Efficiency of anchorage systems for RC beams strengthened in flexure using basalt fiber reinforced polymers

Abstract

Abstract Recently, Basalt Fiber Reinforced Polymer (BFRP) composites emerged as a new FRP type, in addition to the commonly used glass, carbon, and aramid. The common premature debonding failure of externally bonded fiber-reinforced polymer (FRP) composites, when applied to reinforced concrete (RC) structures, has made searching for efficient anchorage systems an inevitable and challenging issue. Many studies through experimental testing and numerical modeling verified that anchorages applied to FRP systems not only enhance the member’s ductility and strength but also prevent the typical debonding of the FRP at a low strain level compared to the rupture strain. Research is needed, however, to understand the efficiency of different anchorage systems when applied to relatively high-strain BFRP sheets to strengthen concrete members. This research presents an experimental study aimed at investigating the efficiency of using anchorage systems in enhancing the flexural behavior of concrete beams strengthened with BFRP sheets. A total of eight concrete beams measuring 3100 mm length, 150 mm width and 350 mm depth were constructed and tested up to failure. The test parameters were the number of BFRP layers, the development length, and anchorage systems. The beam specimens were designed in accordance with ACI 440.2R-17 and tested under four-point bending over a clear span of 2800 mm until failure. The results showed that BFRP strengthening enhanced the flexural capacity of beams by up to 33% compared to the control specimen. However, increasing the number of BFRP layers without proper anchorage did not significantly improve strength due to premature debonding. The use of U-wrap anchorage successfully changed the failure mode from debonding to BFRP rupture, leading to more efficient utilization of the composite material, with anchorage effectiveness factor k fab = 2.36, while spike anchors with anchor dowels 150 mm inside the concrete have an anchorage effectiveness factor k fab = 1.97 which showed limited effectiveness depending on embedment depth. In addition, strengthened beams exhibited a reduction in ductility of approximately 28% compared to the control beam. The findings highlight the critical role of anchorage systems in achieving optimal performance of BFRP-strengthened RC beams.