RC beams strengthened by prestressed CFRP plate subjected to sustained loading and continuous wetting condition: Flexural behaviour

Abstract Time-dependent prestress loss of RC beams strengthened by a prestressed CFRP plate subjected to sustained loading and continuous wetting condition was investigated in a previous study, which showed obvious deflection and crack development after long-term service. Thus, the degradation of flexural behaviour is investigated in this paper for the concern of safety. Eleven RC beams were prepared with different prestressing levels (0, 20% fu and 40% fu), environmental conditions (dried and wet), and sustained loading levels (0, 94 kN and 120 kN). After a year of exposure, four-point bending tests were conducted. The results showed that the cracking load of the strengthened beams was decreased by up to 23.9% after suffering the sustained loading, while the reductions for both the yield load and the ultimate load were insignificant. In addition, moisture exposure can improve the cracking load and stiffness by 6.8% and 26.1% respectively, but the effect on the yield load and ultimate load was not obvious. Moreover, the ultimate utilization ratio of CFRP plate in the 20% prestressed specimens can be decreased by approximately 8.5% due to moisture exposure, whereas there was no change in the higher prestressed specimens. Consequently, the test results reveal that strengthening RC structures by using prestressed CFRP plate could be a reliable method in a moist environment. Finally, a model to predict the bearing capacity was proposed based on the test results and a satisfactory agreement was reached.