• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.2
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• pp.121-128
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• 2005

This study focuses on evaluating the reliability index of a deck of RC slab having chloride contamination and studying the relation of grades of rebar corrosion and the reliability index of a bridge deck For this purpose, first, the failure probability related to flexural strength was calculated using a model for deterioration, which contains the application of deicing salts that usually causes significant long-term deterioration and reduction in the structural safety for strength of structure. And also, according to the depth of covering, the chloride contents depending on time due to depths of RC slab deck, the appearance time for initial corrosion of rebar and the occurrence time for split of covering were investigated using a MCS method.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.3
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• pp.118-122
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• 2010

The study presents a standard time-temperature curve to evaluate the fire performance of subway tunnel structures. The central subway section is 135km long in Korea, the fourth longest in the world. The number of subway tunnels has been increasing rapidly and fire risk is proportional to the tunnel length. However, an adequate time-temperature curve for subway tunnel fires does not exist. Therefore, we studied a proposed foreign fire design model for which the heat rate is based on the traffic, and we present an appropriate time-temperature curve for Korean subway tunnels. The ISO 834 curve was used as a fire design model and the temperature distribution in the tunnel was estimated using numerical analysis. This led to a proposal for effective measures against subway tunnel fires.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.5
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• pp.105-112
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• 2023

Steel fiber reinforced concrete (SFRC) exhibits enhanced strength and superior energy dissipation capacity compared to normal concrete, and it can also reduce crack propagation and fragmentation of concrete even when subjected to blast loads. In this study, the parameters defining failure surface and damage function of the K&C concrete nonlinear model were proposed to be applied for the properties of SFRC in LS-DYNA. Single element analysis has been conducted to validate the proposed parameters in the K&C model, which provided very close simulations on the compressive behavior of SFRC. In addition, blast analysis was performed on SFRC columns with different volume fractions of steel fibers, and the blast resistance of SFRC columns was quantitatively analyzed with Korea Occupational Safety & Health Agency (KOSHA) guidelines.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.1
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• pp.63-70
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• 2019

The number of vehicle-to-barrier collisions has increased due to improved driving environments. In addition, it is reported that the number of accidents led to impact severity larger than current capacity of a median barrier has increased. It is required to develop a high performance median barrier in order to secure expressway safety. This paper aims at proposing impact loading model and locations for a high performance median barrier based on analysis of median-barrier-related accident history. The SB6 test level (Impact severity: 420 kJ, Mass: 25 ton, Impact speed: 80 km/h, Impact angle: $15^{\circ}$) was suggested for target impact severity based on statistical data analysis. The suitable locations also were proposed from investigation of driver behaviors for installation and rehabilitation of high performance median barrier.

• Journal of the Society of Disaster Information
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• v.18 no.4
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• pp.817-827
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• 2022

The real-name safety management system is to indicate "safety" after inspection by construction personnel before workers use it for the purpose of preventing safety accidents caused by unsafe conditions in temporary facilities and temporary constructions installed at construction sites. Purpose: By implementing the real-name system for safety management at construction sites, the objective is to respond to the "Severe Accident Punishment Act" and to improve the level of safety management at the same time. Method: In this study, a hierarchical analysis model was produced through previous studies of actual conditions such as types of safety incidents and causality at construction sites. The AHP model was used to calculate integrated weights and rankings with a pairwise comparison questionnaire for experts. Conclusion: As a result of the analysis of the upper classes, construction machinery was evaluated the highest, and real-name management system was evaluated the lowest. As a result of the lower-level analysis, it was considered that opening doors for safety facility management, tower cranes for construction equipment, management under the "Occupational Safety and Health Act" under the real-name management system, and CEO duties for safety management organizations were the most important.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.1
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• pp.120-128
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• 2011

Recently, safety diagnosis of the existing structures has been emerged as important issue. In particular, systematical and precise safety diagnostics for steel structures for power substation, have been required. Steel structures for power substation are under the periodical impact loads from operations of gas insulated switchgear. These loading condition accelerates damage and aging of structure. The objective of this research is to evaluate damage of structure under periodical impact loads. To evaluate the integrity of structures as organizing mathematical models including the dynamic characteristics of structures, Frequency Domain Decomposition method was choiced and an algorism was proposed. For verifying this methods and algorism, a mathematical model is composed of the development of a variety of reverse analysis and a signal processing technology reflecting physical damage of structures. A series of analysis and test results indicatge that proposed method has a confidence for applying a filed test. Therefore, it is expected to be able to take advantage of system identification to detect damage for the maintenance and management of steel structures under periodical impact loads such as power substation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.11
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• pp.1187-1194
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• 2009

