International Concrete Abstracts Portal

This study explores technological advancements enabling the utilization of GFRP bars in concrete structures, particularly in coastal areas. However, GFRP bars often encounter reduced bend strength at specific bend locations, which may pose a challenge in their practical application. Various properties such as the strength of bent GFRP bars are crucial for quality assurance, yet existing testing methods stated in ASTM D7914M-21 and ACI 440.3R-15 have limitations when applied to different GFRP bent shapes. Furthermore, those methods require special precautions to ensure symmetry and avoid eccentricities in specimens. To address these challenges, CSA S807:19 introduced a simpler standardized testing procedure that involves embedding a single L-shaped GFRP stirrup in a concrete block. However, the specified large block size in CSA S807:19 Annex E may pose difficulties for both laboratory and on-site quality control tests. Therefore, CSA S807:19 Annex E (Clause 7.1.2b) permits the use of a customized block size, as long as it meets the bend strength of the FRP bars without causing concrete splitting. To date, very few prior research has explored the use of custom block sizes. Therefore, this study aims to thoroughly investigate the strength of bent FRP bars with custom block sizes and without block confinement. Such an investigation serves to highlight the user-friendliness and efficiency of the CSA S807:19 Annex E method. The study recommends two block sizes: 200x400x300 mm (7.87x15.75x11.81 in) for bars <16 mm (0.63 in) diameter and 200x200x300 mm (7.87x7.87x11.81 in) for bars <12 mm (0.39 in). Additionally, the study cautions against using confinement reinforcement, especially with smaller blocks, as it could interfere with the embedded bent FRP bar. Furthermore, the study suggests incorporating additional tail length to mitigate the debonding effects resulting from fixing the strain gauges to the bent portion of the embedded FRP bar. By exploring these modifications, the study seeks to enhance the effectiveness of the testing procedure and expand its practical application for both laboratory and on-site quality assurance. The findings hold implications for the reliable testing of GFRP bars' strength, advancing their use as reinforcement in concrete structures.

The compressive strength of glass fiber-reinforced polymer (GFRP) rebars is investigated and a new test method is proposed. The program consists of three test series. In Test Series 1, the strengths and weaknesses of the test methodology outlined in ASTM D695-15 were explored. Specimens with varying length-to-diameter ratios were prepared and tested. Premature failure was observed, and longitudinal splitting was the dominant failure mode. Test Series 2 aimed to prevent failure initiation at the ends by using steel clamps. The clamps confined the specimen ends and prevented failure propagation. The compressive strengths showed an average of around 70% the tensile strength. In Test Series 3, an advanced fixture was designed to overcome the limitations of the previous series by including clamping parts and vertical steel bars. Three different loading speeds were employed, and an average compressive strength of 75% of the tensile strength was found. The tests were followed by a statistical analysis indicating a significant difference between the results of the three test methods. The proposed test method offers a practical and reusable approach for evaluating the compressive strength of GFRP rebars. However, further analysis is recommended for a more comprehensive understanding of the compressive behavior of these rebars.

Most of the research related to interface shear transfer in concrete elements has utilized steel bars as reinforcement, while GFRP reinforcement has received little attention experimentally and analytically. For this reason, only a few design specifications include provisions for the calculation of the interface shear transfer when using GFRP. In this project, an experimental campaign is being conducted to determine the contribution of GFRP bars to the mechanism of shear transfer by using push-off specimens. The literature review and the test methodology are reported in this paper. The obtained results indicate that the use of GFRP reinforcement significantly enhances the interface shear strength, resulting in a capacity that exceeds those of the specimens without reinforcement. When the GFRP-reinforced specimen reaches the first crack at a load similar to that of the unreinforced specimens, it continues carrying load until it reaches a peak, thus indicating that the reinforcement is providing both dowel action and clamping force prior the shear failure. Additionally, once the peak strength is reached, the use of GFRP reinforcement allows the specimen to deform in a pseudo-ductile fashion thus preventing sudden failure.

This paper presents an experimental study that investigated the physical and mechanical properties of the helical wrap glass fiber-reinforced polymer (GFRP) bars. The physical tests are conducted to check the feasibility and quality of the production process through the cross-sectional area and evaluation of the fiber content, moisture absorption, and glass transition temperature of the specimens. While the mechanical tests in this study included testing of the GFRP specimens to determine their tensile properties, transverse shear, and bond strength. Four bar sizes (#3, #4, #5, and #6), representing the range of GFRP reinforcing bars used in practice as longitudinal reinforcement in concrete members subjected to bending, are selected in this investigation. The GFRP bars had a helical wrap surface. The tensile failure of the GFRP bars started with rupture of glass fibers followed by interlaminar delamination and bar crushing. The bond strength of the GFRP bars satisfied the limits in ASTM D7957/D7957M. The test results reveal that the helical wrap GFRP bars had physical and mechanical properties within the standard limits.

The near surface-mounted (NSM) technique utilizing fibre-reinforced polymer (FRP) reinforcements has gained significant popularity in enhancing the shear resistance of reinforced concrete (RC) beams. Various models have been proposed to predict the shear contribution of NSM FRP reinforcement in RC beams. In this study, the performance of five well-established models, namely those proposed by De Lorenzis and Nanni, Rizzo and De Lorenzis, Dias and Barros, Bianco et al., and Mofidi et al., is assessed. A comprehensive database comprising 137 beams from published works is compiled for this assessment. The findings reveal that the model proposed by Bianco et al. exhibits superior predictive performance but tends to produce extremely conservative predictions. On the other hand, the model proposed by Dias and Barros performs well for beams shear strengthened with FRP laminates, although it is not specifically calibrated for specimens shear strengthened with FRP rods. Notably, the latter model results within an appropriate safety domain, avoiding extreme conservatism. Further research is warranted to develop a comprehensive model with enhanced predictive accuracy.