• Journal of Korean Society of Forest Science
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• v.111 no.2
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• pp.276-286
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• 2022

We carried out this study to provide basic data necessary to establish a management plan for concrete erosion control dams in the future by analyzing results of detailed inspections of aged dams conducted in accordance with 「Guidelines for the Maintenance of the Erosion Control Facility」. We analyzed the results of a detailed inspection of 54 concrete erosion control dams which had been built over 20 years previously, located in private forests of Gyeongsangbuk-do using statistical methods. Having conducted exterior defect investigations, we found 18 dams (33.4%) in need of repair or follow-up measures and 15 dams in which the overall grade was changed due to investigator's corrections; we therefore considered that standardization of related standards and indicators would be necessary. After conducting concrete compression strength tests, we found 19 dams (35.2%) to be below the standard value of 21 MPa, and in particular, we included, in grade A, eight dams which we judged to be in good condition as a result of the exterior defect inspection. There was little clear correlation between the total score and the compressive strength of concrete, but there was a statistically significant difference in the compressive strength by overall grade. After analyzing the changes in the characteristics of the erosion control dams according to the elapsed years after construction, we detected no particular trend in the changes of total score and compressive strength over time. However, the cumulative ratio of the dams that required repair and follow-up measures and the dams below the compression strength standard had a strong positive linear relationship over time, suggesting that it would be possible to identify the aging characteristics of concrete erosion control dams.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.56-64
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• 2021

Leakage due to deterioration and damage is one of the major causes of volume change by freezing and thawing, and it leads micro-cracking and surface scaling in concrete structures. The deterioration of damaged concrete accelerates with the chloride attack. Thus, in the detailed guidelines for facility performance evaluation (2020), the quality of cover concrete and the freeze-thaw (FT) repetition cycle were newly suggested for concrete durability assessment. The quality of cover concrete should be evaluated by the rebound hammer test and the FT repetition cycle should be also considered in the deterioration environmental assessment. This study suggested the application of fast dynamic based nonlinear ultrasound method to monitor initial micro-scale damage under freezing and thawing environment. Concrete specimens were fabricated with different water-cement ratios (40%, 60%) and air contents (1.5% and 3.0%). The compressive strength, rebound number, relative dynamic modulus, and nonlinear ultrasound were measured with different FT cycles. The scanning electron microscopy was also performed to investigate the micro-scale FT damage. As a result, both the rebound number and the relative dynamic modulus had difficulty to detect early damage but the proposed method showed a potential to detect initial micro-scale damage and predict the FT resistance performance of concrete.

• Journal of the Korean Society of Safety
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• v.38 no.3
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• pp.77-84
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• 2023

Welding and cutting, which are representative tasks in handling firearms at industrial sites, are the basis for production and maintenance processes across all industries. They are also essential in the root industry. Specifically, they are widely used in the manufacturing industry, including equipment industries such as shipbuilding, automobiles, and chemicals, and subsequent maintenance work and general facility repair. However, such hot work carries a high fire risk owing to sparks scattering and inadequate management, resulting in a high occurrence of accidents. In response, the government and relevant organizations have recently revised the Occupational Safety and Health Act to prevent accidents during hot work. These revisions impose more stringent regulations than before, which are expected to help prevent actual fire accidents. However, whether the fire observer system, which is the core element of the revision, would be practically applied and maintained is unclear. Therefore, this study compared the fire observer system in the revised Occupational Safety and Health Act with those in the laws and systems of developed countries, conducted interviews with safety and health experts to assess the suitability of the new system for fire observer operations, and improvement plans were derived accordingly. Therefore, the laws and systems of developed countries grant more authority to fire observers compared with those of Korea. Moreover, professional training in handling emergency is required. Interviews with safety and health experts revealed that regardless of company size, the same operating standards were applied, and standards for deploying fire observers in various locations were unclear. Furthermore, there was a lack of professional education and training, and the role and authority of fire observers were limited. These findings revealed a problem in this sector. The results of this study are expected to serve as basic data for establishing a practical system for placing fire observers and supplementing laws, guidelines, and systems for preventing fire accidents.

