Carbon Fiber Reinforced Polymer Bars Research Articles

Comparison of Fracture Behavior in Single-Edge Notched Beams Reinforced with Steel Bars or CFRP Bars

To explore and compare the failure modes, deformation behaviors, and load-bearing capacities of single-edge notched (SEN) beams strengthened with carbon fiber-reinforced polymer (CFRP) and steel bars, static and dynamic three-point bending tests on both types of concrete beams have been carried out in this study. During the static tests, the electro-hydraulic servo machine served as a loading device to apply pressure to CFRP beams and reinforced concrete (RC) beams. During the impact experiments, different impact velocities were imparted by adjusting the drop hammer’s height. Thus, information regarding crack propagation, energy absorption, and deformation was obtained. The results from the static tests showed that the RC beams predominantly experienced shear failure. In contrast, the CFRP beams primarily exhibited bending–shear failure, attributed to the relatively weaker bond strength between the bars and the concrete. Impact tests were conducted at three different velocities in this study. As the impact velocity increased, both types of concrete beams transitioned from bending failure to bending–shear failure. At the lowest velocity, the difference in energy absorption between beams reinforced with different materials was insignificant during the bending process. However, at the highest velocity, CFRP beams absorbed less energy than RC beams. The study of structures’ impact failure modes and their mechanical characteristics offers valuable references for the anti-collision design and protection of structures.

Early-age bond behavior of embedded CFRP bars in UHPFRC: Test study and theoretical analysis

The combination of carbon fiber-reinforced polymer (CFRP) bars and ultra-high-performance fiber-reinforced concrete (UHPFRC) has great potential for use in producing structures with exceptional mechanical properties. Nevertheless, a research gap exists regarding the early-age bond behavior of embedded CFRP bars in UHPFRC, which is key to evaluating structural crack resistance. To address this gap, in this study, a series of tests was conducted on 90 pull-out specimens consisting of UHPFRC and CFRP bars. The influences of the concrete age (t), bond length (lb), and cover thickness-to-bar diameter ratio (C/D) on bond behavior were investigated. Each pull-out test generated the acquisition of a complete bond stress–slip curve. The bond interface was analyzed mechanically using the thick-walled cylinder theory and elasticity theory. A bond strength theoretical model that accounted for the surface wear of CFRP bars was proposed. The results of the pull-out test and theoretical analysis indicated that the bond strength tended to grow as t and C/D increased and was negatively correlated with lb. The model predictions agreed well with the test results while exhibiting excellent predictive accuracy compared to existing models. Furthermore, a three-branch bond stress–slip model was established to depict the bond behavior, demonstrating acceptable consistency with test curves.

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.

Enhancing bond performance: Carbon fiber reinforced polymer bar interaction with multi-walled carbon nanotubes cementitious composites in chloride-exposed conditions

A number of studies have been conducted on strengthening structures using carbon fiber reinforced polymers (CFRP) and improving the performance of cement fillers using multi-walled carbon nanotubes (MWCNT). In this study, bond characteristics of CFRP bars to MWCNT cementitious composites is investigated in chloride environment. The bonding advantage of CFRP bars and MWCNT cement filler is due to the mechanical properties of MWCNT and the ability to utilize the corrosion resistance provided by CFRP. This enables highly durable composites that can resist corrosion in chloride-rich environments. A total of 36 pullout (PO) tests were performed on CFRP bars set into MWCNT cementitious composites. Mercury Intrusion Porosimetry (MIP) test and field-emission scanning electron microscopy (FE-SEM) confirmed a decrease in porosity upon addition of MWCNTs. MWCNTs filled the pores of cement with nanoscale particles and increased the bond area of the cement composite with CFRP bar. The reduction in porosity between cement and aggregate not only enhanced strength but also improved chloride resistance. However, agglomeration began at 1.0-wt% concentration owing to van der Waals forces. The results revealed that the 0.5-wt% MWCNT cementitious composite with CFRP bars had the highest bond strength in a chloride environment.

