• Journal of the Korean GEO-environmental Society
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• v.12 no.1
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• pp.61-70
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• 2011

The impact protection system consists of an arrangement of circular sheet pile cofferdams-denoted dolphin structuredeeply embedded in the seabed, filled with crushed rock and closed at the top with a robust concrete cap. Centrifuge model tests were performed to investigation the behaviors of dolphins in this study. Total 7 quasi-model tests and 11 dynamic model tests were performed. The main experimental results can be summarized as follows. Firstly, The experimental force-displacement results for quasi-static tests show a limited influence on the initial stiffness of the structure from the change in fill density and the related change in the stiffness of the fill. And by comparing the dissipation at the same dolphin displacement it was found that the denser fill increase the dissipation by 16% for the 20m dolphin and by 23% for the 30m dolphin. The larger sensitivity for the large dolphin is explained by a larger contribution to the dissipation from strain in the fill. In low level impacts the dynamic force-response is up to 26~58% larger than the quasi-static and the dissipation response is showed larger in small displacement. Hence, it is concluded conservative to use the quasi-static response characteristics in the approximation of the response, and it is further concluded that the dolphin resistance to low level impacts is demonstrated to be equivalent and even superior to the high level impacts.

• (The)Study of the Eastern Classic
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• no.70
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• pp.157-183
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• 2018

Mokjae Lee Samhwan's "MaengHoEum" is the three poems of the Chinese quatrain of 5word 7poetry created according to the previous age. This poem is distinguished from the poem of the general "MaengHoHaeng" series because of it was created in the form of modern-style poetry of series, not a poetry of 5word or 7word or length phrase in a poem. The "MaengHoEum" of MokJae seems to have been built around 1801year when he was 73 years old. Therefore, his "MaengHoEum" can be called an allegory poetry or a society poetry and his poetry can be said that it was created under the criticism of the corrupt political power of the contemporary society, and the 'fierce tiger' which appeared in his poem refers to the factions of Noron Byek line which was the ruling power at that time. However, if you look at the "MaengHoEum" of MokJae, you will see a criticism of the real world, but the feeling is not intense or the description is not concrete. Although his poetry depicts the absurdity of the present reality, but he does not show positive criticism of reality or strong resistance. This characteristic, which can be seen in his poem "MaengHoEum", is the result of the study he pursued for the his life and is thought to be due to the weight of reality. The contradictions of the time of the Mokjae were never silent to him, but on the other hand he could not reveal his own struggle on the surface of the poem. Between his descendants, influenced by his actions, and the stinging gaze watching him, he had no choice but to end his feelings internally.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.1
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• pp.67-72
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• 2022

Concrete prevents corrosion of reinforcing bars due to its strong alkalinity. However, in the sea, strong alkali components with a pH of 12 to 13 are eluted, which adversely affects the ecological environment and growth of marine organisms. In this study, the mechanical properties and durability of the low alkali mortar were evaluated for the development of a low alkali mortar for the 3D printed artificial reefs. As a result of evaluation of strength characteristics, the α-35 mixture, which were produced with fly ash, silica fume and α-hemihydrate gypsum, satisfied the strength requirement 27 MPa in terms of compressive strength. As a result of pH measurement, it was found that mixing with alpha-type hemihydrate gypsum resulted in minimizing pH due to the the formation of calcium sulfate instead of calcium hydroxide production. As a result of the chloride ion penetration resistance test, the α-35 mixture exhibited the best performance, 3844C. As a result of measuring the length change over time, the α-35 mixture showed the shrinkage 33.5% less compared to the Plain mix.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.4
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• pp.62-69
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• 2023