• Journal of Korean Tunnelling and Underground Space Association
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• v.25 no.6
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• pp.479-493
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• 2023

The need for safety management has arisen due to the increasing number of years of operated underground structures, such as tunnels and utility tunnels, and accidents caused by those aging infrastructures. However, in the case of privately managed underground utility ducts, there is a lack of detailed guidelines for facility safety and maintenance, resulting in inadequate safety management. Furthermore, the absence of basic design information and the limited space for safety assessments make applying currently used non-destructive testing methods challenging. Therefore, this study suggests non-destructive inspection methods using ultrasonic and impact-echo techniques to assess the quality of underground structures. Thickness, presence of rebars, depth of rebars, and the presence and depth of internal defects are assessed to provide fundamental data for the safety assessment of box-type general underground structures. To validate the proposed methodology, different conditions of concrete specimens are designed and cured to simulate actual field conditions. Applying ultrasonic and impact signals and collecting data through multi-channel accelerometers determine the thickness of the simulated specimens, the depth of embedded rebar, and the extent of defects. The predicted results are well agreed upon compared with actual measurements. The proposed methodology is expected to contribute to developing safety diagnostic methods applicable to general underground structures in practical field conditions.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.1
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• pp.70-81
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• 2024

In this study, Tridimensional Hybrid Isolation System(THIS) was proposed as a vibration isolator for traffic loads, combining vertical and horizontal isolation systems. Its efficacy in improving serviceability for vertical vibration was analytically evaluated. Firstly, for the analysis, the major vibration modes of the existing apartment were identified through eigenvalue analysis for the system and pulse response analysis for the bedroom slab using commercial structural analysis software. Subsequently, a 16-story model with horizontal, vertical and rotational degrees of freedom for each slab was numerically organized to represent the achieved modes. The dynamic analysis for the measured acceleration from an adjacent ground to high-speed railway was performed by state-space equations with the stiffness and damping ratio of THIS as variables. The result indicated that as the vertical period ratio increased, the threshold period ratio where the slab response started to be suppressed varied. Specifically, when the period ratio is greater than or equal to 5, the acceleration levels of all slabs decreased to approximately 70% or less compared to the non-isolated condition. On the other hand, it was ascertained that the influence of damping ratios on the response control of THIS is inconsequential in the analysis. Finally, the improvement in vertical vibration performance of THIS was evaluated according to design guidelines for floor vibration of AIJ, SCI and AISC. It was confirmed that, after the application of THIS, the residential performance criteria were met, whereas the non-isolated structure failed to satisfy them.

• Land and Housing Review
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• v.15 no.3
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• pp.177-188
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• 2024

This study aims to identify vulnerability factors through comprehensive safety diagnosis and to seek improvement measures for the safety and maintenance of facilities. In this study, the results of road tunnel inspections and diagnostics were converted into a database (DB). Using this data, we explored to identify vulnerable elements (NATM, ASSM) based on structural types and to develop efficient improvement measures. In this study, we analyzed 76 detailed safety diagnosis reports covering 45 different types of road tunnel facilities. In the detailed guidelines for comprehensive safety diagnosis, the database (DB) items for identifying vulnerable factors were selected by categorizing the basic information, such as the year of completion and damage items. In addition, AHP analysis was conducted separately through experts in related fields to analyze the correlation between damages. As a result, the primary vulnerability factors for NATM and ASSM were identified as cracks, leaks, insufficient lining thickness, and joint rear. ASSM was identified as relatively more susceptible to network cracks and material separation compared to NATM. In contrast, flaking and rebar exposure were interpreted as more significant vulnerabilities for NATM than for ASSM. In addition, the correlation between elements in NATM was found to be low, whereas in ASSM, the correlation between elements was high, indicating a more organic relationship.

