Abstract
When studying concrete impairment, the carbonation depth of concrete is regarded to be variable. Therefore, a time-varying reliability evaluation is important to perform a structural safety assessment. By analyzing 13,198 data on the carbonation depth of concrete, we propose a time-varying reliability evaluation based on the third-moment (TM) method to predict the service life of concrete. Validated by Monte Carlo (MC) simulation, the errors of the calculated results using time-varying reliability evaluation were within 4%. It is shown that the TM method proposed in this paper is more practical than traditional approaches such as MC simulation and second-moment (SM) methods in probability analysis. In this paper, exponential distribution was used to characterize the distribution of carbonation depths. Since paint was present on the concrete surface, numerous uncarbonized concrete components were found in the experiments; to develop a time-varying model considering the uncarbonized components, a function for evaluating the ratio of carbonized concretes is proposed. Overall, the time-varying TM method provided in this paper can act as a foundation for other investigations on probabilistic analysis, e.g., of compressive strength, deflection, and crack of concrete, which can be used to evaluate the reliability of concrete.
Highlights
Reinforced concretes have been widely applied in structural engineering as building components, tunnel lining, retaining walls, etc. [1,2,3,4,5]
One of the most important steps to calculate the failure probability is to analyze the integral of probability density function (PDF), leading to the difficulty in probability computation [28]; approximation methods such as the moment methods are generally applied in reliability analysis
Where G(x) is the performance function, c is the concrete cover, x is the random variable of carbonation depth, β2M is the second-moment reliability index, μG is the mean value of of G(x), σG is the standard deviation of G(x), α3G is the skewness observed by Monte Carlo (MC) simulation, β3M is the expression of the Figure 14 presents the time-varying TM reliability index calculated by Equations (7)–(12)
Summary
Reinforced concretes have been widely applied in structural engineering as building components, tunnel lining, retaining walls, etc. [1,2,3,4,5]. In some existing prediction models, carbonation depth is deemed to be a function of the square root of time when carbonation-based. A model to compute the average of carbonation depth at different service years was developed, with the purpose of obtaining an effective time-varying reliability model. To carry out a structural reliability analysis, the most fundamental step is to calculate the failure probability Difficulty in calculating this probability has resulted in the development of diverse approximations, among which the moment methods [28]. This paper proposes a more explicit model for computing the reliability index based on a third-moment (TM) method, which reflects the skew of a random variable effectively [28,30,31]. We suggest that the concrete failure time can be based on the concrete guaranteed rate which can be used to determine concrete quality
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