عنوان مقاله [English]
The strengthening of offshore platforms and structures placed under different environmental conditions are important cases in civil engineering. The use of FRP (Fiber Reinforced Polymer) to strengthen existing steel structures and offshore platforms has become an effective technique. Because the elastic modulus of FRP is close to, or higher than, steel, it has proven to be increasingly favorable for the repair and rehabilitation of the mentioned structures. Despite the evident advantages of FRPs over traditional materials, the greatest impediment to worldwide utilization is represented by the limited knowledge of composite behavior of systems under extreme conditions, such as freeze-thaw or wet-dry. Exposure to extreme environmental conditions will reduce bonding strength and also the durability between CFRP and steel.In some countries, due to seasonal changes, multiple cycles of freezing and thawing effect the service life of offshore structures. This paper discusses the mechanical performance of the environmental durability of the bond of FRP to steel surfaces. In order to investigate this aspect, two series of specimens with different numbers of plies of FRP have been prepared for two conditions; 60, 120 wet and dry cycles for the first specimens and 170, 210 freeze-thaw cycles for the second series.The experimental results present bond strength and stiffness, and the failure mode and deformation of strengthened steel elements. It was shown that when specimens were exposed to freeze-thaw conditions, the lower load was carried and, so, this condition is more extreme for the service life of these types of structure. The experimental results also indicate that the ply number on FRP has a low influence on the mechanical properties of the composite system. It is also observed that the failure mode is when the adhesive interface and piling of FRP from the surface occurred.