Glass Fiber Reinforced Polymer Reinforcement Research Articles

Residual Tensile Properties of GFRP Reinforcing Bars after Loading in Severe Environments

The long-term behavior of glass fiber-reinforced polymer (GFRP) reinforcing bars is one of the most critical issues for the acceptance of these materials as reinforcement for concrete structures. There is a high demand for experimental studies to investigate the stability of the tensile strength, ultimate elongation, and elasticity modulus. GFRP reinforcing bars inherently have a low elasticity modulus, which must not significantly decrease over time under loading or the serviceability behavior of the concrete element containing them will be jeopardized. This paper evaluates the residual tensile properties of three sizes of sand-coated GFRP reinforcing bars in alkaline and water environments combined with sustained loading and elevated temperature. Bar diameters of 15.9 (No. 5), 12.7 (No. 4), and 9.5 mm (No. 3) were loaded for different durations, then tested in axial tension for residual tensile properties. The test periods varied from 1 to 4 months under elevated temperature to hasten degradation and si...

Durability Prediction for GFRP Reinforcing Bars Using Short-Term Data of Accelerated Aging Tests

This paper presents a procedure based on the Arrhenius relation to predict the long-term behavior of glass fiber-reinforced polymer (GFRP) bars in concrete structures, based on short-term data from accelerated aging tests. GFRP reinforcing bars were exposed to simulated concrete pore solutions at 20, 40, and 60°C. The tensile strengths of the bars determined before and after exposure were considered a measure of the durability performance of the specimens. Based on the short-term data, a detailed procedure is developed and verified to predict the long-term durability performance of GFRP bars. A modified Arrhenius analysis is included in the procedure to evaluate the validity of accelerated aging tests before the prediction is made. The accelerated test and prediction procedure used in this study can be a reliable method to evaluate the durability performance of FRP composites exposed to solutions or in contact with concrete.

Embedded smart GFRP reinforcements for monitoring reinforced concrete flexural components

The main objectives of this paper are to demonstrate the feasibility of using newly developed smart GFRP reinforcements to effectively monitor reinforced concrete beams subjected to flexural and creep loads, and to develop non-linear numerical models to predict the behavior of these beams. The smart glass fiber-reinforced polymer (GFRP) rebars are fabricated using a modified pultrusion process, which allows the simultaneous embeddement of Fabry-Perot fiber-optic sensors within them. Two beams are subjected to static and repeated loads (until failure), and a third one is under long-term investigation for assessment of its creep behavior. The accuracy and reliability of the strain readings from the embedded sensors are verified by comparison with corresponding readings from surface attached electrical strain gages. Nonlinear finite element modeling of the smart concrete beams is subsequently performed. These models are shown to be effective in predicting various parameters of interest such as crack patterns, failure loads, strains and stresses. The strain values computed by these numerical models agree well with corresponding readings from the embedded fiber-optic sensors.

Flexural and shear capacities of concrete beams reinforced with GFRP bars

This paper reports test results of 12 concrete beams reinforced with glass fibre-reinforced polymer (GFRP) bars subjected to a four point loading system. All test specimens had no transverse shear nor compression reinforcement and were classified into two groups according to the concrete compressive strength. The main parameters investigated in each group were the beam depth and amount of GFRP reinforcement. Two modes of failure were observed, namely flexural and shear. The flexural failure is mainly occurred due to tensile rupture of GFRP bars either within the mid-span region or under the applied point load. The shear failure is initiated by a major diagonal crack within the beam shear span. This diagonal crack extended horizontally at the level of the GFRP bars indicating bond failure. Simplified methods for estimating the flexural and shear capacities of beams tested are presented. The flexural capacity is estimated based on the compatibility of strains and equilibrium of forces. Comparisons between the flexural capacity obtained from the theoretical analysis and that experimentally measured in the current investigation and elsewhere show good agreement. To predict the shear capacity of the beams tested, four methods recently proposed in the literature for GFRP-reinforced concrete beams are used. These methods have been developed by modifying the ACI 318-99 shear capacity formula for steel-reinforced concrete beams to account for the difference in the axial stiffness of GFRP and steel bars. It has been shown that the theoretical predictions of the shear capacity obtained from these methods are inconsistent and further research needs to be carried out in order to establish a rational method for the shear capacity calculation of GFRP-reinforced concrete beams.

