Carbon Fiber Reinforced Polymer Shear Research Articles

Mechanical Behavior Research on IHB-CFRP Anchorage Scheme to Reinforce the Flexural Performance of Concrete Beams

This article investigates the use of Carbon Fiber Reinforced Polymer (CFRP) plates with additional anchors to enhance reinforced concrete slab beam structure. A test proposes an improved additional anchorage measure to solve the debonding problem during anchoring. Three point bending load test are carried out to analyze the influence of different anchoring positions on the reinforcement effect. An optimized Improved Hybrid Bonding CFRP (IHB-CFRP) additional anchoring measure is given. The shear friction model proposed in the IHB-CFRP anchoring scheme can simulate the additional adhesion resistance well. The article investigates the concrete crack extension, load–deflection relation, the strain distribution of CFRP plate, CFRP and concrete interface shear stress. It can be seen that the IHB-CFRP anchoring scheme improves the interface bonding ability and bearing capacity of the reinforced specimen.

Investigation of the Experimental Shear Resistance of RC T-beams after Strengthening with Carbon Fiber-Reinforced Polymer (CFRP) Bars

This study investigates the stiffness and shear resistance of T-reinforced concrete beams that have been strengthened against shear using the embedded through-section approach. The beams were exposed to a monotonic one-point load until failure. The experimental methodology included the investigation of 12 T beams made of reinforced concrete, consisting of 2 reference beams that were not subjected to any strengthening measures and 10 reinforced beams. The 12 beams were classified into two primary categories: those with stirrups and those without stirrups. The primary factors from each group encompassed the spacing and angle of inclination pertaining to the Carbon Fiber-Reinforced Polymer (CFRP) bars placed along the central axis of the section. Various configurations were used, including varied spacing intervals and degrees of inclination. The results showed that the ratio of the CFRP shear resistance to the total section (Vf / Vsec) ranged between 10 to 21% in group one (with stirrups). This means that the Embedded Through Section (ETS) technique with CFRP bars is useful in increasing the shear resistance of reinforced concrete beams. For group two (without stirrups), this ratio ranged between 56 to 58.5%. That is, ETS with CFRP bars significantly increases the shear resistance of reinforced concrete beams without stirrups.

Deformation capacity of shear-strengthened concrete beams reinforced with FRP bars: Experimental and analytical investigations

This paper presents an analytical model, which was developed based on the variable angle truss, to estimate the shear deformations of fiber-reinforced polymer (FRP) reinforced concrete beams strengthened in shear. The influences of the strengthening system in enhancing the shear strength and shear stiffness of the strengthened beams are considered in the proposed model. The proposed shear deformation is then incorporated into the deflection approach recommended in ACI 440.1 R (2015) to calculate the total deformation of beams. The developed model is validated with the available experimental results of shear-strengthened specimens. The obtained ratio between analytical and experimental deformations and its corresponding standard of deviation at service loads are 1.075 and 0.123, respectively. A test program comprising eight specimens with different aspect ratios strengthened in shear by carbon FRP (CFRP) laminates is conducted to further verify the proposed model. Three groups of tested specimens with aspect ratios of 1.7, 2.3, and 2.8 are enhanced in shear by two U-wrapping CFRP shear strengthening techniques, namely continuous sheets, and 50 mm strips at 100 mm spacings. The experimental results indicate that the proposed model predicts accurately the load-displacement curves and deformations at service loads of the tested beams. The obtained average ratios of analytical over experimental deformations at the service loads ranged from 1.061 to 1.075.

