Bond performance of GFRP bars with mechanical steel anchors using RILEM beam bond tests: Experimental and theoretical study

Abstract

In general, there is a scarcity of practical information currently accessible regarding the bonding characteristics of FRP bars within concrete, and existing guidelines for the design and construction of concrete structures reinforced with FRP, such as ACI 440.1R-15, do not provide equations for different FRP bars, especially when mechanical anchors are used along the bar length. Moreover, the currently available data are from pull-out tests, the reliability of which has been questioned due to unrealistic stress conditions. This paper examines the bond behavior of GFRP bars equipped with mechanical steel anchors through a series of tests on beam specimens. Variables include the diameter of GFRP bars and the compressive strength of concrete as well as the length and thickness of the anchors. The main output parameters under consideration are the maximum transferred stress in the bar, the initial slope of the transferred stress-slip graph, and stress at the initiation of the slip. All investigated steel anchors with different lengths and thicknesses were observed to improve the bond behavior. The rise in the maximum transferred stress due to using anchors ranged between 15% and 60%, depending on the compressive strength of the concrete, GFRP bar diameter, and length and thickness of the steel anchor. The stress at the initiation of the bar slip and the initial bond stiffness were also noticeably greater in specimens containing the anchor compared to those without the anchor. Increasing the anchor length was more effective than the anchor thickness in improving the bond behavior. Based on the experimental results, equations were proposed to predict the values of stress at the first peak of the transferred stress-slip graphs and maximum transferred stress in the bar as a function of the anchor length, anchor diameter, compressive strength of concrete, and diameter of the GFRP bar, which show satisfactory performance in comparison with experimental data.