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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. [ABSTRACT FROM AUTHOR]

The dual‐function retrofitting system that uses the carbon‐fabric reinforced cementitious matrix (C‐FRCM) as both the anode of impressed current cathodic protection (ICCP) system and the structural strengthening (SS) material, that is, an ICCP‐SS system, is investigated. The experimental program mainly focused on the shear behavior of C‐FRCM strengthened reinforced concrete (RC) continuous beam under the dual‐function retrofitting system. The influence of anode polarization on the shear strengthening of RC continuous beams is analyzed. Shear tests were conducted on a total of 14 corroded RC continuous beams to investigate the influence of key parameters, including anode polarization degree of prefabricated C‐FRCM plate, layer of carbon fiber mesh and side‐wrapping. The failure modes, shear capacities, and load‐deflection curves of the shear‐strengthened RC continuous beams are reported. Based on the test results, the applicability of relevant design codes was evaluated and found to provide rather conservative predictions for the shear capacity of the examined C‐FRCM strengthened RC continuous beams. [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 paper investigates the flexural behavior of preloaded reinforced concrete (RC) beams, strengthened with Carbon Fiber Reinforced Polymer (CFRP) plates using an experimental program, analytical procedure, and Finite Element Method (FEM) simulation. The RC beams were subjected to preloads of 30%, 50% and 70% of the yielding load, prior to installation of the strengthening system. The eight RC-strengthened beams with a reinforcement configuration of 3Ø12 and two CarboDur S512 plates have been evaluated using bending tests. The failure modes of all the RC-strengthened beams were governed by the widening of flexural cracks within a constant bending zone, followed by debonding of the CFRP plates. The plates were debonding simultaneously or one plate prior to the other plate. The ultimate moment capacity is not significantly reduced while increasing preload levels from 0% to 70%. The moment capacity is increased by 70% to 80% in the CFRP strengthened beams, compared with un-strengthened beams indicating the potential of capacity enhancement that can be attained by externally bonded CFRP. [ABSTRACT FROM AUTHOR]

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The use of engineered cementitious composites (ECC) can greatly reduce or even entirely prevent premature debonding of externally bonded (EB) fiber-reinforced polymers (FRP). This study examined the flexural behavior of pre-damaged reinforced concrete (RC) beams reinforced by carbon fiber reinforced polymer (CFRP) sheets. Ten beams were created and constructed for four-point bending test. The main testing parameters were the degree of pre-damage, the thickness of the ECC layer, and the reinforcing method. According to the test results, CFRP rupture occurred in the undamaged specimens, while CFRP debonding occurred in all of the pre-damaged specimens. The pre-damaged specimens' flexural stiffness and load-carrying capability can be effectively increased. Best flexural performance and a maximum CFRP utilization of 83.2 % can be achieved by pre-damaged concrete beams when the thickness of the ECC layer entirely surrounds the longitudinal tensile reinforcement. For pre-damage specimens, the increased ECC layer thickness contributed to increased ductility and had little effect on the ultimate load. A mathematical model based on the plane section assumption is proposed to predict the flexural capacity of ECC-CFRP jointly reinforced beams, and the effect of different failure modes is taken into account. The error between the predicted and measured values is within ± 10 %. • We investigated the flexural performance of pre-damaged concrete beams reinforced with ECC-CFRP. • We examined the impact of three factors: the degree of pre-damage, the thickness of the ECC layer, and the reinforcing method. • Better flexural performance can be achieved when the thickness of the ECC layer entirely surrounds the longitudinal tensile reinforcement. • The increased ECC layer thickness at 45 % damage mainly contributed to increase ductility and had little effect on the ultimate load. • A mathematical model based on the plane section assumption is proposed to predict the flexural capacity. [ABSTRACT FROM AUTHOR]

