CFRP Bars Research Articles

Strengthening of RC beams using the combination of EB CFRP sheet, NSM CFRP bar and P‐SWRs

AbstractDebonding issues in the externally bonded (EB) CFRP sheets (or near‐surface mounted [NSM] CFRP bars) and space requirements of edge and spacing clearances for NSM CFRP bars (or the prestressed steel wire ropes [P‐SWRs]) have limited the applications of these strengthening techniques. The combination of these techniques may overcome the drawbacks of each technique and was experimentally and analytically investigated in this paper. Test results demonstrated that the flexural performances of the combinedly strengthened beam are between the flexural performances of the beams strengthened with the corresponding individual strengthening techniques. It is found the combination of the three techniques successfully prevented debonding issues which often occur in EB or NSM techniques and improved the spacing and edge clearances which are necessary for NSM and P‐SWRs techniques. In addition, the combination was demonstrated as effective to limit the crack development and improve the ductility of the strengthened beams.

Effect of using different types of reinforcement on the flexural behavior of ferrocement hollow core slabs embedding PVC pipes

This paper provides an experimental investigation to study the effect of using different types of reinforcement on the flexural behavior of ferrocement thin hollow core slabs with embedded PVC pipes. Twelve slabs of 1100 × 400 × 55 mm dimensions were casted and tested till failure. The effect of four different types of reinforcement was investigated in this study including; steel wire mesh, macro and micro steel fibers or a combination of both, steel bars and CFRP bars. The results showed that the slab reinforced with only macro steel fibers provided the highest flexural strength, while that reinforced with steel bars showed the highest stiffness and lowest deflection among all tested slabs. Also, the dry design density for all the hollow core slabs was determined to be below 2000 kg/m3 which is within the requirements of light weight concrete as set by most codes of practice.

The shear strengthening of reinforced concrete beams by embedded through section technique -analytical study-

Five proposed simply supported RC beams were numerically tested by finite element method using ABAQUS software to investigate their behavior and shear strength when strengthened by embedded through section technique (ETS). All beams have the same dimensions of (160 × 250 ×1140) mm and were insufficient reinforced in shear. One beam is taken as a control beam. While, the other four beams were strengthened ETS CFRP bars and divided into two groups. The first group is with 13mm ETS CFRP bars (one bar per section). While, the second group is with 10mm ETS CFRP bars (two bars per section). For all groups, two styles of ETS inclination are considered, vertical and inclined by 45°. From the numerical tests, it was found that using ETS with 2φ10 inclined CFRP bars is the most effective technique for enhancing both the first cracking load about 100% and ultimate load capacity about 86%.

Flexural Action of Continuous Reinforced Reactive Powder Concrete Beams

In this current study can be split into two aims next its two aims. The first aim was to study the effectiveness of steel fibre ratio from (0 to 2.5%) on the flexural action of RPC continuous beams. The other aim was to investigate the effectiveness of longitudinal reinforcement bar on the flexural behavior of RPC continuous beams by using (CFRP and GFRP). Therefore, seven continuous beams consist of two span were searched under one-concentrated load for each span. All specimens had the same dimensions 150 mm width, 250 mm depth and 2700 mm length. The experimental outcomes display that the continuous samples made with RPC had an excellent compressive strength and that the maximum load improved when steel fibre ratio increased. The maximum load of the continuous sample was also discover to be improved when the using of CFRP bar as a longitudinal reinforcement ratio. In supplement, the maximum load of the continuous beam was decrease when using GFRP bar as a longitudinal reinforcement ratio.

Experimental Investigation of the Flexural Strengthening of Fixed-Supported RC Beams

The performances of seven full-scale, fixed-supported reinforced concrete (RC) beams were investigated with the four-point bending test in this study. One of the RC beams was a reference beam (Ref) and six were strengthened beams. The strengthening of the RC beams was performed with near surface mounted (NSM), external bonded reinforcement (EBR), friction hybrid bonding (FHB), and hybrid techniques. Steel bars, CFRP bars, CFRP sheets, and mechanical fastener systems were used in the strengthening processes, according to the requirements of the applied techniques. The experimental results were evaluated for the effects of strengthening techniques and materials on the load–deflection response, ultimate load-carrying capacity, ductility, dissipated energy, failure modes, strain, and crack pattern. Strengthening applications using the NSM technique, with conventional steel, increased the load-carrying capacity of the RC beams by 22–24.9% while increasing their total energy dissipation by 40.7–68.9%. The load-carrying capacity was increased by 3.7–11.9% in RC beams strengthened by CFRP sheet and CFRP bar. However, except for the FHB technique, CFRP-applied RC beams could not perform the inelastic behavior. The FHB strengthening technique increased the load-carrying capacity and total energy dissipation of the beam by 11.6% and 21.2%, respectively. The results showed that NSM-Steel, NSM-Steel/90, and FHB-CFRP techniques quite improved the performance of the RC beams for both the elastic and plastic regions, while both of EBR-CFRP and Hybrid-CFRP techniques improved the elastic behavior of the RC beams to a great degree.

