Factors affecting the time-dependent behaviour of GFRP prestressed concrete beams

Abstract The time-dependent behaviour of concrete beams prestressed with Glass Fibre Reinforced Polymer (GFRP) bars is not fully investigated in the literature due to the fact that the use of such bars was limited in the prestressing applications due to their high relaxation and susceptibility to creep rupture. Recent material developments have led to GFRP bars that are more suitable for prestressing applications. This paper presents the results of 12 beams that were tested as part of larger test program aiming to investigate the effect of different factors on the long-term behaviour of GFRP prestressed concrete beams. The parameters investigated were the prestressing level (25% and 40%), concrete strength (40 MPa, and 80 MPa), the sustained load level (35%, 60%, and 80%), and the GFRP bar diameter (12 M and 16 M). The experimental results showed that the GFRP bars used in this study had no measurable relaxation over time up to 277 h compared to those reported in the recent literature by Fornůsek et al. [8] where the relaxation of the GFRP bars was 3.3% after 24 h, and 7.3% after 28 days. The results also showed that the concrete strength had no significant effect on the long-term performance of GFRP prestressed concrete beams at the 35% and the 60% sustained load levels, while the effect was more pronounced at the 80% sustained load level.