| This paper takes 46 RC-Beam bridges in Putuo District as research object, reviewing detect data of these bridges in recent years. By investigating the surface diseases of the main structures & added structures of bridges built in different periods, the author brings forward the point that the time when surface diseases appear & the extent to which surface diseases developed are random courses under the influence of multi-factors, explores the mechanism of the diseases on RC-Beam bridges, carrys out the probability statistics taking bridges as swatches.Seeing about the material performance of concrete & steel bar, researches are implemented as follows:(1) A practical random model which is used to forecast the deepness of concrete carbonization is given out;(2) A mathematical model which describes the way concrete strength changes is built up;(3) After investigating quantities of documents of practical projects, negating that the rustiness of steel bars starts from when concrete is completely carbonized.(4) Set up an artifical neural net to forecast the increase of the rustiness of steel bars.Through comparison with Markov deterioration process, the paper brings forward a multi-rooted deterioration model. Taking the carrying capacity of structures as life-rule, a mathematical model based on safety of structures is built up.This study proposes a reliability approach for optimizing the lifetime repair strategy for RC-Beam Bridges: Compute time-dependent reliability of the beam using updated time-dependent deterioration models through inspection. Then the residual life of the existing beam is obtained by comparing its time-dependent reliability index with total reliability index. Then, through comparing the residual life with expected service life, feasible repair strategy is obtained. With the goal of total present value of cost being minimum and constraint condition of time-dependent reliability being greater than target reliability index, optimum repair strategy can be obtained. The...
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