GFRP-reinforced Concrete Beams Research Articles

Nonlinear Finite Element Analysis for Concrete Deep Beam Reinforced with GFRP Bars

This work investigates the behavior of concrete deep beams reinforced with GFRP bars by conducting an experimental test on a half-scale GFRP deep beam and evaluating the findings by ANSYS software. Also, ANSYS was used to perform nonlinear finite element analysis NLFEA on five specimens with different reinforcement ratios of GFRP bars (0.15%, 0.41%, 0.53%, 0.67%, and 0.79%) to examine the influence of the GFRP reinforcement ratio on the behavior of deep beams. The outcomes of the experiment were sufficiently reflected in the analysis. The program's viability was confirmed by comparing it to accessible experimental data, and the agreement was found to be acceptable. Throughout the loading stages, the NLFEA produced a reasonable estimate of the center deflection for the test specimen. It was established that raising the specimen's reinforcement ratio led to an increase in beam capacity by (10 %, 18%, 31% and 47%) for reinforcement ratios (0.41%, 0.53%, 0.67% and 0.79%) and also the ultimate stiffness increased by (6%, 7%, 29%, and 44%) compared to specimen B1. Also found that the energy absorption enhanced by (23 %, 38 %, 106 %, and 152 %), on the opposite, this increase causes the specimen's deflection to decrease by (11 %, 17%, 52%, and 66%) by comparing to specimen B1. From the outputs results, it was found that the code provision was more conservative than the analytical model. For future work, Significant and cost-effective improvements to the manufacture of GFRP bars from locally sourced raw materials. Also, Extensive experimental work to investigate the long-term behavior of GFRP-reinforced concrete beams in harsh situations. The performance of GFRP reinforced specimens subjected to shear, fatigue, and cyclic stresses in service must be evaluated.

The vibration-based assessment of the influence of elevated temperature on the condition of concrete beams with pultruded GFRP reinforcement

Concrete beams reinforced with glass fiber reinforced polymer (GFRP) bars subjected to elevated temperature have been experimentally studied. The influence of high temperatures on GFRP-reinforced concrete beams condition has been check both, destructively and nondestructively. The nondestructive tests foresaw vibration-based tests to obtain the natural frequency values after exposure to varying temperatures. The vibration-based tests allowed for the indirect observation of beams stiffness reduction after exposure to elevated temperature. The approach based on frequency response function (FRF) turned out to be efficient even in the case of relatively low temperatures (120 °C). The investigation involved also destructive tests which were conducted in various conditions: once the bending load and elevated temperature were applied at the same time and in the next case, the destructive tests were conducted after heating and cooling down the experimental objects. The study proved that the increase of the temperature causes the reduction of characteristic mechanical parameters, regardless the beams were cooled down or not. However, the simultaneous action of bending load and elevated temperature resulted in a greater reduction of the ultimate strength of tested objects.

Shear tests of GFRP-reinforced concrete beams strengthened in shear by textile reinforced concrete

Shear tests on six GFRP reinforced concrete beams with aspect ratios ranging from 2.3 to 2.8 are conducted in this research to investigate the effectiveness of using textile reinforced concrete in shear strengthening. The beams are strengthened with either one or two layers of U-wrapping textile reinforced concrete. Two levels of aspect ratios of 2.3 and 2.8 are studied in this experimental program. The load–displacement curves, cracking patterns, strains in FRP bars are recorded and compared between strengthened and un-strengthened GFRP-reinforced concrete beams. Textile reinforced concrete has proved its capability in enhancing the shear strengths of tested beams with various aspect ratios. Increasing the number of fibres layers in textile reinforced concrete has shown its effectiveness in increasing both shear strengths and post-elastic stiffnesses of the beams. The diagonal tension failure together with rupture or slippage of fibres in textile reinforced concrete are observed at the level of maximum shear forces. A simple analytical model is proposed to predict the shear strengths of the tested beams.

Deflection of GFRP-reinforced concrete beams

This paper presents an investigation of the performance of concrete beams reinforced with glass fiber-reinforced polymers (GFRP) under short-term loading. A total of six specimens with rectangular cross-sections (75 mm in height and 150 mm in width) were tested under a four-point bending test to failure. Each specimen was reinforced with two GFRP bars with diameters of 8 mm. The results of this study demonstrated the behavior of GFRP-reinforced concrete members and a validation of the available calculation methods for the deflection of these members and assumed possibilities of the use of a GFRP reinforcement over the long term. The results of the study presented show a very good agreement of an experimentally measured and theoretically calculated instantaneous deflection when using the approaches in the European and American standards. In calculations of long-term deflections, the results are highly inconsistent and seem to be quite overestimated in some cases. The study shows the necessity of real-time long-term measurements to demonstrate the real deformations to be assumed during design of structures reinforced with GFRP reinforcement.