Experimental Behavior of Continuous Hybrid Reinforced Concrete Spliced Girders

This paper conducts an experimental study on the behavior of two-spans continuous reinforced concrete spliced girders strengthened using steel fiber concrete of volume fraction of 1% at splice regions and side near surface mounted carbon fiber reinforced polymer bars of 6 and 10 mm sizes. Five beams with 150 × 250 mm rectangular cross section and 2200 mm total length were cast. The first beam was cast as one unit without joints as a reference while the rest were made from assemblage of three precast segments spliced together using cast in place concrete joints of 170 mm length located at the inflection points. All girders were tested using a single concentrated force at each midspan. The studied parameters were: existence of splices, using of steel fiber concrete at splice region, and strengthening of spliced girders using side near surface mounted carbon fiber reinforced polymer bars. The results showed that existence of splices led to a decrease in the ultimate capacity of the spliced girder of about 33.1% with larger midspan deflections in comparison with the non-spliced girder. But, strengthening of spliced girders using CFRP bars could provide additional load capacity from 69.1% to 98.1% compared with the non-strengthened spliced girder with lower midspan deflections while steel fiber concrete at joints raised the ultimate load of spliced girders by 12.3%. However, the failure mode of the spliced beams were brittle if compared with the ductile failure of the control girder.

Structural behaviour of CFRP reinforced concrete members under bending and shear loads

Reinforcement made of fibre-reinforced polymers (FRP) for concrete members is becoming increasingly important in structural engineering. Compared to conventional ribbed steel reinforcement bars, FRP reinforcement can be different in terms of modulus of elasticity, tensile strength and bond behaviour. This article presents and evaluates experimental investigations on the structural behaviour of concrete members under bending and shear loads. Different types of reinforcement (CFRP textile fabrics, CFRP bars, steel bars), cross-sections (slabs, beams) and types of failure (flexure, shear) are investigated. For a direct comparison with conventionally reinforced members, reference tests with steel reinforcement and comparable mechanical reinforcement ratio are carried out. The material properties and the structural behaviour of the studied concrete members are presented. The load-bearing, cracking and deformation behaviour is precisely described and the applicability of existing engineering models is checked. Additionally, the contributions to shear capacity are analysed using the deformation measurement based on digital image correlation.

Direct shear strengthening of NSC and SCC using NSM CFRP and steel bars

Failure in direct shear is sudden and catastrophic in concrete structures, Several techniques have been developed for shear strengthening of push-off specimens representing direct shear. In this research, the effectiveness of Near-surface mounted (NSM) FRP and steel bars as a strengthening technique for direct shear in normal strength concrete (NSC) and self-compacted concrete (SCC) are studied. As a result of the experimental work, it was observed that the NSM steel bars increased the shear capacity by 48 and 44% for both types of concrete NSC and SCC respectively, while the NSM CFRP rods increased the shear capacity by 30% and 33% for both NSC and SCC respectively. It was also observed that strengthening at 90° was more effective in terms of shear strength compared to 45° with a difference in the range of 8% for NSC and 5% for SCC. The analytical results are very close to the experimental ones.

Short term crack width prediction of CFRP bars reinforced coral concrete

In order to study the crack development of CFRP reinforced coral concrete under different bending conditions, experimental study investigation of crack width of steel and CFRP reinforced coral concrete beams were performed. A comparative study of cracking rate, maximum crack height and crack patterns in CFRP bars reinforced coral concrete beams at different stages is made with ordinary steel reinforced coral concrete beams. The results show that under similar reinforcement ratio, the crack width and crack spacing of CFRP reinforced coral concrete beams are larger than that of steel reinforced concrete beams, increasing the reinforcement ratio of test beams can effectively reduce the crack width. The current deign formula from existing design codes overestimates the value of the relative bond characteristic coefficient (vi) and the strain inhomogeneity coefficient (ψ). Therefore, in this paper, the formula for maximum crack width of CFRP bars reinforced beams is developed based on the experimental data, the relative bond characteristic coefficient, the strain inhomogeneity coefficient of the longitudinal reinforcement, the ratio of the maximum crack width to the average crack width (τs) are included in the formula. The formula is validated with test results, the calculated value agrees well with the experimental results. Therefore, can be used for the future design.

