Creep behavior and prediction modeling of prestretched carbon/glass hybrid FRP bars with different hybrid ratios

Prestretched carbon/glass hybrid fiber-reinforced polymer (C/G-HFRP) bars offer a corrosion-resistant reinforcement for durable and prestressed concrete structures, but their creep response under prestretching and sustained load remains unclear. This study first used 120 h creep tests, residual tensile tests, and SEM observations to determine a suitable prestretching condition, and then performed 1000 h sustained-load creep tests on GFRP and C/G-HFRP bars with different hybrid ratios and stress levels. Prestretching at 0.30 f f for 3 h reduced the subsequent 120 h creep ratio by up to 72%, while no marked loss of residual tensile properties was observed. After 1000 h, runout specimens retained 96.0%-97.8% of their tensile strength. Under the same absolute sustained stress of 487.3 MPa (0.35 f f-1:4 ), prestretched C/G-HFRP (1:4) bars showed a 36% lower creep strain increment than prestretched GFRP bars. Among the tested hybrid bars, higher-carbon groups exhibited lower creep deformation under the equal-absolute-stress condition; however, the corresponding normalized stress levels differed. Creep rupture occurred at 0.85–0.95 f f , with rupture time decreasing sharply as stress level increased. A semi-empirical homogenized formulation considering composition, sustained stress, and prestretching reproduced the measured creep responses (with in-sample R 2 =0.9798–0.9954); for four groups, 1000 h absolute relative fitting deviations were 2.93%-7.95%, while the 120 h group was 4.44%.