Effects of exposure in seawater sea-sand concrete pore solution on fatigue performance of carbon FRP bars

The study aims to propose a methodology to predict the fatigue performance of carbon fiber-reinforced polymer (CFRP) bars under the seawater sea-sand concrete (SWSSC) environment. The effects of exposure in SWSSC pore solution on the fatigue damage mechanisms and fatigue performance of CFRP bars are presented. Firstly, the tensile fatigue tests of reference CFRP bars were performed under various stress levels with a constant stress ratio of 0.1. Secondly, the tensile fatigue tests of exposed CFRP bars subject to the simulated SWSSC pore solution were carried out. The tensile failure modes and fatigue damage mechanisms corresponding to different stress levels, were identified using scanning electron microscopy (SEM). Besides, the relationship between fatigue life expectancy and underlying fatigue damage mechanisms was carefully analyzed. Finally, the effective stress level method (ESLM) was proposed to evaluate the residual fatigue life of exposed CFRP bars based on the benchmark S–N curve. Combined with the degradation models (chemical etching/diffusion models) proposed in our previous research, ESLM could bridge corrosion fatigue life prediction of the exposed CFRP bars and the benchmark fatigue data of the non-exposed CFRP reinforcement. The predicted results have good correlations with the experimental data. This method can also provide valuable insight for the corrosion fatigue life prediction of other types of FRP composites.

Flexural bond behavior and development length of ribbed CFRP bars in UHPFRC

Ribbed carbon fiber reinforced polymer (CFRP) bars in ultra-high-performance fiber reinforced concrete (UHPFRC) are a high-efficiency combination for its sustainable substitute and high strength to weight ratio. This paper aims to investigate the bond stress and development length of ribbed CFRP bar embedded in UHPFRC using the hinged beam test. A total of 12 groups of hinged beam specimens were tested with different parameters, such as bar type (ribbed CFRP, sand coated CFRP, ribbed glass fiber reinforced polymer (GFRP), and steel bar), bonded length (4db, 10db, 20 db, and 40 db), fibers (with and without fibers in ultra-high-performance concrete (UHPC)), and presence of shear reinforcement for assessing the bonding behavior and development length of each bar. Tensile failure occurred in the steel, ribbed GFRP, and ribbed CFRP bars with bonded lengths of 10db, 20db, and 40db, respectively, and pullout failure occurred in sand coated CFRP bars regardless of bonded length. The ultimate load for the bonded length of 10 db was in order of ribbed CFRP, ribbed GFRP, steel, and sand coated CFRP bars. Compared with the bonded length, the bond stress of ribbed CFRP bars is larger than that of the ribbed GFRP and sand coated CFRP bar and these trends became more remarkable as the bonded length increased. There was no difference in the bond stress with presence of the reinforcement cage, and the bond stress increased by 20 % when the fibers were incorporated. The code-based equation for development length of ribbed CFRP bar was found to be underestimated, and ribbed CFRP, sand coated CFRP, ribbed GFRP bar of development length was proposed as 24db, 20db, and 107db.

Assessment of shear capacity in NSM prestressed FRP strengthening with anchorage conditions

Efforts to achieve a defect-free flat groove in near-surface-mounted prestressed fiber-reinforced polymer (FRP) strengthening systems have proven challenging. Despite attempts, attaining an ideal groove remains formidable. In this system, anchorage device installation involves injecting epoxy resin into groove defects to achieve planarity. Structural behavior analysis and optimization of the anchorage device were conducted based on device type, anchor type, and defect depth through shear loading tests. The mechanical anchor demonstrated an ultimate load of 261 kN, with failure modes including concrete cracking, concrete compression failure, and anchor tensile failure. The chemical anchor exhibited an ultimate load of 390 kN, with its final failure attributed to anchor tensile failure. The ultimate load capacity of anchorage device surpassed that of a carbon FRP(CFRP) bar by up to 62.5%. In a parametric study, the shear strength of the anchorage device was explored concerning concrete compressive strength and anchor diameter. The ultimate load of the proposed model with low concrete compressive strength proved insufficient compared to the strength of CFRP rebar.

Strategic use of ultra-high-performance concrete and carbon fiber reinforced polymer reinforcement for end zone design of prestressed girders

The design of end zones to prevent severe cracking is a key requirement toward durable prestressed girders. Traditional approaches employ large amounts of steel reinforcement to attain this requirement, which may result in steel congestion. This paper investigates a hybrid girder concept that uses Ultra-High-Performance Concrete (UHPC) and Carbon Fiber Reinforced Polymer (CFRP) bars to enhance crack control and long-term durability in the end zones of prestressed girders. The objectives of this study are to quantify the UHPC zone lengths needed to restrain end zone cracks, eliminate or reduce the required amount of steel reinforcement, and investigate its replacement with CFRP bars. A finite element modeling (FEM) approach was developed for this purpose and its fidelity was validated with experimental data. The FEM results showed that UHPC zones with lengths below or equal to half of the girder depth can significantly reduce end zone cracking. CFRP bars can be added in the UHPC zones as a conservative measure to crack control, to ensure the long-term corrosion resistance of the girders.

