The requirements for using GFRP bars are growing as several researchers have shown the functionality of bars in concrete columns. The demand to characterize the mechanical properties of GFRP bars is therefore rising, although there is no standardized test method for evaluating the compressive behavior of these bars. This experimental study presents the determination of the mechanical properties of GFRP composite bars in compression, namely the stressstrain curves, compressive strength, ultimate crushing strain, and modulus of elasticity. The compressive properties of these bars were calculated following ASTM D695-10 (Compression Test) with some modifications. A total of 27 specimens were tested for the proposed test procedure. The diameter of the GFRP tendon used in the test was 10, 12, and 14 mm, and the length to bar diameter ratio Le/db (4, 8, and 16) was investigated for the compressive strength of the bars. These two parameters were used to establish the relationship between the length to diameter ratio and strength. Besides, two steel caps with a length of 50 mm each were installed to both ends of each specimen to avoid premature failure. It was observed that the test method enables to successfully evaluate the compressive characteristics of the GFRP bars. Experimental discussions were performed based on the test results from stress-strain curves, bar graphs, and scatter curves. The results indicate the increase in length to diameter ratio decrease the buckling stress and the compressive to tensile strength ratio for Le/db ratio of 16 specimens in buckling failure mode. The failure mode transformed from crushing to buckling and a combination of crushing and buckling between the two different failures modes with an improvement in the Le/db ratio. It shows that there was no yield section on the test specimens during the entire test loading process. The compressive GFRP bars present typical brittle failure.
Glass Fiber Reinforced Polymer (GFRP) rebars have been widely used to solve the corrosion problem of steel bars in concrete structures. It has been produced as a lightweight and corrosion-resistant than steel reinforcement in many structural applications. They are regarded as a promising substitute for steel bars in concrete infrastructures. It is necessary to test GFRP bars to fully understand their material properties to ensure the safe and efficient use of the material. In this study, five specimens of each type of GFRP bars with a diameter of 6, 8, 10, 12, and 14 mm were tested under tension. Therefore, a total of 25 samples were examined from the same manufacturer. According to ASTM's recommendations (D7205/D7205M-06) for tensile tests of GFRP bars, the diameter and thickness of the steel pipes for both ends were considered in the preparation of the test specimens to keep the GFRP bars consistent and aligned throughout the experiment. The experimental test results included the stress-strain curves, tensile strength, ultimate strain, and modulus of elasticity. The study showed an accurate result that indicated the tensile strength of the GFRP bars can be expressed by a linear distribution. For a bar diameter of 10mm, the length to diameter ratio Le/db=8 showed a maximum tensile to compressive strength ratio. In the failure results of the test, there were two-mode failures of GFRP bars: fracture failure and pull-out failure of GFRP bars. Most of the specimens had GFRP bar fracture failures, only two specimens (GBT1-10-2 and GBT1-10-3) were damaged due to the pull-off of the GFRP bars which was not a typical failure mode.
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