Effect of Reinforcement Ratios on Time-Dependent Deflection of Hybrid GFRP/Steel Reinforced Concrete Beams

The paper experimentally investigated the influence of steel reinforcement ratio on time-dependent deflections in hybrid GFRP/steel RC beams. A total of three hybrid RC beams and one reference GFRP RC beam were cast and tested under sustained load for a period of 180 days in varying environmental conditions. The tested beams differed in longitudinal steel reinforcement, resulting in a range of steel reinforcement ratios from 0% to 1.08%. The results revealed the impact of the steel reinforcement ratio on long-term deflections of hybrid GFRP/steel RC beams.

The experimental time-dependent deflections of hybrid GFRP/steel RC beams were compared to theoretical values derived from design equations for FRP RC structures found in ACI 440.1R-15. The outcome showed that these design standards overestimated the long-term deflection of hybrid RC beams. Also, a design method based on ACI 440.1R-15 with experimentally based adjusted time-dependent factors was presented for hybrid GFRP/steel RC beams. The predicted values were in good agreement with the experimental values.