Externally Bonded Reinforcement On Grooves Technique Research Articles

Flexural strengthening of RC beams by advanced concrete canvas

AbstractIn this study, concrete canvas (CC) layers were used as a novel method to strengthen reinforced concrete (RC) beams because of their flexibility, rapid installation, fast curing, and rapid strengthening. Due to the importance of the CC mechanical properties, various combinations of cement including ordinary (OPC) and High Alumina (HAC), as well as silica fume, were investigated to determine the optimal mixture for strengthening RC beams. The results indicate that substituting 75% of HAC with OPC significantly boosted flexural strength by 33%, and increased tensile strength in the warp and weft directions by 25% and 21%, respectively. The study examined six RC beam specimens in a four‐point flexural test, assessing their flexural properties, ductility, cracking behavior, and energy dissipation. The number of CC layers and the bonding method, which involved either the conventional externally bonded reinforcement (EBR) technique or the externally bonded reinforcement on grooves (EBROG) technique were studied. The experimental results revealed the superiority of the EBR method over the EBROG technique due to the uniform bond between CC and the concrete surface. Using the EBR technique, improvements of 35% and 51% were observed in the load‐carrying capacity of the beams strengthened with one and two CC layers, respectively. It is while for the beam with an improved loading capacity of 51%, the crack width decreased from 5.3 to 2.1 mm, and the energy dissipation increased by three times compared to the control specimen. Theoretical analysis also was performed to calculate the load‐carrying capacity of the RC beams strengthened with CC layers.

Prediction of the Bond Strength of Externally Bonded FRP Sheets Applied to Concrete via Grooves Technique Using Artificial Neural Networks

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.

Experimental and theoretical study on the flexural behaviour of RC beams strengthened with externally bonded reinforcement on grooves CFRP laminates

This paper presents a study on the flexural capacity of Reinforced Concrete (RC) beams strengthened with Externally Bonded Reinforcement on Grooves (EBROG) Carbon Fibre Reinforced Polymer (CFRP) laminates. Thirteen single-shear tests and seven RC beams strengthened with CFRP are examined, comparing Externally Bonded Reinforcement (EBR) and EBROG techniques with different groove distributions. The results showed that EBROG improved the bond and flexural performance. Comparison with existing prediction models reveals that while the literature models accurately predict EBR results, they underestimated the bending capacity for EBROG due to calibration based on EBR bond parameters. Consequently, a numerical model is developed to simulate Intermediate Crack Debonding (ICD) for various bond-slip laws, applicable to the different strengthening techniques. The proposed model is validated using experimental flexural tests and calibrated bond-slip laws obtained from single-shear tests, demonstrating accurate prediction of ICD failure for both EBR and EBROG.

Shear Strengthening of RC Deep Beams with Symmetrically or Asymmetrically Positioned Square Openings Using CFRP Composites and Steel Protective Frames

In most cases, openings are made in the Web of deep beams for installations to pass through. These members require to be strengthened since the openings reduce load-bearing capacity. This study utilizes carbon fiber-reinforced polymer (CFRP) composites and steel protective frames (SPF) as strengthening configurations in reinforced concrete (RC) deep beams to improve the strength lost due to the square openings. To this end, eleven specimens with 10 × 50 × 120 cm in size were subjected to the three-point monotonic loading. In each beam, one or two square openings of 18 cm in each side are positioned either symmetrically or asymmetrically along the beam before it is strengthened with CFRP composites or SPFs. The strengthening composites were installed using externally bonded reinforcement (EBR) or externally bonded reinforcement on grooves (EBROG) techniques in two wrapped or inclined configurations. The obtained results indicate that specimens retrofitted by the SPF exhibited a superior performance as their loading capacity and energy absorption were enhanced by 115% and 337% in comparison with the reference beam, respectively, while these values for the specimens retrofitted by the EBROG technique were 58% and 182%, respectively, and 42% and 105% for those strengthened with the EBR technique.