Deformation-based design of hollow coarse-aggregate ultra-high-performance-concrete beams reinforced with CFRP bars

This study aims to develop a novel type of beams strengthened with carbon fiber-reinforced polymer (CFRP) bars and cast using ultra-high-performance concrete (UHPC) with coarse aggregates (CA-UHPC) to address issues such as poor ductility, extensive cracking, and significant deflection observed in FRP-reinforced concrete (FRP-RC) beams. Six hollow beams were fabricated and tested via a four-point-bending test under cycle loading to study the effects of parameters, including CFRP reinforcement ratios, hollow shapes, and hollow ratio on the deformation performances of the beams. The results show that the deformation of all hollow beams under service loads met the requirements of the GB50610 code for deformation. Increasing hollow ratio had a negative impact on the flexural behaviors of beams, and this effect was more pronounced in beams with higher hollow ratios than in beams with lower hollow ratios. The flexural performances of square hollow beams were better than that of circular hollow beams with the same hollow ratio. Compared to other hollow beams, square hollow beams with a hollow ratio of 44.44% demonstrated superior flexural performance and optimal cost-effectiveness. Ultimately, leveraging the computational framework for steel fiber reinforcement and residual deflection, predictive models for deflection were formulated for CFRP-CA-UHPC beams with various hollow configurations under both static and cyclic loading conditions.

Shear Performance of Reinforced Concrete T Beams Strengthened by Carbon Fiber-Reinforced Polymer Bars

The primary purpose of this work is to investigate the shear response of T-reinforced concrete beams strengthened for shear using the embedded through section (ETS) technique when subjected to a monotonic one-point load till failure. The experimental approach included an examination of the twelve reinforced concrete T-beams, including two reference beams without any strengthening and ten strengthened beams. The twelve beams were divided into two main groups, with and without stirrups. The main variables in every group were the spacing and angle of inclination of the carbon fibre-reinforced polymer (CFRP) bars. The beams were strengthened in shear with CFRP bars inserted in the centre line of the section with different spacings and angles of inclination. The experimental analysis was performed to study the effect of spacing and angle of inclination of the CFRP bars on the ultimate load capacity, load-strain relationships, and load-deflection relationships. Results showed that the ultimate load of the beams in group one with inclined CFRP bars (45°) increased by 29.7, 22.4, and 15.5% for beams with CFRP bar spacings of 10, 15, and 20 cm, respectively, compared with the reference beam. In group one (with stirrups), the beam with inclined CFRP bars (45°) and a spacing of 10 cm has an ultimate load higher than that with vertical CFRP bars (90°) with a similar spacing by 2.6%. By contrast, the beam with inclined CFRP bars (45°) and a spacing of 10 cm in group two (without stirrups) has an ultimate load higher than that with vertical CFRP bars (90°) with a similar spacing by 2.5%. Doi: 10.28991/CEJ-2023-09-10-04 Full Text: PDF

Bond behaviour between additional aluminium alloy ribs anchored CFRP bar and ultra-high ductile concrete

This study investigated the impact of incorporating additional aluminium ribs (ARs) on the bond behaviour of carbon fiber reinforced polymer (CFRP) bars in ultra-high ductile concrete (UHDC). The research conducted pull-out tests on 48 specimens with various parametric variables, including the number and location of ARs, the type of concrete material, and the depth of CFRP ribs. The outcomes revealed that the use of ARs significantly enhanced the bond performance of the CFRP bars in UHDC. The ultimate and residual bond strengths of both CFRP bars and AR anchored CFRP bars in UHDC surpassed those in ordinary concrete. The ARs also improved the rigidity of the bond-slip curve. Additionally, the bond performance of shallow-rib CFRP bars was substantially improved and comparable to that of deep-rib bars. The wave propagation method and wavelet packet analysis were employed to monitor the bond-slip process and to quantitatively analyze the degree of interface damage. The results suggested that increasing the extrusion length and number of ARs can improve the bond performance of the interface. Therefore, incorporating ARs can be considered as an effective approach to enhance the anchorage performance of FRP-reinforced concrete structures.

