various factors on the bond strength of FRP sheets bonded to concrete. The parametric study proves that the bond strength increases with increasing the tensile stiffness per width, the FRP sheet width, and the concrete compressive strength; however, the effect of the Groove's width and depth is found to be not monotonous. [ABSTRACT FROM AUTHOR]

This paper deals with reinforced concrete beams strengthened by CFRP in flexure. The debonding between CFRP and the surface of the beam is the main problem. Many researchers around the world have made extensive efforts to study the phenomenon of debonding for efficient applications. Based on these efforts and different related field applications, code previsions and various models have been proposed for predicting debonding failure. Two code previsions and three typical models are presented in the current study. ACI-440.2R 17, CNR-DT 200 R1/2013, Said and Wu, Lu et al., and Teng et al. have been used to estimate the flexural strength of RC beams strengthened by CFRP with and without grooves. Test results of eleven flexural beams strengthened by CFRP sheet/laminate using externally bonded reinforcement (EBR) and externally bonded reinforcement on grooves (EBROG) methods were used in the current paper. The performance and accuracy of each model were evaluated based on these test results. Most of the prediction models that used in this study give a closer prediction of the flexural strength of beams strengthened by EBR compared to that of the beams strengthened by EBROG. Finally, the prediction results of CNR-DT 200 R1/2013 were the most accurate and approval with test results compared with other models in the current study

This study proposes a relation for the failure strain of externally bonded reinforcement on groove (EBROG) joints derived through multivariate regression analysis on the experimental results. In addition to the conventional parameters of concrete compressive strength and groove dimensions studied as independent variables, a novel descriptor variable of great effect, called width of fiber-reinforced polymer (FRP) sheet on a single groove, is also introduced for the first time. Using these descriptors and their variations, 27 specimens are strengthened via the EBROG method and subsequently subjected to the single lap-shear test. First, the proposed relation is assessed with respect to its goodness of fit using certain statistical indices, which reveals a good agreement between estimated and measured values. The relation is also verified in terms of its efficiency and accuracy through a comparison with a previous model using 65 specimens in three groups previously reported in the relevant literature. The comparisons indicate the superior accuracy of the proposed relation in estimating the failure strain of EBROG joints and its higher generality as compared to the rival model. [ABSTRACT FROM AUTHOR]

The growing industrialization over the past century has led to increased exposure of structures to such aggressive conditions as found in sewer networks. The rehabilitation and maintenance of sewer systems call for innovative wastewater collection systems based on their design life cycle and operational conditions. Acid exposure is one such condition whose impacts on sewer systems strengthened with FRP sheets still await adequate research. The present paper reports the results of a study conducted in an aggressive concrete sewer chamber in an industrial zone, chosen as an outdoor test design to investigate the effects of an acid environment on the bond strength of FRP sheets bonded on the concrete surface via either of the two techniques of externally bonded reinforcement (EBR) or externally bonded reinforcement on grooves (EBROG). The results show that the bond strength of the EBR specimens depends on both exposure type and duration while the aggressive environment has no significant effects on the bond strength of EBROG specimens. Generally, maximum bond strength in EBR specimens decreases by up to about 19.7% with increasing exposure duration to 6000 h. In the case of EBROG specimens, however, maximum bond strength initially increases by 8.9% after 3000 h of exposure before it declines by 3.6% after 6000 h. [ABSTRACT FROM AUTHOR]

Despite extensive research on reinforced concrete (RC) members strengthened with fiber-reinforced polymer (FRP) sheets, limited knowledge exists regarding their torsional behavior. This study aims to contribute to this research field by conducting experimental tests on novel strengthening configurations to achieve more efficient strengthening systems under torsion. Two different surface preparation methods of externally bonded reinforcement (EBR) and externally bonded reinforcement on grooves (EBROG) were evaluated and compared in torsional FRP-strengthening. The combined utilization of longitudinal and transverse FRP strips and the impact of different parameters such as spacing between transverse FRP strips as well as an anchoring system of FRP fans, were explored in torsional strengthening of RC members. The strengthening patterns were evaluated by comparing torque-twist curves, cracks documenting, and strain field analysis using digital image correlation (DIC). Results showed that the EBROG technique significantly enhances the transfer of shear stresses to deeper concrete layers and ensures uniform strain distribution across transverse FRP strips, resulting in a significant increase in cracking and ultimate torque, up to 72 % and 63 %, respectively. The results also showed that the deformability index improved by 3.0 and 5.6 times, respectively, in the strengthening systems applied through the EBR and EBROG methods. A comparison of the tested specimens proved that implementation of the EBROG technique and FRP fans can increase the torsional strengthening efficiency by more than 6 times. • Efficient configurations for torsional strengthening systems were evaluated. • The EBR and EBROG techniques for torsional strengthening were compared. • Torque-twist curves, cracks documentation, and DIC analysis of specimens were examined. • Implementation of EBROG method and FRP fans increased strengthening efficiency by over 6 times. [ABSTRACT FROM AUTHOR]