Effect of Shear Reinforcement Ratio on The Shear Capacity of GFRP Reinforced Concrete Beams

Effect of Shear Reinforcement Ratio on The Shear Capacity of GFRP Reinforced Concrete Beams

Monitoring structural behaviour of concrete beams reinforced with steel and GFRP bars using acoustic emission and digital image correlation techniques

The paper investigates the flexure behaviour and cracking pattern of reinforced concrete beams utilizing steel and GFRP reinforcement using a judicious combination of non-destructive testing techniques of Acoustic Emission (AE) and Digital Image Correlation (DIC). AE parameters including amplitude, number of AE hits, average frequency (AF) and rise angle (RA) successfully correlate with cracking initiation and its progression in steel reinforced concrete (RC) and GFRP RC beams. The plot between AF-RA value effectively classifies the different failure modes in the two types of beams. Simultaneous drop in AF and a significant jump in AE duration at the same instant give a fair indication of critical failure points. AE-XY plots and longitudinal strain profiles obtained from DIC give a real-time representation of progressive AE activity and strains respectively. While AE is proposed to characterize the onset and propagation of the cracking pattern and mode of failure in the beams, DIC assists to visualize the displacement and strain fields while highlighting discontinuities in the displacement field. The work is aimed at developing a health monitoring strategy for RC beams with steel or GFRP bars which is in-situ, non-invasive and provides pre-emptive warning in real-time so that catastrophic failures can be completely avoided.

Determination of flexural capacity for GFRP-reinforced concrete beams retrofitted using external CFRP sheet

This paper investigates the flexural capacities and deflection characteristics of ordinary portland cement-based concrete (OPCC) and geopolymer concrete (GPC) beams reinforced with glass-fiber-reinforced polymer bars (GFRP). The applicability of carbon-fiber-reinforced polymer (CFRP) sheets as a strengthening technique for such systems is also studied. A total of 15 beams were tested under a four-point quasi-static load. Eight beams served as a reference, while the remaining seven were damaged by loading up to 50% of their load capacities and subsequently strengthened with CFRP sheets. Moment capacities, strain development, load-deflection relationships, and failure modes are reported. The ACI 440.1R-06 guideline was found to be appropriate to give conservative estimates of flexural capacities of control beams for both OPCC and GPC. The previously proposed deflection models for OPC beams reinforced with FRP bars may be used to determine the deflection of GPC composite beams provided that the modulus of elasticity is adequately adjusted for such concretes. For the strengthened beams, however, the ACI 440.2R17 process does not account for the dissimilarity between the CFRP and GFRP modulus values and therefore overestimates the capacity of these unique composites. Finally, a factor (λ) is proposed to consider the contribution to the flexural capacity of GFRP bars in such strengthened system.

Performance of GFRP-Reinforced Concrete Beams Subjected to High-Sustained Load and Natural Aging for 10 Years

The long-term performance of glass fiber-reinforced polymer (GFRP) bars under high levels of sustained load combined with real field conditioning has not yet been thoroughly investigated. Our experimental investigation examined the flexural behavior of concrete beams reinforced with GFRP bars subjected to a high sustained bending load after 10 years of natural aging. The experimental program consisted of eight rectangular concrete beams measuring 250 × 250 × 2,000 mm. All beams were reinforced with sand-coated GFRP bars. Four beams were subjected to a high sustained load of up to 40% of the ultimate tensile capacity of their GFRP bars with simultaneous exposure to aggressive natural weathering (temperatures ranging from −25°C to 35°C) for 10 years. The remaining four were stored in the laboratory and treated as control specimens without any loading. The conditioned beams were tested up to failure in a four-point bending setup. The results were compared in terms of load–displacement behavior, ultimate strength, displacement capacity, failure modes, and cracking patterns. In addition, the microstructure of the GFRP bars was studied to evaluate the physical changes of the bars, and their bond condition with surrounding concrete at different stress levels. The findings indicate a strength deterioration of only 16% for this early generation of GFRP bars under harsh natural conditioning and high sustained loads for 10 years. On the other hand, the bond between the concrete and GFRP bars, as well as the glass-transition temperature, infrared spectra, and interlaminar shear strength of the GFRP bars, remained unaffected. Finally, analytical approaches were implemented to predict the load–displacement behavior and crack widths of the tested beams.