Flexural strengthening of reinforced concrete beams with NSM-CFRP bars using mechanical interlocking

Flexural strengthening of reinforced concrete (RC) beams using near-surface-mounted (NSM) technique has become an attractive alternative for rehabilitation using fiber reinforced polymer (FRP) materials. Previous studies have recommended using available anchoring techniques to overcome premature bonding failure. In this study, mechanical interlocking grooves were utilized to delay or prevent debonding failure. The first part of the study aimed to investigate the bond characteristics for NSM-CFRP bars by conducting several pullout tests on No. 6, No.10, and No.13 CFRP bars. Results indicate that mechanical interlocking grooves can significantly enhance the bonding capacity and prevent or delay premature bonding failure. In the second part, the proposed NSM CFRP strengthening technique was used to strengthen nine RC beams. In addition to longitudinal grooves, the proposed technique consisted of 6 mm wide lateral grooves (or mechanical interlocking) placed at 76 mm on center along the entire length of the strengthened beams. Steel reinforcement ratios of 0.7% and 0.4% were selected. All beam specimens were tested under four-point bending until failure. Results showed that strengthening was more effective for specimens with a lower steel reinforcement ratio. Percentages of enhancement in flexural strength were between 34-68% and 60–128% for specimens with 0.7% and 0.4% steel reinforcement ratios, respectively. Finally, a simple empirical model was created for the experimental results. Theoretical results showed reasonable agreement with the experimental results. However, the maximum load carrying capacity and flexural stiffness were overestimated for beams with a total reinforcement ratio (steel plus CFRP) larger than 1.1%.

Reinforcement alternatives for beams under cyclic load

The major cause of concrete structures deterioration is steel corrosion. Consequently, this situation has led researchers to study and test other reinforcement alternatives that are noncorrosive in nature. Rapidly emerging developments in the field of material technology has led to the development of fiber reinforced polymers (FRP). This research focuses on the flexural behavior of carbon, glass, aramid, and basalt (CFRP, GFRP, AFRP, and BFRP) fiber reinforced polymers bars as alternatives to the traditional steel reinforcement in concrete. The study involves a nonlinear numerical finite element analysis of a simply supported reinforced concrete beams subjected to cyclic loading, where the ANSYS program is utilized. The numerical model verification is executed on the experimental beams for ensuring the efficiency of ma-terial models, cyclic loading and various elements. Hysteresis curves are produced for each beam and analyzed, where loads, deflections, and cracks propagation are inspected and discussed. The results reveal that, the full replacement of traditional steel bars with CFRP bars gives the greatest increase in the ultimate load capacity by 38.5%. Also, other results are summarized in this paper.Â

Experimental Investigation on Seismic Resistance of RC Shear Walls with CFRP Bars in Boundary Elements

Experimental investigation on seismic performance of RC shear walls reinforced with CFRP bars in boundary elements to enhance the resilience was presented which is expected for stable resistance capacity and small residual deformation. Six RC shear walls reinforced with CFRP bars as longitudinal tensile materials in boundary elements were tested under reversed cyclic lateral loading while subjected to constant axial compression with different axial load ratios of 0.17, 0.26 and 0.33, respectively. Two forms of stirrups were used for each axial load ratio, which were rectangular and circular stirrups in boundary elements. A reference specimen, ordinary RC shear walls, was also introduced to certify the excellence of CFRP bars. The test results indicated that the walls utilizing CFRP bars had small residual deformations and residual crack widths. Lower crack propagation height and larger concrete crushing region, bearing capacity and equivalent viscous damping coefficient (EVDC) could be observed with the increase of axial load ratios. The effects of stirrup forms on experimental results had a relation to the axial load ratio. When the axial load ratio was small, the shear walls with circular stirrups had better energy dissipation than that with rectangular stirrups at a given drift level, while the cumulative energy dissipation (CED) were similar. With the increase of axial load ratio, the walls exhibited similar energy dissipation at the same drift level, however, the shear walls with rectangular stirrups had larger CED.

