عنوان مقاله [English]
Recent studies have indicated that moisture environments can weaken the bond between fiber-reinforced polymer (FRP) jackets, epoxy adhesive, and concrete. Nearly in all of past researches, the specimens have been examined under loading and moisture conditions only after strengthening the structural elements, while one of the important applications of FRP jackets is in restoration and reconstruction of the structures subjected to loading and moisture condition. Additionally, there is a high probability that the structural elements are exposed to surface moisture before strengthening in these conditions. The aim of this study is to investigate the flexural behavior of beams reinforced by FRP jackets similar to the real conditions under which the structure is subjected to two essential factors, including moisture and preloading. For this purpose, 20 specimens of concrete beams with dimensions of $150\times200\times1150$ mm were constructed that falls into two groups with two different arrangements
of tensile reinforcement. Other variables were the amount of surface moisture and the level of preloading of specimens. Before strengthening, the specimens were subjected to preloading and moisture conditions, and then ruptured under flexural tests. The results obtained from the tests were the load-midspan displacement curves of the specimen. The results indicated that the flexural strength of the beam with CFRP jackets without cracks and surface moisture increased up to the 20\% of its ultimate strength, while, in the beams with premier cracks and surface moisture, only 13\% and 9\% increases in flexural strength were reported, respectively. Furthermore, in beams with premier cracks and surface moisture, an increase of 13\% in ultimate strength was simultaneously seen. The results also suggest that using reinforcing bars with a higher diameter and lower number in comparison to using a lower diameter and higher number of bars could decrease the efficiency of FRP jackets and cause brittle failure in the entire mentioned conditions.