Research On The Interfacial Performance Of Metallic Structures Strengthened With Fibre Reinforced Polymers

The research field of structures strengthening is very important in civil engineering. Structures strengthening with fibre reinforced polymers (FRP) is a new strengthening technique, which is a research issue in the strengthening field. Currently FRP is used extensively in the concrete structures strengthening and retrofit. In contrast to the traditional retrofit method for repairing damaged metallic members, the use of FRP composites emerges as an alternative strengthening method and there are several advantages, such as without stress concentrations, no residual stress, easy to construct and low maintenance cost. However, only very limited research has been conducted on the application of FRP composites to metallic members. Therefore in this paper it was focused on the basic performance of metallic structures strengthened with FRP by systematic theoretical analysis and a series of experimental studies.Based on the summary of theory analysis and test research on metallic structures strengthened with FRP both home and abroad. The interfacial stress between FRP and metallic plates in axial tension was derived and the effective bond length and effective stiffness were discussed. The interfacial shear stress and peel stress between the FRP and the surface of tension flange were analyzed when the FRP was bonded to the tension flange of the bending members. Based on the assumption of axis-symmetrical plane strain, the calculating formulas for the hoop stress were derived for the metallic pipelines under internal pressure strengthened by circumferential winding FRP. The use of prestressed FRP for metallic pipelines repair was proposed. The elastic buckling load of axially loaded compression steel pipes strengthened with FRP was presented in this paper by using energy approach.The key problems of metallic structures repaired with FRP were discussed in details, such as bonding mechanism between FRP and metal, the selection methodology of repair materials, surface preparation of FRP and metal, load transfer between metallic members and FRP, the bond durability and galvanic corrosion when applying CFRPcomposites to metal.The suitable adhesives were selected for bonding carbon fibre sheets and CFRP plates according to a series of test results. The bond strength and bond durability between FRP and metal were tested, and the durability of commonly used carbon fibre sheets was also tested. Tensile tests were conducted on ten steel plates repaired with CFRP sheets and the bond stress distributions were derived from tests.The "3D solid-spring-shell" FEM model was proposed in the paper, and the key techniques were discussed when the general purpose software ANSYS? was adopted to analyze the cracked metallic plates and bending steel members strengthened with FRP. The metallic plates with hole and metallic pipeline repaired with FRP were also analyzed with ANSYS?. The influencing factors of repair effectiveness were discussed.The design formulas for locally damaged members in axial tension retrofitted with FRP, bending members strengthened with FRP and metallic pipelines under internal pressure repaired by circumferential winding FRP were suggested in the paper. Several metallic structures repaired with FRP were introduced at home and abroad.The conclusions and suggestions in the paper will play very important reference values for the development of metallic structures rehabilitation with FRP.