The Bearing Capacity Deterioration's Numerical Simulation Of Existing Reinforced Concrete Bridges And Repair Demand Forecast

The rebar corrosion is the important factor that has an effect on the durability of reinforced concrete bridge. With the development of corrosion, the reliability of bridge structures will be reduced and the fail probability will be increased. How to choose repair plan reasonably in the lifetime of bridges will be critical. The thesis includes the transportation process of corrosive substances in the concrete, rebar corrosion model, structural time-varied reliability analysis and repair demand forecast model. At last, all above mentioned models are used in the Wusongjiang Bridge, and as a result, the different repair plans are analyzed and compared.Concrete carbonation, chloride ion permeation and rebar corrosion are the bases of the structural reliability assessment in the lifetime of bridges. Based on existing research achievements, the finite element method is used in the numerical simulation of carbonation process and chloride ion permeation in the concrete, and then the initial time of rebar corrosion in the concrete can be predicted by numerical method. By the comparison of existing models, the rebar corrosion model under normal atmosphere and new repair demand forecast model are proposed. The computational assumptions are verified by test results of Buckhouse beam, and then the sensitivity of structural response, time-varied structure reliability and failure probability are computed. In the finality, the problems in further studies are briefly discussed. The major contributions of the work presented in this thesis are listed as follows:(1) Based on existing rsearch works and mathematical models, the finite element numerical simulation method of concrete carbonation is first proposed, and the predictions of this method are shown to be in close agreement with available test results. Next, the variation principles of substances contents in carbonated zone of concrete are discussed and the results are used in the study of parameters in the long term carbonation process of existing structure.(2) The influence of crack depth on the velocity of chloride ion permeation in concrete is studied by finite element analysis, and the conclusion that the chloride permeation model in cracked concrete should be two-dimensional is given.(3) By the comparison of existing rebar corrosion models, the rebar corrosion model under normal atmosphere is suggested.(4) The finite element method based on constraint in critical section is proposed, and the computation results are shown to be in good agreement with test results. In addition, regarding rebar corrosion as studying parameter, the time-varied structure reliability and failure probability are discussed.(5) Based on existing models, the new repair demand forecast model including target reliability index and cost-benefit analysis is proposed.(6) At last, all above mentioned models are used in the Wusongjiang Bridge, and as a result, the different repair plans are analyzed and compared, which proves the effectiveness and validation of methods proposed in this thesis.