Traditional systems for strengthening concrete structures, such as externally bonded reinforcement-fiber reinforced polymers (EBR-FRP) encounter difficulties associated with premature FRP debonding from the concrete surface. To overcome this challenge, this research introduces a novel strategy referred to as externally bonded reinforcement on grooves (EBROG). This innovative approach aims to efficiently tackle the issue of premature FRP debonding, thereby delaying or averting such occurrences. Despite extensive research on EBROG joints, their behavior under cyclic fatigue loading remains unexplored. In a pioneering effort, this paper provides an empirical exploration into the behavior of carbon FRP (CFRP)-to-concrete bonded joints employing the EBROG installation approach under low and high-cycle fatigue loading by using wide specimens. Twenty-three specimens underwent reinforcement through the EBROG approach with diverse groove dimensions, while an additional five specimens received strengthening via the EBR method. Subsequently, these specimens underwent single-lap shear tests under both monotonic and varying fatigue loading amplitudes. The results revealed that wider concrete specimens exhibited more capacity compared to previous research. Furthermore, the EBROG method significantly extended the fatigue life of CFRP-to-concrete joints within the same loading range as EBR. Conversely, tests indicated that the fatigue life of EBROG specimens is contingent on the loading amplitude and can be enhanced by reducing the maximum load level of cyclic loading. In a pioneering step, the paper introduces a formula to forecast the fatigue life of strengthened FRP/concrete joints employing the EBROG method. • The paper studied the fatigue behavior of FRP-to-concrete bonds using EBROG methods under various loading amplitudes. • It proposed a new equation to predict fatigue life for CFRP-to-concrete joints bonded with EBROG. • EBROG installation significantly increased the fatigue life of bonded joints. • The effect of concrete block width on EBROG bond capacity was examined. [ABSTRACT FROM AUTHOR]

Fiber reinforced polymer (FRP) composites can be efficient for flexural strengthening of flat slabs if debonding of the FRP is postponed. However, with the increase of the flexural capacity, the flat slab becomes more susceptible to punching shear failure. In this context, four flexural or simultaneous flexural and punching shear retrofitting systems are investigated in this study to strengthen a flexure‐deficient flat slab. Externally Bonded Reinforcement on Grooves (EBROG) and externally bonded reinforcement (EBR) methods are used for flexural strengthening in two cases: slabs without punching shear reinforcement and with post‐installed shear bolts as shear reinforcement. According to the results, flexural strengthening of the slab using the EBR and EBROG techniques increased its load capacity by 12% and 21%, respectively. Simultaneous flexural and shear strengthening of the slab using the EBROG technique was the most effective, leading to a 57% enhancement of the load capacity. For specimens whose failure was governed by punching, comparing the results with code predictions showed that Eurocode and ACI (and the respective guide documents fib bulletin 90 and ACI 440.2R) overestimated the capacity of these specimens. In cases where failure was governed by flexure, a simple application of the yield line theory predicted reasonably well the load capacity of the specimens. [ABSTRACT FROM AUTHOR]

