• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.4
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• pp.1-12
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• 2011

Seismic fragility analysis has been developed to evaluate the seismic performance of existing nuclear power plants, but now its applicability has been extended to buildings and bridges. In general, the seismic fragility curves are evaluated from the nonlinear time-history analysis (THA) using many earthquake ground motions. Seismic fragility analysis using the nonlinear THA requires a time consuming process of structural modeling and analysis. To overcome this shortcoming of the nonlinear THA, simplified methods such as the displacement coefficient method (DCM) and the capacity spectrum method (CSM) are used for the seismic fragility analysis. In order to evaluate the accuracy of the seismic fragility curve calculated by the DCM and the CSM, the seismic fragility curves of a reinforced concrete shear wall structure calculated by the DCM and CSM are compared with those calculated by the nonlinear THA. In order to construct a numerical fragility curve, 190 artificially generated ground motions corresponding to the design spectrum and the methodology proposed by Shinozuka et al. are used.

• Composites Research
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• v.25 no.6
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• pp.211-216
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• 2012

FBG sensor peaks could be split due to polarization by shear strain, when the fiber optic sensors embedded or attached to the structure. For the fiber optic sensor packages, sensor grating has to be protected from shear strains. Also, pretension has to be applied to the sensor because compressive strain must be measured. Without pretension of sensor, the sensor does not show any change of signal until it is stretched. In order to mesure compressive and tensile strains, two fixing point and prestressed sensor need. In the fixing point, just holding the optical fiber cause slip between core and cladding in the fiber. A Fixation method of prestressed FBG sensors fixed with partially stripped fibers was developed. The sensor package has the prestress controllable fixtures at the fixing points. Prestress to the sensor imposed by controlling the two fixed points with bolts and nuts make it easy to measure compressive strain as well as tensile strain. The fiber optic sensor packages applied to the actual structure and the structural monitoring system using the package can be applied to safety through surveillance.

• Journal of the Microelectronics and Packaging Society
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• v.12 no.4 s.37
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• pp.331-338
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• 2005

The rapid advances in high power light sources and arrays as encountered in incandescent lamps have induced dramatic increases in die heat flux and power consumption at all levels of high power LED packaging. The lifetime of such devices and device arrays is determined by their temperature and thermal transients controlled by the powering and cooling, because they are usually operated under rough environmental conditions. The reliability of packaged electronics strongly depends on the die attach quality, because any void or a small delamination may cause instant temperature increase in the die, leading sooner or later to failure in the operation. Die attach materials have a key role in the thermal management of high power LED packages by providing the low thermal resistance between the heat generating LED chips and the heat dissipating heat slug. In this paper, thermal transient characteristics of die attach in high power LED package have been studied based on the thermal transient analysis using the evaluation of the structure function of the heat flow path. With high power LED packages fabricated by die attach materials such as Ag paste, solder paste and Au/Sn eutectic bonding, we have demonstrated characteristics such as cross-section analysis, shear test and visual inspection after shear test of die attach and how to detect die attach failures and to measure thermal resistance values of die attach in high power LED package. From the structure function oi the thermal transient characteristics, we could know the result that die attach quality of Au/Sn eutectic bonding presented the thermal resistance of about 3.5K/W. It was much better than those of Ag paste and solder paste presented the thermal resistance of about 11.5${\~}$14.2K/W and 4.4${\~}$4.6K/W, respectively.

• The Journal of Korean Academy of Prosthodontics
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• v.33 no.4
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• pp.693-704
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• 1995

This study was performed to evaluate effective surface conditioning method of In-Ceram core to improve bonding with resin cement. The surface of each sample was avraded with glass bead for 20 seconds and then subjected to one of the following conditions : no modification, sandblasting with $50{\mu}m$ slumimum oxide powders for 20 seconds, etching with 20% hydrofluoric acid for 5, 10, and 15 minutes(half of the etched samples were coated with silane), and sandblasting with $250{\mu}m$ aluminum oxide powders and silica coating whith Silicoater MD system(Kulzer, Germany). The surface morphology changes were examined with scanning electronic microscope(SEM. and the shear bond strength of In-Ceram core samples to resin cement(Panavis 21, Kurayay, Japan) were measured. It was concluded that : 1. By SEM observation, 20% HF acid etching did not create clear microretentive structure and surface roughness diminished with increace in etching time. Sandblasting was more effective than 20% hydrofluoric acid etching in producing microretentive structure. 2. The bond strengths of all In-Ceram core samples surface conditioned were increased that that of control group. 3. Silica coating showed higher bond strength than etching with 20% hydrofluoric acid. 4. The use of silane coating was more effective in improving bond strength than lengthening etching time.

• Journal of the Society of Disaster Information
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• v.12 no.2
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• pp.144-149
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• 2016

Nowaday, most of the low-rise concrete structures which have less than five stories were built before the intensified seismic code was established 2005. According to the fact that our country is not a safety zone ay more, studies are need to reinforce the seismic performance of that structures. The basic frame of low-rise structure are consist of beams and columns with partition walls, therefore that are very weak about secondary wave of earthquake because of the high stiffness. The partition wall are consist of open channel for sunlight or ventilation and intermediate wall. The intermediate walls will enhance the stiffness of columns, but will cause shear failure with short column effects because of the reduced effective depth. But we don't have studies and adequate design code for partition wall effects, therefore some more studies are need for these facts.