During the last decade, possibility of flaw occurrences has been rapidly increased world-widely as the increase of operating times of petro-chemical facilities. For instance, from a recent in-service inspection, three different sized surface cracks were detected in welding parts of a spherical oxygen holder in Korea. While API579 code provides corresponding engineering assessment procedures to determine crack driving forces, in the present work, numerical analyses are carried out for the cracked oxygen holder to investigate effects of complex geometry, analysis model and residual stress. With regard to the detailed finite element analysis, stress intensity factors are determined from both the full three-dimensional model and equivalent plate model. Also, as an alternative, stress intensity factors are calculated for equivalent plate model by employing the noted influence stress function technique. Finally, parametric structural integrity evaluation of the cracked oxygen holder is conducted in use of failure assessment diagram method, J/T method and DPFAD method. Effects of the geometry and so forth are examined and key findings from the simulations are fully discussed, which enables to determine practical safety margins of spherical components containing a defect.

• International Journal of High-Rise Buildings
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• v.9 no.4
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• pp.351-360
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• 2020

Monitoring civil structures periodically is necessary for ensuring the fitness of the structures. Cracks on inner and outer surfaces of the building plays a vital role in indicating the health of the building. Conventionally, human visual inspection techniques were carried up to human reachable altitudes. Monitoring of high rise infrastructures cannot be done using this primitive method. Also, there is a necessity for more accurate prediction of cracks on building surfaces for ensuring the health and safety of the building. The proposed research focused on developing an efficient crack classification model using Transfer Learning enabled EfficientNet (TL-EN) architecture. Though many other pre-trained models were available for crack classification, they rely on more number of training parameters for better accuracy. The TL-EN model attained an accuracy of 0.99 with less number of parameters on large dataset. A bench marked METU dataset with 40000 images were used to test and validate the proposed model. The surfaces of high rise buildings were investigated using vision enabled Unmanned Arial Vehicles (UAV). These UAV is fabricated with TL-EN model schema for capturing and analyzing the real time streaming video of building surfaces.

• Structural Engineering and Mechanics
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• v.31 no.5
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• pp.507-526
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• 2009

Based on numerical and experimental methods, a systematic structural evaluation of a steel natatorium in service was carried out in detail in this paper. Planning of inspection tasks was proposed firstly according to some national codes in China in order to obtain the economic and reliable results. The field visual inspections and static computation were conducted in turn under in-service environmental conditions. Further a three-dimensional finite element model was developed according to its factual geometry properties obtained from the field inspection. An analytical modal analysis was performed to provide the analytical modal properties. The field vibration tests on the natatorium were conducted and then two different system identification methods were used to obtain the dynamic characteristics of the natatorium. A good correlation was achieved in results obtained from the two system identification methods and the finite element method (FEM). The numerical and experimental results demonstrated that the main structure of the natatorium in its present status is safe and it still satisfies the demand of the national codes in China. But the roof system such as purlines and skeletons must be removed and rebuilt completely. Moreover the system identification results showed that field vibration test is sufficient to identify the reliable dynamic properties of the natatorium. The constructive suggestion on structural evaluation of the natatorium is that periodic assessment work must be maintained to ensure the natatorium's safety in the future.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.12
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• pp.717-724
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• 2018

To prepare for the explosive increase in maintenance costs of bridges according to the aging of infrastructure, future maintenance costs of bridges should be predicted. For this purpose, the management status of bridges was investigated and modeled as the upper limit of the performance level and the target management level according to the life cycle. This paper proposes methodologies and procedures for estimating the bridge maintenance costs using two models and existing cost and performance prediction models that consist of unit repair cost model according to the safety score, performance degradation model of bridges, unit reconstruction cost, and average reconstruction time. To verify the applicability, future maintenance costs can be forecasted for specific management agency considering the number of bridges, degree of aging, and current management status. As a result, it is possible to obtain the maintenance cost and safety level of an individual bridge level for each year. In addition, by summing them up to the agency level, the average safety score, ratio of the safety level, inspection costs, repair costs, and reconstruction costs can be obtained. In a further study, the changes in maintenance costs can be analyzed according to the changes in the target management levels using the developed method. The optimal management level can be suggested by reviewing the results.