In this study, the grooving method was employed to strengthen reinforced concrete (RC) columns with longitudinal fiber-reinforced polymer (FRP) sheets, and the performance of columns was investigated under both concentric and eccentric loadings. Furthermore, the effects of longitudinal FRP sheets and the grooving method on the ductility of strengthened concrete columns were studied. For this study, 12 slender square concrete columns with a slenderness ratio of 25 were subjected to eccentric loading with various eccentricity-to-cross section ratios (e/h) equal to 0, 0.24, 0.48, and 0.72 (i.e., eccentricities of 0, 30, 60, and 90 mm). Externally bonded reinforcement (EBR) and externally bonded reinforcement on grooves (EBROG) methods were utilized for FRP strengthening of the specimens. The results demonstrated that for the eccentricity ratios of 0, 0.24, 0.48, and 0.72, the load-carrying capacity of the columns strengthened with the EBROG method increased by 10.6%, 19.6%, 68.8%, and 99.3%, respectively, compared to those of the nonstrengthened columns. Particle image velocimetry (PIV) analyses demonstrated that under all the loading conditions investigated, the grooving method effectively improved the column performance, including load-bearing and flexural capacities. Such analysis also revealed that the application of longitudinal FRP sheets led to significant enhancements in the ductility of the columns tested. [ABSTRACT FROM AUTHOR]

• Affirming the efficiency of EBROG method to bond the precured CFRP strips to concrete structure. • A two-fold increase in bond strength of EBROG joints compared to that of EBR joints. • Proposing an experimental-analytical model to predict bond strength of CFRP strips-to-concrete. • Utilizing a digital image analysis (DIC) measurement system to determine full-filed deformations. The bond behavior of precured FRP strips and steel plates to concrete substrate was investigated in this research in terms of the load capacity, slip and strain distribution and debonding mechanism. Experimental single lap shear tests were performed and an experimental-analytical model was proposed to determine the bond strength of the FRP-bonded joints. Two strengthening methods, including externally bonded reinforcement (EBR) and externally bonded reinforcement on groove (EBROG), were compared. A two-dimensional digital image correlation (2D-DIC) system was utilized to measure the full-field deformations. Compared to the 90 mm effective bond length for the EBR method, the effective bond lengths for the EBROG method were equal to 145 and 160 mm for 5 × 5 and 5 × 10 mm groove cross sections, with 92% and 112% higher loads, respectively. In addition, the results showed that the EBROG method improved the bond resistance of steel-to-concrete joints, but it was not as efficient as it was for the FRP-to-concrete bonded joints. Furthermore, the crack propagation underneath the strip was assessed for the first time for the EBROG method, by using a side-view measurement. [ABSTRACT FROM AUTHOR]

• Deficient exterior RC joints were constructed and tested under reverse cyclic loading. • Proposed strengthening schemes provided a more ductile behavior for joint specimens. • Seismic capacity of the retrofitted specimens was significantly increased. • EBROG method together with CFRP fans eliminated any debonding or slipping of the FRP. Beam-column assemblies of many existing reinforced concrete (RC) buildings are typically designed and built before the development of the current seismic codes; that may permanently fail in non-ductile behaviors, including column flexural hinging or joint shear failure mode, during ground motions. The current experimental research, therefore, was conducted to evaluate the efficiency of newly proposed rehabilitation schemes in retrofitting of deficient RC beam-column connections using fiber reinforced polymers (FRPs). To do so, five half-scale exterior beam-column joints were constructed and tested under constant axial and reversal-cyclic lateral loadings. The joint specimens were designed with strong beam-weak column theory and insufficient transverse reinforcement in the joint region. Of these, four specimens were strengthened with CFRP sheets and the remaining specimen was used as a control. In the strengthening patterns, to eliminate any surface debonding of FRP, the recently developed externally bonded reinforcement on grooves (EBROG) method was used. Besides, CFRP anchor fans were employed in the beam-column interface to completely anchor the longitudinal FRP sheets and also transfer the forces between the beam and the column. The test results showed that the adopted strengthening schemes successfully prevented the brittle failure of the specimens and were able to provide a more ductile mechanism by relocating the plastic hinge away from the weak column and the joint zone toward the beam. Furthermore, a significant enhancement was observed for specimens in terms of their strength, ductility and energy dissipation up to 73%, 139%, 144%, respectively. Additionally, the EBROG technique together with the CFRP fans at the interface of the beam-column joints eliminated any debonding or slipping of the longitudinal CFRPs. [ABSTRACT FROM AUTHOR]

