Experimental Study on Mechanical Behaviour of Glass Fiber Reinforced Polymer Bars under Compression

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 stress-strain 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 L e /d b (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 L e /d b 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 L e /d b 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.