RETRACTED: Effect of EBR- and EBROG-GFRP laminate on the structural performance of corroded reinforced concrete columns subjected to a hysteresis load

The reinforced concrete (RC) columns infiltrated by chloride ions in the marine environment are much vulnerable under seismic loading and corrosion can severely reduce their load-bearing capacity. To improve the load-bearing capacity of RC columns subjected to different load conditions and hazardous environments using glass fibre reinforced polymers (GFRP) have been gained a great deal of attention. Therefore, this paper investigated the seismic behaviour of RC columns strengthened by GFRP laminate exposed to the different rebars corrosion levels. A total of 15 square RC columns were fabricated and tested under the lateral seismic load. A novel wrapping method was employed to perform different longitudinal rebar corrosion at levels of 0%, 5%, 10%, 15% and 20%. To introduce GFRP laminate on the specimens’ surfaces, two strengthening techniques were applied: Externally Bonded Reinforcement (EBR) and Externally Bonded Reinforcement on Grooves (EBROG), and the effect of these strengthening techniques on the hysteresis behaviour, energy dissipation, stiffness, ductility, load-bearing capacity, and deformation of specimens were studied. Additionally, new models were developed to predict the ductility, stiffness, and energy absorption of EBR- and EBROG-GFRP strengthened RC columns with various rebar corrosion levels. Results showed that using GFRP laminate improved the maximum load-bearing capacity, stiffness, ductility and energy absorption of corroded RC columns, and these properties were further improved using the EBROG technique. However, the difference between the improvement effect of EBR and EBROG techniques was declined with increasing the longitudinal rebars corrosion level. Additionally, the proposed models with high accuracy could be utilized as an efficient tool to anticipate the ductility, stiffness and energy absorption of EBR- and EBROG-GFRP strengthened RC columns exposed to different rebar corrosion levels.

An empirical FRP-concrete bond-slip model for externally-bonded reinforcement on grooves

The externally-bonded reinforcement on grooves (EBROG) has been recently developed as a substitute for the conventional externally-bonded reinforcement (EBR) technique used to retrofit reinforced concrete (RC) structural members with fiber-reinforced polymer (FRP) composites. While the presently available bond-slip models predict the bond-slip behavior of FRP composites adhered to the concrete surface via the conventional EBR method, there is a lack of reports in the literature on rigorous bond-slip model for FRP composites attached to concrete surfaces via the EBROG technique. Using a nonlinear regression on experimental data, the current research attempts to introduce an empirical model for such bond-slips. For this purpose, FRP composite strips were bonded to 68 concrete prism specimens retrofitted through the EBR and EBROG technique, before subjecting them to the single lap-shear experiment (108 tests in all). The test parameters included compressive strength of concrete, grooves dimensions (width and depth), composite strip width, and composite stiffness. A bilinear bond-slip model was proposed. Maximum shear stress, fracture energy, and associated slip were determined by analyzing on-groove and out-of-groove stresses and strains via the image processing method of particle image velocimetry (PIV). Finally, analysis of variance and different statistical tools were employed to validate the results obtained from the bond-slip model developed.

Shear and flexural strengthening of deficient flat slabs with post‐installed bolts andCFRPcomposites bonded throughEBRandEBROG

AbstractFiber 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.

Flexural strengthening of flat slabs with FRP composites using EBR and EBROG methods

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.

Behavior of RC columns confined with CFRP using CSB method under cyclic axial compression

It is the aim of this study to investigate the influences of the recently developed corner strip-batten (CSB) technique on reinforced concrete (RC) columns strengthened with carbon fiber reinforced polymer (CFRP) under cyclic axial loading. In CSB technique, CFRP battens do not undergo any curvature in transverse strengthening the specimen but are stretched as flat sheets. For the purposes of this study, 11 one-third scale RC columns were subjected to cyclic axial loading. The columns were strengthened with transverse FRP sheets using the three confining techniques of FRP composites employed as wraps, corner strip-wrap (CSW), and CSB. Furthermore, the two different strengthening procedures of externally bonded reinforcement on grooves (EBROG) and externally bonded reinforcement (EBR) were employed for bonding longitudinal composite strips. Results revealed that the columns confined using the CSB method exhibited improved load carrying capacity, ductility, equivalent damping ratio, energy dissipation, and secant stiffness under cyclic axial compression loading by 41.9%, 102.5%, 47.6%, 31.0%, and 25.9%, respectively, when compared with the reference column. Moreover, EBROG was discovered to have a significantly greater contribution to delaying the buckling of longitudinal CFRP composites and to improving column performance than did the conventional EBR technique. Finally, based on the compressive stresses of the carbon fibers in CFRP, the EBROG technique led to higher values of compressive strength of FRP sheets.