The advantages of using prestressed carbon fiber reinforced polymer (CFRP) for strengthening and retrofitting structures have been reported in recent years. In this regard, most of the studies on prestressed CFRP technique have been carried out in the laboratory test with small-scale and no damage (reinforced concrete) RC beam. However, the real structures that need to be retrofitted in service are often degraded or damaged due to early cracking. This paper aims at studying the effect of prestressed CFRP method on full-scale and damaged RC beams. The damaged levels of four full-scale damaged hollow RC beams taken from an old bridge were evaluated. One damaged beam was tested to check the residual capacity, and the other three were strengthened with prestressed composite strengthened CFRP and steel-carbon fiber reinforced polymer (SCFRP). The flexural behavior of non-strengthened and prestressed strengthened beams was investigated. During the experiments, the failure modes, deflection, yield and ultimate load, strains of concrete, steel reinforcements, and SCFRP were measured and analyzed. The results showed that the stiffness at the elastic stage was increased by 64.9%, 66.9%, and 67.1% after strengthened by SCFRP with 30%, 40%, and 60% prestressing level. Moreover, the ultimate load of damaged hollow RC beams were improved by 19.53%, 21.82%, and 31.9%, respectively. The flexural behavior of the severely damaged RC beam with strength reduction coefficient of 0.65 can be recovered after being strengthened by SCFRP with 40% prestressing levels. Meanwhile, SCFRP-concrete interface debonding failure occurred when the prestressing level exceed 60%, and the characteristics of brittle failure became more evident with increased prestressing level of the SCFRP. [ABSTRACT FROM AUTHOR]

This experimental study aims to investigate the effects of the strengthening arrangement on the behavior and the performance of strengthened beams, according to the Near-Surface Mounted (NSM) and the Externally Bonded Reinforcement (EBR) techniques. In total five rectangular beams including a Control Beam (CB) and four Carbon Fiber Reinforced Polymer (CFRP) strengthened beams with NSM and EBR techniques. The beams were tested to failure in Four-Point Bending (FPB) test. The experimental program comprises two beams strengthened by one and two strips according to the NSM technique. Two other beams were strengthened by the same configuration with the EBR, whereas the last beam was un-strengthened and considered as the CB. The responses of control and strengthened beams were compared. The efficiency and the effectiveness of different CFRP configurations were evaluated. The test results showed that the flexural load capacity, the deflection, the ductility and the stiffness of strengthened beams increased with increasing of plates distribution. This increase was more significant for the EBR technique than the NSM. This paper also highlights the beams failure modes due to the different configurations of strengthening. The obtained results revealed that the crack patterns were affected by the arrangement of the strips. [ABSTRACT FROM AUTHOR]

The externally bonded reinforcement on grooves (EBROG) method is increasingly recognized as an alternative strengthening method that can overcome the debonding problem. This study aims to experimentally investigate the effectiveness of EBROG as compared to the conventional externally bonded reinforcement (EBR) method in strengthening reinforced concrete (RC) beams. Twelve RC beams have been tested under four point load bending. One of these beams has been designated as a reference beam, seven beams have been strengthened with carbon fiber reinforced polymer (CFRP) sheets, and four beams have been strengthened with CFRP laminates using EBROG or EBR methods. The effect of CFRP type, number of layers, as well as the type of strengthening methods on the flexural performance have been also investigated. The load, deflection, stiffness, and failure modes were recorded and discussed intensively. Overall, test results indicated that the flexural strength and stiffness of the strengthened specimens using EBR or EBROG methods increased compared to the control beam, where the increase in the load carrying capacity of beams strengthened using the EBR method ranged between 24.8 and 48.2% and by the EBROG method ranged between 31.7 and 76.7% of the control beam. The most interesting result obtained is that the failure mode of beams has been changed from debonding of CFRP material to rupture of CFRP in some samples strengthened by EBROG, which demonstrates the superior behavior of this strengthening technique as compared to the traditional strengthening using EBR. [ABSTRACT FROM AUTHOR]