Effect of Sustained Load and Environment on Long-Term Tensile Properties of Glass Fiber-Reinforced Polymer Reinforcing Bars

Glass fiber-reinforced polymer (GFRP) bars are gaining popularity as reinforcement for concrete bridge deck slabs and other concrete structures. This article reports on a study of the creep behavior of GFRP bars in different environments under sustained load. Twenty GFRP bars (E-glass in vinylester matrix) 9.5 mm in diameter in four series were tested for over 417 days (10,000 h) under combinations of different sustained load levels and surrounding mediums in ambient temperature. The bars were subjected to two levels of sustained tensile stress at 25% and 38% of guaranteed tensile strength while being surrounded by either alkaline solution (pH 12.8) or de-ionized water (pH 7.0). Axial strain in the central conditioned part of the bars was monitored with time to evaluate the creep behavior. Following the extended creep test, the GFRP bars were tested in axial tension until failure for residual tensile strength, elastic modulus, and axial strain. Results showed that the tested GFRP bar performed very well under these extreme loading and environmental conditions. Creep strain in the GFRP bars is less than 5% of the initial value after 10,000 h of sustained tensile loading. The average residual tensile strength was found to be 139% and 144% of the design tensile strength for bars conditioned in de-ionized water at 25% and 38% stress level, respectively. Alkaline solution tends to have more harmful effects on the bars than de-ionized water at higher stress levels. In alkaline solution, this range was 126% and 97% at 25% and 38% stress level, respectively. More importantly, the modulus of elasticity of the bars is very stable and almost unaffected by the conditions and sustained stress levels used. The authors note that this finding is critical in the design of concrete elements reinforced with FRP bars because the modulus is directly related to the crack width, deflection, and other serviceability concerns.

Performance of Glass Fiber-Reinforced Polymer Reinforcing Bars in Tropical Environments - Part I: Structural Scale Tests

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Performance of Glass Fiber-Reinforced Polymer Reinforcing Bars in Tropical Environments- Part II: Microstructural Tests

In this part of a two-part paper, the authors pursue microstructural studies of glass fiber reinforced polymer (GFRP) reinforcing bars in concrete, including the nature, quantum, and mechanism of deterioration. A scanning electron microscope was used to show the changes in the microstructure. Energy-dispersive x-ray analysis (EDX) and inductively coupled plasma mass spectrometry (ICP-MS) were used to determine the chemical changes in the composite.

Strengthening of dapped timber beams using glass fibre reinforced polymer bars

An economical rehabilitation scheme to strengthen creosote-treated dapped timber stringers in both flexure and shear is proposed. An experimental program was conducted to test stringers under monotonic load in three-point bending load configuration. Eight control beams with no reinforcement, 12 reinforced for flexure only, and 6 reinforced for flexure and shear were tested. Glass fibre reinforced polymer (GFRP) dowel bars were placed at an angle of 60° from the horizontal to reinforce for shear and to bridge the dapped end. Test results from previous studies by Gentile et al. (C. Gentile, D. Svecova, and S.H. Rizkalla. ASCE Journal of Composites for Construction, 6(1): 11–20, 2002.) and Svecova and Eden (D. Svecova and R.J. Eden. Canadian Journal of Civil Engineering, 31: 45–55, 2004) are combined with the results of this investigation for a total sample size of 54 beams. Large sample sizes are essential to study the performance of timber beams strengthened using GFRP bars in various schemes. An overall increase of 70% in the 10th percentile ultimate strength was obtained for stringers reinforced for both flexure and shear. Ductility was increased with the addition of the GFRP reinforcement, but the modulus of elasticity appeared to be unaffected.Key words: timber, bridge, glass fibre reinforced polymer, rehabilitation, modulus of rupture, analysis.

Flexural and shear strengthening of timber beams using glass fibre reinforced polymer bars — an experimental investigation

An experimental program was undertaken at The University of Manitoba to test timber stringers strengthened with glass fibre reinforced polymer (GFRP) bars. Various strengthening schemes were investigated as a means of increasing the load carrying capacity of timber stringers in shear and flexure. The shear strengthening was achieved by inserting GFRP dowels in the centre of the cross section along the length of the stringers. The flexural strengthening used the concept of near-surface-mounted GFRP bars. Fifty beams were tested to evaluate the performance of the various strengthening schemes. The behaviour of the beams is described in terms of mode of failure, mechanical properties, and load–deflection behaviour. This study found that strengthening timber stringers with GFRP reinforcement increased the ultimate strength of the stringers and reduced its variability. It is believed that the shear and flexural GFRP reinforcements act as a truss member within the timber beam and bridge the local defects and discontinuities of the timber.Key words: timber, glass fibre reinforced polymer, bridge, stringers, dowels, strengthening, ductility.