Shear strengthening of RC short columns with CFRP grid-reinforced FRC matrix: Cyclic loading tests

This study investigated the shear behaviors of reinforced concrete (RC) short columns retrofitted with a new textile-reinforced mortar (TRM) system made of carbon fiber-reinforced polymer (CFRP) grid-reinforced short-fiber-reinforced concrete (FRC) (referred to as “TR-FRC”). Six RC specimens, including two control specimens and four specimens strengthened with TR-FRC jacket, were tested under the combined action of constant axial load and cyclic horizontal load. The experimental parameters were the reinforcement ratios of CFRP grid and shear span-to-depth ratios. The test results indicated that the shear capacity, deformability, ductility and energy dissipation capacity of the strengthened columns were superior to those of as-built counterparts. The stiffness degradation of the strengthened columns was further delayed as the reinforcement ratio of the CFRP grid in composites overlay increased. Under smaller shear span-to-depth ratio, the TR-FRC system was still very effective in increasing the shear capacity of the RC columns. Moreover, based on the current code and superposition principle, considering the effective strain of the fiber grid, a design equation was proposed to predict the shear capacity of strengthened members.

EFFECT OF SHEAR-SPAN RATIO ON SHEAR FAILURE AND SIZE EFFECT OF CONCRETE BEAMS WITHOUT WEB REINFORCEMENT STRENGTHENED BY CFRP

The shear-span ratio has an important influence on the crack development and on the failure mode of reinforced concrete (RC) beams strengthened with carbon fiber reinforced polymer (CFRP). However, there were few studies on the effects of its shear strength and size effect. A mechanical analysis model for shear failure of reinforced concrete beams strengthened with CFRP was established by using three-dimensional numerical meso-scale simulation method, considering the meso-heterogeneity of the concrete and the interaction between the CFRP and concrete. Based on the verification of the rationality of the meso-scale method, the influence mechanism and law of the shear-span ratio on the shear failure and size effect of CFRP-strengthened RC beams were simulated and analyzed. The results show that: the shear-span ratio has a great influence on the shear failure mode of the strengthened beam, and the larger the shear-span ratio, the closer the beam is to the cable-stayed failure with better ductility. The shear-span ratio had better shear capacity for CFRP-strengthened beams and the influence on the size effect of shear strength was small. The shear-span ratio has a greater influence on the CFRP shear contribution in the strengthened beam. The larger the shear-span ratio, the better the shear effect of CFRP on strengthened beams. The beam reinforcement effect of the shear-span ratio (λ = 2.5) is most effective.

Interfacial Interaction of CFRP Reinforced Steel Beam Structures

Due to the increase of service life, the phenomenon of performance degradation of bridge structures becomes more and more common. It is important to strengthen the bridge structures so as to restore the resistance level and extend the normal service life. Carbon fiber reinforced polymer (CFRP) materials are thus used for the assembly reinforcement of bridges for the advantages of high strength, light weight, corrosion resistance and long-term stability of physical and chemical properties, etc. In view of this, based on the previous theoretical study and the established formula of the interfacial shear stress of CFRP reinforced steel beam and the normal stress of CFRP plate, this paper discusses the sensitive parameters that affect the interfacial interaction of CFRP strengthened beam structures. Through the analysis, the priority design indicators and suggestions are accordingly given for the design of reinforced beam structures. Young’s modulus of CFRP composite and shear modulus of the adhesive have the greatest influence on the interfacial interaction, which should be carefully considered. It is suggested that CFRP material with Ec close to 300 GPa and thickness no less than 3 mm, and adhesive material with Ga less than 5 GPa and 3-mm thickness can be adopted in CFRP reinforced steel beam. The conclusions of this paper can provide guidance for the interfacial damage control of CFRP reinforced steel beam structures.

Experimental Study on Shear Strengthening of Reinforced Concrete Box Beam by CFRP

Numerous theoretical and experimental studies have been conducted on fiber-reinforced polymer (FRP) shear strengthening rectangular and T-section beams; however, few researches focused on box beam, which is widely used in bridge superstructures. This paper presented experimental study on shear strengthening reinforced concrete (RC) box beam by carbon-fiber-reinforced polymer (CFRP) with four common strengthening patterns. The CFRP strengthening schemes, failure modes, deflection, and effective strain in fibers were investigated and recorded. As for CFRP shear contribution, it showed best performance with a 52.7% increase for the specimen with a continuous U-jacket sheet. Besides, all the strengthened RC box beams exhibited the debonding of CFRP strips or sheets in the ultimate state. It was found that the maximum strains in fiber recorded from strengthened specimen were approximately 3000μe accounting for 17% of the ultimate strain of CFRP sheet. The model in fib Bulletin 90 was used to predict CFRP shear contribution in the strengthened specimen, but it overestimated the values compared with experimental results because of higher effective strain calculated by model. A coefficient of 1.31 was therefore proposed for the equation of effective strain in the model, and the calculated CFRP shear strength by fib Bulletin 90 combined with modified effective strain was in good agreement with the experimental values.

