Influence of sustained stress on the durability of glass FRP reinforcing bars

Glass fiber reinforced polymer (GFRP) bars can be employed as an alternative to steel bars for internal reinforcement of concrete elements. Although GFRP bars have been used to reinforce concrete for the last two decades, their long-term behavior is still an open issue. The tensile strength of bars subjected to aggressive exposure conditions has been investigated by different authors. However, clear and reliable indications on the bar residual strength are still lacking. Furthermore, the effect of sustained stress on the bar tensile strength is not completely clear and severe limitations on the stress level attained by the bar are imposed by available design guidelines. In this paper, the effect of sustained stress on GFRP bars exposed to different environmental conditions, namely air, alkaline environments, deionized water, and salt solutions, is studied by analyzing a database comprising 127 GFRP bar tensile tests collected from the literature. The results are analyzed and discussed to investigate the effect of sustained stress on the tensile strength of GFRP bars and to calibrate characteristic and design values for tensile strength long-term reduction factors.