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) off the concrete substrate in retrofitted structures. In FRP application, the effective bond length is defined as a length over which the majority of the bond stress is transferred and the maximum load-bearing capacity is obtained. The present study endeavors to develop an original empirical model of the effective bond length of FRP sheets applied on concrete via the EBROG technique. For this purpose, an experimental program is conducted in which 95 specimens prepared through the EBROG and EBR techniques are subjected to the single lap-shear test. The effective bond length is evaluated by analyzing the strain and stress fields on the FRP bond area using the image processing technique of particle image velocimetry (PIV). A model is then developed based on a nonlinear regression analysis along with a probability study performed on the results obtained from the experiments; and the goodness of fit to the data is confirmed. In this model, the effects of groove dimensions, concrete compressive strength, as well as FRP sheet width and stiffness are taken into account. The feasibility of the well-known existing models developed for EBR method was investigated in the EBROG technique and the prediction accuracy was compared with the proposed model. [ABSTRACT FROM AUTHOR]

The main objective of this study is strengthening of flat slabs in punching shear with a new model. For this purpose 15 numerical samples include a control and 14 strengthened defined and nonlinearly analyzed up to failure. The strengthening method is new method of grooving in two orthogonal direction (x and y axes of slab plan) and then mounting the external bars (sticking) in one direction and FRP in EBROG (externally bonded reinforcement on groove) method in another direction. The results showed the great efficiency of the method so that the punching shear capacity of strengthened samples increased between 28 and 62% compare to control one. Also the mode of failure changed in strengthened specimens from shear to flexure-shear and the punching critical area was broader and developed from the loading point. In the grooving method the sticking bars yielded in all specimens and the FRP tensile strain was closer to rupture strain compared to EBR. [ABSTRACT FROM AUTHOR]

Abstract Retrofitting of reinforced concrete (RC) members with fiber reinforced polymers (FRPs) by means of Externally Bonded Reinforcement On Groove (EBROG) method was confirmed as a brilliant substitute to conventional method of externally bonded reinforcement (EBR). However, efficiency of EBROG method on improving bond properties of pre-cured strips with high fiber content and high load carrying capacity has not been studied before. In this research, a set of 10 single lap-shear tests were carried out to assess the behavior of FRP-to-concrete bonded joints. Pre-cured CFRP strips were bonded to concrete using EBR and EBROG methods. Full-field displacement measurements were carried out through a 2D digital image correlation system, DIC. All tests were carried out at the Isfahan University of Technology in Iran. In addition, analytical modeling was conducted for the first time to obtain bond shear stress-slip behavior for EBROG methods. Based on experimental results, bond resistance in EBROG system increased considerably compared to EBR. For instance, EBROG method with two 5 × 5 mm (width × depth) grooves led to more than 90% increase in bond capacity, in comparison to EBR method. Furthermore, debonding in concrete substrate was eliminated when EBROG method was used. Cohesion failure in adhesive accompanied with FRP delamination was observed as the dominant failure mode. Analytical results revealed that bond shear stress resistance increased in EBROG joints compared to EBR ones. Moreover, the effective bond length increased in EBROG method when CFRP strips were utilized. Interfacial shear stresses, therefore, transferred to the concrete substrate through a larger bond area. So, the specimen resisted higher anchorage load and larger slip, and debonding was postponed. [ABSTRACT FROM AUTHOR]