Experimental and analytical study on flexural strengthening of RC beams via prestressed EBROG CFRP plates

The present manuscript reports results obtained from both experimental and analytical studies on the behavior of reinforced concrete (RC) beams strengthened in flexure using prestressed carbon-fiber-reinforced polymer (CFRP) plates via the externally bonded reinforcement on grooves (EBROG) method. A major concern in strengthening beams with prestressed FRP plates is the proper transfer of prestressing force to the beam. The present study pioneers the use of EBROG technique in prestressed CFRP plates considering the proven superiority of the bond efficiency created by the EBROG technique over that by the EBR. For the purposes of this study, seven RC beams with cross-sections of 200 × 300 mm and lengths of 2600 mm were subjected to the four-point loading test in order to investigate the effects of different parameters including prestressing level, using anchorage system, and the strengthening technique employed. Experimental results indicated that the EBROG technique, in the absence of any end anchorage, was well capable of transferring the prestressing stresses to the beam, which obviously led to significant reductions in strengthening costs. Compared to the specimens strengthened through the EBR technique, those strengthened via the EBROG technique exhibited an enhanced flexural behavior as evidenced by their increased load carrying capacity, ductility, and CFRP debonding strain that were higher by 18, 53, and 36%, respectively. It was also observed that prestressing CFRP plates attached via EBROG method was able to postpone the debonding and increase the strength efficiency of the FRP plates. A maximum enhancement of 20% in ultimate load-carrying capacity was measured in prestressed beams strengthened via the EBROG technique relative to the non-prestressed ones.

Seismic retrofit of reinforced concrete strong beam–weak column joints using EBROG method combined with CFRP anchorage system

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.

Empirical FRP-concrete effective bond length model for externally bonded reinforcement on the grooves

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.

A generic non-linear bond-slip model for CFRP composites bonded to concrete substrate using EBR and EBROG techniques

In this study, a generic bond-slip model is proposed for carbon fiber reinforced polymer (CFRP) reinforcement bonded to concrete substrate. The model is applicable to concrete members strengthened by the conventional externally bonded reinforcement (EBR) technique, as well as to those members strengthened using the recently introduced externally bonded reinforcement on grooves (EBROG) method. The model was first calibrated using 39 single lap-shear tests performed on EBR and EBROG joints having various concrete strength, CFRP thickness, and groove depth (in case of EBROG joints). Afterwards, the excellent performance of the model in terms of its high prediction accuracy of the bond-slip behavior and ultimate capacity of EBR and EBROG joints was verified using a set of independent experimental data collected from the existing literature. Owing to the certain advantages of the proposed model including its high accuracy and applicability to predict the bond behavior and strength of both EBR and EBROG joints, the proposed model can be an efficient alternative to the existing ones for predicting the CFRP-to-concrete bond behavior. Furthermore, single lap-shear tests performed on CFRP strips bonded to concrete substrates demonstrated that the interfacial fracture energy of EBROG joints is almost three times that of the EBR joints.

Grooving methods in square RC columns strengthened with longitudinal CFRP under cyclic axial compression

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.

Influence of bonding technique on bond behavior of CFRP-to-clay brick masonry joints: Experimental study using particle image velocimetry (PIV)

This paper presents a comparative study on the performance of three different techniques for bonding carbon fiber reinforced polymer (CFRP) sheets to masonry substrate. To do so, eight CFRP-to-clay brick masonry joints were prepared using conventional externally bonded reinforcement (EBR) technique, with and without surface preparation. Moreover, for the first time, grooving method (GM) in the form of externally bonded reinforcement on grooves (EBROG) technique was used for bonding CFRP sheets to masonry substrate in six other joints. The specimens were tested under single lap-shear loading and the influence of bonding technique as well as effect of fiber reinforced polymer (FRP) bond length were comprehensively investigated and discussed based on the experimental results. A non-contact full field deformation measurement technique, i.e. particle image velocimetry (PIV), was used to obtain the load–slip diagrams, strain profiles along the bonded length, and strain fields of all tested specimens. Experimental results and PIV measurements demonstrated that bond behavior of CFRP sheets attached to masonry substrate was significantly improved by using EBROG technique. Consequently, the technique can be used as an alternative to conventional EBR method to more efficiently utilize the tensile capacity of FRPs used for external strengthening of unreinforced masonry (URM) structures.