• Korean Journal of Human Ecology
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• v.7 no.1
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• pp.217-233
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• 1998

Foodservice management practices in 52 educare centers in Jeonbuk province were evaluated in order to provide basic informations and guidelines for the standardization of foodservice management and facilities in the educare centers. The survey was conducted using the structured questionnaire. The results are summarized as follows: 1. Only 10% of the centers investigated had the stationed dietitian, therefore most of foodservice management was not conducted by a professional personnel. The average number of kitchen employees was 1.3 and significantly different with type(p<0.05) and size(p<0.001) of the centers, which was not enough to meet the regulation. 2. Menu planning was performed mostly(59.6%) by managers and teachers of educare centers. Food items were purchased(94.7%) and recieved(91.6%) by kitchen employees or center managers and teachers. Produced foods were also evaluated(97.7%) and distributed(100%) by kitchen employees or center managers and teachers depending on their experience without any supervision of the professional personnel for the mass production. 3. Among the centers studied, 84.6% of them conducted nutrition education programs regularly by teachers. About 77.3% of them evaluated that these programs did not accomplish the proper training for good food habit because of the lack of nutritional knowledge(54.5%) and educational media(27.3%). 4. In general, the hygienic maintenance was evaluated as fair state to need the improvement. 5. Kitchen facilities and equipments were similar to those of home cooking and did not meet the standards for institutional practices. Besides, automated machinery and tools for safety, sanitation and improvement of work efficiency were far short. 6. Log book for the foodservice management was not prepared properly, which made the systematic planning and operation of the foodservice facilities difficult.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.7
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• pp.3518-3527
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• 2013

The new developed train(HEMU-430X) faces running at high speed over 400km/h. But The Korea railway design code gives guidelines below 350km/h speed. Honam HighSpeed Railway was also designed based on the design standard below 350km/h. Existing infra structures have to be reviewed at high speed running and the design guideline for the speed over 350km/h should be prepared as soon as possible. This paper presents (1) the simulation results of composite steel girder bridge(Kaya Bridge of Seoul-Pusan HighSpeed Railway), (2) values measured at this bridge and the comparison with simulation results, and (3) the prediction of Yonjung bridge being constructed in Honam HighSpeed Railway.

• Journal of Korean Society of Water and Wastewater
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• v.26 no.2
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• pp.191-199
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• 2012

Rainwater harvesting systems (RWHS), one of measures for on site rainwater management, have been promoted by laws, regulations and guidelines and have been increased. However, more evaluation of economic feasibility on RWHS is still needed due to seasonal imbalance of rainfall and little experiences and analysis on design and operation of RWHS. In this study, we investigated tank capacity of RWHS to secure economic validity considering catchment area and water demand, which is affected by building scale. Moreover, sensitivity analysis was performed to examine the effect of design factors, cost items and increase rate of water service charge on economic feasibility. The BCR (benefit cost ratio) is proportional to the increase in tank capacity. It is increased steeply in small tank capacity due to the effect of cost and, since then, gently in middle and large tank capacity. In case of 0.05 in the rate of tank volume to catchment area and 0.005 in water demand to catchment area, BCR was over one from the tank capacity of 160 $m^{3}$ taking into account of private benefits and from the tank capacity of 100 $m^{3}$ taking into account of private and public benefits. Sensitivity analysis shows that increase of water demand can improve BCR values with little cost so that it is needed to extend application of rainwater use and select a proper range of design factor. Decrease of construction and maintenance cost reduced the tank volume to secure economic validity. Finally, increase rate of water service charge had considerable impact on economic feasibility.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.1
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• pp.285-292
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• 2014

BIM (Building Information Modeling) is a new paradigm that includes construction life-cycle, and BIM has become mandatory regulation according to the Public Procurement Service since 2016, which accelerates its application. BIM is now expand from architectural field to infrastructure industry. Through pilot projects, BIM has been challenged with verification process. This trend has affected to maintenance and operation (M&O) phase of construction life-cycle. Advanced country has already published their research and result with feasibility study and guidelines. In this paper, we conduct the feasibility study to adopt BIM-based infrastructure management system. Bridges and tunnels were selected as application target, and benefit/cost ratio were used. The result shows that BIM-based infrastructure management system is feasible when the level of detail is more than "Medium" in bridge, and "High" in tunnel.