Combined effects of Carbon Fiber Reinforced Polymer flexural reinforcements and post installed shear dowels on the performance of flat slabs

The sudden punching shear failure of flat slabs is a critical issue. The combined effects of externally strengthened Carbon Fiber Reinforced Polymer (CFRP) flexural reinforcements and post-installed CFRP shear reinforcements which explain the real behavior in the strengthening phase of a shear deficient slab, on the punching shear performance are not fully explained. In this study, the flat slab panels of 1200 mm × 1200 mm × 100 mm were retrofitted with seven alternative bonding arrangements of CFRP to investigate the combined effects of shear dowels and flexural reinforcements. A transient load was applied using a stub column, size 100 mm × 100 mm located at the center of the slab. The non-strengthened specimens failed in punching shear. The strengthened specimens showed a maximum punching shear capacity enhancement of 120%. A numerical model was also developed to identify the load transfer behavior of post-installed CFRP shear dowels. Further, the effects from the end anchorage of external CFRP and the refilling material at drilled locations to install CFRP shear strengthening scheme were also determined.

Experimental study on the bond behavior between CFRP plates and steel substrates under fatigue loading

This paper reports an experimental study on the fatigue behavior of bonded interfaces between carbon fiber reinforced polymer (CFRP) plates and steel plates. A total of 20 single-shear bonded joints were tested under monotonic and fatigue loading. The digital image correlation (DIC) method was employed. The effects of the load ratio, adhesive thickness and adhesive type on the fatigue life were investigated. The failure mode, fatigue life, relative slip, load-slip curve, CFRP strain and interfacial shear stress are presented. The results indicated that the cohesive failure was the dominated failure mode for all specimens. With the increase of the loading cycles, the debond initiated firstly at the loaded end and then propagated gradually toward the free end, which was obviously reflected by CFRP strain and shear stress distributions. The hysteresis was observed in the load-slip curve, indicating the energy dissipation occurred in the interfaces. The fatigue life decreased dramatically with the increase of the load ratio. When the load ratio was the same, the fatigue life decreased with an increasing adhesive thickness, and the fatigue life of the specimen with Sikadur-30 was longer than that with Araldite-2015. However, when the load range was similar, the fatigue life increased with an increase in the adhesive thickness, and the fatigue life of the specimen with Araldite-2015 was longer than that with Sikadur-30. The distribution shapes of the shear stress for two types of the specimens were approximately trapezoidal and triangular under monotonic and fatigue loading.

Models Reviewed for Predicting CFRP Shear Contribution of Strengthened Reinforced Concrete Box Beam

Eight various models for calculating the FRP (fiber-reinforced polymer) contribution to shear from different codes and studies were reviewed and discussed. From all the models, it is found that the effective strain is the most important parameter which lies in all equations except JSCE model. Besides, the six models from guidelines and two from latest literature with different parameters were discussed and applied for calculating shear contribution of 181 FRP shear strengthening specimens collected from existing literature. It reveals that all ratios of calculation related to experimental results showed distributions around the bisector in all equations of models. From the values of total members, the predictions of FRP shear contribution of the beam with a T-section or rectangular section using two models (fib Bulletin 14 and Sayed et al.) were very close to the experimental values and also stood safe sides. Furthermore, one control and four strengthened reinforced concrete (RC) box beam by carbon fiber-reinforced polymer (CFRP) were tested for shear strength. Compared with the experimental results, all theoretical values predicted by the reviewed models overestimated the FRP shear contribution of strengthened members, because the effective strain was overestimated. A coefficient of 1.31, therefore, was also proposed, which divided the formula of the effective strain in the fib Bulletin 14 model according to the experimental effective strain in fiber. The model with the modified effective strain presented a rational prediction in CFRP shear contribution of strengthened RC box beams.

