Effect of material properties on long-term deflections of GFRP reinforced concrete beams

The influence of compressive concrete strength and reinforcement ratio on long-term deflections in GFRP reinforced concrete beams is analysed in this paper. A total of 20 beams, cast with two different concrete strengths (30 and 50 MPa), and different reinforcement amounts of GFRP and steel, were tested under short-term loading and then subjected to different levels of sustained loading for a period of between 250 and 700 days. The results obtained revealed the influence of the concrete and reinforcement properties on long-term deflections. Thus, the higher the reinforcement ratio and the lower the compressive strength were, the higher the total-to-instantaneous deflection ratio was. asured long-term deflections were compared to those calculated using available design equations for FRP RC structures, such as those from ACI 440.1R-06 and CSA-S806-02, as well as being compared to the CEB-FIP procedure. In addition, the experimental data were evaluated with a methodology proposed by the authors, based on multiplicative coefficients, obtained from a rational simplification of the Effective Modulus Method. Long-term deflections obtained with CEB-FIP and the proposed methodology were in good agreement with the experimental values. However, some differences were found when ACI 440.1R-06 or CSA-S806-02 procedures were applied.