Enhancement of the bond behaviour between sand coated GFRP bar and normal concrete using innovative composite anchor heads (original) (raw)
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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...
Bond mechanism and bond strength of GFRP bars to concrete: A review
Glass fiber-reinforced polymer (GFRP) reinforcements are taken as an alternative solution for the deterioration of civil infrastructures. GFRP bars have received increasing attention due to low cost compared to carbon fiber-reinforced polymer (CFRP) bars. Bond characteristic of GFRP bars in concrete is the most critical parameter for implementation of the material to the corrosion-free concrete structures. Unlike steel reinforcement, GFRP materials behave anisotropic, non-homogeneous and linear elastic properties, which may result in different force transfer mechanism between reinforcement and concrete. With the purpose of covering the most valuable contributions regarding bond mechanism in the past work, a comprehensive review focusing on the failure mode and bond strength is carried out in this paper. A database consisted of 682 pullout-test specimens was created to observe the factors affecting bond behavior. Basic relationship between bond strength/slip and factors was analyzed accordingly. In addition , the development of bond degradation under environmental conditions, such as freezing-thawing cycling, wet-dry cycling, alkaline solutions and high temperature was presented thereafter. These environmental influences need to be further investigated.
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 ...
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).
Use of sand coating to improve bonding between GFRP bars and concrete
Glass fiber-reinforced polymer bars are currently used to reinforce concrete in an attempt to overcome the corrosion issue encountered with ordinary steel. Different types of surface treatment were applied to the smooth rods in order to enhance bonding with concrete. Experimental results show that using bars coated with coarse sand notably improve the bond strength. The influence of granulometry sand, rebar diameter, length embedded, and concrete strength are analyzed. Rebars coated with finer sand lead to a stronger chemical adhesion with concrete. However, the effect of friction and interlocking forces produced by coarse sand prevails over the chemical adhesion in the pull-out test.
Bond Behavior of Ribbed-Surface, Headed-End, GFRP Bars Embedded in High-Strength Concrete
Glass Fiber Reinforced Polymer (GFRP) bars as a proper substitute for traditional reinforcing steel bars not only eliminate the durability problem due to corrosion of reinforcing steel, but also provide remarkably enhanced capacity due to their high tensile strength compared to that of the steel bars. This paper presents the experimental findings of pullout tests conducted on GFRP bars embedded into highstrength concrete blocks covering different parameters. The studied parameters were bar diameter size, embedment length, bar end condition (headed), and concrete cover to bar. Based on the results of the parametric study, the bond stress was shown to be inversely proportional to the embedment length and bar diameter as expected. In addition, the smaller concrete cover appeared to have significant effect on bond stress, leading to side blow-out failure rather than bar pullout or concrete splitting in the case of headed-end GFRP bars. In addition, the GFRP bar with headed-end showed significant increase in pullout strength compared to that for the straight-end bars. Finally, an empirical expression was proposed to calculate the development length of GFRP bars with headed-end cast in high-strength concrete.
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.
Investigation of bond in concrete member with fibre reinforced polymer (FRP) bars
Construction and Building Materials, 1998
Bond strength of fibre reinforced polymer FRP rebars was experimentally investigated in this study and compared to that of steel rebars. A total of 64 concrete beams reinforced with two types of FRP rebars, respectively, were tested. Four nominal diameters of FRP and steel rebars, namely, 12.7, 15.9, 19.1 and 25.4 mm and three embedment lengths, six, 10 and 16 times the rebar diameter were used. Moreover, three concrete depths of 200, 600 and 1000 mm were investigated in the 18 pullout specimens. Results of the tests indicated that the applied tensile load approached the tensile strength of rebars as the embedment length increased and the GFRP rebars showed lower bond strength values compared to steel rebars. The average maximum bond strength of the FRP rebars varied from 5.1 to 12.3 MPa depending on the diameter and the embedment length. The GFRP rebars showed lower bond strength values compared to steel rebars. A modification factor of 1.30 is recommended for computing the development length, to account for the top bar effect. A new model is proposed for the ascending branch of the bond᎐slip law.
Bond characteristics of glass-fibre-reinforced polymer bars in high-strength concrete
Journal of Structures and Buildings, 2020
Fibre-reinforced polymer bars are rapidly becoming an approved alternative to conventional reinforcing steel bars, especially for severely exposed structures such as bridges. This paper reports on an experimental study on the bond characteristics of both sand-coated and ribbed-surface glass-fibre-reinforced polymer bars embedded in high-strength concrete (HSC). A total of 145 pull-out tests were conducted to examine the effect of varying parameters on the bond characteristics, namely embedment length, bar diameter, surface treatment and concrete cover. In addition, 45 pullout tests were conducted to investigate the effect of providing headed-end anchorage for the sand-coated bars. The experimental results showed that the sand-coated bars exhibited better bond strength than the ribbed-surface bars, which entailed lower development lengths. Thus, based on the experimental results, expressions for the development length of both sand-coated and ribbed-surface bars embedded in HSC were developed and compared against the results of formulae in available design standards. The comparison revealed that ACI 440-1R-06 produced lower conservative results than CAN/CSA S806-12.