Comparative Approach to Flexural Behavior of Reinforced Beams with GFRP, CFRP, and Steel Bars

The replacement of conventional steel bars with GFRP or CFRP is one of the main topics discussed in this paper, including the main parameters and properties of the materials. The design procedures should account for the properties and will focus on the tensile strength and modulus of elasticity. It will also consider corrosion under environmentally aggressive conditions. This paper presents an experiment on the flexural behavior of concrete beams reinforced with GFRP and CFRP bars and compares these results with theoretical analysis based on different standards such as ACI, Eurocode, and CSA. Twelve reinforced concrete beams will be tested using four-point loading. The geometrical parameters of the tested beams are 130×220×2200 mm, reinforced with different diameters for GFRP and CFRP. The reinforcement ratio and strength of concrete influence the behavior of GFRP, CFRP, and RC beams and contribute to reduce the deflection and crack width. Based on this research, the closest approximation of the experimental results is observed with ACI standards. At this stage, these bars can be used in structures without strict requirements for exceeding the Serviceability Limit State. The non-integration of tension stiffening and regression performance of cracking moment in prediction expressions imposed the differences from experimental results.

Numerical Investigation of the Behavior of Reinforced Concrete Beam Reinforced with FRP Bars

In this study, the behavior of reinforced concrete beams reinforced with FRP bars was investigated. A total of seventeen models were carried out based on the finite element software (ABAQUS). The concrete damage plasticity modeling was considered. Two types of fiber polymer bars, CFRP and GFRP as longitudinal reinforcement for concrete beam were used. The validation of numerical results was confirmed by experimental results, then the parametric study was conducted to evaluate the effect of change in different parameters, such as (diameter size, number of bars), type of FRP bars, longitudinal arrangement for FRP bars. All results were analyzed and discussed through, load-deflection diagram, according, to the difference parameter considered. The results showed that the use of FRP bars in rebar concrete beam improves the beam stiffness and enhance the cracking load. The load capacity enhanced in the range of (7.88-64.82%) when used CFRP bars. The load-carrying capacity of beams strengthened with CFRP is higher than that of strengthened with GFRP. Furthermore, the use of FRP bars in bottom and steel in top reinforcement is useful to overcome the large deflection, and improving the beam ductility. Finally, the results of finite element models were compared with the prediction equation, according to ACI440.1R-15.

Invistigating the effects of frp bars on the seismic behavior of reinforced concrete coupling beams

Sometimes, it is necessary to install regular openings like windows or doors in the shear walls. Such openings require special reinforcement. There are several methods for reinforcing deep beams, one of which is the use of fiber reinforced polymer bars. In this study, an experimental work on a coupled shear wall has been used to mode the system by using finite element method with ABAQUS software. The finite element model was established based on part of the experimental study and verified with the other parts of the experimental results. The comparison shows good agreement. In the study, three different types of fiber reinforced polymer bars were considered in improving the mechanical and structural behavior of RC coupling beams. Results of the finite element analysis showed the superiority of the CFRP bars in improving seismic behavior of the coupled shear wall comparing to GFRP and BFRP.

Performance of Reinforced–Concrete Frame with Embedded FRP rod

Most of the researchers have mainly focused on using of FRP rod to repair, retrofit and using it as additional strength besides steel rebars in structural which have a lack of lateral loading resistance. Application of using FRP rod as the main reinforcement is still rarely used in many areas, especially in the strengthening of the Structure. In present study, nonlinear finite element models have been developed by ABAQUS software to evaluate the effect of using CFRP rod and GFRP rod instead of steel rebars on efficiency of frame to prevent the seismic effect. Also, verifying is conducted by development nonlinear finite element models using ARCS3D software and compare with Experimental Results. Numerical results show superior performance of CFRP rod in terms of the ultimate loads, the energy dissipation, the ductility index, and Plastic hinge formation, which was around 34% improvement for ultimate loads, 6.61% increasing in energy dissipation, and 1.12 for ductility. Besides, frames reinforced with CFRP bars showed different behaviour than frames reinforced with GFRP bars due to the low elastic modulus of GFRP bars, which was increased dramatically the deflection. Comparisons between the two numerical software results showed slightly different between them. Also, verifying the numerical results with previous experimental results confirmed the accuracy of the finite elements models.

