Study On Time-varying Reliability Of Reinforced Concrete Aqueducts In Service

It is very important to study the reliability of the existing reinforced concrete aqueduct for its safe operation.At present,there are a large number of aqueduct structures in our country,which are lack of reliability and durability,such as structural instability,aging of concrete structure,water seepage,water leakage,corrosion of steel bars,etc.However,there are relatively few specifications and researches related to the reliability of aqueduct,and the failure factors are relatively single.Therefore,the research on the reliability of the existing reinforced concrete aqueduct structure has become an urgent need for the stable service of the aqueduct.Taking the reinforced concrete aqueduct in service in YinQin irrigation area of Jiaozuo city in Henan province as an example,based on the field test results and reliability theory,considering the multi-mode failure mode and system failure mode of aqueduct structure,combined with the non-probability reliability theory,this paper studies the reliability of the reinforced concrete aqueduct in service.(1)Based on the degradation model of concrete compressive strength and steel yield strength,the calculation model of compression,tension and bending bearing capacity of single component of aqueduct is established.The calculation method of time-varying reliability of single component based on finite element stress analysis is given by using Monte Carlo method.On the basis of time-varying reliability of single component,the time-varying reliability of aqueduct system is established by using PNET algorithm According to this model,the time-varying reliability of reinforced concrete aqueduct structure is calculated and analyzed.The results show that the degradation rate of yield strength of corroded steel bar is faster than that of compressive strength of concrete,and more attention should be paid to the corrosion damage of steel bar in the existing reinforced concrete aqueduct structure.The correctness of the calculation model is verified through the calculation and analysis of practical engineering,which can effectively predict the service life and maintenance period of the existing aqueduct structure.(2)Based on the principle of probability reliability,a time-varying reliability model of single failure mode of aqueduct material is established.Based on the single failure mode ofmaterial and PNET algorithm,a time-varying reliability model of multiple failure modes of reinforced concrete aqueduct in service is proposed.The single failure model and multiple failure model of aqueduct materials are used to calculate and analyze the time-varying reliability and failure probability of aqueduct project in service in YinQin irrigation area of Jiaozuo city.The results show that the reliability index value considering multiple failure modes of aqueduct is smaller than that of single failure mode,and the calculation result is more reasonable;the time-varying reliability index value considering multiple failure modes of aqueduct is more reasonable The dynamic change of aqueduct reliability can be grasped in time.(3)Based on the depth model of concrete carbonation and non-probabilistic reliability theory,a non-probabilistic time-varying reliability model for carbonation of reinforced concrete aqueducts in service is proposed.The calculation model and the traditional probability reliability theory are used to calculate and analyze the aqueduct project,and the calculation results are compared with the specifications.The results show that the service life of the calculation model in this paper is slightly smaller than the value specified in the code,and the method will make the aqueduct structure more safe;the reliability index of the non-probabilistic time-varying reliability calculation model in this paper is smaller than that of the probabilistic reliability calculation model,and it can accurately and simply calculate and analyze the reliability of the aqueduct carbonization.