• 한국통신학회논문지
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• 제23권7호
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• pp.1807-1816
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• 1998

1GHz 이하의 주파수 대역에서 비정지궤도 위성이동지구국과 육상이동국간의 주파수 공유에 따른 간섭 확률을 계산하였다. 전파전파 모델(Propagation model)로서 Flat earth 모델과 Hata 대도시 모델을 사용하고 그에 따른 이동 지구국(MES:Model earth station)의 전력값에 대한 확률밀도함수를 구한 후 이를 이용하여 간섭 기준을 초과할 확률을 도출하였다. 비정지궤도 위성이동서비스(MSS: Mobile staellite service) 전체 영역의 단위 시간당 평균 전송량과 단말의 비율을 변화시킴으로서 단위시간당 평균전송량을 구하였고, 이로부터 주어진 전력 한계값을 초과하는 확률을 통계적인 방법으로 예측하였다. 그 결과, MSS 전체 영역의 단위 시간당 평균 전송량과 단말의 비율이 각각 증가함에 따라 간섭허용기준을 초과할 확률이 증가하였다. 또한, LMS(Land Mobile Service)와 MSS의 사용 주파수의 중심주파수로부터의 편차에 따른 분리 효과를 고려하였다.

• Structural Engineering and Mechanics
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• 제49권4호
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• pp.463-477
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• 2014

In this paper, seismic performance of Kozyatagi Bridge is evaluated by employing nonlinear elasto-plastic dynamic analysis and the deformation-based performance. The time-history records of the 1999 Izmit, 1971 San Fernando and 1989 Loma Prieta earthquakes are modified by adopting a probability of exceedance of 2% in 50 years corresponding to the return period of 2475 years. The analysis is carried out for three different bearing cases which are movable bearings, restrained bearings, and movable bearings with viscous fluid dampers in the radial direction. The analysis results show that the bridge can be retrofitted with viscous fluid dampers. In this case the reinforced concrete piers need not be strengthened by any jacketing techniques in order to preserve the original architectural appearance of the bridge. The retrofitting design of the bridge with viscous fluid dampers is also presented in detail.

• Earthquakes and Structures
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• 제10권3호
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• pp.589-611
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• 2016

This paper presents an analytical study aimed at evaluating the seismic performance of steel moment resisting frames (MRFs) retrofitted with different approaches. For this, 3, 6 and 12 storey MRFs having four equal bays of 5 m were selected as the case study models. The models were designed with lateral stiffness insufficient to satisfy code drift and hinge limitations in zones with high seismic hazard. Three different retrofit strategies including traditional diagonal bracing system and energy dissipation devices such as buckling restrained braces and viscoelastic dampers were used for seismic upgrading of the existing structures. In the nonlinear time history analysis, a set of ground motions representative of the design earthquake with 10% exceedance probability in fifty years was taken into consideration. Considering the local and global deformations, the results in terms of inter-storey drift index, global damage index, plastic hinge formations, base shear demand and roof drift time history were compared. It was observed that both buckling-restrained braces and viscoelastic dampers allowed for an efficient reduction in the demands of the upgraded frames as compared to traditional braces.

• Earthquakes and Structures
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• 제26권4호
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• pp.269-283
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• 2024

When a reinforced concrete (RC) structure is exposed to a corrosive environment for an extended period of time, the material qualities deteriorate, resulting in a loss in seismic performance. Engineered Cementitious Composites (ECC) have been used to reinforce the corroded RC structure, which can achieve reinforcement effectiveness for a small change in cross-section size. In this work, finite element models of unjacketed RC pier and ECC jacketed pier were established and verified by experimental tests, with the buckling effect of longitudinal reinforcement considered. Compared with the unjacketed pier, the displacement of the pier top of the ECC jacketed pier was reduced by about 9.52% under earthquake action. In the case of moderate and major earthquakes, the probability of exceedance of ECC jacketed pier is significantly reduced. For the case of rare earthquake loading, with the ECC jacket, the e of the pier experiencing serious damage and complete damage states is reduced by 10.29% and 29.78%, respectively.

