• Journal of the Korea Concrete Institute
• /
• v.15 no.4
• /
• pp.606-614
• /
• 2003

The major cause of deterioration for the concrete bridge decks exposed to de-icing chemicals would be chloride-induced reinforcement corrosion. Thus, in this paper, in order to predict time to corrosion for concrete bridge decks in the urban area, chloride concentration was measured with depth from the surface. A frequency analysis on surface chloride concentration and chloride diffusion coefficient of concrete bridge deck equals 0.192, 29.828 in the scale parameter and 7.899, 1.983 in the shape parameter of gamma distribution. The average value of surface chloride concentration equals 1.5 kg/㎥ and condenses from 1 to 2 kg/㎥ in the level of probability 70%. From the probabilistic results, it is confirmed that 26mm of minimum cover depth in order to target 20 years over is calculated. The countermeasure strategy to extend the service life of concrete bridge deck exposed to de-icing chemicals would be an effective method to increase cover depth and to place high performance concrete, which could lead to reduce the chloride diffusion coefficient and distribution range.

• Journal of Ocean Engineering and Technology
• /
• v.31 no.3
• /
• pp.233-240
• /
• 2017

Subsea structures are always vulnerable to accidental risks induced by fishing gear, dropped objects, etc. This paper presents the design of a subsea manifold protective structure that protects against dropped object impacts. Probable dropped object scenarios were established considering the shapes and masses of the dropped objects. A design layout for the manifold protective structure was proposed, with detailed scantlings and material specifications. A method applicable to the pipelines specified in DNV-RP-F107(DNV, 2010) was applied to calculate the annual probabilities of dropped objects hitting the subsea manifold. Nonlinear finite element analyses provided the structural consequences due to the dropped object impacts such as the maximum deflections of the protective structure and the local fracture occurrences. A user-subroutine to implement the three-dimensional fracture strain surface was used to determine whether local fractures occur. The proposed protective structure was shown to withstand the dropped object impact loads in terms of the maximum deflections, even though local fractures could induce accelerated corrosion.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2009.05a
• /
• pp.275-276
• /
• 2009

This paper provides a new approach for predicting the corrosion resistivity of reinforced concrete structures exposed to carbonation. In this method, the prediction can be updated successively by a Bayesian theory when additional data are available. The stochastic properties of model parameters are explicitly taken into account into the model. To simplify the procedure of the model, the probability of the durability limit is determined from the samples obtained from the Latin hypercube sampling technique. The new method may be very useful in designing important concrete structures and help to predict the remaining service life of existing concrete structures which have been monitored.

• Nuclear Engineering and Technology
• /
• v.49 no.2
• /
• pp.349-359
• /
• 2017

During the past 25 years, in the context of probabilistic safety assessment, efforts have been directed towards establishment of comprehensive pipe failure event databases as a foundation for exploratory research to better understand how to effectively organize a piping reliability analysis task. The focused pipe failure database development efforts have progressed well with the development of piping reliability analysis frameworks that utilize the full body of service experience data, fracture mechanics analysis insights, expert elicitation results that are rolled into an integrated and risk-informed approach to the estimation of piping reliability parameters with full recognition of the embedded uncertainties. The discussion in this paper builds on a major collection of operating experience data (more than 11,000 pipe failure records) and the associated lessons learned from data analysis and data applications spanning three decades. The piping reliability analysis lessons learned have been obtained from the derivation of pipe leak and rupture frequencies for corrosion resistant piping in a raw water environment, loss-of-coolant-accident frequencies given degradation mitigation, high-energy pipe break analysis, moderate-energy pipe break analysis, and numerous plant-specific applications of a statistical piping reliability model framework. Conclusions are presented regarding the feasibility of determining and incorporating aging effects into probabilistic safety assessment models.

• Earthquakes and Structures
• /
• v.3 no.5
• /
• pp.649-673
• /
• 2012

Recent studies have highlighted the importance of accounting for aging and deterioration of bridges when estimating their seismic vulnerability. Effects of structural degradation of multiple bridge components, variations in bridge geometry, and comparison of different environmental exposure conditions have traditionally been ignored in the development of seismic fragility curves for aging concrete highway bridges. This study focuses on the degradation of multiple bridge components of a geometrically varying bridge class, as opposed to a single bridge sample, to arrive at time-dependent seismic bridge fragility curves. The effects of different exposure conditions are also explored to assess the impact of severity of the environment on bridge seismic vulnerability. The proposed methodology is demonstrated on a representative class of aging multi-span reinforced concrete girder bridges typical of the Central and Southeastern United States. The results reveal the importance of considering multiple deterioration mechanisms, including the significance of degrading elastomeric bearings along with the corroding reinforced concrete columns, in fragility modeling of aging bridge classes. Additionally, assessment of the relative severity of exposure to marine atmospheric, marine sea-splash and deicing salts, and shows 5%, 9% and 44% reduction, respectively, in the median value bridge fragility for the complete damage state relative to the as-built pristine structure.

