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

This paper presents an experimental study on the effect of the steel reinforcement ratio on time-dependent deflections in hybrid glass fiber-reinforced polymer (GFRP)/steel reinforced concrete (RC) beams (HGSRC beam). Three HGSRC 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 longitudinal steel reinforcement ratio was varied to achieve a range from 0 to 1.08%. The results revealed that the steel reinforcement ratio had a remarkable impact on the time-dependent deflections of HGSRC beams. Moreover, the experimental time-dependent deflections of HGSRC beams were compared with theoretical values derived from design equations for fiber-reinforced polymer RC structures found in ACI 440.1R-15. The outcome showed that this design standard overestimated the long-term deflection of HGSRC beams. Also, a design method based on ACI 440.1R-15 with experimentally based adjusted time-dependent factors was presented for HGSRC beams. The predicted deflection values using the proposed method were found to be highly consistent with the experimental ones.