In the present work, thirteen reinforced concrete beams with openings at different locations were tested under four-point bending to investigate the efficiency of strengthening techniques of such openings. Different strengthening techniques around the opening were used before casting as internally reinforced by diagonal or upper and lower additional steel bars or after casting as externally bonded sheets of carbon fiber reinforced polymers (CFRP). The stiffness, mid-span deflection, maximum load, and failure mode of the strengthened beams were discussed. Experimental results showed that the best opening location is in the constant moment region around the neutral axis. The strengthening of such beam by internal reinforcements exhibited a higher ultimate load than that of the beam without opening. At the same time, the strengthening by external bonded CFRP failed to store the strength of such beam. The upper and lower additional steel bars technique is the best technique to restore the beam with the opening in mid-span or beneath the applied load. The worst opening location is in shear span. The beam's strength with the opening in shear span was restored using CFRP, while internal reinforcement's techniques failed. It can be concluded that the strengthening technique type depends on the opening location. [ABSTRACT FROM AUTHOR]

This article presents the results of an experimental parametric study on reinforced concrete (RC) beams strengthened by an external bonding of carbon fiber reinforced polymer (CFRP) laminates to their tensile faces. This experimental work investigates the effects of both CFRP laminate sizes and concrete compressive strength on the flexural behavior of strengthened RC beams. Accordingly, a total of 10 RC beams have been cast, eight of which were strengthened in flexure by external bonding of CFRP laminate by varying its sizes, such as length, width, and thickness, and two control beams. All prepared beams were tested under standard four‐point bending until failure. The load–deflection response curves and failure modes were recorded and compared. Results show that failure modes of strengthened beams varied with the CFRP laminate characteristics from steel yielding, CFRP peeling off, and interfacial debonding laminate, Also, the load–deflection curves showed a considerable increase in the load capacity by up to 1% and 112%, compared to the unstrengthen beam, if the CFRP laminate length ratio passes from 0.40 to 0.94, respectively. In addition, the load capacity contribution increases from 56% to 112% when the CFRP laminate width increases from 50 to 100 mm. On the other hand, when laminate thickness increases from 1.2 to 2.4 mm, the load capacity contribution increases from 56% to 76%. Finally, it is concluded that the mechanical behavior of strengthened beam is strongly affected by the CFRP laminate sizes. [ABSTRACT FROM AUTHOR]

An experimental program was conducted to examine the seismic performance of flexural beam members strengthened with carbon fiber-reinforced polymer (CFRP) sheet and anchored using carbon fiber splay anchors. This research study extends the use of carbon fiber anchors to secure the top and bottom CFRP flexural sheets under cyclic loading. In this study, low strength concrete is examined, with lightly reinforced steel ratio (0.0034) to test full-scale rectangular beams. Five reinforced concrete beams were cast, strengthened, and tested under reversed cycles of four-point bending to failure. The beams were categorized into a control specimen, strengthened specimens with thin sheets with and without fiber anchors, and strengthened specimens with thick sheets with and without fiber anchors. They were tested cyclically under displacement control according to the AC 125 loading protocol. The failure modes ranged from classical ultimate failure for the control beam to rupture and intermediate crack (IC) debonding for the beam with unanchored thin CFRP sheets. On the other hand, debonding took place for the thicker sheets with no anchors, while the thicker sheets with fiber anchors underwent cover delamination failure mode despite the fact that the sheets were extended very close to the simple supports. The hysteresis response loops were compared for the different specimens and the analytical envelop curves were predicted resulting in a close agreement to the experimental finding. • Seismic performance of flexural beams CFRP strengthened with and without carbon fiber anchors is successfully examined. • Thicker CFRP sheets yield lower energy dissipation, ductility, but higher strength and seismic pinching. • Failure modes varied from sheet debonding to CFRP rupture and cover delamination. • The use of anchors at sheet ends was not very effective in extending the hysteretic cycles beyond those without anchors. • The need to apply fiber anchors along the entire shear span to harness improved behavior is clearly evident. [ABSTRACT FROM AUTHOR]