Short-term flexural performance of seawater-mixed recycled-aggregate GFRP-reinforced concrete beams

Combining seawater, recycled coarse aggregate (RCA), and glass fiber reinforced polymer (GFRP) reinforcement in concrete is potentially advantageous from a sustainability perspective. This paper reports on the results of an experimental study on the short-term flexural performance of seawater-mixed recycled-aggregate concrete beams with GFRP bars. Twelve medium-scale reinforced concrete (RC) beams (150×260×2200 mm) were tested under four-point loading. The test variables included the mixing water (seawater/freshwater), aggregate type (conventional/recycled), and reinforcement material (black steel/GFRP). A wide range of flexural properties, including failure mode, cracking behavior, load-carrying capacity, deformation, energy absorption, and ductility were characterized and compared among the beam specimens. The results suggest that the use of seawater and RCA in concrete has insignificant effects on the flexural capacity of RC beams, especially if concrete strength is preserved by adjusting the mixture design. Altering reinforcement material had a strong influence on the flexural capacity and performance of the tested specimens: the GFRP-RC beams exhibited higher load-carrying capacities (on average 25%) but inferior deformational characteristics as compared to their steel-reinforced counterparts. Theoretical predictions were obtained for the flexural capacity, crack width, and deflection of steel- and GFRP-RC beams based on their corresponding design guides, and compared with the experimental results.

Long-term performance monitoring of GFRP-reinforced concrete beams using sensor-mounted supplemental rebars under harsh environmental conditions

Fiber-optic sensors (FOS) are increasingly being used in reinforced-concrete (RC) structures for their accuracy and durability. One of the drawbacks of FOS is their fragility at installation. One recently developed method to address such deficiency is to install the FOS on a short bar (supplemental bar) that is rigidly connected to the structural reinforcement bars prior to concrete pouring. However, the durability of such systems under harsh environmental conditions has not been well established. In order to better understand the behavior of the aforementioned FOS systems under harsh environmental conditions, seven half-scale RC beams with glass fiber-reinforced polymer bars were exposed to four different exposure regimes, in the present study. After 14 months of exposure to harsh environmental conditions, the RC beams were subjected to static flexural testing to evaluate the FOS system behavior under each environmental condition. In addition, the strain responses of the sensors mounted on the supplemental bars and those in the main bars were monitored to validate the newly developed FOS mounting system. The results of this study show that the proposed FOS mounting system can efficiently capture the actual strain in all environmental conditions tested in this study except immersion exposure under high alkali solution. In addition, the flexural deformation and the exposure impact to the beam capacity were evaluated.

Evaluation of the flexural strength and serviceability of concrete beams reinforced with different types of GFRP bars

The current available glass-fiber-reinforced polymer (GFRP) bars have a modulus of elasticity ranges from 40 to 60 GPa in accordance with CSA S807-10 Canadian standard. The surface profile of GFRP bars, however, can be smooth, sand-coated, deformed, grooved, or ribbed. This study aimed at investigating the flexural behavior and serviceability performance of concrete beams reinforced with different types of GFRP bars. The test parameters were: (i) modulus of elasticity (46.4–69.3 GPa); (ii) surface profile (sand-coated and helically-grooved), and (iii) reinforcement ratio. The study included testing of 17 full-scale beams measuring 4,250 mm long × 200 mm wide × 400 mm deep reinforced with GFRP bars. The test results are presented and discussed in terms of deflection, crack width, strain, and load-carrying capacity. The cracking behavior of the tested beams tends to confirm that sand-coating of GFRP bars enhances the bond performance in concrete more than the helically-grooved profile. The curvature limit of 0.005/d seems to be feasible in controlling the serviceability of GFRP-reinforced concrete (GFRP-RC) beams. In addition, ACI 440.1R-06 and ACI 440.1R-15 underestimated the deflection, while ISIS M-03 and CSA S806-12 provided conservative deflection values at 0.30 of nominal moment capacity, Mn.

Establishment and experimental validation of an updated predictive equation for the development and lap-spliced length of GFRP bars in concrete

Glass fibre-reinforced polymer (GFRP) reinforcement due to its physical and mechanical behavior has a completely different bond behavior compared to the steel bars. In this paper, an equation is proposed to predict the splice length in GFRP-reinforced concrete beams. First, equations for the local bond strength and displacement modulus of GFRP bars are obtained by using the eccentric and concentric pull-out test results given in the literature. Then, an equation is derived for the bond strength of spliced GFRP bars in beams. In the derivation of this equation, the non-uniform distribution of the bond stress along the splice length and the effect of elastic modulus of GFRP bars are taken into account. Compared to other available equations and design guidelines, the proposed equation for bond strength calculation shows good agreement with the experimental results. Using the proposed equation for bond strength, an equation is also proposed for the splice length of GFRP bars.

