• 한국석유지질학회:학술대회논문집
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• spring
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• pp.56-65
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• 1998

Methane hydrate is ice-like solid compound consisting of mainly methane and water, and is stable under specific low temperature and high pressure conditions (HSZ : methane hydrate stability zone) that occurs in permafrost regions and in the ocean floor sediments. Geophysical survey was implemented in the southern area of the East Sea, and the HSZ of the study area is determined by the temperature, pressure and local heat flow obtained from the survey and well data. In the study area, methane hydrates could exist in the sediments below the water depths of about $300{\cal}m$, and the base of HSZ is about 600m beneath the seafloor. The acoustically blanking zones in the sediment and phenomena of gas seepage were detected from the seismic section. These sediments have the sufficient physical condition for the formation of methane hydrate. The temperature and pressure conditions were experimentally measured for the dissociation of methane and propane hydrates in Pure water. Equilibrium conditions of methane and propane hydrates were obtained in the pressure range up to 19050Kpa and 401.3Kpa. Under same temperature condition, propane hydrate was dissociated at lower pressure than that of methane hydrate.

• Earthquakes and Structures
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• v.6 no.2
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• pp.217-235
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• 2014

In this paper, different feedback control strategies are presented for active seismic control using proportional-integral-derivative (PID) type controllers. The parameters of PID controller are found by using an numerical algorithm considering time delay, maximum allowed control force and time domain analyses of shear buildings under different earthquake excitations. The numerical algorithm scans combinations of different controller parameters such as proportional gain ($K_p$), integral time ($T_i$) and derivative time ($T_d$) in order to minimize a defined response of the structure. The controllers for displacement, velocity and acceleration feedback control strategies are tuned for structures with active control at the first story and all stories. The performance and robustness of different feedback controls on time and frequency responses of structures are evaluated. All feedback controls are generally robust for the changing properties of the structure, but acceleration feedback control is the best one for efficiency and stability of control system.

• Proceedings of the Korean Geotechical Society Conference
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• 2007.09a
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• pp.39-52
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• 2007

A new type bridge combining an integral bridge and a pair of geosynthetic-reinforced soil (GRS) retaining walls having full-height rigid (FHR) facings, called the GRS integral bridge, is proposed. The geosynthetic reinforcement layers are connected to the FHR facings (i.e., RC parapets) that are integrated with a girder without using any girder-support. GRS integral bridges are basically much more cost-effective in construction and long-term maintenance while having a much higher seismic stability than conventional-type bridges having a girder via movable and fixed supports on a pair of cantilever abutments. GRS integral bridges are better than bridges using GRS retaining walls as abutments and also than conventional integral bridges with unreinforced backfill. To validate the above, a series of static cyclic lateral loading tests of the facing and a series of shaking table tests were performed on smallscaled models of different bridge types.

• Proceeding of KASS Symposium
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• 2008.05a
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• pp.212-217
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• 2008

This paper is concerned with the structural design of Angola Stadium. The Angola stadium is composed of a Steel moment frame system and a Cantilever steel truss roof. Whole structural analysis is necessary to ensure the stability. Considered FEM analysis, Design of Wind load & Seismic, Stand diaphragm, interaction between stand and Roof, Serviceability.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2011.11a
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• pp.197-198
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• 2011

Most of buildings' exterior walls are curtain wall systems and in the respect, the cleaning robot system is the main research item for cleaning and maintenance of them. We have structurely analysed the cases to review on the structural stability of the mullion members where the cleaning robot is attached. The result is showing that the largest stress is formed by the basic wind speed, which is specified in Korean Building Code-Structural.

• Geophysics and Geophysical Exploration
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• v.7 no.1
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• pp.19-24
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• 2004

Frequency-space domain full-wave tomography is a promising technique for delineating detailed subsurface structure with high resolution. However, this method requires criteria for the selection of a set of optimal temporal frequency components, to achieve stability in the sequence of inversion processes together with computational efficiency. We propose a method of selecting optimal temporal frequencies, based on wavenumber continuity. The proposed method is tested numerically and is shown to be able to select an optimal set of frequency components that are sufficient to image the anomalies.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1998.10a
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• pp.423-430
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• 1998

Elastomeric bearings are frequently used as a means to isolate structural systems from earthquake loadings. The combination of rubber layers and reinforcing steel shims makes the bearings stiff axially but soft laterally The shear flexibility of these short columns can lead to relatively low buckling loads which may be further reduced when high shear strains are simultaneously imposed. The area reduction formula has been proposed to account for the reduction in buckling load due to shear. The result obtained from the formula is presumed to be conservative but the degree of conservatism is unknown. This paper describes a numerical study which aims at determining the effect of high shear strain on the critical load of rubber bearings. The results from the finite element analysis which accounts for both the material and geometric non-linearities are compared against the theoretical results in order to examine the validity of the theoretical formulas.

• Geomechanics and Engineering
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• v.21 no.2
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• pp.143-152
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• 2020

Korean society experienced successive earthquakes exceeding 5.0 magnitude in the past three years resulting in an increasing concern about earthquake stability of urban infrastructures. This study focuses on the significant aspects of earthquake risk assessment for the cut-and-cover underground railway station based on two-dimensional dynamic numerical analysis. Presented are features from a case study performed for the railway station in Seoul, South Korea. The PLAXIS2D was employed for numerical simulation and input of the earthquake ground motion was chosen from Pohang earthquake records (M5.4). The paper shows key aspects of earthquake risk for soil-structure system varying important parameters including embedded depth, supported ground information, and applied seismicity level, and then draws several meaningful conclusions from the analysis results such as seismic risk assessment.

• Smart Structures and Systems
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• v.2 no.4
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• pp.305-312
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• 2006

In the case of hospital buildings, where seismic design requirements are very high, existing structuresand especially those attacked by past earthquakes, appear, often, unable to fulfil the necessary safety prerequisites. In this paper, the retrofitting of hospital buildings is investigated, using alternative methods of repair and strengthening. Analysis of an existing hospital building in Patras, Greece, is performed. The load-bearing system is a reinforced concrete system. Two solutions are proposed: strengthening using concrete jackets around column and beam elements and application of viscoelastic dampers for the increase of the stability of the structure. Adequate finite element models are constructed for each case and conclusions are drawn on the efficiency of each rehabilitation method.

• Structural Engineering and Mechanics
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• v.69 no.3
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• pp.307-315
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• 2019

This paper proposes a chattering-free sliding mode control (CFSMC) method for seismically excited structures. The method is based on a fuzzy logic (FL) model applied to smooth the control force and eliminate chattering, where the switching part of the control law is replaced by an FL output. The CFSMC is robust and keeps the advantages of the conventional sliding mode control (SMC), whilst removing the chattering and avoiding the time-consuming process of generating fuzzy rule basis. The proposed method is tested on an 8-story shear frame equipped with an active tendon system. Results indicate that the new method not only can effectively enhance the seismic performance of the structural system compared to the SMC, but also ensure system stability and high accuracy with less computational cost. The CFSMC also requires less amount of energy from the active tendon system to produce the desired structural dynamic response.