Theoretical and experimental investigations into flexural behavior of existing reinforced concrete beams strengthened by CFRP bars

Strengthening existing reinforced concrete (RC) beams using carbon fiber reinforced polymer (CFRP) bars have gained greater interest and increased field applications. Theoretical and experimental investigations have been conducted in this research to learn the flexural behavior of RC beams strengthened by CFRP bars. Bending tests were performed on seven specimens to obtain the load-displacement curves of the beams with different strengthening methods. Different features of the failure modes were observed in the bending tests. Strengthened beams by CFRP bars can significantly increase the flexural bearing capacity of RC beams and retard the development of cracks, which is an effective means to improve flexural stiffness. In addition, the experimental results revealed the influences of the bar connection mode. RC beams strengthened by continue bars have a greater ultimate load than those strengthened by lapped bars. A refined finite element (FE) model was built and validated by the experimental results. This validated FE model clarified the failure mode of beams from the perspective of displacement evolution and strain development. Furthermore, theoretical formulas were established to calculate the ultimate flexural capacity of the strengthened beams, which was proved to have acceptable accuracy in predicting the flexural behavior of the CFRP-strengthened beams. This research may provide a valuable reference for strengthening the existing RC beams.

Durability of GFRP and CFRP Bars in the Pore Solution of Calcium Sulfoaluminate Cement Concrete Made with Fresh or Seawater.

Calcium sulfoaluminate cement concrete (CSAC) reinforced by fiber-reinforced polymer (FRP) bars, termed bars for brevity, is a good alternative to steel-reinforced concrete in marine environments due to the corrosion resistance of FRP and the lower pH of CSAC. For the first time, multi-mechanical tests are conducted to compare the durability of glass FRP (GFRP) to that of carbon FRP (CFRP) after exposure to CSAC pore solution. The bars were immersed in a simulated pore solution of CSAC made with either fresh water and river sand or with seawater and sea sand. Solution temperature was held constant at 30 °C, 45 °C or 60 °C for 30, 60, 90 and 180 days of immersion. Tensile, horizontal and transverse shear tests, as well as detailed microstructural analyses, were conducted to determine the level and mechanisms of degradation for each type of bar. Sea salt increases the degradation of both bars, but it degrades GFRP more than CFRP. The bars' retained tensile strength is a reliable indicator of their durability, while their post-exposure horizontal and transverse shear strengths are found inconsistent and counter intuitive. In the GFRP, the fiber, the epoxy matrix and their interface suffered damage, but in the CFRP, the carbon fiber was not damaged. Under the test conditions in this study, the maximum reduction in the tensile strength of the GFRP was 56.9% while that of CFRP was 15.1%. Based on the relevant ASTM standard, the CFRP bar satisfies the alkaline resistance requirement of the standard in the CSAC pore solution with and without salt, whereas the GFRP bar does not meet the same requirement in the above pore solution with salt.

Punching Shear Behavior of FRP Grid-Reinforced Ultra-High Performance Concrete Slabs

Fiber-reinforced polymer (FRP) grid-reinforced ultra-high performance concrete (UHPC) slabs are new structural solutions that take advantage of the mechanical properties of FRP and UHPC. However, the punching shear behavior of this new slab type has not been characterized. Therefore, punching shear tests were conducted to eight carbon fiber-reinforced polymer (CFRP) bars or grid-reinforced UHPC square slabs (600 mm side width × 40 mm thick). Several influential factors [e.g., use of CFRP bars or grids as flexural reinforcements, type of strengthening short fiber, steel fiber (SF) content, and presence of shear reinforcements] were investigated. The test results showed that FRP grids and short fibers helped to distribute the applied loads and dissipate the input energy; therefore, more cracks were observed, and higher punching shear capacities were achieved. Furthermore, increasing the reinforcement ratio in the FRP grids led to a more significant postcrack ductility response, which increased the punching shear capacity by 17%. In addition, SF addition could enhance the initial cracking load of the slab (Vcr), and polyethylene (PE) fiber addition could intensify the postcrack ductility response, both enhanced the punching shear capacity. The installation of shear reinforcements (eight pieces of 80 mm long CFRP grid strips) appeared to be more cost-effective than increasing SF content. Finally, compared with the current design provisions for conventional reinforced concrete slabs, a more accurate (average error of 8%) punching shear model was proposed for FRP grid-reinforced UHPC slabs with or without SF additions. However, the robustness of the proposed model will be assessed with more test data in the future.