EBROG and EBRIG methods for strengthening of RC beams by FRP sheets

This paper presents an experimental study on reinforced concrete (RC) beam specimens flexurally strengthened by fibre-reinforced polymer (FRP) sheets using conventional externally bonded reinforcement (EBR) method and recently introduced grooving method (GM) in the form of externally bonded reinforcement on grooves (EBROG) and externally bonded reinforcement in grooves (EBRIG) techniques. The concrete beam specimens were strengthened with one, two or three FRP layers, and their load–displacement relationships as well as their failure loads were compared with each other. The performances of EBR, EBROG and EBRIG techniques for flexural strengthening of RC beams were found to be very close when one layer of FRP sheet was used; however, for two FRP layers, beams strengthened with GM in the form of both EBROG and EBRIG techniques experienced up to 25% higher ultimate loads compared to those strengthened with EBR method. Furthermore, for three FRP layers, this increase was 19 and 24%, respectively, for EBROG and EBRIG strengthening techniques compared to EBR method.

Effect of groove characteristics on CFRP-to-concrete bond behavior of EBROG joints: Experimental study using particle image velocimetry (PIV)

Externally bonded reinforcement on grooves (EBROG) technique has been recently introduced as a promising alternative to conventional externally bonded reinforcement (EBR) to eliminate debonding of fiber reinforced polymer (FRP) sheets from concrete substrate. FRP-to-concrete bond behavior in EBROG technique, however, has not been comprehensively investigated up to now due to the novelty of the technique. Consequently, the intention of the current study is to experimentally investigate the effect of groove characteristics on CFRP-to-concrete bond behavior of EBROG joints. To do so, a set of single-shear bond tests were conducted on 9 concrete prism specimens and the effects of groove dimensions (i.e. width and depth) on CFRP-to-concrete bond behavior of tested specimens including load bearing, failure mode, load–slip behavior, and strain distribution were discussed. Bond–slip behavior of CFRP sheets in EBROG technique was obtained for the first time, utilizing an accurate image-based deformation measurement technique, i.e. particle image velocimetry (PIV). PIV analyses demonstrated that EBROG technique can significantly improve the interfacial fracture characteristics of CFRP-to-concrete bonded joints.

Experimental investigation into bond behavior of CFRP sheets attached to concrete using EBR and EBROG techniques

Over the last decade, an extreme increase in the application of fiber reinforced polymers (FRPs) for strengthening of reinforced concrete (RC) structures has been observed. The most common technique for strengthening of RC members utilizing FRP reinforcements is externally bonded reinforcement (EBR) technique. Despite certain benefits of the technique such as simple and rapid installation, the main problem which has greatly hampered the use of EBR method is premature debonding of FRP composite from concrete substrate. Recently, grooving method (GM) has been introduced as an alternative to conventional EBR technique. Grooving with the special technique of externally bonded reinforcement on grooves (EBROG) has yielded promising results in postponing or, in some cases, completely elimination of undesirable debonding failure in flexural/shear strengthened RC beams. Consequently, the main intention of the current study is to make a comparison between FRP-to-concrete bond behavior of EBR and EBROG techniques by means of single-shear bond tests. To do so, CFRP sheets were adhered to 16 concrete prism specimens using EBR and EBROG techniques. The specimens were then subjected to single-shear bond test and the results were compared. A non-contact, full field deformation measurement technique, i.e. particle image velocimetry (PIV) was utilized to investigate the bond behavior of the strengthened specimens. Successive digital images were taken from each specimen undergoing deformation during the test process. Images were then analyzed utilizing PIV method and load–slip behavior as well as slip and strain profiles along the strengthening CFRP strips were reported. Experimental results of the current study strongly verify the capability of GM for strengthening RC members to completely eliminate the debonding failure.

Externally bonded reinforcement in grooves (EBRIG) technique to postpone debonding of FRP sheets in strengthened concrete beams

Recently a new method for flexural strengthening of concrete beams with FRP sheets, named as grooving method (GM) with the special technique of externally bonded reinforcement on grooves (EBROG), has been introduced as alternative to conventional externally bonded reinforcement (EBR). Based on some experimental investigations, the EBROG method can considerably postpone the debonding phenomenon and in some cases may completely eliminate it. The aim of the current study is to introduce and to examine another improved strengthening procedure by using the GM method when the FRP sheets are in direct contact with the internal surfaces of the grooves on the tension face of concrete beam in a wet-lay-up application. This technique is named externally bonded reinforcement in grooves (EBRIG). For this purpose, 32 beam specimens with dimensions of 120×140×1000mm were cast, strengthened with one, two or three layers of FRP sheets and then subjected to four-point flexural loading. Results showed considerable increase in ultimate limits for beams strengthened with EBROG and EBRIG techniques compared to those strengthened with EBR method. The EBRIG technique performed as good as EBROG for one layer of strengthening FRP sheet; however, it permitted for higher failure loads and displacements compared to EBROG method when multiple-layer FRP sheets were used.