Externally Bonded Carbon Fiber Reinforced Polymer Research Articles

Hybrid strengthening of RC beams with externally bonded carbon fiber reinforced polymer laminate and engineered cementitious composites transition layer

This paper presents the experimental study on the reinforced concrete (RC) beam strengthened with externally bonded carbon fiber reinforced polymer (EB-CFRP) laminate and engineered cementitious composites (ECC) material. A total of six beams were tested under the four-point bending test to investigate the influence of strengthening scheme, type of CFRP laminate and the width of CFRP plate on the flexural response. The results revealed that hybrid strengthened beam with the technical of EB-CFRP and ECC transition layer significantly enhanced the crack load (29.0%–133.3%), yield load (50.9%–96.5%) and ultimate load (50.0%–81.9%) of the beams relative to the control beam. The employment of ECC material was an ideal transition layer for delaying the interfacial debonding of CFRP laminate, where the ultimate tensile strain of CFRP plate in hybrid strengthened beams was 13.2%–33.33% higher than that of beam merely strengthened with EB-CFRP plate. Beams strengthened with CFRP sheet had the greater flexural performance and higher utilization of CFRP than its counterparts strengthened with CFRP plate. Moreover, the predicted model associated with ultimate bearing capacity of the hybrid beams was provided based on ACI 440.2R-08, which was relatively conservative with a margin for the ultimate load of the hybrid strengthened beams.

Experimental and numerical investigation of the flexural behavior of one–way RC slabs strengthened with near–surface mounted and externally bonded systems

This study investigated the flexural performance of one-way reinforced concrete (RC) slabs strengthened with two distinct strengthening systems: near–surface mounted (NSM) bars and externally bonded (EB) carbon fiber-reinforced polymer (FRP) strips. The NSM bars comprised four types: carbon FRP (CFRP), basalt FRP (BFRP), glass FRP (GFRP), and stainless–steel (SS) bars. The NSM–strengthened slabs showcased substantial enhancements in yield and ultimate load capacity, ranging from 20 % to 55 % and 59–123 %, respectively. In comparison, those strengthened with EB–CFRP strips displayed increases from 46 % to 107 % and 45–177 %, respectively, depending on the axial stiffness ratio of the strengthening system provided. Furthermore, the slabs reinforced with NSM–BFRP bars showed an 11–25 % improvement in their ductility indices. In contrast, the slabs reinforced with EB experienced a decrease in ductility ranging from 38 % to 50 %. This reduction was attributed to the differences in the modes of failure observed in both strengthening systems. The rupture of the NSM–FRP bars and the strain readings associated at the end of testing confirmed that the tensile strength of the NSM–FRP bars was fully exploited whereas the EB–CFRP strips utilized only 29–36 % of their ultimate tensile strain due to debonding. A finite element (FE) model was formulated to anticipate the behavior of the strengthened slabs. A strong correlation between the numerical predictions and the experimental outcomes was observed. The experimental–to–numerical ratios of the ultimate load ranged between 1.0 and 1.08 for the NSM–strengthened slabs and between 0.98 and 1.38 for the EB–strengthened slabs. This validated the FE models’ ability to capture the nonlinear performance of the strengthened slabs.

Nonlinear FE analysis of RC slabs strengthened with prestressed EB CFRP strips under high-cyclic fatigue loading

A significant issue in structural health monitoring is identifying fatigue damage in concrete structures that have been retrofitted with externally bonded Carbon Fiber Reinforced Polymer (EB-CFRP). Although the finite element method has significantly contributed to modeling the damage mechanisms of concrete, reinforcement, and CFRP, further research is still needed in this area. For instance, RC slabs reinforced with EB-CFRP technology must be evaluated and predicted for high-cyclic fatigue and progressive damage. Therefore, this research aimed to develop intricate numerical models that could be utilized to analyze the dynamics of fatigued RC slabs and find damage in slabs that have prestressed EB-CFRP reinforcement. It was discovered that prestressed EB-CFRP-reinforced RC slabs can significantly affect the vibration response of specimens. When the prestressing and fatigue loads were high, the prestressing altered the damage distribution at the CFRP-concrete interface, leading to debonding of the CFRP near the ends of the RC slabs. Additionally, for high-cyclic fatigue progressive damage, the mixed damage mode—steel yielding and CFRP debonding—was the primary failure mechanism of RC slabs reinforced with prestressed EB-CFRP.