Highlights • EBR, EBROG, and EBRIG methods were used for longitudinal strengthening of columns. • Half of the RC columns were confined by intermittent CFRP wraps. • GM considerably increased the compressive strength and ductility of columns. • The best performance was observed in combination of EBRIG and wrapping techniques. Abstract The current research investigates the application of carbon-fiber reinforced polymer (CFRP) composites with longitudinally aligned fibers for enhancing the compressive strength and ductility of square reinforced concrete (RC) columns under cyclic axial compression. Global buckling of the composite described may result in the debonding of CFRP off the specimen surface, which hinders proper enhancement in the ductility and compressive strength of the strengthened specimens. To postpone the buckling of the longitudinal CFRP sheets under compression, the recently developed grooving method (GM) was employed in the current research and compared with the externally bonded reinforcement (EBR) technique using the conventional surface preparation technique. For this objective, 8 square RC columns were subjected to cyclic axial compression. The experimental parameters consisted technique employed for longitudinal strengthening of the columns and the presence (absence) of intermittent confining wraps. Two grooving techniques, the externally bonded reinforcement on grooves (EBROG) and the externally bonded reinforcement in grooves (EBRIG), were used. Experimental results indicated the considerably higher contribution of the grooving method, relative to that of the conventional EBR, to limiting the buckling of CFRP sheets and to enhancing the ductility and compressive strength of the columns. It was observed that when the GM is employed, the compressive strength of FRP is enhanced based on the exploitation of the compressive capacity of the carbon fibers in the longitudinal sheets. The results illustrated that in the specimens longitudinally strengthened using the EBROG or EBRIG techniques, fiber compressive capacity in the composite reached 43.9% and 69.3% of ultimate tensile strength of fibers in flat coupons; this amount was only 9.6% for the columns strengthened through the EBR technique. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate the effect of reinforcement arrangement in strengthened RC beams on the concrete cover separation. For this purpose, 12 beam specimens with the dimensions of 250 mm × 300 mm × 2200 mm and different reinforcement ratios were prepared and tested under four-point bending. From the standpoint of the strengthening technique, the specimens were categorized into two groups: six specimens were strengthened by Externally Bonded Reinforcement (EBR) method and the other six specimens were strengthened using Externally Bonded Reinforcement on Grooves (EBROG). On the condition that the reinforcement ratio is constant, reducing the diameter and increasing the number of bars increased the probability of concrete cover separation. The specimens with low and medium ratios of reinforcement, in which small-diameter bars are used, demonstrated a higher load carrying capacity sustaining more deflections at mid-span before debonding of FRP sheets. [ABSTRACT FROM AUTHOR]

Application of fiber-reinforced polymer (FRP) composites to enhance the flexural strength of members in the expected plastic hinge regions of ductile reinforced concrete (RC) moment frames for resisting seismic loads are stipulated in the current construction codes and guidelines. The main issues of concern in these documents include provisions for appropriate anchorage details for FRP composites at the beam-column interface, debonding of FRP composites off the concrete substrate, and the effect of cyclic load reversal on FRP reinforcement. The present experimental study was conducted to gain insight into the effectiveness of an innovative FRP anchor fan at the beam-column joint interface flexurally strengthened with carbon FRP (CFRP) sheets. To avoid any likely debonding of FRP composites off the concrete substrate, surface preparation of the test specimens was performed according to a recently developed grooving method (GM) in the form of externally bonded reinforcement on grooves (EBROG). For the purposes of this study, seven half-scale RC beam-column subassemblies, including a control specimen and six rehabilitated ones, were tested under constant axial and reversal cyclic lateral loadings. The primary test variables were the FRP sheet length along the beam and fiber volume in the CFRP anchor fan. The results indicated that the adopted rehabilitation strategy enhanced the lateral strength of RC joints up to 80% compared to the control one. It was also found that deformation-controlled classification action could be justified for strengthened specimens under specific circumstances. [ABSTRACT FROM AUTHOR]

• This study was the first attempt to evaluate the behavior of EBRIG FRP-concrete joints in comparison with EBR and EBROG joints. • A novel setup was developed to prepare the EBRIG specimens and carry the lap-shear tests on them. • The results including bond strength, failure modes, and other bond properties, confirmed the significant superiority of EBRIG installation method over the EBR and EBROG ones. • PIV technique was adopted to achieve the deformations fields and other bond properties. Grooving methods (GM) have remarkably shown higher efficiency than Externally Bonded Reinforcement (EBR) in anchoring the Fiber Reinforced Polymers (FRP) used for flexural retrofitting concrete structures. They are categorized into two types: Externally Bonded Reinforcement on Grooves (EBROG) and Externally Bonded Reinforcement In Grooves (EBRIG). The behavior of the EBR and EBROG joints were evaluated in many studies, but the behavior of EBRIG ones has not been assessed yet, and the present study is the first attempt to achieve the above aim. Accordingly, 12 concrete prisms were strengthened using one or two-layer of Carbon FRP (CFRP) sheets bonded via the EBR, EBROG, and EBRIG methods and then tested by a single lap-shear setup. In addition to evaluating bond strengths and failure modes, the bond behavior, including load-slip and shear stress-slip curves, and the slip, strain, and shear stress longitudinal profiles were acquired by Particle Image Velocimetry (PIV) technique. The results indicated substantial enhancement in the bond properties of specimens strengthened using grooving methods over the EBR. Besides, the EBRIG joint revealed a higher performance compared to the EBROG joint. For instance, applying the EBRIG method instead of EBROG led to 39% and 120% bond strength enhancement for one and two-layer FRP reinforced specimens, respectively. Additionally, all the EBROG joints failed due to cohesive debonding, whereas FRP sheets either ruptured or deeply debonded in the EBRIG joints reinforced with one or two layers of FRP. [ABSTRACT FROM AUTHOR]

