• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.2
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• pp.425-433
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• 2019

In this study, a simple method of calculating the passive earth pressure coefficient, which is based on the limit equilibrium method, was proposed and the calculated earth pressure coefficients were compared with those of several researchers. The angle of the linear failure surface, which is combined with the logarithmic spiral arc, to the failure surfaces of the passive zone was derived and the whole passive thrust acting on the Rankine passive zone was considered in the proposed method instead of considering the horizontal component of passive thrust. The variations of the passive earth pressure coefficients of the proposed method showed the same tendency as that of the Coulomb's passive earth pressure coefficients with an inclined angle of backfill and internal friction angle. The magnitude of passive earth pressure coefficients of the proposed method were smaller than those of the Coulomb in almost all cases. A comparison of the passive earth pressure coefficients with the wall friction angle revealed the passive earth pressure coefficients of the proposed method to be smaller than those of the Coulomb and the differences between the two values increased with increasing internal friction angle and wall friction angle. A comparison of the passive earth pressure coefficients of the proposed method with those of the existing researchers for the considered internal friction angles of $25^{\circ}$, $30^{\circ}$, $35^{\circ}$, and $40^{\circ}$ and three wall friction angles revealed the maximum percentage differences for the Kerisel and Absi method, Soubra method, Lancellotta method, $Ant\tilde{a}o$ et al. method, Kame method, and Reddy et al. method to be 4.8%, 3.8%, 31.1%, 4.0%, 20.6%, and 12.8% respectively. The passive earth pressure coefficient and existing pressures were similar in all cases.

• Korean Journal of Heritage: History & Science
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• v.38
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• pp.329-358
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• 2005

The Three storied Stone pagoda in Gameunsa Temple site, one of the early staged stone pagodas, has been known as a standard for Silla stone pagodas. A stone pagoda is not only a stone art work and but also a stone structure. Most studies and investigation of the stone pagoda has done mainly based on style and chronological research according to an art historical view. However, there is not an attempt to research the stone pagoda as a stone architecture. Most Korean experts at the stone pagoda has art history in their background. Engineers who can understand the structure of the stone pagoda are very limited. More architectural and engineering approach is need to research not only art historial understanding but also safety as a structure. We can find many technical know-how from our ancestors who made stone pagodas. 1. To reduce any deformation such as relaxation and sinking of BuJae which is caused by a heavy load, the BuJae (consist of a foundation stone and lower stereobates) should be enlarged. 2. A special construction method for connection between Myonsuk and Tangjoo was invented. This unique method is not used any longer after the Three storied Stone pagoda in Gameunsa Temple site. 3. The upper BuJae and the lower BuJae are missed each other by making a difference of Okgaesuk and Okgaebatchim in size. It is done for a distribution of perpendicular load and a prevention for relaxation of BuJae. 4. The center of gravity in the BuJae is located to the center of the stone pagoda by trimming the upper surface of the Okgaebatchim into a convex shape. The man who made stone pagodas had excellent knowledge on the engineering and techniques to understand the structure of the stone pagodas. We can confirm it as follows: the enlarged BuJae, dislocated connection between upper Bujae and lower BuJae, and moving the center of gravity close to the center of the stone pagoda.

• Journal of the Korean Society of Radiology
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• v.83 no.2
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• pp.344-359
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• 2022

Purpose To develop a denoising convolutional neural network-based image processing technique and investigate its efficacy in diagnosing breast cancer using low-dose mammography imaging. Materials and Methods A total of 6 breast radiologists were included in this prospective study. All radiologists independently evaluated low-dose images for lesion detection and rated them for diagnostic quality using a qualitative scale. After application of the denoising network, the same radiologists evaluated lesion detectability and image quality. For clinical application, a consensus on lesion type and localization on preoperative mammographic examinations of breast cancer patients was reached after discussion. Thereafter, coded low-dose, reconstructed full-dose, and full-dose images were presented and assessed in a random order. Results Lesions on 40% reconstructed full-dose images were better perceived when compared with low-dose images of mastectomy specimens as a reference. In clinical application, as compared to 40% reconstructed images, higher values were given on full-dose images for resolution (p < 0.001); diagnostic quality for calcifications (p < 0.001); and for masses, asymmetry, or architectural distortion (p = 0.037). The 40% reconstructed images showed comparable values to 100% full-dose images for overall quality (p = 0.547), lesion visibility (p = 0.120), and contrast (p = 0.083), without significant differences. Conclusion Effective denoising and image reconstruction processing techniques can enable breast cancer diagnosis with substantial radiation dose reduction.