Fire endurance tests of CFRP-strengthened RC beams with different insulation schemes

The fire performance of externally bonded (EB) carbon fiber-reinforced polymer (CFRP)-strengthened reinforced concrete (RC) beams is an important issue in practical strengthening design. The cable mechanism of CFRP sheets in a fire can improve the fire endurance of the strengthened beams. This paper presents a feasible method to activate the cable mechanism of EB CFRP sheets in the strengthened beams by using appropriate insulation schemes and a mechanical anchorage system. Seven beams were constructed: three were tested at room temperature, while the remaining four were subjected to the ISO 834 standard fire. The experimental results showed that the three insulation schemes could provide reasonably good protection for the specimens, and thus all of them achieved a fire endurance of 2.5 h. The combined use of fire insulation and a mechanical anchorage system could reduce the deflection responses, mainly due to the active cable mechanism of the EB CFRP sheets during fire exposure. A finite element (FE) model was then proposed to predict the thermal and structural responses of insulated CFRP-strengthened RC beams. The FE parametric results further indicated that different insulation schemes with various thicknesses and thermal conductivities had significant effects on the fire performance of the strengthened beams.

Employing Carbon Fiber Reinforced Polymer Composites toward the Flexural Strengthening of Reinforced Concrete T-Beams.

Reinforced concrete structures are exposed to various loads under critical environmental conditions, which might lead to the deterioration of the structures prior to their designed service life. Hence, to improve the serviceability of the reinforced concrete (RC) structures and meet the design requirements, the structures are strengthened using carbon fiber reinforced polymer (CFRP) composites. The application of CFRP is done using two major techniques, namely externally bonded (EB) reinforcement and near surface mounted (NSM) techniques. The purpose of this study was to examine and compare the behavior of RC T-beams that had been flexurally reinforced utilizing EB and NSM techniques. Six full-size RC T-beams were evaluated, including a reference beam and four beams that had been flexurally reinforced using laminates made of EB and NSM CFRP. The findings of the experimental tests reveal that, when using the same quantity of CFRP, the beams strengthened with NSM laminates outperformed those strengthened with EB laminates in terms of ultimate load.

EFEKTIVITAS ANGKUR EPOKSI TERHADAP KEKANGAN EKSTERNAL BALOK BETON BERTULANG DENGAN PERKUATAN CFRP

Externally Bonded Carbon Fiber Reinforced Polymer (EB-CFRP) with U-wrap is one of the alternative external strengthening of modern reinforced concrete beams, which has been proven effective in significantly increasing flexural and deformation capacities. Although quite effective in increasing the structural capacity, external reinforcement needs to be studied further about its failure behavior, the avoided failure is called debonding, an interface bond failure between the FRP composite material and the concrete material. Epoxy has a fairly high material resistance, but its use as a reinforcing composite bonding material needs further investigation. Adding epoxy anchors at the ends of CFRP can mobilize the tensile strength in CFRP, eliminating or delaying debonding failure. Epoxy anchors (epoxy-filled grooves) are expected to be effective and flexible for application to various forms of components of reinforced concrete structures that have been reinforced with EB-CFRP. Currently, there are no standards and guidelines for applying FRP anchors. However, research has been conducted on the failure pattern of FRP anchors with U-style wrapping which can avoid debonding so that failure with FRP rupture can be achieved. This study examines the effectiveness of epoxy anchorage in improving the external strengthening of reinforced concrete beams with EB-CFRP reinforcement. The behavior of epoxy anchors in reinforced concrete beams with EB-CFRP will be investigated through experimental tests.

