Research On Chloride Diffusion Parameter Model And Service Life Calculation Model Of Offshore Concrete Structure In Beibu Gulf

The durability and service life of concrete structures have long been a hot issue.Especially for concrete structures exposed to chloride environment,chloride ion erosion has become the dominant factor affecting the durability of concrete structures.Therefore,building a reasonable chloride diffusion model to study the diffusion law of chloride ions is to study the durability and clothing of concrete structures in chloride environment Secondly,building an efficient and concise service life calculation model is also a key problem to be solved.Based on the data of splash area in Beibu Gulf,the multi factor surface chloride model and chloride diffusion coefficient model are established.The reliability method and Monte Carlo method are used to calculate the service life of marine concrete structures in the splash area of Beibu Gulf.The error between apparent diffusion coefficient and instantaneous diffusion coefficient is discussed.In addition,the influence of time-varying diffusion coefficient and its randomness on service life is also discussed.Based on the inverse reliability method,an iterative calculation model for the service life of concrete structures is established,in which the secant slope is used instead of the tangent slope to avoid the derivation of the reliability index.The main research work is as follows:1.Based on the data of splash zone in Beibu Gulf,considering material,exposure time and environmental factors,the multi factor surface chloride model and chloride diffusion coefficient model were established by nonlinear fitting method.Considering the factors of material and time,the multi factor chloride diffusion model in Beibu Gulf was built.2.The apparent diffusion coefficient is transformed into instantaneous diffusion coefficient,and the service life of concrete structure in chloride environment is calculated by two kinds of diffusion coefficient.It is found that the service life calculated directly by apparent diffusion coefficient is obviously lower.3.Through the discussion and analysis of chloride diffusion coefficient of concrete,it is found that the time-varying and randomness of chloride diffusion coefficient play a leading role in the durability of concrete structure.Ignoring the time-varying will lead to significantly underestimate the service life of the structure,and if only considering the time-varying and not considering its randomness,the service life of the structure will be overestimated obviously.4.The influence of random variables on the service life of concrete structures in chloride environment is analyzed by the total differential sensitivity coefficient method.The leading factor influencing the service life of concrete structures in chloride environment is the thickness of concrete cover in the early stage,followed by the age attenuation coefficient of diffusion coefficient,but after a certain time,the dominant factor becomes the age attenuation coefficient of diffusion coefficient,and the second is the age attenuation coefficient of diffusion coefficient Thickness of concrete cover.5.Through the establishment of the service life iterative calculation model which can calculate the service life of concrete structure iteratively,the secant slope is used instead of the tangent slope to avoid the problem of deriving the reliability index.The calculation results of this model have high accuracy,stable convergence and fast speed.The initial value selection of iterative calculation model has no influence on the final calculation results.Although they can converge to the correct solution,the convergence speed will be slow.The initial value calculation model is established by taking the service life calculated by approximate checking point as reference value,which provides suitable iterative initial value model and value for the service life iterative calculation model to obtain stable and reliable calculation results,and solves the problem of slow iteration speed.