• Computational Structural Engineering
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• v.6 no.3
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• pp.67-80
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• 1993

This paper presents the results of an analytical study to evaluate the inelastic seismic response characteristics of multistory building structures, the effects of gravity load on the seismic responses and its implications on the earthquake resistant design. Static analyses for incremental lateral force and nonlinear dynamic analyses for earthquake motions were performed to evaluate the seismic response of example multistory building structures. Most of considerations are placed on the distribution of inelastic responses over the height of the structure. When an earthquake occurs, bending moment demand is increased considerably from the top to the bottom of multistory structures, so that differences between bending moment demands and supplies are greater in lower floos of multistory structures. As a result, for building structures designed by the current earthquake resistant design procedure, inelastic deformations for earthquake ground motions do not distribute uniformly over the height of structures and those are induced mainly in bottom floors. In addition, gravity load considerded in design procedure tends to cause much larger damages in lower floors. From the point of view of seismic responses, gravity load affects the initial yield time of griders in earlier stage of strong earthquakes and results in different inelastic responses among the plastic hinges that form in the girders of a same floor. However, gravity load moments at beam ends are gradually reduced and finally fully relaxed after a structure experiences some inelastic excursions as a ground motion is getting stronger. Reduction of gravity load moment results in much increased structural damages in lower floors building structures. The implications of the effects of gravity load for seismic design of multistory building structures are to reduce the contributions of gravity load and to increased those of seismic load in determination of flexual strength for girders and columns.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.4
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• pp.21-32
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• 2004

A Seismic analysis procedure of bi-directional brideg motions is developed by using mechanical bridge model. A three-dimensional mechanical model can consider major phenomena under bi-directional seismic excitations, such as nonlinear pier motion under biaxial bending, pounding and bearing damage due to the rotaion of the superstructure, etc. The analyses utilizing the uni-directional and the bi-directional bridge model for the 3-span simply supported bridge are then performed. The seismic responses in two cases are examined and compared by investigating the relative displacements of each superstructure to both ground and adjacent superstructures and the restoring forces of RC pier. The analysis using either the uni-directional model or bi-directional model is acceptable for estimating the displacement responses of a bridge, but the bi-directional analysis is found to give more conservative results for resisting forces of RC piers. To make general conclusions, therefore, the analysis using the bi-directional bridge model should be performed in evaluating the seismic safety of bridges.

• Journal of the Earthquake Engineering Society of Korea
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• v.22 no.3
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• pp.175-184
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• 2018

In this paper, comparative analysis of the 9.12 Gyeongju and 11.15 Pohang earthquakes was conducted in order to provide probable explanations and reasons for the damage observed in the 11.15 Pohang earthquake from both earthquake and structural engineering perspectives. The damage potentials like Arias intensity, effective peak ground acceleration, etc observed in the 11.15 Pohang earthquake were generally weaker than those of the 9.12 Gyeongju earthquake. However, in contrast to the high-frequency dominant nature of the 9.12 Gyeongju earthquake records, the spectral power of PHA2 record observed in the soft soil site was highly concentrated around 2Hz. The base shear around 2 Hz frequency was as high as 40% building weight. This frequency band is very close to the fundamental frequency of the piloti-type buildings severely damaged in the northern part of Pohang. Unfortunately, in addition to inherent vertical irregularity, most of the damaged piloti-type buildings had plan irregularity as well and were non-seismic. All these contributed to the fatal damage. Inelastic dynamic analysis indicated that PHA2 record demands system ductility capacity of 3.5 for a structure with a fundamental period of 0.5 sec and yield base shear strength of 10% building weight. The system ductility level of 3.5 seems very difficult to be achievable in non-seismic brittle piloti-type buildings. The soil profile of the PHA2 site was inversely estimated based on deconvolution technique and trial-error procedure with utilizing available records measured at several rock sites during the 11.15 Pohang earthquake. The soil profile estimated was very typical of soil class D, implying significant soil amplification in the 11.15 Pohang earthquake. The 11.15 Pohang earthquake gave us the expensive lesson that near-collapse damage to irregular and brittle buildings is highly possible when soil is soft and epicenter is close, although the earthquake magnitude is just minor to moderate (M 5+).