Plate end debonding is a common failure mode for fiber reinforced polymer (FRP) strengthened beams. FRP sheets and shape memory alloy (SMA) composites can effectively slow down plate end debonding and improve beam ductility owing to the anchorage effect of SMA wires on the FRP ends. This work aims to comprehensively study the anchorage performance of FRP/SMA composite strengthened beams through both model analysis and experimental investigation. The plate end debonding strength models of existing FRP strengthened beams were initially summarized and analyzed, and an improved model was proposed to predict the debonding strength of FRP/SMA composite strengthened beams at the plate end. Moreover, the anchorage performance and flexural behavior of beams strengthened with carbon fiber reinforced polymer (CFRP) and SMA composites were studied through experiments. The failure mode of the FRP sheet strengthened beams was plate end debonding failure, while the plate end debonding failure of the CFRP/SMA composite strengthened beams occurred at the strengthening zone end, and the peeling failure was delayed owing to the anchorage effect of SMA wires on the ends of the strengthening CFRP sheets. The recovery effect of SMA wires could successfully introduce prestress into CFRP sheets. Moreover, the CFRP strain corresponding to plate end debonding increased because of the anchorage of SMA wires on the CFRP sheet in the strengthening zone. The strength and ductility of the CFRP/SMA composite strengthened beam significantly improved. The proposed model for predicting the plate end debonding strength of FRP/SMA composite strengthened beams was validated through experiments. • An improved model is proposed to predict the debonding strength of beams strengthened with FRP/SMA composites at the plate ends. • The debonding failure was delayed due to the anchorage effect of SMA wires on CFRP sheets in the strengthening zone. • The strength and ductility of the beam strengthened with CFRP/SMA composites have been significantly improved. • The proposed model for predicting the plate end debonding strength of FRP/SMA composite strengthened beams was validated through experiments. [ABSTRACT FROM AUTHOR]

Copyright of Romanian Journal of Civil Engineering / Revista Română de Inginerie Civilă is the property of Matrix Rom and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper investigates the influence of cyclic preloading on the fatigue behavior of reinforced concrete (RC) beams rehabilitated with near surface mounted (NSM) carbon fiber reinforced polymer (CFRP) reinforcement. The study includes eight RC beams with dimensions of 152.4 × 152.4 × 1,521 mm. Strengthened and nonstrengthened specimens were tested under monotonic loading to obtain the flexural static capacity. Two strengthened specimens were tested as a reference under constant amplitude cyclic stress without prefatiguing. Four nonrehabilitated RC beams were prefatigued to simulate service loading conditions. Later, these RC beams were rehabilitated with NSM CFRP reinforcement and tested under the same cyclic stress range of the reference specimens. Mid‐span deflection, strain of tension steel rebars and CFRP rods, stiffness degradation, and energy dissipation were analyzed and evaluated. Experimental results show that the rehabilitated prefatigued RC beams had similar stiffness degradation and failure modes to the reference strengthened RC beams. The rehabilitated RC beams had an improvement in the fatigue responses when compared to the reference strengthened RC beams. Moreover, the postfatigue monotonic behavior of the rehabilitated RC beams showed an increase in the elastic modulus and a decrease in ductility. [ABSTRACT FROM AUTHOR]

