• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.3
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• pp.307-313
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• 2009

In general, pyroshock is generated from the actuation of separation devices for several stage, fairing, and satellite separation in the flight of a launch vehicle. During these events, transient vibration phenomenon called pyroshock, which shows large acceleration in the high frequency range, occurs and it can result in the malfunction of electronic components which is equipped inside the launch vehicle or satellite. In this paper, mesh washer isolators made out of SMA were introduced for the isolation of pyroshock. One type of isolator primarily used pseudoelastic characteristics of SMA and the other type of isolator used shape memory effect of SMA. For the study of basic load-displacement relationship of each SMA isolator, compressive loading tests were performed and the results showed the capability of the isolator itself. Pyroshock isolation tests were followed and verified the outstanding isolation performance of isolator. In addition, random vibration tests were also performed and checked the dynamic characteristics of each SMA isolator.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.5
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• pp.22-29
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• 2015

Modern structures is the tendency of being increasingly taller and larger. The concrete with large weight has the disadvantage of increasing the weight on the structure. therefore, the method of carrying out the weight saving of the concrete is required. one of such method is to use a lightweight aggregate. However, studies on structural lightweight concrete, lacking for the recognition of the lightweight concrete, so also is lacking. therefore it is necessary to study on the physical characteristic value of the lightweight concrete. In this study, in order to investigate the tensile properties of lightweight concrete, Crack mouth opening displacement (CMOD) experiments were carried out. the fracture energy of the lightweight concrete subjected to inverse analysis were derived from the CMOD experimental results.

• Journal of the Korean Geosynthetics Society
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• v.13 no.4
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• pp.109-117
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• 2014

Using the finite element analysis model presented in accompanying paper, parametric study was performed in this paper. Various parameters were considered such as the width of wheel loads-induced permanent plastic deformation, backfill, equivalent thickness and orthogonal characteristic of steel mats. The effects of these parameters were analyzed for vertical and rotational displacements, maximum moment and tensile stress. From the parametric studies, it is found that great vertical deflection and tensile stress above allowable flexural tensile strength are developed in steel mats by the wheel loads-induced permanent plastic deformation. Backfill or increasing the thickness of steel mats is a feasible solution on this problem.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.20-27
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• 2021

The present study presents a nonlinear finite element analysis (FEA) approach using the general program of Abaqus to evaluate the seismic response of unreinforced masonry walls strengthened with the steel bar truss system developed in the previous investigation. For finite element models of masonry walls, the concrete damaged plasticity (CDP) and meso-scale methods were considered on the basis of the stress-strain relationships under compression and tension and shear friction-slip relationship of masonry prisms proposed by Yang et al. in order to formulate the interface characteristics between brick elements and mortars. The predictions obtained from the FEA approach were compared with test results under different design parameters; as a result, a good agreement could be observed with respect to the crack propagation, failure mode, rocking strength, peak strength, and lateral load-displacement relationship of masonry walls. Thus, it can be stated that the proposed FEA approach shows a good potential for designing the seismic strengthening of masonry walls.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.8
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• pp.362-370
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• 2019

The internal pressure capacity of a modular containment structure requires analysis to prevent the release of radioactive material in the case of an accident. To analyze the capacity, FEM models were prepared while considering the tendon arrangements and the contact surfaces between precast concrete modules, and then static analyses were carried out. The changing characteristics in the displacement and stress under step-wise loading were analyzed, along with the effects of selected parameters. For comparison, the capacity of a monolithic containment structure was also analyzed. Parametric analyses were done to suggest ranges of parameters such as the tendon force, tendon spacing, tendon location in concrete thickness direction, friction coefficient, and concrete thickness. The tendon force and frictional force provide a combined effect between contact surfaces of modules. The same level of internal pressure capacity can be secured even in the modular containment structure as in the monolithic containment structure by increasing the tendon force with additional tendons.

