Application Study On Frp Composite Materials In Marine Steel Structure Repairing And Reinforcing

Nowadays, infrastructures in application usually contains a large number of metal structures. These structures under the combined action of long-term working loads and particular environmental effects are prone to produce many sorts of damages and need to be repaired or reinforced. The weld reinforcing method, which is commonly used, is to weld steel plates or other materials on the structures to be reinforced. This reinforcing method has been maturely developed and widely applied. However there also exist some problems, such as local tissue embrittlement and high residual stress after welding. Besides these, welding quality is quite dependent on the environment and the operators. The composite reinforcing method is a kind of new method and has attracted more and more attentions in recent years, with the advantages of composite materials, such as high strength, high elastic modulus, corrosion resistance, durability and fatigue resistance, etc.Currently composite reinforcing method has been applied to a certain extent in the field of civil engineering and aerospace, while the application and study in the field of ship and marine engineering is still inadequate. The Systematic reinforcing design method and fatigue reinforcing design method still need further experimental and theoretical analysis. These two problems are considered in this thesis.Firstly, the reinforced characteristics and research status of composite materials reinforcing various types of steel structures were explored, as well as the fundermental theories involved, classical laminated plate theory, the crack-tip stress intensity factor calculation of steel plate reinforced by composite materials, Dugdale model theory, etc. with the objective that the load capacity of the reinforced specimen would not be lower than th e one without flaws, the composite materials volume for reinforcing was investigated by the Dugdale model. The values of effective length and width of CFRP strip for reinforcing were estimated by finite element method. The specimens for static tensile test were designed after the study of parameters related to reinforcement. The failure process and failure modes of reinforced specimens were probed by static tensile tests. The effective reinforcement parameters were verified by analyses of displacement-load curves, failure modes and characteristic loads. The remaining fatigue life under cycle loads was analysed by estimating the crack-tip stress intensity factor and Paris formula. The analytical results agree well with the fatigue tests of one-sided and double-sided reinforced specimens. Finally, the test of CFRP reinforcing steel structures in corrosive environments was carried out to explore the corrosion protection of CFRP and the impacts of environmental factors on the bonding properties.