Efficient near surface mounted CFRP shear strengthening of high strength prestressed concrete beams – An experimental study

Shear behavior of prestressed concrete members and its strengthening is complex due to its brittle nature of failure and a number of variables affecting its behavior. The main goal of this investigation is to assess the efficiency of different near surface mounted (NSM) strengthening configurations using CFRP (Carbon Fiber Reinforced Polymer) laminates on the shear behavior of prestressed concrete beams. The parameters considered in this study are (i) the presence of vertical stirrups and (ii) different NSM FRP shear strengthening configurations. Twelve prestressed concrete beams with and without vertical stirrups were cast and strengthened using different NSM CFRP configurations and tested under shear. All the beams were tested under three point bending at a shear span to depth (a/d) ratio of 2.5 to simulate the shear dominant behavior. Test results revealed that NSM strengthening of prestressed concrete beams using CFRP laminates at 45° was more efficient in improving the shear capacity of beams with and without vertical stirrups. It was also observed that the shear mode of failure could be converted to the flexural mode with improved ductility by designing a suitable NSM shear-strengthening scheme. Shear strength calculations of NSM strengthened beams were made using ACI codes and other analytical models. ACI calculations were found to be conservative in estimating the shear contribution of NSM laminates.

Finite element analysis of CFRP laminate repairs on damaged end regions of prestressed concrete bridge girders

Over the past couple decades, externally bonded fiber reinforced polymer (FRP) composites have emerged as a repair and strengthening material for many concrete infrastructure applications. This paper presents an analytical investigation of the use of carbon FRP (CFRP) for a specific problem that occurs in concrete bridge girders wherein the girder ends are damaged by excessive exposure to deicing salts and numerous freezing/thawing cycles. A 3D finite element (FE) model of a full scale prestressed concrete (PC) I-girder is used to investigate the effect of damage to the cover concrete and stirrups in the end region of the girder. Parametric studies are performed using externally bonded CFRP shear laminates to determine the most effective repair schemes for the damaged end region under a short shear span-to-depth ratio. Experimental results on shear pull off tests of CFRP laminates that have undergone accelerated aging are used to calibrate a bond stress-slip model for the interface between the FRP and concrete substrate and approximate the reduced bond stress-slip properties associated with exposure to the environment that causes this type of end region damage. The results of these analyses indicate that this particular application of this material can be effective in recovering the original strength of PC bridge girders with damaged end regions, even after environmental aging.

A New Approach of Shear Connectors to Delay Debonding of CFRP Laminates Used for Shear Strengthening of RС Beams

Shear strengthening of RC beam with adhesively bonded carbon fiber reinforced-polymer (CFRP) laminates is becoming both environmentally and economically more preferable than replacement. However, the early separation of these plated stripes was the most critical failure which leads to prevent reaching the full capacity required from the strengthening. This study aims to present a new method to prevent debonding failure of CFRP laminates adhesively glued to concrete surface using embedded connectors to enhance the interfacial bond strength. Therefore, steel bar and adhesive connectors were fabricated and used at the interface of the bonded CFRP laminates. Five beam specimens including one control beam were tested to investigate the effects of the connectors to prevent or delay the premature debonding of the EB CFRP laminates. The experimental results showed that both steel and adhesive connectors completely prevented premature debonding failure of CFRP shear strip and allowed the beams to fail by flexure with full ductility and strength. Steel and adhesive connectors would enhance 33% and 38% failure loads respectively as compared to strengthened beam without connectors.

