• Journal of the Earthquake Engineering Society of Korea
• /
• v.25 no.6
• /
• pp.261-266
• /
• 2021

Nuclear power plants in Korea were designed and evaluated based on the NRC's Regulatory Guide 1.60, a design response spectrum for nuclear power plants. However, it can be seen that the seismic motion characteristics are different when analyzing the Gyeongju earthquake and the Pohang earthquake that has recently occurred in Korea. Compared to the design response spectrum, seismic motion characteristics in Korea have a larger spectral acceleration in the high-frequency region. Therefore, in the case of equipment with a high natural frequency installed in a nuclear power plant, seismic performance may be reduced by reflecting the characteristics of domestic seismic motions. The failure modes of the equipment are typically structural failure and functional failure, with an anchorage failure being a representative type of structural failure. In this study, comparative analyses were performed to decide whether to consider the inelastic behavior of the anchorage or not. As a result, it was confirmed that the seismic performance of the anchorages could be increased by considering the inelastic behavior of an anchorage.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.41 no.1
• /
• pp.65-74
• /
• 2021

This study empirically analyzes the effect of pedestrians' personal and household characteristics and accessibility to public facilities on a walking safety satisfaction (WSS) level. The aim is to find ways to improve vulnerable pedestrians' WSS level and contribute to the creation of an inclusive urban environment. As a result of the analysis, age and gender variables were important for elderly people, and education was an important factor for disabled people. The WSS level was impacted by the factors of single-person households, income, and residential areas. In the case of accessibility to public facilities, the greater the satisfaction with accessibility to public institutions, urban parks and green areas, and public transport, the greater the WSS for the elderly and the disabled. And, the greater the satisfaction with accessibility to commercial facilities, the greater the WSS was for the elderly's WSS. However, the satisfaction with access to medical facilities was the opposite in the case of the elderly.

• Advances in concrete construction
• /
• v.11 no.5
• /
• pp.419-428
• /
• 2021

The pH of cement-based materials (CBMs) is an important factor for their durability, sustainability, and long service life. Currently, the use of supplementary cementitious materials (SCMs) is becoming mandatory due to economic, environmental, and sustainable issues. There is a decreasing trend in pH of CBMs due to incorporation of SCMs. The determination of numerical values of pH is very important for various low and high volume SCMs blended cement mortars for the better understanding of different defects and durability issues during their service life. In addition, the effect of cement hydration and pozzolanic reaction of SCMs on the pH should be determined at initial and later ages. In this study, the effect of low and high-volume fly ash (FA) and ground granulated ballast furnace slag (GGBFS) cement mortars in different curing conditions on their pH values has been determined. Thermal gravimetric analysis (TGA) was carried out to support the findings from pH measurements. In addition, thermal conductivity (k-value) and strength activity indices of these cement mortars were discussed. The results showed that pH values of all blended cement mortars were less than ordinary Portland cement (OPC) mortar in all curing conditions used. There was a decreasing tendency in pH of all mortars with passage of time. In addition, the pH of cement mortars was not only dependent on the quantity of Ca(OH)₂. The effect of adding SCMs on the pH value of cement mortar should be monitored and measured for both short and long terms.

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.57 no.4
• /
• pp.351-364
• /
• 2021

In this study, the vertical distribution of giant jellyfish analyzed echo counting method and such survey methods as sighting and trawl were used to compare its density estimates. In May and July 2021, surveys were conducted in the East China Sea and the coastal waters of Korea. As a result, Nemopilema nomurai were evenly distributed in all water layers in East China Sea in May and July. When considered the correlation by each survey methods, it is possible to identify jellyfish in the surface area by sighting method and using sampling net; however, it has a low correlation with acoustic estimates due to marine environmental factor such as weather condition, wind and atmospheric pressure. Therefore, the result can be utilized by basic data when estimating jellyfish's distribution patterns and density estimates from each survey methods hereafter.