Effect of Using ECC Layer on the Flexural Performance of RC Beams Previously Strengthened with EB CFRP Laminates

This paper studies the efficiency of applying an engineered cementitious composite (ECC) layer to the tensile surface of (RC) beams that were previously strengthened using externally bonded (EB) carbon fiber-reinforced polymer (CFRP) laminates. One control and ten strengthened RC beams were produced and tested utilizing a four-point loading regime. For strengthened beams, two beams were kept strengthened using only CFRP, and additional ECC layers were added to the rest of the strengthened beams. The CFRP width and overlap length and position were among the test factors. Experimental results revealed that strengthening RC beams with CFRP laminates enhanced both the stiffness and flexural capacity of beams. Additional enhancements were obtained through the application of the additional ECC layers. The existence of the ECC layer alongside the CFRP laminate improved the flexural capacity by 102% and 125% when using CFRP widths of 50 mm and 100 mm, respectively, and the stiffness was improved by an average value of 318%. Three-dimensional (3D) finite element models (FEMs) were developed using ABAQUS software and verified against the experimental results to model the response of the tested beams. The verified model was used to conduct a parametric study to consider the effect of the ECC layer thickness and the reinforcement ratio on the strengthened beam behavior. The numerical results revealed that the effect of the reinforcement ratio was more significant than the ECC layer thickness in enhancing the load-displacement response, especially after the cracking stage.

Effect of Normal and Rubberized Concrete Properties on the Behavior of RC Columns Strengthened with EB CFRP Laminates and Welded Wire Mesh under Static Axial Loading.

The huge amounts of old and damaged tires spread worldwide has caused many complex environmental risks. The old tires have been converted to crumb rubber (CR) and tire recycled steel fiber (RSF) to facilitate their use. This study used CR to partially replace natural sand in reinforced (RC) columns. Externally bonded (EB) carbon-fiber-reinforced polymer (CFRP) laminates, welded wire mesh (WWM), and RSF were used to enhance the axial behavior of the tested columns to overcome the concrete deficiencies resulting from the inclusion of the CR instead of natural sand. Eighteen columns were prepared and tested to discuss the effects of strengthening type, CR content, RSF, and strengthening area on the axial behavior of the RC columns. Certain columns were internally reinforced with WWM, while others were externally strengthened with EB CFRP laminates. Partially or fully EB CFRP laminates were used to strengthen the columns. Moreover, one column was cast with NC and 0.2% RSF to investigate the role of RSF in confining the column. The results demonstrated a concrete strength reduction for the rubberized concrete (CRC) as the CR content increased. Conversely, the strengthened columns experienced higher load capacities than the corresponding un-strengthened ones cast with the same concrete mix. Moreover, adding 2% RSF to the NC mix could enhance the column capacity, although it decreased the concrete strength. Furthermore, using two CFRP layers increased the load capacity and ductility of the strengthened columns. The strengthened column cast with 50% CR showed the highest load efficiency (334.3% compared to the un-strengthened one).

Effect of the Cyclic Crack Opening-Closure during Epoxy-Curing Period of a CFRP Strengthening System Bonded on Concrete Substrate

This article investigates the potential detrimental effects of cyclic load during the installation of externally bonded (EB) carbon fiber-reinforced polymer (CFRP) on a damaged reinforced concrete (RC) structure. Four RC specimens were tested in three point bending to study the consequences of crack cyclic opening-closure during epoxy-curing period. A first RC specimen (without bonded CFRP) was loaded monotonically up to failure to serve as undamaged control sample. The three other specimens were pre-cracked before being subjected to a fatigue loading procedure to simulate service condition of a damaged RC structure. Two of the three pre-cracked specimens were strengthened by EB CFRP. One specimen was repaired before the fatigue test while the other one was repaired during the fatigue test. Finally, remaining capacities of all three pre-cracked specimens were measured through monotonic bending tests until failure. It was found that, although bonding of CFRP reinforcement during cyclic load can induce some interesting features with regard to serviceability, cyclic crack opening and closing alters the cure process of epoxy located below the initial crack and decreases the effectiveness of the strengthening at ultimate state. Extended experimental studies are then needed to assess reliable safety factor for the design of repairing operations in which the bridge has to be maintained in service during CFRP installation.