• Journal of the Korea Concrete Institute
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• v.29 no.4
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• pp.415-424
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• 2017

The purpose of this study is to investigate the effect of sulfate (${SO_4}^{2-}$) and magnesium ($Mg^{2+}$) ions on sulfate resistance of Alkali-activated materials using Fly ash and Ground granulated blast furnace slag (GGBFS). In this research, 30%, 50% and 100% of GGBFS was replaced by sodium silicate modules ($Ms(SiO_2/Na_2O)$, molar ratio, 1.0, 1.5 and 2.0). In order to investigate the effects of $Mg^{2+}$ and ${SO_4}^{2-}$, compression strength, weight change, lengh expansion of the samples were measured in 10% sodium sulfate ($Na_2SO_4$), 10%, 5% and 2.5% magnesium sulfate ($MgSO_4$), 10% magnesium nitrate ($Mg(NO_3)_2$), 10% [magnesium chloride ($MgCl_2$) + sodium sulfate ($Na_2SO_4$)] and 10% [magnesium nitrate $(Mg(NO_3)_2$ + sodium sulfate ($Na_2SO_4$)] solution, respectively and X-ray diffraction analysis was conducted after each experiment. As a result, when $Mg^{2+}$ and ${SO_4}^{2-}$ coexist, degradation of compressive strength and expansion of the sample were caused by sulfate erosion. It was found that the reaction of $Mg^{2+}$ with Calcium Silicate Hydrate (C-S-H) occurred and $Ca^{2+}$ was produced. Then the Gypsum ($CaSO_4{\cdot}2H_2O$) was formed due to reaction between $Ca^{2+}$ and ${SO_4}^{2-}$, and also Magnesium hydroxide ($Mg(OH)_2$, Brucite) was produced by the reaction between $Mg^{2+}$ and $OH^-$.

• Journal of the Korea Institute of Building Construction
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• v.18 no.2
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• pp.141-149
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• 2018

In this study, compacting, passing performance, segregation resistance and rheological properties were tested to improve the stability of fresh concrete in the production and construction of self-compacting concrete (SCC) using hollow glass powder(GB). As a result, T50 reaching time was shortened up to amount of GB $2.0kg/m^3$. The compacting according to the amount of GB was improved by ball bearing effect of GB. However, T50 reaching time was slightly increased at $4.0kg/m^3$. In the case of passing performance, the result showed that plain was Class 1, GB $0.5{\sim}2.0kg/m^3$ was Class 0, GB $4.0kg/m^3$ was Class 1. Therefore, the passing performance was improved with 'No blocking' up to amount of GB $2.0kg/m^3$. Passing performance Block step (PJ) number by J-ring method was also best at GB $1.0kg/m^3$. In the case of segregation resistance according to the amount of GB, dynamic segregation resistance was increased compared to plain regardless of the amount of GB. And static segregation resistance showed 2.5% of segregation rate at GB $1.0kg/m^3$. Therefore, it was greatly improved compared to plain (12.5%). In the case of rheology property according to the amount of GB, plastic consistency by increasing of GB content didn't show big difference. However, yield stress by increasing of GB content was decreased with GB $1.0kg/m^3$. In conclusion, GB $1.0kg/m^3$ was effective for improvement of compacting, passing performance and yield stress. Also, it will be useful for stability of SCC by improving segregation.

