A comparative study between beam and pull-out tests on bond behavior of ribbed GFRP bar in concrete conforming to RILEM standards

Abstract

Different researchers have perused the bond behavior of concrete and rebar employing the beam or pull-out tests; nonetheless, results were not precisely comparable owing to different test methods. Hence, a comprehensive research study is necessary in this field. In contrast to steel bars, there is no standard approach for FRP bar surface characterization. Moreover, previous studies reveal that FRP bars with different surfaces exhibit various bonding mechanisms. Therefore, determining the bond characteristics of various FRP bars with different surfaces is essential for their application in structures. A recent study experimentally compared beam and pull-out test results for ribbed GFRP bars, with and without anchors, conforming to RILEM standards. The variables included two different test methods (beam test and pull-out test), steel anchor (presence and absence of anchor), and concrete compressive strength level (25 and 45 MPa). It was found that the maximum transferred stress in the ribbed GFRP bar from the beam test was higher than in the pull-out test for all specimens. On average, they are about 24% higher than the pull-out test values. In the pull-out test, the bar slip threshold stress and the initial slope of the stress–slip graph were higher than in the beam test for all specimens. A comparative analysis was conducted on studies using beam and pull-out test results without anchors. The impact of anchors on reducing development length was evaluated by comparing the existing length with the straight and hook development lengths specified by ACI 440.1R-15. The difference suggests a conservative approach in the code.