• 한국해양환경ㆍ에너지학회지
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• 제13권2호
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• pp.112-120
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• 2010

이 논문에서는 Yura 해역에서 폭풍 중 24시간 연속으로 측정된 freak wave가 포함된 파랑자료를 분석하여 비선형 파도의 통계적 특성을 살펴보았다. 파고의 초과확률분포는 Edgeworth-Rayleigh(ER) 분포와, Rayleigh 분포를 이용하여 계측된 자료와 비교하였다. 파형이 stationary 상태를 유지하는 10시간 동안 계측된 파랑자료(파랑의 개수가 4600 내외)에서는, 파형의 분포는 Gram-Chalier분포가 Gaussian분포보다 파랑자료와 일치를 한다. 전반적인 파고의 확률분포는 Rayleigh($H_{rms}$)분포를 잘 따르는 것을 볼 수 있다. Freak wave 발생확률은 Rayleigh($m_{o}{^{1/2}}$) 분포로 잘 표시가 되며, ER 분포는 과대하게 예측하는 것을 볼 수 있다. 30분간 계측된 파랑자료(파랑 개수가 250개 내외)에서 freak wave가 발생된 경우는 ER 분포가 freak wave 발생확률과 잘 일치한다. 그러나 전반적인 파고의 발생확률이 과대평가된다. Freak wave가 발생하지 않은 경우는 거의 모든 파고에 걸쳐 Rayleigh($H_{rms}$)분포가 계측된 파고분포와 잘 일치를 한다. 파고가 10 m 이하의 freak wave의 파고확률분포는 10 m 이상의 파고를 가지는 freak wave와 비슷한 경향을 보인다. $H_{max}/H_{1/3}$은 파형의 kurtosis와 연관이 있는 것을 보여주었다. Freak wave의 발생은 높은 kurtosis 값과 관계가 있으며, freak wave가 발생하는 임계 kurtosis 값이 존재할 가능성이 있을 것으로 추정된다.

• Earthquakes and Structures
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• 제11권3호
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• pp.483-503
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• 2016

This study aims to evaluate seismic performance of existing low and mid-rise reinforced concrete buildings by comparing their displacement capacities and displacement demands under selected ground motions experienced in Turkey as well as demand spectrum provided in 2007 Turkish Earthquake Code for design earthquake with 10% probability of exceedance in 50 years for soil class Z3. It should be noted that typical residential buildings are designed according to demand spectrum of 10% probability of exceedance in 50 years. Three RC building sets as 2-, 4- and 7-story, are selected to represent reference low-and mid-rise buildings located in the high seismicity region of Turkey. The selected buildings are typical beam-column RC frame buildings with no shear walls. The outcomes of detailed field and archive investigation including approximately 500 real residential RC buildings established building models to reflect existing building stock. Total of 72 3-D building models are constructed from the reference buildings to include the effects of some properties such as structural irregularities, concrete strength, seismic codes, structural deficiencies, transverse reinforcement detailing, and number of story on seismic performance of low and mid-rise RC buildings. Capacity curves of building sets are obtained by nonlinear static analyses conducted in two principal directions, resulting in 144 models. The inelastic dynamic characteristics are represented by "equivalent" Single-Degree-of- Freedom (ESDOF) systems using obtained capacity curves of buildings. Nonlinear time history analysis is used to estimate displacement demands of representative building models idealized with (ESDOF) systems subjected to the selected ground motion records from past earthquakes in Turkey. The results show that the significant number of pre-modern code 4- and 7-story buildings exceeds LS performance level while the modern code 4- and 7-story buildings have better performances. The findings obviously indicate the existence of destructive earthquakes especially for 4- and 7-story buildings. Significant improvements in the performance of the buildings per modern code are also obvious in the study. Almost one third of pre-modern code buildings is exceeding LS level during records in the past earthquakes. This observation also supports the building damages experienced in the past earthquake events in Turkey.

• 한국음향학회지
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• 제8권1호
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• pp.5-12
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• 1989

RMS, Kurtosis, Crest factor, Probability of exceedance와 Probability density function 등의 통계적 파라미터를 선정하여 베어링의 사용조건과 결함진전에 따른 변화특성을 조사하였다. 이를 위해 4볼 시험기에서 하중, 회전수 및 시간을 변화시키면서 실험하여 진동신호를 수집하고, 이를 A/D변환시킨 후 디지털 필터링하여 주파수 대역별 통계적 파라미터 값을 계산하였다. 실험결과, 하중이나 회전수와 같은 운전조건이 변화하는 경우 RMS의 값은 운전조건 변화에 따라 변하지만 Kurtosis 등의 통계적 파라미터들은 운전조건과 무관하게 steady한 결과를 나타내었다. 또한 통계적 파라미터와 시간과의 상관관계에 대한 실험으로부터 통계적 파라미터들을 결함의 진전 상태를 나타내는 파라미터로 사용할 수 있음을 확인하였으며, 따라서 파손방지를 위한 예측지표로서 이들 통계적 파라미터를 이용할 수 있을것으로 판단되었다.