This study investigated the electromechanical properties of cement based smart repair materials (SRMs) according to the different amounts of fine steel slag aggregates (FSSAs). SRMs can self-diagnose the quality of repairing and self-sense the damage of repaired zone. The replacement ratios of FSSAs to sand for SRMs were 0% (FSSA00), 25% (FSSA25), and 50% (FSSA50) by sand weight. The electrical resistivity of SRMs generally decreased as the compressive stress of SRMs increased: the electrical resistivity of FSSA25 at the age of 7 hours decreased from 78.16 to 63.68 kΩ-cm as the compressive stress increased from 0 to 22.37 MPa. As the replacement ratio of FSSAs by weight of sand increased from 0% to 25%, the stress sensitivity coefficient (SSC) of SRM at the age of 7 h increased from 0.471 to 0.828 %/MPa owing to the increased number of partially conductive paths in the SRMs. However, as the replacement ratio of FSSAs further increased up to 50%, the SSC decreased from 0.828 to 0.649 %/MPa because some of the partially conductive paths changed to continued conductive ones. SRMs are expected to self-sense the quality and future damage of repaired zone only by measuring the electrical resistivity of the repaired zone in addition to fast recovery in the mechanical resistance of structures.

• Journal of the Korean Geosynthetics Society
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• v.22 no.2
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• pp.71-83
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• 2023

It is very important to predict the amount of settlement in order to maintain the function of the coastal structure. Finite element analysis methods and real and model experiments are used as methods for this, but this has the disadvantage of requiring a lot of cost and time. Therefore, this study was conducted for the purpose of a simple formula proposal that can easily predict the amount of settlement of the caisson-type quay wall structure. In the research process, after calculating the PSI (Power Spectrum Intensity) of the velocity, the amount of settlement of the structure is calculated by substituting it into the simple formula of the existing gravity breakwater. By comparing and analyzing the amount of settlement of the structure obtained through numerical analysis, it was confirmed that the error between the amount of settlement of the existing simple formula and the amount of settlement of the numerical analysis was large, and it was confirmed that the background could not be considered in the case of the existing simple formula. Therefore, this study proposed a correction factor for the background of the quay wall structure, indicating a simple formula that can obtain the amount of settlement of the caisson-type quay wall structure. Compared to the numerical analysis settlement amount, it was judged that this simple formula had sufficient precision in calculating the caisson-type quay wall settlement amount. In addition, facilities vulnerable to earthquake resistance can be easily extracted in situations where time and cost are insufficient, and it is expected to be used as a screening technique.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2A
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• pp.169-176
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• 2010

Generally, poly-urea is widely used as waterproof coating material due to its superior adhesiveness, elongation capacity, and permeability resistance. In addition, it can be quickly and easily applied on structure surfaces using spray application. Since it hardens in about 30 seconds after application, its construction efficiency is very high and its usage as a special functional material is also excellent. However, currently, poly-urea is mostly used as waterproof coating material and the researches on its usage as a retrofitting material is lacking at best. Therefore, basic studies on the use of poly-urea as a general structural retrofitting material are needed urgently. The objective of this study is to develop most optimum poly-urea composition for structure retrofitting purpose. Moreover, the structural strengthening capacity of the developed poly-urea is evaluated through flexural capacity experiments on RC beams and RC slabs. From the results of the flexural test of poly-urea strengthened RC beam and slab specimens, the poly-urea and concrete specimen showed monolithic behavior where ductility and ultimate strength of the poly-urea strengthened specimen showed slight increase. However, the doubly reinforced specimens with FRP sheet and poly-urea showed lower capacity than that of the specimen reinforced only with FRP sheet.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4A
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• pp.647-657
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• 2006

Probabilistic Risk Assessment considering statistically random variables is performed for the preliminary design of a Cable Stayed Bridge, which is Prestressed Concrete Bridge consisted of cable and plate girders, based on the method of Working Stress Design and Strength Design. Component reliabilities of cables and girders have been evaluated using the response surface of the design variables at the selected critical sections based on the maximum shear, positive and negative moment locations. Response Surface Method (RSM) is successfully applied for reliability analyses for this relatively small probability of failure of the complex structure, which is hard to obtain through Monte-Carlo Simulations. or through First Order Second Moment Method that can not easily calculate the derivative terms of implicit limit state functions. For the analysis of system reliability, parallel resistance system consisting of cables and plate girder is changed into series connection system and the result of system reliability of total structure is presented. As a system reliability, the upper and lower probabilities of failure for the structural system have been evaluated and compared with the suggested prediction method for the combination of failure modes. The suggested prediction method for the combination of failure modes reveals the unexpected combinations of element failures in significantly reduced time and efforts compared with the previous permutation method or system reliability analysis method, which calculates upper and lower bound failure probabilities.