Shear behavior of concrete beams reinforced with CFRP sheet strip stirrups using wet-layup technique

Fiber-reinforced polymers (FRP) are being used in reinforced concrete structures featuring their lightweight, high tensile strength, nonmagnetic, and corrosion resistance properties, contrasting conventional steel reinforcement. However, low bend strength, anisotropic and non-plastic nature of FRP composites are the major concerns for their assertive applications in construction industry. Pultruded FRP bar stirrups are characterized by premature failure either due to slippage at overlapping region or rupture at bend portion due to kinking of fibers. In this experimental study, close-type direct wound rectangular cross-section CFRP sheet strip stirrups (CSS) were proposed to mitigate the shortcomings of pultruded CFRP bar stirrups (CP). Total of seven full-scale beam specimens reinforced with steel longitudinal bars and CFRP stirrups were cast and tested to investigate the performance of proposed stirrups. The main study parameters include shear reinforcement material type, the cross-sectional geometry of CFRP stirrups, and the inclination angle of CSS stirrups with the beam axis. Specimens reinforced with CSS stirrups provided better shear capacity and crack control ability compared to steel and CP stirrups for same shear reinforcement ratios. Shear capacity of beam corresponding to serviceability limit state was improved up to 13% by changing the inclination of CSS stirrups from 90° to 45°.

Shear behavior of large-scale concrete beams reinforced with CFRP bars and handmade strip stirrups

To obviate the premature failure of pultruded FRP stirrups due to low bent portion strength and slippage at overlapping region, this study fabricated handmade strip stirrups with a rectangular cross-section and investigated the shear behavior of concrete beams reinforced with handmade CFRP strip stirrups and CFRP longitudinal bars. Five large-scale concrete beams with the cross-section of 200 mm × 500 mm and the shear span ratio of 2.26 were tested under three-point loading. The effects of stirrups inclination and stirrups spacing were studied. Test results showed that inclined stirrups improved both the shear capacity and the serviceability performance. The beams reinforced with inclined stirrups exhibited 1.19–1.26 times higher shear capacities than the beam reinforced with vertical stirrups. Inclined stirrups not only increased the load corresponding to the maximum allowable crack width to 1.10–1.89 times higher, but also improved the ratio of the load corresponding to allowable crack width to the peak load. Moreover, inclined stirrups are more effective in improving the serviceability performance even compared with vertical stirrups with a halved spacing. The shear provisions in CSA S806-12 produced the most accurate predictions of the experimental shear capacities, while the predictions of ACI440.1R-15 and CSA S6-14 were relatively conservative.

Comparative Analysis of Dynamic Characteristics of Concrete Frames Reinforced with GFRP Bars and CFRP Bars

FRP bars have the advantages of light weight, high strength and corrosion resistance, and it can be used as a substitute for steel bars. There are relatively few studies on seismic performance of FRP reinforced concrete frame structures at home and abroad, so it is necessary to carry out research on seismic performance of FRP reinforced concrete frame structures. In order to analyze the structural performance of FRP reinforced concrete frame, the dynamic characteristics and dynamic responses of CFRP and GFRP reinforced concrete frame model structures under different seismic intensity are analyzed. The finite element model of shaking table test scale model of CFRP and GFRP reinforced concrete frame structures is established. The correctness of the finite element model is verified by comparing the structural dynamic responses of the two models. Then the acceleration response and floor displacement envelope diagram are analyzed and compared to evaluate the displacement response of the model. The results show that the displacement response of the two models under bidirectional seismic wave is obviously larger than that under unidirectional seismic wave, the displacement in X direction is obviously larger than that in Y direction, and the inter-story displacement of FRP reinforced concrete frame structure gradually increases from bottom to top. The lateral deformation of the structure is mainly the bending deformation of the beam and column.

Test Design and Finite Element Analysis of Shaking Table of Concrete Frame Structure Reinforced with CFRP Bars

The shaking table test is an irreversible process for a nonlinear model structure. Therefore, how to choose ground motion and determine the input sequence are particularly important for the success of the shaking table test. In this paper, a 1/4 scale CFRP reinforced concrete frame structure specimen model is designed and made according to the similarity theory. By using the finite element analysis software SAP2000, the finite element model of CFRP reinforced concrete frame specimen is established. Four seismic waves are selected in the simulated shaking table test process, and the dynamic time history analysis of a total of 52 working conditions is carried out, including unidirectional, bidirectional and three-directional ground motion input, and the acceleration and displacement response of the structure are obtained. Taking story drift ratio as the evaluation index, the seismic performance of the structure is evaluated. This paper provides theoretical guidance for the subsequent shaking table test.