Experimental study on shear response of GFRP reinforced concrete beams strengthened with externally bonded CFRP sheets

An experimental investigation into the shear behavior of Glass Fiber Reinforced Polymer (GFRP) reinforced concrete beams is presented. The study also looks at the effectiveness of shear strengthening of such beams using externally-bonded Carbon Fiber Reinforced Polymer (EB-CFRP) sheets and investigates the possibility of interaction between internal and externally bonded shear reinforcement. A total of 18 beams, 2.4 m long with a rectangular cross-section of 300x200, reinforced with GFRP bars and stirrups were tested. Three types of concrete were used in this study; ordinary Portland cement (OPC) concrete, Fiber Reinforced concrete (FRC), and Geopolymer concrete (GPC). Six beams, two for each concrete type, severed as control while the other twelve were strengthened using “U” shape EB-CFRP sheets. The CFRP sheets were placed in two different arrangements, above and in-between internal stirrups locations. The results indicate that GFRP is a viable reinforcement for GPC, OPCC, and FRC, whereas EB-CFRP proves to be a feasible strengthening technique for such composite systems. The gain in shear strength for EB-CFRP strips beams on the location of internal stirrups is 5–10% lower as compared to the other arrangement. The difference in the strength gain may indicate a possible interaction between the internal and external shear reinforcement.

Behavior of cracked steel plates strengthened with adhesively bonded CFRP laminates under fatigue Loading: Experimental and analytical study

The strengthening of steel structures using externally bonded (EB) carbon fiber-reinforced polymer (CFRP) laminates has gained popularity due to the advantages such as their high strength-to-weight ratio and corrosion resistance. Even though previous studies showed the application of EB CFRP laminates can enhance the fatigue performance of cracked steel plates, little is known regarding the high-cycle fatigue performance of CFRP-to-steel bonded joints. As debonding of the CFRP laminate from the steel substrate is a commonly observed failure mode under fatigue loading, a sound understanding of the behavior of CFRP-to-steel bonded joints is crucial for a better understanding of the behavior of CFRP-strengthened cracked steel plates under fatigue loading. This study experimentally and theoretically investigates the fatigue performance of CFRP-strengthened cracked steel plates. Five pre-cracked steel plates were strengthened with CFRP laminates and tested under fatigue loading. The test results for the failure modes, the fatigue-life extension, and the behavior of the CFRP-to-steel bonded joint were discussed. A numerical modeling approach based on a recently developed bond-slip model for the behavior of the CFRP-to-steel bonded interface under fatigue loading is presented for modeling the behavior of the CFRP-strengthened cracked steel plate. Although the proposed theoretical model is conservative, this method accurately predicted the remaining fatigue life of CFRP-strengthened cracked steel plates.

Comparative study on the flexural strengthening of RC beams using EB CFRP sheets, NSM CFRP bars, P-SWRs, and their combinations

The externally bonded (EB) carbon fiber reinforced polymer (CFRP), near-surface-mounted (NSM) CFRP and the prestressed steel wire ropes (P-SWRs) has been proven to be feasible and reliable flexural strengthening methods for concrete structures. However, debonding issues in EB CFRP sheets (or NSM CFRP bars) and space requirements for edge and spacing clearance of NSM CFRP bars (or P-SWRs) has limited the application of these three strengthening techniques. Therefore, the combinations of these methods need to be investigated and clarified. In this paper, experimental investigations on the flexural performances of seven concrete beams are presented, in which three of the beams were separately strengthened with EB CFRP sheets, NSM CFRP bars, and P-SWRs, respectively, and three of the beams were combinedly strengthened with two of the three techniques. Test results demonstrated that the flexural performances of beams strengthened with the combination with EB CFRP sheets, NSM CFRP bars, and P-SWRs are between the flexural performances of the beams strengthened with the corresponding individual strengthening techniques. It is found that the P-SWRs is favorable for combinations. In case the P-SWRs was combined with EB CFRP sheets or NSM CFRP bars for strengthening, the cracking load was increased to more than 230% and the maximum ultimate load-bearing capacity was increased to 150% when compared with the control beam. The debonding which occurred more or less in the beams strengthened with EB CFRP sheets or NSM CFRP bars or their combination was successfully eliminated by using the combination strengthening technique with P-SWRs. Also, the combination of P-SWRs with EB CFRP sheets or NSM CFRP bars is also favorable to improve the ductility of strengthened beams.