• The Southeast Asian review
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• v.19 no.2
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• pp.1-56
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• 2009

It is generally acknowledged that Philippines politics has achieved a basic soil for democracy at the macro-level by the two incidents of 'People Power' (1986 & 2001). However, in spite of such an achievement, Philippine politics at the micro-level, does not enjoy the same reputation. Institutionalized 'Bossism' or 'patron/clientelism' political culture has been attributed to make such a gap. This paper aims to bridge the gap by a longitudinal observation on local politics of a particular province in the Philippines. Surigao del Norte is the province picked up for the study. The reason why this particular province attracts special concerns is that there appears to come a very dynamic local politics, led by an indigenous Christian organization, the PBMA (Philippines Benevolent Missionary Association), which was founded in the mid 1960s. With the coming of the organization in the province, the political power of the traditional families has been narrowed. On the other hand, new families, not only the leader family of the PBMA but also the family allied with the PBMA, has expanded political influence. Following steps are adopted to understand the meaning of such a change. First, institutional frame of Philippine politics and elections will be reviewed. Second, demographic changes will be investigated on Surigao del Norte province to find out how popular the PBMA organization is among the people. Third, local election outcomes will be examined to describe the changing nature of political landscape of the province. This will reveal how the relationship between the old and new families has been developed in the province. Lastly, based on the facts discovered by a longitudinal observation, an attempt to evaluate theories on Philippines politics will be made Conclusions are as follows. To understand the dynamics of Philippine politics, 'expectations from the below,' or, 'passions of the people,' suggested by Ileto, needs more attention. Furthermore, 'mutual accommodation' between domination and resistance, coined by Abinales, also demands more appreciation. The case of local politics in the Surigao del Norte, with the coming of the PBMA, is sure to show a concrete example of changing politics in the 'changeless land.'

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.3
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• pp.184-191
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• 2023

With increasing corrosion in RC (Reinforced Concrete) structures, cracks occurred due to corrosion products and bearing load resistance decreased. In this study, corrosion was induced through an accelerated corrosion test (ICM: Impressed Current Method) with 140 hours of duration, and changes in USV (Ultra-Sonic Velocity), flexural failure load, and corrosion weight were evaluated before and after corrosion test. Three levels of cover depth (20 mm, 30 mm, and 40 mm) were considered, and the initial cracking period increased and the rust around steel decreased with increasing cover depth. In addition, the USV linearly decreased with decreasing cover depth and increasing amount of corrosion. In the flexural loading test, the bending capacity decreased by more than 10% due to corrosion, but a clear correlation could not be obtained since the corrosion ratio was small, so that the effect of slip was greater than that of reduced cross-sectional area of steel due to corrosion. As cover depth increased, the produced corrosion amount and USV changed with a clear linear relationship, and the cracking period due to corrosion could be estimated by the gradient of the measured corrosion current.

• Journal of the Korean Geotechnical Society
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• v.40 no.1
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• pp.5-14
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• 2024

PHC piles demonstrate superior resistance to compression and bending moments, and their factory-based production enhances quality assurance and management processes. Despite these advantages that have resulted in widespread use in civil engineering and construction projects, the design process frequently relies on empirical formulas or N-values to estimate the soil-pile friction, which is crucial for bearing capacity, and this reliance underscores a significant lack of experimental validation. In addition, environmental factors, e.g., the pH levels in groundwater and the effects of seawater, are commonly not considered. Thus, this study investigates the influence of vibrating machine foundations on PHC pile models in consideration of the effects of varying pH conditions. Concrete model piles were subjected to a one-month conditioning period in different pH environments (acidic, neutral, and alkaline) and under the influence of seawater. Subsequent repeated direct shear tests were performed on the pile-soil interface, and the disturbed state concept was employed to derive parameters that effectively quantify the dynamic behavior of this interface. The results revealed a descending order of shear stress in neutral, acidic, and alkaline conditions, with the pH-influenced samples exhibiting a more pronounced reduction in shear stress than those affected by seawater.