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.6
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• pp.305-314
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• 2017

Ocean wave energy harvesting is still too expensive despite developing a variety of wave energy converter (WEC) devices. For the cost-effective wave energy harvesting, it can be an effective measure to use existing breakwaters or newly installed breakwaters for both wave control and energy harvesting purposes. In this study, we investigated the functionality of both breakwater and wave-power generator for the oscillating water column (OWC)-type wave energy converter (WEC) installed in a pneumatic floating breakwater, which was originally developed as a floating breakwater. In order to verify the performance of the breakwater as a WEC, the air flow velocity from air-chamber to WEC has to be evaluated properly. Therefore, air flow velocity, wave transformation and motion of floating structure was numerically implemented based on BEM from linear velocity potential theory without considering the compressibility of air within the chamber. Air pressure, meanwhile, was assumed to be fluctuated by the motions of structure and the water level change within air-chamber. The validity of the obtained values can be determined by comparing the previous results from the numerical analysis for different shapes. Based on numerical model results, wave transformation characteristics around OWC system mounted on the fixed and floating breakwaters, and motions of the structure with air flow velocities are investigated. In summary, all numerical results are almost identical to the previous research considering air compressibility. Therefore, it can be concluded that this analysis not considering air compressibility in the air chamber is more efficient and practical method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.6
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• pp.637-644
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• 2012

In a nuclear power plant, fretting wear due to impact motion between U-tubes and support structures located in steam generators can cause serious problems. In order to guarantee the reliability of the steam generator, the damage due to fretting wear should be thoroughly investigated. The purpose of this study is to elucidate the fretting wear mechanism qualitatively and quantitatively. Hence, fretting wear simulation is performed for the environments to which the actual steam generators in nuclear power plants are exposed. Initial experimental results are obtained for various experimental parameters, and the effect of the work rate and temperature on fretting wear is evaluated. In water, the wear coefficients for $90^{\circ}C$, $200^{\circ}C$, and $340^{\circ}C$ are found to be $9.051{\times}10^{-16}\;Pa^{-1}$, $3.009{\times}10^{-15}\;Pa^{-1}$, and $2.235{\times}10^{-15}\;Pa^{-1}$, respectively. It is also found that the wear coefficient at room temperature is larger than that at low temperature in water because of the dynamic viscosity of water.

• The Journal of Engineering Geology
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• v.23 no.4
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• pp.435-445
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• 2013

Since design response spectrum does not reflect local soil characteristics, site specific response spectrum of observed ground motions appears relatively higher than design response spectrum at high frequency range. These problems have been pointed out from the domestic seismic design industry. Among various estimation methods, this study used the method H/V ratio of ground motion for estimating site amplification. This method has been extended to background noise, Coda waves and S waves recently for estimating site amplification. This study applied this method to the background noise and Coda wave energy. This study analysed more than 267 background noises from 15 macro earthquakes including main Fukuoka earthquake (2005/03/20, M=6.5) and then compared to results from S waves, at 8 main domestic seismic stations. The results showed that most of the domestic seismic stations gave similar results to those from S waves. Each station showed its own characteristics of site amplification property in low, high and specific resonance frequency ranges. Comparison of this study to other studies using different method can give us much information about dynamic amplification of domestic sites characteristics and site classification.

• Science of Emotion and Sensibility
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• v.13 no.3
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• pp.467-474
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• 2010

Recently, Study of functional clothing for Vital sensing is focused on reducing artifact by human motions, in order to enhance the electrocardiogram(ECG) sensing accuracy. In this study, considering the factors for each element found from the analysis, a 3-lead electrode inside textile embroidered with silver yarn was developed, and draft designs off our types of vital-signal sensing garments, which are 'chest-belt typed' garment, 'cross-typed' garment 'x-typed' garment and 'curved x-typed' garment, were prepared. The draft designs were implemented on a sleeveless male shirt made of an elastic material so that the garment and the electrodes can remain closely attached along the contour of the human body, and the acquired data was sent to the main computer over a wireless network. In order to evaluate the effects caused by body movements and the ECG-sensing capability for each type in static and dynamic states, displacements were measured from one and two dimensional perspectives. ECG measurement evaluation was also performed for Signal-to-noise ratio(SNR) analysis. Applying the experimental results, the draft garment designs were modified and complemented to produce two types of modular approaches 'continuous-attached' and 'insertion-detached' for the ECG-sensing smart clothing.