• Economic and Environmental Geology
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• v.49 no.6
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• pp.459-467
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• 2016

Due to the limited areal space for installation, borehole heat exchangers (BHEs) at depths deeper than 300 m are considered for geothermal heating and cooling in the urban area. The deep vertical closed-loop BHEs are unconventional due to the depth and the range of the typical installation depth is between 100 and 200 m in Korea. The BHE in the study consists of 50A (outer diameter 50 mm, SDR 11) PE U-tube pipe in a 150 mm diameter borehole with the depth of 300 m. In order to compensate the buoyancy caused by the low density of PE pipe ($0.94{\sim}0.96g/cm^3$) in the borehole filled with ground water, 10 weight band sets (4.6 kg/set) were attached to the bottom of U-tube. A thermal response test (TRT) and fundamental basic surveys on the thermophysical characteristics of the ground were conducted. Ground temperature measures around $15^{\circ}C$ from the surface to 100 m, and the geothermal gradient represents $1.9^{\circ}C/100m$ below 100 m. The TRT was conducted for 48 hours with 17.5 kW heat injection, 28.65 l/min at a circulation fluid flow rate indicates an average temperature difference $8.9^{\circ}C$ between inlet and outlet circulation fluid. The estimated thermophysical parameters are 3.0 W/mk of ground thermal conductivity and 0.104 mk/W of borehole thermal resistance. In the stepwise evaluation of TRT, the ground thermal conductivity was calculated at the standard deviation of 0.16 after the initial 13 hours. The sensitivity analysis on the borehole thermal resistance was also conducted with respect to the PE pipe diameter and the thermal conductivity of backfill material. The borehole thermal resistivity slightly decreased with the increase of the two parameters.

• Journal of the Korea Concrete Institute
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• v.19 no.1
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• pp.121-130
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• 2007

To investigate the enhancement in strength and deformation capacities of concrete confined by FRP composites, tests under axial loads were carried out on three groups of thirty six short columns in circular section with diverse GFRP confining reinforcement. The major test variables considered include fiber content or orientation, wrap or tube type by varying the end loading condition, and continuous or discontinuous confinement depending on the presence of vortical spices between its two halves. The circumferential FRP strains at failure for different types of confinements were also investigated with emphasis. Various analytical models capable of predicting the ultimate strength and strain of the confined concrete were examined by comparing to observed results. Tests results showed that FRP wraps or tubes provide the substantial increase in strength and deformation, while partial wraps comprising the vertical discontinuities fail in an explosive manner with less increase in strength, particularly in deformation. A bilinear stress-strain response was observed throughout all tests with some variations of strain hardening. The failure hoop strains measured on the FRP surface were less than those obtained from the tensile coupons in all tests with a high degree of variation. In overall, existing predictive equations overestimated ultimate strengths and strains observed in present tests, with a much larger scatter related to the latter. For more accuracy, two simple design- oriented equations correlated with present tests are proposed. The strength equation was derived using the Mohr-Coulomb failure criterion, whereas the strain equation was based on entirely fitting of test data including the unconfined concrete strength as one of governing factors.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.3
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• pp.147-160
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• 2020

A stochastic probabilistic model for harbor structures such as rubble-mound breakwater has been formulated by using the generalized Wiener process considering the nonlinearity of damage drift and its nonlinear uncertainty, by which the damage path with real-time can be tracked, the residual useful lifetime at some age can also be analyzed properly. The formulated stochastic model can easily calculate the probability of failure with the passage of time through the probability density function of cumulative damage. In particular, the probability density functions of residual useful lifetime of the existing harbor structures can be derived, which can take into account the current age, its present damage state and the future damage process to be occurred. By using the maximum likelihood method and the least square method together, the involved parameters in the stochastic model can be estimated. In the calibration of the stochastic model presented in this paper, the present results are very well similar with the results of MCS about tracking of the damage paths as well as evaluating of the density functions of the cumulative damage and the residual useful lifetime. MTTF and MRL are also evaluated exactly. Meanwhile, the stochastic probabilistic model has been applied to the rubble-mound breakwater. The related parameters can be estimated by using the experimental data of the cumulative damages of armor units measured as a function of time. The theoretical results about the probability density function of cumulative damage and the probability of failure are very well agreed with MCS results such that the density functions of the cumulative damage tend to move to rightward and the amounts of its uncertainty are increased as the elapsed time goes on. Thus, the probabilities of failure with the elapsed time are also increased sharply. Finally, the behaviors of residual useful lifetime have been investigated with the elapsed age. It is concluded for rubble-mound breakwaters that the probability density functions of residual useful lifetime tends to have a longer tail in the right side rather than the left side because of the gradual increases of cumulative damage of armor units. Therefore, its MRLs are sharply decreased after some age. In this paper, the special attentions are paid to the relationship of MTTF and MRL and the elapsed age of the existing structure. In spite of that the sum of the elapsed age and MRL must be equal to MTTF deterministically, the large difference has been shown as the elapsed age is increased which is due to the uncertainty of cumulative damage to be occurred in the future.