3D Finite Element Modeling of GFRP-Reinforced Concrete Deep Beams without Shear Reinforcement

This paper presents the numerical investigation of nine Glass Fiber-Reinforced Polymer (GFRP) concrete deep beams through the use of numerically-efficient 20-noded hexahedral elements. Cracking is taken into account by means of the smeared crack approach and the bars are simulated as embedded rod elements. The developed numerical models are validated against published experimental results. The validation beams spanned a practical range of varying design parameters; namely, shear span-to-depth ratio, concrete specified compressive strength and flexural reinforcement ratio. The motivation for this research is to accurately yet efficiently capture the mechanical behavior of the GFRP-reinforced concrete deep beams. The presented numerical investigation demonstrated close correlations of the force–deformation relationships that are numerically predicted and their experimental counterparts. Moreover, the numerically predicted modes of failure are also found to be conformal to those observed experimentally. The proposed modeling approach that overcame previous computational limitations has further demonstrated its capability to accurately model larger and deeper beams in a computationally efficient manner. The validated modeling technique can then be efficiently used to perform extensive parametric investigations related to behavior of this type of structural members. The modeling method presented in this work paves the way for further parametric investigations of the mechanical behavior of GFRP-reinforced deep beams without shear reinforcement that will serve as the base for proposing new design guidelines. As a deeper understanding of the behavior and the effect of the design parameters is attained, more economical and safer designs will emerge.

Nonlinear finite-element analysis for the behavior prediction and strut efficiency factor of GFRP-reinforced concrete deep beams

The recent experimental results and proposed strut-and-tie model (STM) for deep beams reinforced entirely with glass-fiber-reinforced polymer (GFRP) bars have suggested that a comprehensive examination is required to improve the strut efficiency factor and its affecting parameters. This study uses nonlinear finite-element analysis (FEA) to perform an in-depth investigation. FEA response was compared against the experimental results in terms of crack patterns, failure modes, strains in reinforcement and concrete, and load–deflection relationships. The results show that the simulation procedures employed were stable and compliant, and that they provided reasonably accurate simulations of the behavior. FEA was used to confirm some hypotheses associated with the experimental investigations. A comprehensive parametric study was conducted to investigate the effect of web reinforcement and loading-plate size on the strut efficiency factor. It was shown that vertical web reinforcement has no clear effect on the strength, but it is required for crack control. On the other hand, horizontal web reinforcement should be accompanied with vertical reinforcement. Loading-plate size showed a clear effect on the deep-beam strength. Based on the numerical simulation results, a modification to a recently proposed STM is suggested. The modified STM was compared to available STMs in design codes and provisions, yielding better correlation with experimental results.

Effect of cold temperatures on the behavior and ultimate capacity of GFRP-reinforced concrete beams

This study evaluated the effects of subfreezing temperatures on the behavior and ultimate capacity of GFRP-reinforced concrete beams. Duplicate beam specimens at four temperatures (20°C, 0°C, −20°C, and −40°C) were tested in four-point bending until failure, while monitoring applied load and resulting deflection. The ultimate capacity of the beams was observed to increase with decreasing temperature, a result attributed to the effects of temperature on the compressive and tensile capacities of the concrete. Further, the increased tensile capacity of the concrete with decreasing temperature caused a noted difference in the post-cracking response of the beams: an increase in magnitude of drops in the force-deflection response associated with cracking. The method proposed by ACI 440 (2006) for calculating the ultimate capacity of GFRP reinforced beams accurately predicted the capacity of the beams in this investigation, with an average measured to predicted ratio 1.00 using the measured concrete properties and 1.03 using the design concrete properties.

Numerical Simulation of GFRP Reinforced Concrete Beams

Experiment on the constitutive model of fiber reinforced concrete with volume fraction of alkali-resistant glass fiber of, respectively, 0.0%, 0.5%, 1.0%, and 1.5% was conducted, and the constitutive relation of tension stress-strain full curve of GFRC shaft was obtained; the constitutive relation of GFRP is obtained by experiment, and the secant modulus was obtained by the fitting of univariate cubic equation. The finite element numerical simulation of GFRP fiber reinforced concrete beam was carried out, and the load deflection nephogram of fiber reinforced concrete beam, strain nephogram, crack nephogram, and GFRP stress nephogram were obtained. When the fiber content is 1.0%, the bearing capacity of GFRP reinforced concrete beams is the best, and it could play a “bridging” effect when the incorporation of fiber is within the load range of about 60%, which inhibited the developing speed of cracks, but with the gradual increase of the load, the “bridging” effect disappeared.