Highlights: [•] FRP-strengthened RC beams with different tensile steel and FRP ratio were tested. [•] Grooving method was compared with EBR method in different flexural failure modes. [•] Grooving method compared to EBR makes more increase in the ultimate load of beams. [•] More ductility and energy absorption was observed in beams with grooving method. [•] In all beams the premature FRP debonding was eliminated by using grooving method. [Copyright &y& Elsevier]

• Concrete blocks were strengthened by prestressed CFRP composites. • Bond resistance was determined through prestress force-release tests. • EBROG method increased the bond resistance with a factor of 2.4. • EBROG method increased the fracture energy by introducing crack growth in a large failure plane. Strengthening reinforced concrete (RC) beams and slabs with prestressed carbon fiber-reinforced polymer (CFRP) composites is of high interest since the FRP material can be used more efficiently. Developing a non-mechanical prestressed strengthening system entails evaluating the bond resistance of prestressed FRP to the substrate. To increase the bond resistance of prestressed CFRP strips to the concrete substrate, a new method called externally bonded reinforcement on grooves (EBROG) was investigated and compared with the conventional externally bonded reinforcement (EBR) method. For this purpose, prestress force-release tests were performed to study the bond behavior of prestressed FRP to concrete. In-plane and out-of-plane deformations were measured through a three-dimensional digital image correlation (3D DIC) system. All the tests were carried out at Empa Structural Engineering Laboratory in Dübendorf, Switzerland. Experimental results showed that the average bond resistances of EBR and EBROG joints in prestress force-release experiments were 34.4 and 81.4 kN, respectively; indicating an increased bond resistance for the EBROG method with a factor of 2.4. By using the EBROG method, the failure plane incorporated massive crack development in concrete bulk and therefore, the fracture energy and bond resistance of prestressed joints increased significantly. Besides, it was shown that prestressed joints experienced large out-of-plane deformations, emphasizing the fact the bond behavior of prestressed FRP to concrete should be treated as a mixed shear/tension fracture mode in the future studies. [ABSTRACT FROM AUTHOR]

• Externally Bonded Reinforcement on Grooves (EBROG) technique was used in flat slabs; • EBROG was successful in postponing debonding of FRP composites in strengthened flat slabs; • EBROG was successful when the geometry of the strengthening solution was conditioned by column continuity; • Debonding strain values in case of EBROG were much higher than those in case of EBR. One of the major disadvantages of conventional fibre-reinforced polymer (FRP) strengthening techniques is the premature debonding of the FRP, leading to an underutilization of the materials. The externally bonded reinforcement on grooves (EBROG) method, which has been proven successful in postponing debonding in several structural applications, is examined in this study for the first time for realistic conditions in flat slabs. To this end, two different layouts of the strengthening solution are tested under concentric monotonic loading: one representing roof-level slab-column connections in which carbon FRP (CFRP) sheets are laid on top of the joint region (cross layout); and another one representing intermediate floors, in which the aforementioned layout is not possible due to the presence of the column (grid layout). For each layout, two FRP bonding techniques are used: conventional externally bonded reinforcement (EBR) and EBROG. Another specimen, without FRP strengthening, is used as a reference. It is shown that the EBROG technique is effective in postponing debonding for both layouts. Compared to the specimens in which EBR was used, the load capacity was increased in case of EBROG by 36% when FRP sheets were bonded on top of the joint (cross layout) and by 15% when sheets were attached outside the joint region (grid layout). Debonding strains are shown to be significantly higher in the case of EBROG compared to EBR. The experimentally observed debonding strains were compared with code provisions and predictions of models from the literature. A simple calculation method giving reasonably good results for the load capacity of the FRP-strengthened specimens is presented. [ABSTRACT FROM AUTHOR]