Research On Resistance Assessment Method Of Existing Bridges Based On Theory Of Probability

The reliability assessment, repairing, improving and strengthening for the existing structures have aroused public attention, and become an important research topic of engineering structure field. Some efforts have been made in the assessment for RC highway-bridge based on the probability theory. The major contents are summarized as follow:1. The difference and relation of existing structure and designing structures are summarized. A method for calculating time-dependent reliability index is given in the paper according to stochastic resistance and loading effect based on the characteristic of existing structures, the effects of various parameters such as degradation of resistance and increasing tendency of traffic loading on the time-dependent bridge reliability index are studied. This paper considers influence of proof load, structures age and re-service term to the reliability index on the basis of formula given.2. The formula for calculating failure probability of engineering structures is given, with loading of locomotive vehicle modeled as Poisson impulse process and time-dependent variety of resistance considered. The influences on failure probability by resistance degradation function, average occurrence rate of loading and service time are analyzed qualitatively.3. On the basis of design load in force, the revised factors of variable load used in estimating existing bridge structures are given according to the theory, which is the probability that the load used exceeding the re-service term should be equal to the probability that the load used in designed exceeds the service term. The theory of time-dependent ability is adopted to evaluate the residual service life of structure and a method is adopted to revise the variable load.4. The service life of structure can be calculated according to the time-dependent reliability formula with the given critical reliability index and service environments. The program composition with MATLAB is used to calculate the time-variant reliability index.5. On the basis of hazard-benefit theory and reliability theory, the residual service life of existing structure can be given taking into account the safe reli-ability and economic optimization;with the residual service life the optimum repairing strategy can be developed, and the optimum time for repairing is determined with the economic benefit being maximual.6. Based on the inspection and assessment of an exising bridge, the work of the paper is proved.