• Efficiency of WWS technique in anchoring longitudinal CFRP sheets was investigated. • Influence of different parameters on the performance of WWS anchors were investigated. • Efficiency of WWS method was much better than that of conventional U-shaped anchors. • Simultaneous use of WWS technique with corner strip led to rupture of longitudinal CFRP. U-shaped straps are an effective means to postpone premature debonding failure when fiber-reinforced polymer (FRP) composites are applied in structures. However, the U-wrap anchors are not cost-effective and in many cases cannot completely prevent the debonding phenomenon. In the current study, an innovative technique named "warp and woof strap" (WWS) is introduced for anchoring longitudinal FRP sheets, in which some parts of FRP fibers are manually made bi-directionally. Unlike the conventional U-shaped anchors, the anchorage system in this method is in direct contact with the tension side of the beam. Totally, 20 reinforced concrete (RC) beams, 120 × 160 × 1400 mm in size, were subjected to the four-point loading to evaluate the efficiency of the introduced anchorage system in comparison to the U-shaped anchorage. The effect of different parameters including the method employed for anchoring the longitudinal carbon fiber reinforced polymer (CFRP) sheet, anchorage height and width, location of FRP anchorage application, use of the corner strip and rounding corner method, and configuration of WWS anchorage were investigated. The experimental results indicated that the efficiency of the WWS method in preventing undesired debonding mode of failure is much better than that of conventional U-shaped anchor. It was also observed that using WWS method can improve the load carrying capacity and ductility up to 32% and 80%, respectively, compared to U-shaped anchors. [ABSTRACT FROM AUTHOR]

Over the past several decades, textile reinforced concrete (TRC) materials have been developed due to their superior mechanical properties, corrosion resistance, lightweight application, and high load-bearing capacity. In this study, the effect of three main factors on bending load capacity of carbon fiber reinforced concrete (CFRC) beams is investigated; the number of reinforcements (carbon-fiber rovings), penetration of the cement within the fibers, and the post-cracking factor. The second and third factors are defined as the fiber performance index (FPI) for evaluating bending load capacity of CFRC beams. The best FPI for a different number of reinforcements was estimated using empirical values of bending load capacity of CFRC beams. The results were indicative of the efficiency and accuracy of the proposed FPI for a wide range of roving numbers, namely 2-24 with 800 tex as the titer. The post-cracking factor was suggested as 2.67 for TRCs and CFRCs materials, which are reinforced by rovings. In order to improve the FPI, the roving was impregnated partially with epoxy, which increased the maximum load capacity and displacement of the beams up to 26.68 and 23.24%, respectively. In addition, the impacts of roving numbers, the first factor, on the failure mode, load-bearing capacity, ductility, and toughness of the CFRC beams were investigated. [ABSTRACT FROM AUTHOR]

• The impact and post-impact performance of RC beam strengthened with CFRP was investigated experimentally and numerically. • The strengthening effect by various CFRP anchorage methods was discussed. • CFRP slipping played an important role in the strengthening effect of strengthened beam. • The post-impact performance was quantified by residual resistance, residual stiffness and energy absorption ratio. • CFRP strengthened beams show better residual performance and resilience. Carbon fiber reinforced polymer (CFRP) external bonding is a common approach to strengthen the bearing capacity of the reinforced concrete (RC) members. In this study, two types of RC beams, i.e., CFRP strengthened beam and conventional RC beam, were tested under drop hammer impact and subsequent quasi-static loading. The strengthening effect of the CFRP on the dynamic responses, failure modes and residual load-carrying performance of the RC beams were fully investigated. Then, a high-resolution explicit numerical simulation was conducted to further investigate the residual load-carrying mechanism of the CFRP strengthened beam. The experimental results demonstrate that even though the CFRP sheet peels off from the soffit of the investigated beam instantaneously upon impact, which provides a little contribution to the impact damage elimination in the mid-span of the beam, the oblique cracks within the flexure-shear zone were reduced moderately. Further, the bonded CFRP sheet can effectively reduce the maximum and residual displacement of the beam and improve the recovery performance of deformation. In addition, the residual resistance, residual stiffness and post-impact energy absorption capacity of the beams with CFRP are shown to be higher than those of the unstrengthened ones. The experimental and numerical results both show that the effective anchoring approach has an important effect on the residual loading performance enhancement. Larger impact energy and more significant impact dynamic effect tend to degrade the bearing performance of the beam more. [ABSTRACT FROM AUTHOR]

