Mechanical Property Of Corroded Steel And Composite Beams Strengthened With Prestressed CFRP Sheets

With the further development of urbanization, the requirements on the scale of construction are getting higher and higher, and this provides wider space for steel structure, which has higher bearing capacity, smaller sectional dimension, convenient construction and economical investment. However, due to the aging of materials, the earthquakes, and the differential settlement, the impact of foreign object, the using and the environmental factors, the building structures are inevitably suffered from the defect and damage. Also, under the action of the loads, the gradual expansion and convergence of the micro-defects lead to the macro deterioration of the mechanical properties of materials. Therefore, the study on the reinforcement and restoration of steel structures has become an important part in the field of civil engineering. Carbon Fiber Reinforced Polymer (CFRP) sheets with the light weight, the high strength, the corrosion resistance and other characteristic, have provided an effective method for the strengthening and repairing of the steel structures. However, the study on the strengthening of the corroded steel beams with the prestressed CFRP sheets is relatively less. Especially, the study on the strengthening of the composite steel-concrete beams with the prestressed CFRP sheets has not been reported. Based on the domestic and foreign research results, considering the mechanical characteristics of the corroded steel and composite steel-concrete structures, and by experimental research, theoretical analysis and computer simulation, the mechanical properties of the corroded steel and composite steel-concrete beams strengthened with (prestressed) CFRP sheets were studied. The main research contents are given as follows:According to the mechanical experiments of the (corroded) steel beams strengthened with (prestressed) CFRP sheets, the working mechanism, failure mode were studied, and the impact of the corrosion extent of the steel beams, CFRP sheets and prestress on the reinforced steel beams was discussed. The results showed that, the yield and ultimate strength of the uncorroded steel beams respectively increased by4%,6.1%compared with the corroded steel beams with50%corrosion; the yield and ultimate strength of the reinforced steel beams respectively increased by4.2%,9.4%compared with unreinforced steel beams; the yield and ultimate capacity of the prestressed beams respectively increased by12%,2.9%compared with the non-prestressed beams. The. results showed that the corrosion extent of the steel beams, CFRP sheets and prestress had a certain influence on the bearing capacity of the reinforced steel beams. In limit state, the prestressed CFRP sheets achieved limit strain. Inversely, the non-prestressed CFRP sheets did not. Therefore, the utilization rate of the CFRP sheets can be effectively increased by being given the prestress.According to the mechanical experiments of the (corroded) composite steel-concrete beams strengthened with (prestressed) CFRP sheets, the working mechanism,failure mode, and the impact of the corrosion extent of the steel beams, CFRP sheets and prestress on the reinforced steel beams was discussed. The results showed that, the yield and ultimate strength with30%corrosion composite beams respectively increased by10.3%,2.5%compared with50%corrosion; the yield and ultimate strength of the reinforced composite beam beams respectively increased by3.1%、8.8%compared with unreinforced steel beams; the yield and ultimate capacity of the prestressed beams respectively increased by22%,11.4%compared with the non-prestressed beams. The results showed that the corrosion extent of the steel beams, CFRP sheets and prestress had significantly impact on the bearing capacity of the reinforced composite beams. In limit state, the prestressed CFRP sheets achieved limit strain. Inversely, the non-prestressed CFRP sheets did not. Therefore, the utilization rate of the CFRP sheets can be effectively increased by being given the prestress.According to the mechanical characteristics of the corroded steel beams and corroded composite steel-concrete beams strengthened with prestressed CFRP sheets, we could establish the yield of bearing capacity, limit bearing capacity and the deformation calculating formula of strengthening of corroded steel beams and corroded composite steel-concrete beams with CFRP sheets, and the theoretical formula in good agreement with experimental results.According to the mechanical characteristics of the interface of the corroded composite steel-concrete beams strengthened with prestressed CFRP sheets, we could establish differential equations and the corresponding formula of interface shear stress, the interface normal stress and deformation under the prestress stage and use phase among CFRP sheets, steel beams and concrete. The results showed that the deformation of composite beams increase with the increasing of the load and the thickness of CFRP sheets, and decrease with the increasing of connector stiffness; The interfacial shear stress increase with the number CFRP sheets layer increasing, the increasing of initial prestress and the stiffness of connector and rubber layer increases; The interface normal stress increased with the number CFRP sheets layer increase, the increasing of the initial prestress, the stiffness of connector and the stiffness of rubber layer.According to the mechanical characteristics of corrosive steel beams and corrosive composite steel-concrete beams strengthened with prestressed CFRP sheets. By using ABAQUS finite element program, the calculation model of prestressed CFRP sheets strengthened corrosion steel beams and corrosion steel-concrete composite beams is established, and the working mechanism is studied. The calculation results show that: the bearing capacity of strengthened beams increase with the increasing of the initial prestress and CFRP sheets thickness, and decrease with the increase of steel corrosion degrees.