• Journal of Korean Society of Steel Construction
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• v.15 no.3
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• pp.291-298
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• 2003

Recently, as the size of buildings structure becomes large increases, their mat area of building structure is supported or by an inhomogeneous foundation. This paper presents a vibration analysis on thick plates subjected to in-plane force is presented in this paper. The rectangular plate is isotropic, homogeneous, and composed of a linearly elastic material. A vibration analysis of the rectangular thick plate iwas done by useing ofarectangular finite element with 8 nodes and 9 nodes. In this study, the foundation was idealized as a Pasternak foundation model. A Pasternak foundation haves a shear layer on Winkler's model, which idealizes the foundation as a vertical spring. In order tTo analysze the vibration of a plate supported on by an inhomogeneous Pasternak foundation, the value of the Winkler foundation parameter of the central and border zones of the plate awere chosen as WFP1 and WFP2. (fFigure 4.). The Winkler foundation parameter of WFP1 and WFP2 is varied from 0 to 10, $10^2$, and $10^3$ and the shear foundation parameters is were 0, 5, and 10. The ratio of the in-plane force to the critical load iwas applied as 0.4 to 0.8

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.4
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• pp.443-448
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• 2016

A novel Permanent Magnet based Magneto Rheological (PM-MR) damper is proposed in this paper. The principle of proposed MR damper is achieved by designing a linearly varying magnetization area with-respect to the movable permanent magnetic based piston setup. Nowadays, commercially available MR damper uses electromagnetic coils for generating the variable magnetic fields corresponding to the variable damping force. The amount of magnetic field produced by the electromagnetic coils are depends on the biasing current of voltage source. The key enabling concept of the proposed MR damper is to replace the electromagnetic coils and the voltage sources by utilizing the variable area based permanent magnetic piston setup. The proposed unique design structure of PM-MR damper has an increasing shear mode damping force with the piston movement in both jounce and rebound motion. In this research, analytical model of the proposed structure is derived and the structural design of proposed concept is verified using numerical CAD tool. As a result, the damping force is increase when piston movement in both jounce and rebound motion.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.1
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• pp.54-61
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• 2005

Characteristics of sprays injected by gas/liquid coaxial atomizers operated at atmospheric pressure are studied using shadowgraph, mechanical patternator and PDPA. The gas-to- liquid momentum flux ratio(M) and the liquid Reynolds number(Re) are selected as key parameters in characteristics of gas/liquid coaxial sprays from the dimensional analysis. The properties of shear coaxial sprays are compared with those of swirl coaxial sprays through the macroscopic and microscopic analysis. Macroscopic similarities between shear and swirl coaxial sprays are revealed under flow conditions of high momentum flux ratio. Also, empirical correlations between the mean drop diameters(D32) and operating conditions of coaxial sprays are proposed in this paper.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.03a
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• pp.7-7
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• 2010

Energy harvesting from the environment has been of great interest as a standalone power source of wireless sensor nodes for Ubiquitous Sensor Networks(USN). In particular, the piezoelectric energy harvesting from ambient vibration sources has intensively researched because it has a relatively high power density comparing with other energy scavenging methods. Through recent advances in low power consumption RF transmitters and sensors, it is possible to adopt a micro-power energy harvesting system realized by MEMS technology for the system-on-chip. However, the MEMS energy harvesting system has some drawbacks such as a high natural frequency over 300 Hz and a small power generation due to a small dimension. To overcome these limitations, we devised a novel power generator with a spiral spring structure as shown in the figure. The natural frequency of a cantilever could be decreased to the usable frequency region (under 300 Hz) because the natural frequency depends on the length of a cantilever. In this study, the natural frequency of the energy harvester was a lower than a normal cantilever structure and sufficiently controllable in 50 - 200 Hz frequency region as adjusting weight of a proof mass. Moreover, the MEMS energy harvester had a high energy conversion efficiency using a shear mode ($d_{15}$) is much larger than a 33 mode ($d_{33}$) and the energy conversion efficiency is proportional to the piezoelectric constant (d). We expect the spiral type MEMS power generator would be a good candidate for a standalone power generator for USN.

• Journal of the Korea Concrete Institute
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• v.23 no.6
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• pp.749-756
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• 2011

Most experimental studies on durability of FRP reinforcements subjected to high temperature have focused on the effect of high temperature only on tensile properties. But FRP reinforcement used in newly constructed concrete structure is first degraded by moisture and alkaline environment of concrete. When the structure is subjected to fire, the degraded FRP reinforcement is exposed to high temperature. Therefore, the effects of concrete environment and high temperature should be simultaneously considered for evaluation of FRP reinforcement damaged by fire. In this study, FRP reinforcements submerged in simulated solutions of pH 12.3 and 7 for extended period of time were subjected to temperatures of $60^{\circ}C$, $100^{\circ}C$, $150^{\circ}C$, and $300^{\circ}C$ to be examined. In order to investigate the effect of the high temperature, interlaminar shear strengths were measured and compared to those of control ones. The experimental results demonstrated that the combined effect of concrete environment and high temperature on properties of FRP reinforcement was more significant than the effect of high temperature or concrete environment solely.