• The Journal of Engineering Geology
• /
• v.31 no.1
• /
• pp.83-101
• /
• 2021

The high-density polyurethane method uses the instantaneous expansion pressure of injected material to stabilize soft ground, allowing reinforcement, restoration, and construction to be carried out in suboptimal ground conditions. Under normal and, even poor conditions, the method is easily applied because the working time is very short. The method is environmentally friendly and results have excellent durability. The purpose of this study was to verify the physical and mechanical properties of high-density polyurethane in the ground. Initial testing of strength, direct shear, and soil environment stability was followed by testing for permeability in order to address environmental concerns. The results of the experiments showed that the internal friction angle was about twice as high and the adhesion was about 2.5 to 3.5 times higher than for dense and hard clay, and that the permeability factor was significantly lower compared with the existing grouting method, within the range of 1.0 × 10-5.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.10 no.4
• /
• pp.402-410
• /
• 2022

The present study introduces a calibration method of the CSC model implemented in the LS-DYNA program for considering the material properties of ultra-high performance concrete(UHPC). Based on previous experimental studies, various parameters, which constitute three shear failure surfaces, pressure-volumetric strain curve, fracture energy, dynamic increase factor(DIF), and so on, are modified. Then, the proposed calibration method is verified by comparing the numerical result with the experimental data through the single element analysis. In addition, based on the established finite element models, the applicability of the calibrated CSC model is examined for UHPC structures subjected to impact and blast loadings.

• Journal of Software Assessment and Valuation
• /
• v.17 no.1
• /
• pp.75-82
• /
• 2021

Mastitis in cows is a major factor that hinders dairy productivity of farms, and many attempts have been made to solve it. However, research on mastitis has been limited to diagnosis rather than prediction, and even this is mostly using a single sensor. In this study, a predictive model was developed using multivariate data including biometric data and environmental data. The data used for the analysis were collected from robot milking machines and sensors installed in farmhouses in Chungcheongnam-do, South Korea. The recurrent neural network model using three weeks of data predicts whether or not mastitis is diagnosed the next day. As a result, mastitis was predicted with an accuracy of 82.9%. The superiority of the model was confirmed by comparing the performance of various data collection periods and various models.

• Geomechanics and Engineering
• /
• v.28 no.6
• /
• pp.637-644
• /
• 2022

Loess soils are unsaturated and widely distributed in the northwest zone in China. Many steep slope of unsaturated are observed are observed to be naturally stable. However, a low factor of safety (FoS) for these slopes would be computed from the slope stability analysis following local code practices. It seems that the analyzed results following the local code practices do not agree with the real condition as observed in the field. It is commonly known that soil suction plays an important role in slope stability due to a higher shear strength of the unsaturated soil as compared with that of the saturated soil. In this paper, it is observed that the computed FoS can also be affected by unsaturated unit weight of the soil. However, the effect of unsaturated unit weight of the soil on the slope stability is commonly ignored in engineering practice. Therefore, both the effects of shear strength and unit weight of the unsaturated soil on the computed FoS of unsaturated soil slope are investigated in this study. It is observed that the unsaturated unit weight of soil on the computed FoS increases with increase in slope angle. It is also observed that the effects of the unsaturated shear strength and unsaturated unit weight on the computed FoS are more significant than the effect of 3D analyses compared to the 2D analyses on the FoS.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.26 no.6
• /
• pp.112-119
• /
• 2022

Recently, as carbon neutrality has been important factor in the construction industry, many studies have been conducted on the high-volume fly ash concrete. High volume fly ash concrete(HVFC) is usually made by replacing more than 50% of cement with fly ash. However, HVFC has a disadvantage of low compressive strength in early age. To overcome this shortcoming of HVFC, improve this, interest in techonolgy using nanomaterials is increasing. Nano silica is expected to improve the early age strength of HVFC as a pozzolanic material. This study investigated the effect of nano silica on the early hydration reaction and microstructure of HVFC. The early hydration reaction of HFVC was analyzed through setting time, isothermal calorimeter, compressive strength and thermal weight analysis. In addition, the microstructure of HVFC was measured by mercury intrusion porosimetry. From the test results, it was confirmed that nano silica increased the early age strength and improve the microstructure of HVFC.

• Journal of the Korean Geotechnical Society
• /
• v.24 no.8
• /
• pp.81-88
• /
• 2008

In this study, to determine the priority of the effect factors and the preferences of commonly used reinforcing methods for the cut-slope, the reasonable analysis using AHP technique was performed. Analytic Hierarchy Process (AHP) technique is the most widely used method out of all existing decision making methods. On choosing the methods, the most important factor is analyzed to be the stability and durability. Stability, durability and environmental compatibility took up over 50% of the total contributing factors. Cut-slope reinforced method preference with increasing stability method confirmed that concrete retaining wall, reinforced-soil wall and cutting method showed the highest preference rate. Also, in practical field conditions, the cutting method out of four methods was chosen to be the most effective method. This reflected that the methods that are equally superior in all aspects of evaluation factors are more important than the methods with superiority in highly prioritized evaluation factors.