• CFRP grid and ECC were employed to repair load-damaged RC beams. • Failure modes, load-deformation response, and flexural capacities were evaluated. • Prediction model for the flexural bearing capacity were proposed. In this study, the flexural behavior of pre-damaged reinforced concrete (RC) beams repaired with carbon fiber reinforced polymer (CFRP) grids and engineered cementitious composite (ECC) was investigated. Fifteen beams were designed and subjected to four-point bending tests. Three types of specimens were tested: undamaged, pre-damaged with removed load (i.e., loaded to the target level and then unloaded), and pre-damaged under sustained load. The main testing parameters were strengthening material (ECC alone, or CFRP grid plus ECC), CFRP grid thickness, main reinforcement ratio, preloaded level, and repairing process. The experimental results showed that most of the repaired beams exhibited flexural failure caused by concrete crushing, and a few others failed by debonding. The proposed repairing technique was effective in enhancing the flexural stiffness and bearing capacity of pre-damaged RC beams. For the repaired beams, the flexural bearing capacities did not significantly decrease as the preloaded level increased from 0 to 0.45 and slightly decreased when the preloaded level exceeded 0.65. A mathematical model based on the plane section assumption was proposed to predict the flexural capacities of the repaired beams, considering whether the load causing the damage was removed or sustained. The predicted capacities were in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

[Display omitted] • RC beams failed in flexure while RC beams + CFRP failed in shear. • RC beams + CFRP failure loads are lower than theoretical flexural and shear strengths. • Higher CFRP ratio delaminates more and failure load approaches a steady value. • Analytical load–deflection agrees with the experiment up to a certain % of CFRP. • FE modeling captures the behavior and an adjusted capacity model is provided. This study investigates the shear behavior and debonding characteristics of initially ductile RC beams (failing in flexure when unstrengthened) at the verge of transitioning to a more brittle shear failure upon strengthening using external flexural carbon fiber reinforced polymer (CFRP). Despite the absence of shear CFRP strengthening, various degrees of improvement in the shear capacity were achieved depending on the flexural CFRP amount. However, steeper shear cracks that bypass the stirrups in addition to the nonyielding stirrups results in shear capacities that cannot be reliably predicted using the ACI and other similar codes' provisions. Instead of adopting capacity models that focus on the shear failure alone or the crack-induced debonding as oneway cause-effect (shear crack-debonding) relationship, a more holistic capacity prediction approach (calibrated with finite element anlaysis) that considers the synergistic effect between the shear failure and the CFRP debonding is provided. Since any enhancement in flexure must be checked against shear, the presented capacity prediction approach could be a more handy means to assess the shear strengthening level needed in such cases where the flexural strengthening is insufficient to achieve the overall structural upgrade sought. The designed beams – i.e. at the verge of changing failure mode with flexural FRP strengthening – and the test program could serve as a bond assessment philosophy in the sense that this upper bound brittle failure mechanism provides more realistic behavior of the crack-induced debonding performance of FRP-strengthened beams. Analytical load–deflection assessment of the tested specimens is also provided. [ABSTRACT FROM AUTHOR]

The premature debonding of Fiber Reinforced Polymer (FRP) sheets has been well studied and understood for normal weight concrete. This type of failure mode can be averted by keeping the maximum FRP strain below the debonding strain of FRP as specified by ACI 440.2R-17. However, the debonding strain in lightweight concrete has not been addressed or evaluated yet. Accordingly, this paper investigates the debonding strain in lightweight concrete using full-scale reinforced concrete T beams strengthened with different layers of carbon fiber reinforced polymer (CFRP). These beams were prepared and strengthened in two series. The first series included three T beams that were cast with normal weight concrete. The second series consisted of another group of three T beams using lightweight concrete. Both series had identical geometry, reinforcement, and span lengths. Furthermore, they had almost identical concrete properties and the same FRP material to effectively examine the deboning strain difference in both types of concrete. The debonding strains of the lightweight and normal weight concrete are compared and the reduction factor is addressed in light of the current design equation in ACI 440.2R-17. [ABSTRACT FROM AUTHOR]