Experimental Investigation of Reinforced Concrete T-Beams Strengthened in Shear with Externally Bonded CFRP Sheets

AbstractAn experimental investigation was undertaken into the effectiveness of unanchored and anchored externally bonded (EB) U-wrapped carbon fiber–reinforced polymer (CFRP) shear strengthening for reinforced concrete T-beams at a range of realistic sizes. The T-beam sizes, geometry, and reinforcement were chosen to reflect existing slab-on-beam structures with low levels of transverse steel shear reinforcement. Geometrically similar reinforced concrete T-beams were tested across three sizes ranging from 360 to 720 mm in depth and with different amounts of EB CFRP shear reinforcement. The beams were subjected to three-point bending with a span-to-depth ratio of 3.5. All the beams failed in diagonal shear. The experimental results indicate significant variability in the capacity of unstrengthened control beams, and a number of these control beams showed greater shear capacity than their EB CFRP-strengthened counterparts. Greater thicknesses of CFRP reinforcement did not lead to increased shear capacity co...

CFRP Shear Strengthening of Reinforced-Concrete T-Beams with Corroded Shear Links

This paper investigates the structural behavior of uncorroded as well as corroded RC T-beams strengthened in shear with either externally bonded (EB) carbon fiber–reinforced polymer (CFRP) sheets or embedded CFRP rods. Nine tests were carried out on RC T-beams having an effective depth of 295 mm and a shear span to effective depth ratio of 3.05. The investigated parameters are the shear link corrosion level (uncorroded, 7% corroded, or 12% corroded) and type of CFRP strengthening system (EB CFRP sheets or embedded CFRP rods). The unstrengthened beams with shear link corrosion levels of 7 and 12% had shear strengths that were 11 and 14%, respectively, less than the shear strength of the uncorroded unstrengthened beam. Both the embedded CFRP rods and EB CFRP sheets were effective in enhancing the shear strength of tested beams but the effectiveness of both strengthening systems decreased with increasing shear link corrosion level. The shear strength enhancement provided by the embedded CFRP rods and EB CFRP sheets decreased from 19 and 15%, respectively, to 12 and 11%, respectively, with an increase in shear link corrosion level from 7 to 12%. Corrosion of the shear links did not have a significant effect on the beam stiffness. Premature debonding limited the effectiveness of the EB CFRP sheets whereas the embedded CFRP rods did not exhibit signs of debonding and therefore showed higher effectiveness.

Phased Nonlinear Finite-Element Analysis of Precracked RC T-Beams Repaired in Shear with CFRP Sheets

Phased nonlinear finite-element (FE) analyses were carried out to predict the behavior of precracked reinforced concrete (RC) T-beams repaired in shear with externally bonded (EB) carbon fiber–reinforced polymer (CFRP) sheets and subjected to two loading patterns (LPs). Appropriate constitutive relationships were employed to model the behavior of concrete, internal steel reinforcement, EB CFRP reinforcement, and CFRP-to-concrete interface and consequently predict the structural behavior and capture the failure modes of the strengthened beams. Three constitutive models for the behavior of concrete in shear were evaluated, namely, a total strain rotating crack model and two fixed-angle crack models with either constant or variable shear retention factors. The majority of published FE studies have considered rectangular sections that were strengthened before testing. The key feature of the FE models presented in this paper is the use of the phased-analysis technique to model realistically the process of strengthening RC T-beams under load and predict the structural response of the beams to different loading patterns. Furthermore, the paper provides insight into and evaluates the accuracy of the three concrete shear models named above. A detailed comparison between the numerical and experimental results included the shear forces at failure, shear force-deflection curves, crack patterns, failure modes, and strains in the internal steel and external CFRP shear reinforcement. The FE models predicted the experimental shear force capacities and crack patterns with sufficient accuracy but underestimated the postrepair stiffness for the beams subjected to Loading Pattern 1 and overestimated the strain in the CFRP sheets.