Performance of NSM and EB methods on the flexural capacity of the RC beams strengthened with reinforced HSC layers

The near-surface mounted (NSM), in which strips or rods are fixed by an adhesive in slits formed inside the concrete cover, and the externally bonding (EB), in which the reinforcement is glued to the concrete surface, are well-known strengthening methods. In the present work, an experimental and numerical study was carried out on reinforced concrete (RC) beams strengthened with NSM and EB-reinforced high-strength concrete (RHSC) layers. The RHSC layers were reinforced by steel or glass fiber reinforced polymer (GFRP) rods and bonded to the RC beams without and with a concrete cover. Seven specimens were cast and loaded in flexure up to failure to investigate the effect of RHSC layer position and reinforcement on the RC beams' efficiency. The three-dimensional finite element program (ABAQUS) verified the experimental results numerically. Also, a parametric study was numerically performed to examine the factors affecting the flexural performance of the strengthened RC beams using NSM and EB RHSC layers. The strengthened beams by NSM steel RHSC layers increased the load capacity by 147.9% compared to the control beam (CB). Changing the RHSC layer reinforcement from steel to GFRP bars enhanced the load's efficiencies from 147.9% to 172.0% compared to the CB. Decreasing the width and reinforcing area of the RHSC layer decreased the beam load capacity by about 17.5 %. Due to their longer bending arms, the EB RHSC layers showed lower load capacity than the NSM ones, which accelerated the EB RHSC failure. When the carbon fiber-reinforced polymer bars were utilized to reinforce the HSC layers, the strengthened beams showed higher load efficiency than those strengthened with HSC layers reinforced by GFRP rods.

Comparative bond-slip response of ribbed CFRP bar to UHPC after exposure to high temperature

Ribbed carbon fiber reinforced polymer (CFRP) bar and ultra-high-performance concrete (UHPC) have high potential in terms of utilization of load-carrying capacity and maintenance of the concrete structure. Bonding behavior of ribbed CFRP bars to UHPC after exposure to elevated temperature is of importance due to its susceptibility of thermal effects. This study investigated the residual bond strength of the ribbed CFRP bar embedded in UHPC at ambient temperature and after exposure to elevated temperature. The bond strength of ribbed CFRP bars with different embedded length and cover thickness were also considered and the bond strength was compared with the sand coated CFRP bars. Both at ambient temperature and after exposure to elevated temperature, the bond strength of the ribbed CFRP bar increased with an increased embedment length and cover layer due to the mechanical resistance of the ribs. However, the difference reduced as the elevated temperature increased. Compared with the sand coated CFRP bars, the decreasing rate of bond strength is slightly lower in ribbed CFRP bars and the residual bond strength after exposure to elevated temperature at 400 ℃ was more than 10 MPa, which satisfies bond strength of FRP bar suggested by ACI 440.5 M. The critical temperature of the ribbed and sand coated CFRP bars was suggested as 300 ℃ with consideration of decreasing rate in this study. The modified bond equations were presented to reflect the reduction of bond strength due to the elevated temperature, and the bonding behavior of the ascending branch was compared using the modified BPE and CMR models and presented the coefficient of each parameter.

Flexural behaviours of pretensioned prestressed concrete-UHDC composite beams reinforced with CFRP bars

Prestressing fiber reinforced polymer (FRP) bars is widely acknowledged as an effective method for exploiting their high strength. However, compared to FRP reinforced concrete structures, prestressed FRP reinforced concrete structures exhibit weaker deformation capacity. To address this issue, ultra-high ductile concrete (UHDC) was employed to enhance the flexural behaviours of pretensioned prestressed concrete (PPC) beams reinforced with carbon fiber reinforced polymer (CFRP) bars, while additional aluminium alloy ribs (ARs) were utilized to ensure proper anchorage. A total of eight beams were designed and tested, consisting of four PPC beams and four PPC-UHDC composite beams, which featured different types of CFRP bars, reinforcement ratios and UHDC placement. The test results revealed that the CFRP-reinforced PPC-UHDC composite beams exhibited significantly improved flexural performance in terms of cracking load, ultimate load and ultimate displacement. For specimens with lower reinforcement ratio, the UHDC effectively controlled the cracks and promoted uniform strain in the CFRP bars, leading to increased ultimate load capacity and ultimate displacement. For specimens with higher reinforcement ratios, the flexural performance was comprehensively improved when the UHDC was placed in the compression zone. Numerical analysis was conducted to further investigate the flexural behaviours of PPC-UHDC composite beams under various conditions.