This paper presents an experimental program that was carried out for the purpose of studying the global flexural performance of reinforced concrete beams strengthened internally with Carbon Fiber Reinforced Polymer (CFRP) rods using the Side Near Surface Mounted (SNSM) technique. The CFRP rods were placed laterally, adjacent to the longitudinal steel bars inside precut grooves. The strengthening length and position of CFRP rods as well as the type of filling material were the main variables investigated in this study. Moreover, a detailed comparison between the Side Near Surface Mounted (SNSM) and the Near Surface Mounted (NSM) techniques for the strengthening of RC beams using CFRP rods was conducted as well; in order to validate and assess the effectiveness of the SNSM technique. The test results showed that using the SNSM-CFRP rods technique allowed improving in a significant way the load carrying capacity of RC beams but decreased their ductility along the deflection at maximum load. The results obtained indicated that the failure mode was influenced by the length of CFRP rods and the filling material characteristics, while the strengthening position did not have significant impact. The SNSM strengthening technique can be used as an alternative method to the NSM method, and in some cases, it may be used to prevent the non-conventional failure modes, due to degradation of the NSM strengthening system, such as the pull out of CFRP-rods or premature debonding failure. The conventional analytical model accurately predicted the strength capacity and mid-span deflection of the SNSM strengthened beams. [ABSTRACT FROM AUTHOR]

The strengthening reinforcement is glued to the soffit of the reinforced concrete (RC) beams in the mainstream externally bonded reinforcement (EBR) technique for flexural strengthening. However, the soffit of RC beams could be inaccessible for strengthening due to limited or no space at the soffit because of walls or doors, or the spalling of concrete. To overcome such difficulties, this paper investigates the feasibility of the flexural strengthening of lightweight non-pre-cracked and pre-cracked reinforced concrete (RC) beams using the side externally bonded reinforcement (S-EBR) technique with carbon fiber reinforced polymer (CFRP) fabric. A total of eight full-sized RC specimens were fabricated, strengthened, and tested under four-point loading until failure. The test variables were the internal reinforcement ratio, percentage of pre-cracking loads, and the effect of cracking loads on the flexural performance. The loads, deflection, and ultimate failure of the specimens were recorded and the types of modes of failure were also observed. The S-EBR strengthening technique with CFRP fabric significantly enhanced the flexural capacity of non-pre-cracked and pre-cracked lightweight RC beams compared to the control specimen. An analytical model in accordance with ACI 440.2R-08 was developed to verify the experimental results. The flexural capacity predicted by the model was in reasonable agreement with the experimental results. [ABSTRACT FROM AUTHOR]

• Parametric analysis of pre-cracked RC beams shear-strengthened with CFRP strips is made. • Different failure modes related to CFRP strips are observed. • Shear behaviors and the failure mechanisms of specimens are revealed. • A revised model to evaluate the shear capacity of CFRP shear-strengthened beam is proposed. Experimental studies on shear capacity of eighteen pre-cracked reinforced concrete (RC) beams shear-strengthened with carbon fiber reinforced polymer (CFRP) strips are carried out in this study. The effects of CFRP strips spacing, shear span ratio and pre-cracked degree on the failure mode, shear capacity, load-deflection curve and moment-curvature relationship of strengthened specimens are analyzed. Three failure modes related to the failure of CFRP strips, that is the bonding failure, the debond failure and the fracture failure of CFRP strips, are observed for specimens with different structural parameters. Moreover, with decrease of CFRP strips spacing, the shear capacity, the ultimate deflection and the bending stiffness of specimens increase. With increase of pre-cracked degree, the increment of shear capacity of RC beams shear-strengthened with CFRP strips is lower than that of non-cracked beams. The pre-cracked degree presents slight effect on the stiffness of CFRP strips-strengthened beams. Further, a revised model to determine the shear capacity of CFRP strips is proposed by accounting for the strain distribution of CFRP strips and the pre-cracked degree. Comparison between the experimental results and the calculated values indicates that the proposed formula can versatilely evaluate the shear capacity of CFRP strips strengthened RC beams. [ABSTRACT FROM AUTHOR]