Flexural performance of CFRP grid-reinforced ultra-high performance concrete (UHPC) plates under cyclic incremental loading

Carbon fiber-reinforced polymer (CFRP) grid-reinforced ultra-high performance concrete (UHPC) thin plates offer significant potential for offshore applications. To enhance their robustness for future applications, this study investigates their flexural behavior under cyclic incremental loading, simulating the storm progression conditions. The experimental program evaluates the effects of short fiber types (steel vs. polyethylene (PE)), steel fiber volume fractions (1% vs. 2%), and CFRP grid reinforcement ratios (0.4% vs. 0.6%). All specimens failed by CFRP grid rupture, with some exhibiting interfacial cracks due to untreated CFRP grid surfaces. Monotonic load-deflection curves exhibited bi-linear behavior, whereas cyclic envelope curves deviated from the monotonic responses in the second ascending branch. The load at the deviation point (50–80% of ultimate capacity, corresponding to CFRP strains of 3000–4000 µε) is proposed as the design capacity. PE fibers and higher CFRP ratios improved cumulative damage resistance and delayed deviation, whereas increased steel fiber content only enhanced the initial cracking load. Existing models underestimated cracking loads for steel fiber-reinforced specimens. After calibration, CSA S806–12 yielded the most accurate deflections at the deviation points. However, all models overestimated the reinforcement effect of CFRP grids, highlighting the need for future research to quantify synergistic contributions of short fibers and CFRP grids.