Effect of the NSM material and area on the flexural response of normal strength concrete beams internally reinforced with GFRP and steel bars

Strengthening the steel-reinforced concrete (RC) beams by fiber-reinforced polymer (FRP) elements have become common several years ago. Recently, the RC beams internally reinforced with FRP reinforcement, especially Glass FRP (GFRP) bars, became popular worldwide. The carbon FRP (CFRP) elements (strips and bars) were recently used to strengthen the internally GFRP RC beams. In contrast, using the GFRP elements to upgrade the RC beams, especially those with GFRP bars as the main tensile reinforcement, was rarely studied. In this paper, the GFRP bars were implemented as near-surface mounted (NSM) elements to upgrade the beams reinforced in their tension side with GFRP or steel bars. All beams were experimentally loaded in flexure using a four-point loading scheme. The experimentally studied parameters were the main tensile reinforcement area, NSM area, and main reinforcement properties. Moreover, a numerical model was established and validated using the available experimental data to investigate the impact of main and NSM materials properties and areas on RC beam response. The experimental results highlighted that increasing the internal and NSM GFRP area by 96% and 100 % increased the beam capacity by 61.6% and 59.7%, respectively, which underlined a slightly higher efficiency of the main reinforcement than NSM bars on the beam load capacity. In addition, substituting the main steel with GFRP bars for the beams upgraded with NSM GFRP reinforcement enhanced their capacities by 11.33–15.1%. This emphasized the great effect of the linear response of the FRP materials and their higher tensile strengths than steel on the interaction between the main and NSM reinforcement, especially after the steel yielding. The FE results showed the highest load capacity using CFRP and GFRP bars as main and NSM reinforcement for the simulated beams. Conversely, using CFRP bars as NSM strengthening was more efficient than GFRP bars for the RC beams with steel or GFRP bars.

Bonding behavior and prediction of helically ribbed CFRP bar embedded in ultra high-performance concrete (UHPC)

In this study, pull-out tests were carried out to evaluate the bond strength of helically ribbed carbon fiber reinforced polymer (CFRP) bars embedded in ultra-high-performance concrete (UHPC). For this purpose, different parameter such as bar profile, embedment length and diameter of the CFRP bar were investigated and the bond strength of ribbed CFRP bar to UHPC were compared with that of the normal strength concrete (NC) and high strength concrete (HC). Also, the failure modes and bonding characteristics of CFRP bar to concrete were presented with combination of the compressive strength of concrete with different cover thickness. The critical cover thickness of concrete for normal strength concrete (NC) and high strength concrete (HC) to prevent splitting failure is 2.5db and 3.5db respectively, and the bond strength of helically ribbed CFRP bar to UHPC is continuously increased as the cover thickness of concrete increased. The bond strength of helically ribbed CFRP bar continued to increase with increasing compressive strength of concrete, and the bond strength of the helically ribbed CFRP bar is more than two times that of the sand coated CFRP bar. In addition, bond strength increased with increasing embedment length (less than 4db of embedded length) and diameter of the CFRP bar. Finally, the experimental results were compared with the bond design codes and the proposed formula, and the modified formula of bond equations with helically ribbed and sand coated were presented and improved the accuracy of the prediction with artificial neural network (ANN).

Serviceability behavior of High Strength Concrete I-beams reinforced with Carbon Fiber Reinforced Polymer bars

Fiber Reinforced Polymer (FRP) bars are anisotropic in nature and have high tensile strength in the fiber direction. The use of High-Strength Concrete (HSC) allows for better use of the high-strength properties of FRP bars. The mechanical properties of FRP bars can yield to large crack widths and deflections. As a result, the design of concrete elements reinforced with FRP materials is often governed by the Serviceability Limit States (SLS). This study investigates the short-term serviceability behavior of FRP RC I-beams. Eight RC I-beams reinforced with carbon-FRP (CFRP) and four steel RC I-beams, for comparison purposes, were tested under two-point loading. Deformations on the concrete and crack widths and spacing are measured and analyzed. A discussion on the main aspects of the SLS of FRP RC is introduced. The service load that fulfills the serviceability requirements, at a cross-section level, ranges between 0.27 and 0.38 times the ultimate load for sections dimensioned to fail in concrete crushing. The determinant criterion is the deflection limitation