Papers by Keyword: Probabilistic Assessment

Abstract: This study is to propose time-variant probabilistic models of surface chloride and diffusion coefficient based on the survey data of 16 concrete bridge decks with the attack of de-icing salts. These models are developed, because there is no study that simultaneously considers both time-variance and probabilistic descriptors in the model for concrete bridge decks. From the study, it can be found that long-term surface chloride and its time-variant development are fitted with Log-normal and Weibull distributions, respectively. In addition, the 28-day diffusion coefficient and age factor are fitted with Log-logistic and Triangular distributions, respectively. Considering only the mean value in the models, the corrosion-free residual life of concrete bridge decks is equal to 18.3 years based on the target value of critical chloride of 1.2 kg/m³, whereas their cracking-free residual life is equal to 29.5 years based on the target value of critical chloride of 2.0 kg/m3. In comparison with the probabilistic analysis, it was nevertheless found that at year 18.3, there are 38% and 20% probabilities to have rebar corrosion and concrete cracking, respectively. However, at year 29.5, there are 63% and 42% probabilities to have rebar corrosion and concrete. Specifically, there are 6 and almost 7 out of 16 bridge locations having rebar corrosion in the year 18.3 and concrete cracking in the year 29.5, respectively.

Abstract: This paper is aimed at the reliability analysis of an existing reinforced concrete bridge from 1908. The load bearing capacity is assessed in accordance with valid standards using the partial factor method and probabilistic approach. Load bearing capacities obtained by these methods are critically compared. The application of probabilistic method leads to 40 % higher load bearing capacity then the partial factor method used for structural design.

Abstract: An approach which combines the Latin Hypercube technique with Crank-Nicolson based finite difference approach is developed for probabilistic assessment of chloride diffusion in concrete structures with repairs. Two random variables, i.e., surface chloride and diffusion coefficient, are considered. Four repair strategies are proposed by varying the diffusion coefficient of repair concrete and the repair depth. A repair by cover replacement is applied at a critical time which the chloride content at a threshold depth reaches its critical value for concrete cracking. The critical time is defined as the repair time, which the CO₂ due to repair concrete production and replacement processing occurs. By this method, the median of repair time and the probabilistic time-dependent CO₂ can be assessed. The mean and the percentiles of cumulative total CO₂ are compared.

Abstract: The conventional deterministic methods have been unable to accurately assess the active power output of the wind farm being the random and intermittent of wind power, and the probabilistic methods commonly used to solve this problem. In this paper the multi-state fault model is built considering run, outage and derating state of wind turbine, and then the reliability model of the wind farm is established considering the randomness of the wind speed, the wind farm wake effects and turbine failure. The active wind farm output probability assessment methods and processes based on the Monte Carlo method. The related programs are written in MATLAB, and the probability assessment for active power output of a wind farm in carried out, the effectiveness and adaptability of built reliability models and assessment methods are illustrated by analysis of the effects of reliability parameters and model parameters on assessment results.

Abstract: The objective of the present study is the development of a micromechanically based probabilistic model for the assessment of the cleavage fracture probability of ferritic steels. Brittle fracture of ferritic steels is a probabilistic process, triggered by the failure of randomly distributed brittle particles. These particles fracture due to plastic deformation of the surrounding matrix, resulting in the nucleation of micro-cracks. Once nucleated, the local stress state controls the possible instability of the defects. In this context, the local stress-triaxiality is assumed to govern the blunting of freshly nucleated micro-defects. The local approach models available in literature account for the above-mentioned correlations only in a simplified manner. Based on Representative Volume Elements (RVE) of the microstructure, accounting for the grain-structure as well as for the brittle particles, the cleavage initiation process was modelled in order to investigate the relevant parameters and their interactions. The RVE’s were loaded according to the local mechanical field quantities determined numerically for a variety of specimen types at the cleavage-origins. Thus, the behaviour of the particles against the micromechanical conditions could be specified, resulting in a better understanding of the processes at cleavage fracture initiation. Based on the results, an enhanced probabilistic cleavage model is proposed.