Method of analysis to evaluate the CFRP Shear- Strengthened in Reinforced Concrete

Different models of shear-strengthened calculation by means of Carbon Fiber-Reinforced Polymer (CFRP) are compared in this investigation works classified according to the way of failure. We take into account the modification of the behavior of the beam for the reinforcement in its design. The surveys show that as long as it is possible the main direction of the fibers must be perpendicular to the shear crakc. The contribution of the reinforcement to the resistance to shear-strengthened of the beam depends on the steel stirrups in the original beam. When the reinforcement strips thickness increases the resistance to shear-strengthened of the beam also increases. This relation tends to be lineal when the beam is not cracks. At last we must state that both the inclination angle of the crack and the shear-strengthened resisted by the reinforcement depend on the inclination angle of the fiber.

Shear Strengthening of RC Beams with Externally Bonded FRP Composites: Effect of Strip-Width-to-Strip-Spacing Ratio

The results of an experimental and analytical investigation of shear strengthening of reinforced concrete (RC) beams with externally bonded (EB) fiber-reinforced polymer (FRP) strips and sheets are presented, with emphasis on the effect of the strip-width-to-strip-spacing ratio on the contribution of FRP (Vf). In all, 14 tests were performed on 4,520-mm-long T-beams. RC beams strengthened in shear using carbon FRP (CFRP) strips with different width-to-spacing ratios were considered, and their performance was investigated. In addition, these results are compared with those obtained for RC beams strengthened with various numbers of layers of continuous CFRP sheet. Moreover, various existing equations that express the effect of FRP strip width and concrete-member width and that have been proposed based on single or double FRP-to-concrete direct pullout tests are checked for RC beams strengthened in shear with CFRP strips. The objectives of this study are to investigate the following: (1) the effectiveness of EB discontinuous FRP sheets (FRP strips) compared with that of EB continuous FRP sheets; (2) the optimum strip-width-to-strip-spacing ratio for FRP (i.e., the optimum FRP rigidity); (3) the effect of FRP strip location with respect to internal transverse-steel location; (4) the effect of FRP strip width; and (5) the effect of internal transverse-steel reinforcement on the CFRP shear contribution.

Behavior of precast, prestressed concrete sandwich wall panels reinforced with CFRP shear grid

This paper describes the structural behavior of precast, prestressed concrete sandwich wall panels reinforced with carbon-fiber-reinforced polymer (CFRP) shear grid to achieve composite action. Use of CFRP as a shear transfer mechanism was intended to increase the thermal insulation efficiency, enhance the service life, and increase the overall structural capacities of the panels. This study included testing of six full-scale sandwich wall panels, each measuring 20 ft x 12 ft (6.1 m x 3.7 m). The panels consisted of two outer prestressed concrete wythes and an inner insulation wythe. The study included two types of insulation and several shear transfer mechanisms with different CFRP reinforcement ratios to examine the degree of composite action developed between the two concrete wythes. All panels were simultaneously subjected to applied gravity and lateral loads. Reverse-cyclic lateral loads simulated the effects of wind pressure and suction. All panels were subjected to approximately 4000 cycles of lateral loading with the presence of factored gravity load. Following each fatigue regime, the lateral loads were increased until failure was achieved. Test results of the experimental program were compared with theoretical predictions of fully composite and noncomposite actions to evaluate the percent composite action and to assess the optimum panel configuration.

Analysis and design guidelines of precast, prestressed concrete, composite load-bearing sandwich wall panels reinforced with CFRP grid

This paper presents newly developed design guidelines for precast/prestressed concrete wall panels reinforced with carbon-fiber-reinforced-polymer (CFRP) shear grid to achieve the composite interaction. The analytical approach provides a general methodology to determine the behavior of fully and partially composite wall panels. The effects of an imperfect connection between the two concrete wythes are considered by varying the total shear force transmitted through the shear connectors at the interface. The predicted strains along the thickness of the panel at different load levels compared well with recent test results conducted at North Carolina State University in Raleigh. The shear-flow capacity of the insulating materials and the CFRP shear grid are determined using the proposed approach. The influence of the degree of the composite interaction on the induced curvature and slip-strain behavior is presented. A simple design chart for estimating the flexural capacity of the wall panels with different shear-reinforcement ratios is proposed. The approach is also verified by using finite-element analysis up to the service-load level. The predicted displacement and strains compared well with the measured values reported by the experimental program.