• Journal of the Korean Geotechnical Society
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• v.25 no.4
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• pp.77-90
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• 2009

In this study, experimental analysis was performed about lateral load capacity and behavior of laterally loaded-bored rigid piles in muti-layered soil conditions. Lateral pile load tests were performed for muti-layerd soils consisting of different relative density. Ultimated lateral load capacities were measured from lateral load-displacement curves and compared with estimated values using theoretical methods. Bending moments and unit lateral capacity distribution of surrounding piles were measured from attached strain gauges and earth pressure sensors on the pile. It was found that ultimated lateral load capacities were different from the muti-layered soil conditions, and measured values were lower than estimated values. The bending moment distributions of the pile were similar all the time. Unit lateral capacity distributions were a little different from muti-layered soil conditions, but basically similar to the distribution proposed by Prasad and Chari (1999).

• Journal of the Korean Geotechnical Society
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• v.23 no.5
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• pp.131-141
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• 2007

Because pile behavior is governed by geotechnical characteristics of surrounding soils, it is therefore necessary to monitor ground responses during pile driving and analyze the relation between the behaviors of pile and ground. In this research, the 57 m long PHC pile was driven into deep soft clay in the Nakdong River estuary area. During and after the pile driving, the ground responses and the residual load of pile have been monitored for about a year, by using piezometers, inclinometers, level posts for surface settlement, and strain gauges in piles etc. As the results, the residual load by the negative skin friction along the pile increased with the dissipation of the excess pore pressure, which was developed by pile driving and reclamation. About 30% of the maximum residual load developed due to the dissipation of the increased excess pore pressure during the driving. It is thus emphasized that most piles driven in clay deposits need to be designed by considering negative skin friction along the pile.

• Composites Research
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• v.20 no.5
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• pp.1-6
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• 2007

This study was performed to make a comparison on low-velocity impact behavior between graphite/epoxy composite laminate and steel plate. In order to validate the proposed scheme fur the impact behavior of the plate, the Karas's impact model was used. The impact models for this comparative study are the graphite/epoxy composite plate having $[0/90/45/-45/-45/45/90/0]_{8S}$ laminate sequence and the steel plate with a steel ball impactor. The low-velocity impact behaviors for two types of plates were comparatively investigated and performed by considering different impactor velocities and weights respectively. In this investigation, it was found that the composite laminate has impact energy absorption effect due to more flexible behavior than the steel plate, and also it has better characteristics on impact damage and weight.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.6
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• pp.89-96
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• 2008

The purpose of this study is to investigate the flexural strengthening effectiveness for the beams reinforced with NSM CFRP strips. To accomplish this objective, concrete T beams were made and tested. From this study, it is found that the flexural stiffness and strength of the beams reinforced with NSM strips were significantly improved compared to the beams without CFRP strip. The maximum increase of flexural strength was 247%. Failure of the beam reinforced with NSM was initiated by a part of separation of NSM strips along the longitudinal direction, and the second failure of strips was investigated. After the first rupture of the NSM strips, the load dropped suddenly and the second rupture was succeeded. This result shows that a perfect composite reaction with NSM strips and concrete is possible in the beam reinforced with NSM CFRP strips the NSM strips and Near surface mounted(NSM) is one of the most recent and promising strengthening techniques for reinforced concrete structures.

• Journal of the Korean GEO-environmental Society
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• v.21 no.7
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• pp.17-26
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• 2020

The soft ground in the southwest coastal area composed of marine clay is greatly influenced by sediment composition, particle size distribution, particle shape, adsorption ions and pore water characteristics, tide and temperature. In addition, the geotechnical properties are very complex due to stress history, change in pore water, dissolution process and gas formation. In this study, the physical and mechanical properties of the soft ground were evaluated through field tests and laboratory tests to investigate the strength increase characteristics according to consolidation on the soft ground in the southwest coast. In addition, in order to understand the consolidation behavior of soft ground such as subsidence, pore water pressure, horizontal displacement of soil by embankment load, measuring instruments such as pore water pressuremeter, settlement gauge, inclinometer and differential settlement gauge was installed, and a piezocon penetration test was carried out step by step to confirm the increase in shear strength of the ground. Through this, it was confirmed that the shear strength of the ground is increased according to the stages of filling. In addition, by evaluating the properties of consolidation behavior, strength increase and consolidation prediction by empirical methods and theories were compared to analyze the characteristics of strength increase rate and consolidation behavior in consideration of regional characteristics.