Effect of CFRP strengthening systems on the fatigue limit of reinforced concrete beams

This paper aims to study the effect of Carbon Fiber Reinforced Polymer (CFRP) strengthening techniques on the fatigue limit of Reinforced Concrete (RC) beams. An accelerated fatigue method was utilized to find the fatigue limit based on the hypothesis of linear cumulative damage as determined by the Palmgren-Miner rule. Six RC beams with dimensions of 152.4 × 152.4 × 1,520 mm were tested under monotonic and cyclic loading using a four-point bending configuration: two non-strengthened RC beams, two RC beams strengthened with Near Surface Mounted (NSM) CFRP rods, and two RC beams strengthened with Externally Bonded (EB) CFRP sheets. Strengthened RC beams had less stiffness degradation and more energy dissipation when compared to the non-strengthened RC beam. The NSM CFRP technique demonstrated a better monotonic flexural strength than the EB CFRP technique. NSM CFRP rods and EB CFRP sheets increase the fatigue limit when compared to the non-strengthened RC beam by 19% and 33%, respectively.

Repair and strengthening of shear-deficient reinforced concrete beams using Carbon Fiber Reinforced Polymer

This paper presents the results of an experimental investigation on the behavior of Reinforced Concrete (RC) beams repaired and strengthened using Externally Bonded Carbon Fiber Reinforced Polymer (EB-CFRP). The experimental program involved 19 static tests on 16 simply supported rectangular RC beams in which seven were tested without CFRP and 12 were wrapped with one or two layers of CFRP. Out of the 12 beams, six were first tested to failure, repaired with epoxy, then wrapped with CFRP sheets before the second and final test. The remaining six were wrapped with CFRP, while virgin, before testing. Among the objectives of this study was the analysis of the effectiveness of EB-CFRP as a strengthening method for shear strengthening of damaged RC beams and the identification of interaction between conventional shear reinforcement and the EB-CFRP strips. Analysis of test results suggests that the EB-CFRP strengthening of damaged beams repaired using epoxy injection not only helps the beams to recover but also significantly increase their shear capacity. Moreover, one layer of CFRP discrete strips improved the overall capacity of the shear-deficient beams by more than 60% and an additional layer further increased the shear capacity by another 30%. The results also confirmed that an interaction exists between steel stirrups and EB-CFRP strips when carrying the applied load. For instance, test results demonstrated that the contribution of CFRP in shear strength is affected by the quantity of steel stirrups. Finally, when compared to test results, the ACI and fib formula provided reasonable estimation of the additional shear strength contributed by the EB-CFRP discrete strips, except for the beams with moderate ratio of steel stirrups. However, Chen et al. model better estimated the EB-CFRP contribution to the shear capacity of RC beams with moderate ratio of steel stirrups.

Experimental research on fire-damaged RC continuous T-beams subsequently strengthened with CFRP sheets

This paper presents experimental results of the structural performance of fire-damaged continuous reinforced concrete (RC) T-beams subsequently strengthened with externally bonded carbon fiber reinforced polymer (EB-CFRP) sheets. A series of seven specimens were tested with different fire exposure time and subsequent strengthening techniques. Experimental results showed that both the unexposed control beams and unstrengthened fire-damaged continuous RC T-beams exhibited flexure failure modes and significant redistribution of moment between hogging and sagging regions. The fire-exposed beams had notably degraded strength and stiffness attributable to the internal temperatures exceeding 500 °C for some portion of the exposure. The EB-CFRP strengthening of fire damaged beams was shown to mostly mitigate the effects of fire exposure. The EB-CFRP retrofit measures successfully restored the virgin capacity of the beam and were sufficient to also restore most of the lost initial stiffness. Simple prediction using plane sections analysis and the assumptions of the 500 °C isotherm method [1] were shown to accurately predict the behaviour of the fire-damaged specimens.

Reliability Analysis of Debonding in Steel Beams Strengthened with Externally Bonded CFRP Composites

AbstractThis paper presents the details of a reliability analysis of the debonding in steel beams strengthened with externally-bonded carbon fiber-reinforced polymer (CFRP) composites. A comprehens...