Cracking and deflections in GFRP RC beams: An experimental study

Fibre Reinforced Polymers (FRPs) have emerged as an alternative to steel for Reinforced Concrete (RC) elements in aggressive environments. The low modulus of elasticity of FRP bars can yield to large crack widths and deflections and, as a result, the design of FRP RC elements is often governed by serviceability limit state criterion. This paper presents the results of an experimental programme on the cracking and deflections of 14 Glass-FRP RC beams. The adequacy of the most representative prediction models for the serviceability limit states of cracking and deflections of FRP RC beams is investigated. The influence of the most relevant parameters is analysed, and the suitability of different prediction models, as well as the adjustment of empirical coefficients, is analysed and discussed.

Shear Strength of GFRP-Reinforced Concrete Continuous Beams with Minimum Transverse Reinforcement

This paper investigates the shear behavior of continuous concrete beams reinforced with glass fiber–reinforced polymer (GFRP) bars and stirrups. A total of six beams, with 200×300 mm rectangular cross section and continuous over two spans of 2,800 mm each, were constructed and tested. Three main variables, namely, concrete strength, longitudinal reinforcement ratio, and transverse shear-reinforcement ratio, were investigated. Two beams were without transverse reinforcement to evaluate the concrete contribution to the shear strength and four beams had GFRP stirrups to examine the minimum shear-reinforcement contribution to the shear strength. All test specimens were designed to satisfy an assumed 20% moment redistribution. It was observed that all test specimens failed in shear near the interior support after significant moment redistribution from hogging moment to sagging moment regions. In addition, the test results were compared with the predictions of the CSA-S806-12, CSA-S6-06, and ACI 440.1R-06.

Shear characteristics of GFRP-reinforced concrete deep beams without web reinforcement

This article investigates the shear behavior of deep concrete beams reinforced with glass fiber reinforced polymer for flexure and without shear reinforcement. A total of 13 beams were tested under four-point loading until failure. Nine of which reinforced with glass fiber reinforced polymer bars and four with steel bars. The ultimate shear capacity along with the load–deformation relationship of all beams was studied. The effects of the shear span to depth ratio a/d, reinforcement ratio ρ, beam effective depth d, and concrete compressive strength on the ultimate shear capacity and mode of failure of all beams were also investigated. Results show that the stiffness of steel-reinforced concrete beams (slope of the ascending portion of load–deflection curve) is higher than that of beams reinforced with fiber-reinforced polymer bars as expected, due to the low axial stiffness of the fiber-reinforced polymer material. A slight variation in the ultimate shear capacity was noticed but no clear trend was observed. In addition, beams reinforced with fiber-reinforced polymer exhibited larger deformation at their ultimate failure load, after which a sudden failure occurred especially for beams having high shear capacity.

Flexural Behavior of Innovative Hybrid GFRP-Reinforced Concrete Beams

Fiber-reinforced polymer (FRP) bars are emerging as a competitive option for replacing steel bars as reinforcement in various concrete structures exposed to aggressive environments. However, the low elastic modulus and brittleness of FRP bars significantly reduce the stiffness and the ductility of FRP-reinforced concrete (FRP-RC) members. In order to improve the flexural behavior of FRP-RC members and meanwhile ensure their satisfactory corrosion-resistant performance, an innovative FRP-reinforced concrete encased steel composite (FRP-RCS) member, which consists of ductile structural steel shapes in combination with corrosion-resistant FRP-reinforced concrete, was conceived and studied. An experimental investigation on the flexural behavior of the proposed FRP-RCS beams was conducted by testing a total of five large-scale simply supported beam specimens subjected to four-point bending loads. The test specimens included one FRP-RC beam reinforced with GFRP bars only and four FRP-RCS beams reinforced with both GFRP bars and encased structural steel shapes. The main parameters considered in this study were concrete compressive strength and amounts of GFRP reinforcement. The test results indicated that using encased steel shapes provided a significant enhancement in load carrying capacity, stiffness, ductility and energy absorption capacity of test beams. The tested FRP-RC beam suffered a brittle failure caused by sudden fracture of tensile GFRP bars whereas the proposed FRP-RCS beams behaved in a ductile manner due to the beneficial residual strength of encased steel shapes following concrete crushing. In addition, the experimental results also demonstrated that the concrete compressive strength had little effect on load carrying capacity of FRP-RCS beams whereas the load carrying capacity can be enhanced by increasing the reinforcement ratio. Analytical methods were also constructed using OpenSEES2.2.2 to simulate the load-deflection response of tested beams..