• 한국물환경학회지
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• 제28권6호
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• pp.890-895
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• 2012

Duration curves describe the percentage of time that a certain water quality (total/fecal coliform (=TC/FC)) or discharge is exceeded. The curves methodology are usually based on daily records and are useful in estimating how many days per year and event will be exceeded. The technique was further applied to estimated TC/FC loading to the Geumho River, using the daily mean flow rate and TC/FC concentration data during January, 2001 and December, 2011 for the Geumhogang6 (=Seongseo water level station) where an automated monitoring station is located in Gangchang-bridge. Low flow of the Seongseo (=11.1 cms) was equivalent to 75.3% on an exceedance probability scale. Load Duration curve for TC/FC loading at the Seongseo was constructed. Standard load duration curve was constructed with the water quality criteria for class III (TC/FC concentration = 5000/1000 CFU/ 100 mL). By plotting TC/FC observed load duration curve with standard load duration curve, it could be revealed that water quality do not meet the desired water quality for 68.8/11.2% on an exceedance probability scale. IF linear correlation between flow rate and coliform concentration is assumed, it can be interpreted that water quality exceed desired criteria when daily average flow rate is over 11.9/109.9 cms.

• Structural Engineering and Mechanics
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• 제37권2호
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• pp.233-251
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• 2011

The seismic provisions of the current edition (2005) of the National Building Code of Canada (NBCC) differ significantly from the earlier edition. The current seismic provisions are based on the uniform hazard spectra corresponding to 2% probability of exceedance in 50 years, as opposed to the seismic hazard level with 10% probablity of exeedance in 50 years used in the earlier edition. Moreover, the current code is presented in an objective-based format where the design is performed based on an acceptable solution. In the light of these changes, an assessment of the expected performance of the buildings designed according to the requirements of the current edition of NBCC would be very useful. In this paper, the seismic performance of a set of six, twelve, and eighteen story buildings of regular geometry and with concrete moment resisting frames, designed for Vancouver western Canada, has been evaluated. Although the effects of non-structural elements are not considered in the design, the non-structural elements connected to the lateral load resisting systems affect the seismic performance of a building. To simulate the non-structural elements, infill panels are included in some frame models. Spectrum compatible artificial ground motion records and scaled actual accelerograms have been used for evaluating the dynamic response. The performance has been evaluated for each building under various levels of seismic hazard with different probabilities of exceedance. From the study it has been observed that, although all the buildings achieved the life-safety performance as assumed in the design provisions of the building code, their performance characteristics are found to be non-uniform.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2015년도 학술발표회
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• pp.106-106
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• 2015

The information of flow regimes continues to be norm in water resource and watershed management, in that stream flow regime is a crucial factor influencing water quality, geomorphology, and the community structure of stream biota. The objectives of this study were to estimate Korean stream flows from landscape variables, classify stream flow gages using hydraulic characteristics, and then apply these methods to ungaged biological monitoring sites for effective ecological assessment. Here I used a linear modeling approach (MLR, PCA, and PCR) to describe and predict seasonal flow statistics from landscape variables. MLR models were successfully built for a range of exceedance discharges and time frames (annual, January, May, July, and October), and these models explained a high degree of the observed variation with r squares ranging from 0.555 (Q95 in January) to 0.899 (Q05 in July). In validation testing, predicted and observed exceedance discharges were all significantly correlated (p<0.01) and for most models no significant difference was found between predicted and observed values (Paired samples T-test; p>0.05). I classified Korean stream flow regimes with respect to hydraulic and hydrologic regime into four categories: flashier and higher-powered (F-HP), flashier and lower-powered (F-LP), more stable and higher-powered (S-HP), and more stable and lower-powered (S-LP). These four categories of Korean streams were related to with the characteristics of environmental variables, such as catchment size, site slope, stream order, and land use patterns. I then applied the models at 684 ungaged biological sampling sites used in the National Aquatic Ecological Monitoring Program in order to classify them with respect to basic hydrologic characteristics and similarity to the government's array of hydrologic gauging stations. Flashier-lower powered sites appeared to be relatively over-represented and more stable-higher powered sites under-represented in the bioassessment data sets.