• Journal of the Korean Institute of Landscape Architecture
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• v.46 no.5
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• pp.44-58
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• 2018

Cities face new challenges not only in natural disasters by climate change but also in social and economic fluctuations. With the existing simple reconstruction method, it is difficult to solve the overall problems that a city or region may face. As a new approach to cope with various changes, the concept of resilience is emerging. Resilience is also one of the themes of recent major urban design projects. Design with the concept of resilience is a new strategy that can deal with various changes of urban space, rather than a temporary trend. The purpose of this paper is to explore the design method by analyzing cases where the concept of resilience is employed. We aim to examine what kind of design strategies are needed for the resilience design and how this design process differ in character, as compared to general design projects. Cases for this study include the "Rebuild by Design" competition held in 2013 and the "Resilient by Design/Bay Area Challenge" competition held in 2017. This paper consists of literature reviews and case studies. The latter is divided into two aspects: content analysis based on the theory of resilience and characteristics of the design process. Cases are analyzed through literature reviews and process characteristics of resilience design in response to the general design process. The main categories for urban resilience used as the framework for analysis include: Urban Infrastructure, Social Dynamics, Economic Dynamics, Health and Wellbeing, Governance Networks, and Planning and Institutions. As a result, the aspects of resilience concepts considered and design strategies undertaken by each team were identified. Each team tried to connect all 6 categories to their design strategies, placing special value on the role of governance, a system that enables collaborative design and project persistency. In terms of the design process, the following characteristics were found: planning the whole project process in the pre-project phase, analyzing predictable socioeconomic risk factors in addition to physical vulnerabilities, aiming for landscape-oriented integrated design, and sustainable implementation strategies with specific operations and budget plans. This paper is meaningful to connect the concept of resilience, which has been discussed in various articles, to design strategy, and to explore the possibility of constructing a practical methodology by deriving the characteristics of the resilience design process. It remains a future task to research design strategies that apply the concept of resilience to various types of urban spaces, in addition to areas that are vulnerable to disasters.

• Journal of Korean Society of Environmental Engineers
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• v.39 no.5
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• pp.246-254
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• 2017

Microcystin-LR (MC-LR) is one of most abundant microcystins, and is derived from blue-green algae bloom. Advanced oxidation processes (AOPs) are effective process when high concentrations of MC-LR are released into a drinking water treatment system from surface water. In particular, UV-based AOPs such as UV, $UV/H_2O_2$, $UV/O_3$ and $UV/TiO_2$ have been studied for the removal of MC-LR. In this study, UV-LED was applied for the degradation of MC-LR because UV lamps have demonstrated some weaknesses, such as frequent replacements; that generate mercury waste and high heat loss. Degradation efficiencies of the MC-LR (initial conc. = $100{\mu}g/L$) were 30% and 95.9% using LED-L (280 nm, $0.024mW/cm^2$) and LED-H (280 nm, $2.18mW/cm^2$), respectively. Aromatic compounds of natural organic matter changed to aliphatic compounds under the LED-H irradiation by LC-OCD analysis. For application to raw water, the Nak-dong River was sampled during summer when blue-green algae were heavy bloom in 2016. The concentration of extracellular and total MC-LR, geosmin and 2-MIB slightly decreased by increasing the LED-L irradiation; however, the removal of MC-LR by UV-LED (${\lambda}=280nm$) was insufficient. Thus, advanced UV-LED technology or the addition of oxidants with UV-LED is required to obtain better degradation efficiency of MC-LR.