Development and Validation of a Testing Procedure for Determining Tensile Strength of Bent GFRP Reinforcing Bars

The current study aims to develop and standardize laboratory and on-site testing procedures to determine the tensile strength of bent glass fiber-reinforced polymer (GFRP) bars for quality control and quality assurance purposes. The proposed method involves embedding L-shaped bent GFRP bars in concrete blocks and subjecting the bars to tensile pullout forces. The test results were verified by comparing the strength of 25 bent GFRP bars produced by five different manufacturers to that of 25 other samples tested according to current standards. In addition, another 110 specimens were also tested to investigate the influence of all the parameters on the results yielded by the testing protocol, including bar size, concrete compressive strength, tail length, concrete block and cover dimensions, loading rate, confinement with steel reinforcement, and GFRP shape. The comparison between the L-shaped testing procedure and that following the standard specification requirements resulted in a 4%–20% difference in tensile strength, with a lower coefficient of variations obtained from the L-shaped for all the tested bars. The results of the parametric study revealed that regardless of the bar type, a 300 × 300 × 600-mm concrete block without reinforcement with an anchor length equivalent to 12 times the bar diameter and a loading rate to induce failure within 1–10 min is suitable for any shape of GFRP bar up to No. 6 (20 mm). A fast-setting concrete that can attain a compressive strength of 48 MPa can be used to promptly determine the tensile strength of the bent bars on-site or in testing laboratories for qualification purposes. The testing procedure developed in the current study has been adopted and included in the new edition of Canadian’s specification for fiber-reinforced polymers.