• Journal of the Korean institute of surface engineering
• /
• v.54 no.6
• /
• pp.331-339
• /
• 2021

Environmental barrier coatings(EBCs) are applied to the SiC/SiC ceramic matrix composites(CMCs) in order to protect CMCs from being corroded with water vapor by combustion gas in gas turbine engines. Ytterbium silicates, such as ytterbium monosilicate and ytterbium disilicate, are ones of the candidate materials for EBCs due to their excellent resistance to water vapor corrosion as well as thermal-expansion match with SiC. In this study, ytterbium silicates are fabricated with 2-step solid-state synthesis targeting ytterbium disilicate. After synthesizing ytterbium monosilicate, the mixtures of ytterbium monosilicate and SiO₂ are heat-treated and densified by using pressureless sintering or hot pressing with a variety of heating conditions. The phase formation, thermal expansion, and oxidation behavior are examined with fabricated specimens. The final densified bodies are found to be composites between ytterbium monosilicate and ytterbium disilicate with different ratios, which results in 4.43 to 6.72×10^-6/K range of coefficients of thermal expansion. The probability of these ytterbium silicates for EBC applications is also discussed.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.19 no.12
• /
• pp.70-79
• /
• 2020

This paper describes a comparative study of characteristics of probabilistic design using various reliability analysis methods in the structure design of an automatic salt collector. The thickness sizing variables of the main structural member were considered to be random variables, including the uncertainty of corrosion, which would be an inevitable hazard in the work environment of the automatic salt collector. Probabilistic performance functions were selected from the strength performances of the automatic salt collector structure. First-order reliability method, second-order reliability method, mean value reliability method, and adaptive importance sampling method were applied during the reliability analyses. The probabilistic design performances such as reliability probability and numerical costs based on the reliability analysis methods were compared to the Monte Carlo simulation results. The adaptive importance sampling method showed the most rational results for the probabilistic structure design of the automatic salt collector.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2022.11a
• /
• pp.49-50
• /
• 2022

There are continuous cases of fire expansion due to fire door problems around the world, including the 2010 Shanghai Apartment Fire, the 2017 Grenfell Tower Fire in England, and the 2020 Ul-san Residential and Commercial Complex Fire. In order to prevent such fire damage, the country has strengthened the performance standards of fire doors, and recently, efforts have been made to ensure the best performance of fire doors by introducing a quality recognition system. Securing the performance of fire doors is a very important aspect. However, there is a concern that old fire doors may not function normally in the event of fire due to natural deterioration, corrosion, and damage during the use process, but countermeasures are insufficient. Therefore, from a management perspective, it is very important to maintain fire doors and secure an appropriate replacement time. Therefore, the purpose of this study is to determine whether the fire door has durability to prevent fire spread in the process of use through operation probability analysis and expert surveys, and to propose an appropriate useful life of the fire door.

• Korean Chemical Engineering Research
• /
• v.55 no.3
• /
• pp.322-331
• /
• 2017

District heating was first introduced in Korea in 1985. As the service life of the underground thermal piping network has increased for more than 30 years, the maintenance of the underground thermal pipe has become an important issue. A variety of complex technologies are required for periodic inspection and operation management for the maintenance of the aged thermal piping network. Especially, it is required to develop a model that can be used for decision making in order to derive optimal maintenance and replacement point from the economic viewpoint in the field. In this study, the analysis was carried out based on the repair history and accident data at the operation of the thermal pipe network of five districts in the Korea District Heating Corporation. A failure probability model was developed by introducing statistical techniques of qualitative analysis and binomial logistic regression analysis. As a result of qualitative analysis of maintenance history and accident data, the most important cause of pipeline damage was construction erosion, corrosion of pipe and bad material accounted for about 82%. In the statistical model analysis, by setting the separation point of the classification to 0.25, the accuracy of the thermal pipe breakage and non-breakage classification improved to 73.5%. In order to establish the failure probability model, the fitness of the model was verified through the Hosmer and Lemeshow test, the independent test of the independent variables, and the Chi-Square test of the model. According to the results of analysis of the risk of thermal pipe network damage, the highest probability of failure was analyzed as the thermal pipeline constructed by the F construction company in the reducer pipe of less than 250mm, which is more than 10 years on the Seoul area motorway in winter. The results of this study can be used to prioritize maintenance, preventive inspection, and replacement of thermal piping systems. In addition, it will be possible to reduce the frequency of thermal pipeline damage and to use it more aggressively to manage thermal piping network by establishing and coping with accident prevention plan in advance such as inspection and maintenance.

• Journal of Energy Engineering
• /
• v.18 no.2
• /
• pp.125-131
• /
• 2009

Physical characteristics of metals such as hardness, wear-resistance and corrosion-resistance can be artificially controlled by ion implantation. The interaction between ion and solid surface was modeled in molecular scale and simulated by the molecular dynamics method in order to understand the ion implantation mechanism. From the microscopic point of view, the molecular behaviors were observed for improving characteristics of ion implantation. For these purposes, the implantation mechanism and the influences of incident energy, surface temperature and molecular weight were discussed in this study. As the results, the penetration probability was even decreased if incident energy was exceeded any values in the case of high temperature of solid surface. Moreover, it was confirmed that ion implantation into solid surface with amorphous state could be more effective for some conditions.