STUDY ON FLEXURAL PERFORMANCE AND LIMIT REINFORCEMENT RATIO OF CFRP-STEEL COMPOSITE BAR REINFORCED CORAL SEA-SAND AGGREGATE SEAWATER CONCRETE BEAMS

To investigate the flexural performance of CFRP-steel composite bar (C-FSCB) reinforced coral sea-sand aggregate seawater concrete (CSSC) beams and to verify the accuracy of the calculated formula for the limit reinforcement ratio based on an ideal failure mode, a total of 22 beam specimens were designed and fabricated for four-point static bending tests. The main variables considered were longitudinal reinforcement ratio, concrete strength, shear span ratio, reinforcement type, and concrete type. During the experiments, the failure modes, moment-deflection curves, crack widths, and strain development patterns of the beam specimens were recorded. The investigation results showed that the failure modes of C-FSCB reinforced CSSC beams under different reinforcement ratios included C-FSCB rupture control, concrete crushing control after C-FSCB yielding, and concrete crushing control. One calculated formula for the limit reinforcement ratio established in this study could control the failure mode of C-FSCB reinforced CSSC beams. Within the appropriate reinforcement ratio range, as the reinforcement ratio increased, the peak moment and flexural stiffness of the beam specimens gradually increased, while the ductility coefficient first increased and then decreased. Compared to reinforced CSSC beams, the C-FSCB reinforced CSSC beams exhibited a 14% increase in peak moment, a 27% decrease in ductility coefficient, a 7% decrease in flexural stiffness K₁, and a 52% increase in flexural stiffness K₂ at the same reinforcement ratio. The maximum crack width of the reinforced CSSC beams was significantly smaller than that of the C-FSCB reinforced CSSC beams. Considering the utilization ratio of structural strength, the recommended maximum crack width limit for normal serviceability of C-FSCB reinforced CSSC beams was determined to be 0.5 mm. Based on the stress analysis of the section during the failure of the balanced-reinforced beams, one calculation formula for the ultimate flexural capacity of C-FSCB reinforced CSSC beams was established, which exhibits excellent calculation accuracy.