The Research On Mechanical Behavior And Influence Of Temperature Difference And Freeze-thawing Of The Reinforced Concrete Structure Strengthened With Prestressed CFRP Plates

The technique of strengthening reinforced concrete structure with prestressed CFRP laminates can make full use of the high tensile strength of CFRP and improve the service performance of the strengthened structure, and attracted much attention from researchers in recent years. However, these studies were conducted on the load-carrying behavior of the reinforced concrete structures strengthened with prestressed CFRP laminate, and the dimension of the specimens in the experimental works is often small, which results in the difference in the load-carrying behavior between the specimens and the actual structures. As the structures applied a new technique, the influence of temperature and freeze-thawing on the behavior of the reinforced concrete structures strengthened with prestressed CFRP plates needed be further studied. Therefore, in the presented paper the experimental studies of the reinforced concrete beams strengthened with prestressed CFRP plate were conducted. The mechanical behaviorin and influence on Temperature difference and freeze-thawing of the strengthened beams were researched as the following.(1) Based on the test studies with the large-size specimens, the load-carrying behavior of the large-size reinforced concrete members was researched. The difference in the behavior of the beams strengthened with prestressed and non-prestressed CFRP plate was analyzed, and the effect of the initial stress and the bonding capacity of the CFRP-concrete interface on the failure mode of the strengthened beams were discussed. Moreover, the calculation formulas of the load-carrying capacity and the flexural stiffness of the strengthened beams were presented.(2) Through on-the-spot long-term monitoring study on strengthening real bridge, the mechanical property of prestressed CFRP plates strengthening concrete bridge under the temperature was investigated. Through diurnal observation of strain of prestressed CFRP plates of the reinforced bridge, and the temperature variation of beam top and beam bottom, based on the plane surface assumption, the concrete strain under temperature changes was divided into temperature free strain, self-constrained strain and external constrain strain according to the causing reasons. Furthermore, by using superposition principle, the calculation formula of prestressed CFRP plates temperature strain was derived. (3) The stress behavior variation law of prestressed CFRP plates strengthening steel bar concrete beams under the effect of freeze-thaw cycles was studied. Rechered the effects of freeze-thawing cycles and prestress level on the failure mode and load capacity of strengthened, beams The influential law of freeze-thawing cycles frequency, concrete intensity, magnitude of stress and other factors on carbon fiber plate-concrete interface bonding performance was analyzed. The degradation mechanism of prestressed carbon fiber strenthening concrete structure under the freeze-thaw erosion environment was determined. The calculation model of the loading capacity of prestressed CFRP strenthening steel bar concrete beams functioning with freeze-thaw cycles was presented.(4) Through experimental research, the CFRP-concrete interface bonding behavior of ultimate loading capacity, interface strain distribution and others was examined and the effects of factors of bonding length and others on interface bonding behavior were analyzed. Based on the experimental research, the finite element analysis model of CFRP-concrete interface bonding was built. With the finite element analysis, the fitting method of interface bond-slip relations was given to compare the coincide degree of experimental results of this paper with the main bond-slip relations at present, from which a CFRP-concrete interface bond-slip model in accordance with the experiments in this paper was calculated.