Bond mechanism and bond strength of GFRP bars to concrete: A review (original) (raw)
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Buildings
It is becoming accepted that glass-fibre-reinforced polymer (GFRP) is a credible and effective replacement for steel in reinforced concrete (RC) to meet structural requirements whilst addressing durability concerns posed by steel over the long term. A better understanding of the bond behaviour between GFRP and concrete is essential for reliably and efficiently designing concrete structures with reinforced GFRP bars. This paper presents a parametric study of the bond behaviour of GFRP bars to concrete where the effects of the length, diameter, concrete strength, concrete cover thickness and rebar surface morphology of GFRP bars were investigated via a series of pull-out tests. The test results indicate that the bond strength of GFRP bars is predominantly influenced by their surface morphology, embedment length and diameter. On the other hand, the effects of concrete strength and cover thickness appear to have a limited impact on the bond strengths of GFRP rebars to concrete. It is sh...
Effect of Bonding Area on Bond Stress Behavior of GFRP Bars in Concrete
Civil Engineering Journal, 2023
The application of Glass Fiber Reinforced Polymer (GFRP) bars is suitable for concrete structures that are susceptible to corrosion, owing to their corrosion-resistant characteristics. Therefore, it is feasible to reduce the concrete cover on reinforced concrete beams by utilizing GFRP bars. However, this can reduce the bonding strength between GFRP bars and concrete. Therefore, this study aims to investigate the bonding behavior between GFRP bars and concrete as a preliminary test for structural applications. The bond stress behavior between GFRP bars and concrete was analyzed by 18 pull-out tests. The test specimens comprised GFRP bars with three different variations, namely GFRP bars with concrete cover (GFRP-C), GFRP bars without concrete cover (GFRP-E), and GFRP bars with a complete wrapping of GFRP sheet (GFRP-C-Sheet). The bond stress-slip curve, bond strength, and failure pattern were utilized to analyze the effect of each variation. The research results indicate that the bonding stress between GFRP bars and concrete was strongly influenced by the concrete cover, where the bonding strength decreased by 65%. Nevertheless, the utilization of a complete wrapping GFR) sheet resulted in a 26.4% increase in bonding stress. The present study has identified three distinct modes of failure, including pull-out (GFRP-C), concrete crushing (GFRP-E), and GFRP sheet debonding (GFRP-C-Sheet).
This study presents the bond durability of glass fiber-reinforced polymer (GFRP) bars to fiber-reinforced concrete (FRC) exposed to saline solutions. Total 105 pullout specimens reinforced with steel and polyvinyl alcohol (PVA) fibers were prepared and immersed in the saline solutions at 50 and 70 ℃ under 30, 45, and 60 days, respectively. Their durability was quantified in terms of failure mode, adhesion stress as well as the bond strength. Test results revealed that the steel FRC samples exhibited the better bond durability than that of PVA FRC ones, when the same fiber volume fraction was used. Besides, the experimental data also aided to calibrate the analytical models, mBPE and CMR models, to better define the GFRP bond to FRC by considering the environmental effects. Also, a detailed procedure using Arrhenius law and time shift factor (TSF) methods was developed to predict the long-term bond degradation under different environmental temperatures and relative humidity. Degradation predictions over 75 years showed the FRC with 1.0% steel fiber volume fraction will have 96.76%, 92.88%, and 74.47% bond strength retention under dry, moist, and saturated environments in cold regions, respectively; while these values will decrease to 95.83%, 90.85%, and 67.19% in warm regions, respectively.
Materials, 2021
FRP bars and steel strands are widely used in civil engineering. In this study, three different types of high-strength reinforcement materials, carbon fiber reinforced polymer (CFRP) bar, glass fiber reinforced polymer (GFRP) bar, and steel strand, were investigated for their interfacial bond performance with concrete. A total of 90 sets of specimens were conducted to analyze the effects of various parameters such as the diameter of reinforcement, bond length, the grade of concrete and stirrup on the bond strength and residual bond strength. The results show that CFRP bars possess a higher bond strength retention rate than steel bars in the residual section. In addition, with the increase in bond length and diameter of the CFRP bar, the residual bond strength decreases, and the bond strength retention rate decreases. Furthermore, the bond strength retention rate of GFRP bars was found to be higher than that of CFRP bars. With the increase in grade of concrete, the bond strength and ...