• Progress in Medical Physics
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• v.14 no.3
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• pp.151-160
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• 2003

The application of more complex radiotherapy techniques using multileaf collimation (MLC), such as 3D conformal radiation therapy and intensity-modulated radiation therapy (IMRT), has increased the significance of verifying leaf position and motion. Due to thier reliability and empirical robustness, quality assurance (QA) of MLC. However easy use and the ability to provide digital data of electronic portal imaging devices (EPIDs) have attracted attention to portal films as an alternatives to films for routine qualify assurance, despite concerns about their clinical feasibility, efficacy, and the cost to benefit ratio. In this study, we developed method for daily QA of MLC using electronic portal images (EPIs). EPID availability for routine QA was verified by comparing of the portal films, which were simultaneously obtained when radiation was delivered and known prescription input to MLC controller. Specially designed two-test patterns of dynamic MLC were applied for image acquisition. Quantitative off-line analysis using an edge detection algorithm enhanced the verification procedure as well as on-line qualitative visual assessment. In conclusion, the availability of EPI was enough for daily QA of MLC leaf position with the accuracy of portal films.

• Journal of Biomedical Engineering Research
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• v.38 no.1
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• pp.9-15
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• 2017

Recently, flexible cages have been introduced in an attempt to absorb and reduce the abnormal load transfer along the anterior parts of the spine. They are designed to be used with the pedicle screw systems to allow some mobility at the index level while containing ROM at the adjacent level. In this study, a finite element (FE) study was performed to assess biomechanical efficacies of the flexible cage when combined with pedicle screws with flexible rods. The post-operated models were constructed by modifying the L4-5 of a previously-validated 3-D FE model of the intact lumbar spine (L2-S1): (1) Type 1, flexible cage only; (2) Type 2, pedicle screws with flexible rods; (3) Type 3, interbody fusion cage plus pedicle screws with rigid rods; (4) Type 4, interbody fusion cage plus Type 2; (5) Type 5, Type 1 plus Type 2. Flexion/extension of 10 Nm with a compressive follower load of 400N was applied. As compared to the Type 3 (62~65%) and Type 4 (59~62%), Type 5 (53~55%) was able to limit the motion at the operated level effectively, despite moderate reduction at the adjacent level. It was also able to shift the load back to the anterior portions of the spine thus relieving excessively high posterior load transfer and to reduce stress on the endplate by absorbing the load with its flexible shape design features. The likelihood of component failure of flexble cage remained less than 30% regardless of loading conditions when combined with pedicle screws with flexible rods. Our study demonstrated that flexible cages when combined with posterior dynamic system may help reduce subsidence of cage and degeneration process at the adjacent levels while effectively providing stability at the operated level.

• Korean Journal of Remote Sensing
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• v.29 no.4
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• pp.423-441
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• 2013

On 21 September 2010, one of Chuseok holidays in Korea, localized heavy rainfalls occurred over the midwestern region of the Korean peninsula. In this study MTSAT-2 infrared and water vapor channel imagery are examined to find out some features which are obvious in each stage of the life cycle of convective cell for this heavy rain event. Also the kinematic and thermodynamic features probably associated with them are investigated. The first clouds related with the Chuseok heavy rain are detected as low-level multicell cloud (brightness temperature: $-15{\sim}0^{\circ}C$) in the middle of the Yellow sea at 1630~1900 UTC on 20 Sept., which are probably associated with the convergence at 1000 hPa. Convective cells are initiated in the vicinity of Shantung peninsula at 1933 UTC 20, which have developed around the edge of the dark region in water vapor images. At two times of 0033 and 0433 UTC 21 the merging of two convective cells happens near midwestern coast of the peninsula and then they have developed rapidly. From 0430 to 1000 UTC 21, key features of convective cell include repeated formation of secondary cell, slow horizontal cloud motion, persistence of lower brightness temperature ($-75{\sim}-65^{\circ}C$), and relatively small cloud size (${\leq}-50^{\circ}C$) of about $30,000km^2$. Radar analysis showed that this heavy rain is featured by a narrow line-shaped rainband with locally heavy rainrate (${\geq}50$ mm/hr), which is located in the south-western edge of the convective cell. However there are no distinct features in the associated synoptic-scale dynamic forcing. After 1000 UTC 21 the convective cell grows up quickly in cloud size and then is dissipated. These satellite features may be employed for very short range forecast and nowcasting of mesoscale heavy rain system.