Fatigue Assessment of Shear-Strengthened RC T-Beams with Externally Bonded CFRP Closed Stirrups

AbstractResearch studies on reinforced concrete T-beams shear strengthened with externally bonded carbon fiber reinforced polymer (EB-CFRP) have shown that debonding at the CFRP–concrete interface ...

Finite element modelling and testing of two-span concrete slab strips strengthened by externally-bonded composites and mechanical anchors

Abstract Ten three-dimensional finite element (FE) models were developed in this paper to simulate the nonlinear behaviour of two-span reinforced concrete (RC) slab strips. Two slabs were unstrengthened and eight slabs were strengthened in either the sagging or the hogging region by externally-bonded carbon fiber-reinforced polymer (EB-CFRP) laminates with or without mechanical anchors. The tensile steel in the strengthened region was approximately 30% of that of the unstrengthened region to represent a continuous RC flexural element in need of strengthening. Laboratory tests were carried out to verify the accuracy and validity of the FE models. Each specimen had a total length of 3800 mm, a width of 400 mm and a depth of 125 mm. The provision of mechanical anchors in the hogging strengthening prevented the CFRP debonding mode of failure, slightly improved the strength gain, and significantly improved the slab ductility. Failure of the slab strips strengthened in the sagging regions was not dominated by CFRP debonding, and hence, the effect of including mechanical anchors in the sagging strengthening was concealed. Unstrengthened specimens exhibited significant deviations from the elastic response. Sagging strengthening decreased the deviation from the elastic response. Specimens strengthened in the hogging region exhibited insignificant moment redistribution ratios. The developed FE models captured the nonlinear behaviour of the tested slab strips with good accuracy. The inclusion of an interfacial bond stress-slip model in the analysis between the CFRP and the concrete had insignificant effect on the predicted response of strengthened specimens.

Experimental investigations of repair of pre-damaged steel-concrete composite beams using CFRP laminates and mechanical anchors

This paper investigates the flexural performance of pre-damaged steel-concrete composite beams repaired using externally-bonded carbon fiber-reinforced polymer (CFRP) laminates with and without mechanical anchors. A total of 10 beams were prepared, one beam was left undamaged, whereas nine beams were artificially damaged by cutting different U-shaped notches in the bottom flange at the beams’ mid-span that resulted in 45%, 73% and 100% losses in the flange thickness. Three damaged beams were not strengthened, whereas six damaged beams were repaired in flexure using externally-bonded CFRP laminates with and without mechanical anchors. The load-carrying capacities of the unstrengthened beams with damage states of 45%, 73% and 100% were approximately 11%, 23%, and 50% lower than that of the control-undamaged beam, respectively. The CFRP repair schemes were capable of restoring the original load capacity of the damaged beams with the lower damage state of 45%. For the beams with the higher damage states of 73% and 100%, the repair schemes could restore a maximum of 81% of the original load capacity. The inclusion of mechanical anchors in the repair regime improved the strength gain from 15% to 19% and from 46% to 63% for the beams with 45% and 100% damage states, respectively, relative to the strength of the corresponding damaged-unstrengthened beam.

Repair of reinforced concrete beams using carbon fiber reinforced polymer

This research paper is part of an ongoing research on the behaviour of Reinforced Concrete (RC) beams retrofitted with Externally Bonded Carbon Fiber Reinforced Polymer (EB-CFRP). A total of 5 large-scale rectangular beams, previously damaged due to shear loading, were repaired and strengthened with EB-CFRP and tested in this study. The major cracks of the damaged beams were injected with epoxy and the beams were wrapped with 2 layers of EB-CFRP discrete strips with 100mm width and 150mm center to center spacing. The beams were instrumented and tested to failure under three points loading in simply supported configuration. The measured test parameters were the beams deflection, maximum load, and the strain in the FRP strips. The failure mode was also observed. The results showed that applying EB-FRP strips increased the shear strength significantly relative to the original shear capacity of the beam. The results demonstrate that the application of EB-FRP strips used in this study is an effective repair method that can be used to repair and strengthen damaged beams.