Bond of GFRP Bars in Concrete: Experimental Study and Analytical Interpretation
Journal of Composites for Construction, 2006
The local bond mechanics of glass-fiber reinforced polymer ͑GFRP͒ bars in normal strength concrete was investigated through experimental testing and analytical modeling. The experimental program was comprised of 30 direct tension pullout specimens with short anchorages. A novel test setup, specially designed so as to minimize the spurious influence of testing conditions on measured bond properties was adopted in the study. Parameters considered were the bar roughness and diameter, the size effect expressed by the constant cover to bar diameter ratio, and the external confining pressure exerted over the anchorage length by transverse externally bonded FRP sheets. Results of the study were summarized in the form of local bond-slip curves, whereby performance limit states were quantified by the amount of loaded end slip and bond strength. An analytical model of the bond stress-slip response of a GFRP bar was derived from first principles and calibrated against the test data of the present investigation. Using the calibrated model, design values for bond and slip were estimated with reference to the code limit state model for bond.
This study presents an experimental investigation on the bond durability of GFRP bars in concrete when subjected to harsh environments. The pullout specimens having different concrete covers were designed based on a created database to demonstrate the generality of the current experimental program. The freeze-thaw (FT) cycles, alkaline-saline (AS) solution, and both coupled effects were used to simulate environmental conditions in cold regions. The durability performance in terms of the failure mode, weight loss, relative dynamic modulus of elasticity, durability factor, as well as the bond strength, were measured and investigated accordingly. The test results revealed that the concrete cover with three times of the bar diameter was not sufficient to resist the environmental agents when exposed to weathering, including FT cycles, in which all the pullout specimens failed by concrete splitting. The coupled scenario of FT cycles and AS solution was observed to be the worst case among all the environmental conditions. Moreover, the analytical models: modified Bertero-Eligehausen-Popov (mBPE) model and Cosenza-Manfredi-Realfonzo (CMR) model, were calibrated by considering the environmental influences based on the experimental data to better demonstrate the degradation of GFRP-concrete bond.
Experimental study of bond-slip of GFRP bars in concrete under sustained loads
Composites Part B: Engineering, 2015
The structural behaviour of reinforced concrete (RC) elements depends heavily on the bond performance between the concrete and the reinforcing material. Bond behaviour under short-term testing has been extensively analysed for steel reinforcement and many studies have been carried out for fibre reinforced polymer (FRP) reinforcement. However, there has only been limited investigation of the long-term effects of this interaction. Several factors can affect the long-term bond behaviour of these elements, the most important being bond length and the immediate and time-dependent properties of reinforcement and concrete (concrete grade, creep, shrinkage and stiffness). This time-dependent behaviour is likely to cause changes and redistributions in bond stresses not properly considered in the limited existing literature. In this experimental study, the bond performance of GFRP RC under sustained load is investigated through pull-out tests. A total of 12 pull-out specimens were tested for a period of between 90 and 130 days. Two concrete strengths (35 MPa and 50 MPa), two bond lengths (5 and 10 times the diameter of the reinforcing bar) and two reinforcing materials (glass fibre reinforced polymer (GFRP) and steel) were used. Experimental results regarding immediate and time-dependent slip are presented and analysed here. In addition, some specimens were instrumented, with internal strain gauges in the reinforcing bar to provide data on the reinforcement strain, thus allowing the distribution of bond stresses and their evolution during sustained loading to be also presented and analysed.
Beam Bond Tests of GFRP and Steel Reinforcement to Concrete
Archives of Civil Engineering, 2018
The paper presents research program of bond between glass fiber reinforced polymer bars and concrete in reference to the steel bars. Bond between the reinforcement and concrete is a crucial parameter governing a behaviour of reinforced concrete members and transferring of the internal forces from concrete to the reinforcement. The use of FRP bars as an equivalent reinforcement to steel in concrete structures has increased in recent years. The FRP bars are very different from steel, mainly due to much lower elasticity modulus and their anisotropic structure. Good performance of FRP reinforced concrete requires sufficient interfacial bond between bars and concrete. However, there are no specific standards referring to the surface preparation of these bars, that leads to variable bond behaviour of the composite reinforcement to the concrete. The objective of the study was to investigate the influence of variable parameters on the bond behaviour to concrete. The experimental program con...
Bond behavior of Concrete Beam Reinforcement by GFPR Bars
2014
In recent years, some attempts have been performed to extend general design rules reported in the codes for steel reinforced concrete to Fiber Reinforced Polymer (FRP) materials; this is the case of relationships adopted in the evaluation of the development length clearly derived by extension of the formulations used for steel bars. However, such relationships seem to be inappropriate for FRP reinforcing bars: in fact, experimental test results have shown that bond behavior of FRP bars is different from that observed in case of deformed steel ones. As a consequence, a new procedure for the evaluation of development length based on an analytical approach is needed in order to directly account for the actual bond-slip constitutive law as obtained by experimental tests on different types of FRP reinforcing bars. During this research contribution, an experimental study of GFRP bar concrete bond test is carried out and presented to investigate the bond stress–slip behavior for normal and...