Serviceability of Concrete Bridge Deck Slabs Reinforced with Fiber-Reinforced Polymer Composite Bars

Serviceability concerns, especially cracking and deflection, usually govern the design of reinforced concrete flexural members reinforced with fiber-reinforced polymer (FRP) bars. This work aimed to investigate the flexural behavior and serviceability performance of concrete deck slabs reinforced with different types of FRP composite bars. A total of 10 full-size, 1-way concrete slabs were constructed and tested. The slabs were 3100 mm long x 1000 mm wide x 200 mm deep. The test parameters were type and size of FRP reinforcing bars and the reinforcement ratio. Five slabs were reinforced with glass FRP (GFRP), 3 were reinforced with carbon FRP (CFRP) bars, and 2 control slabs were reinforced with conventional steel. The slabs were tested under 4-point bending over a simply supported clear span of 2500 and a shear span of 1000 mm. The test results are reported in terms of deflection, crack width, strains in concrete and reinforcement, ultimate capacity, and mode of failure. Comparison with the predictions of CAN/CSA-S806-02, CAN/CSA-S6-00 codes, and ACI 440.1R-01 design guidelines is also presented. Test results show that slabs with a CFRP or GFRP reinforcement ratio equivalent to the balanced reinforcement ratio satisfy serviceability and strength requirements of the considered design codes.

Durability of Glass Fiber-Reinforced Polymer Reinforcing Bars in Concrete Environment

Accelerated aging tests are being conducted on more than 20 types of glass fiber-reinforced polymer (GFRP) reinforcing bars, which are produced from different combinations of constituent materials, manufacturing parameters, sizes and shapes, and surface coatings. The specimens are being subjected to various sustained tensile loading (22 to 68% of ultimate strength) in three types of alkaline environments: NaOH, simulated pore-water solution, and embedded in concrete. Time to rupture or residual strength, as applicable, have been determined. Additionally, stress corrosion mechanisms were evaluated by various microstructural analyses. The results showed clearly that alkaline ions and moisture could penetrate or diffuse through the resin (or through cracks and voids) to the interphases and the fibers. For GFRP bars embedded in moist concrete under various sustained stress levels, three types of stress corrosion mechanisms have been identified: stress dominated, crack propagation dominated, and diffusion dominated.

Fibre reinforced polymer reinforcing bars for bridge decks

This paper describes the behaviour of two full-scale models of a portion of highway bridge slab reinforced with fibre reinforced polymer (FRP) reinforcement. The first slab was reinforced totally with carbon FRP (CFRP), and the second slab was reinforced with hybrid glass FRP (GFRP) and steel reinforcement. The models were tested under static loading up to failure using a concentrated load acting on each span of the continuous slab and the two cantilevers to simulate the effect of a truck wheel load. Load-deflection behaviour, crack patterns, strain distribution, and failure mode are reported. The measured values are compared to values calculated using nonlinear finite element analysis model. The accuracy of the nonlinear finite element analysis is demonstrated using independent test results conducted by others. The analytical model is used to examine the influence of various parameters, including the type of reinforcement, boundary conditions, and reinforcement ratio. Based on serviceability and ultimate capacity requirements, reinforcement ratios for using CFRP and GFRP reinforcement for typical bridge deck slabs are recommended.Key words: bridges, deflection, FRP, reinforcement, concrete, punching, slabs, shear, finite element model, strain.

Fibre reinforced polymer reinforcing bars for bridge decks

This paper describes the behaviour of two-scale models of a portion of highway bridges slab reinforced with fibre reinforced polymer (FRP) reinforcement. The first slab was reinforced totally with carbon FRP (CFRP), and the second slab was reinforced with hybrid glass FRP (GFRP) and steel reinforcement. The models were tested under static loading up to failure using a concentrated load acting on each span of the continuous slab and the two cantilevers to stimulate the effect of a truck wheel load. Load-deflection behaviour, crack patterns, strain distribution, and failure mode are reported. The measured values are compared to values calculated using nonlinear finite element analysis model. The accuracy of the nonlinear finite element analysis (FEA) is demonstrated using independent test results conducted by others. The analytical method is used to examine the influence of various parameters, including the type of reinforcement, boundary conditions, and reinforcement ratio. Based on serviceability and ultimate capacity requirements, reinforcement ratios for using CFRP and GFRP reinforcement for typical bridge deck slabs are recommended. (A)