• 콘크리트학회논문집
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• 제21권2호
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• pp.187-197
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• 2009

본 논문은 진동수에 따른 취약도 곡선과 손상확률을 제시하였다. 취약도곡선과 손상확률은 주어진 지진동에 의해 임의의 구조물이 견딜 수 있는 손상의 정도를 나타낸다. 지진에 의한 피해는 지진이 가지는 불확실성으로 인하여 확률적으로 예측하여야 한다. 기존 연구와 달리 본 연구에서는 비선형 동적 해석과 실험 결과를 이용하였다. 본 연구에서는 프리스트레스트 콘크리트 교량에 대한 수치적 시뮬레이션을 통하여 주어진 최대지반가속도에 따른 5단계의 손상 단계별 손상확률을 구하였다. 취약도 곡선을 산출하기위해 해석적 연구를 수행하였다. 이를 위해 지반조건에 따라 각각 100개의 인공지진파를 생성하고 비선형 시간이력해석을 수행하였다. 손상단계는 기존의 실험 결과에 기초한 성능기반에 따라 정의하였으며 RC 교각의 지진거동을 변위연성도로 나타내었다. 손상단계 및 지반가속도를 이용하여 PSC교량의 지반조건에 따른 손상곡선을 도출하여 비교분석하였다. 연구 결과에 따르면 지반조건 및 구속철근량에 따른 손상확률의 차이를 확인할 수 있다.

• 한국방재안전학회논문집
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• 제15권4호
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• pp.87-98
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• 2022

최근 짧은 시간 동안 많은 강우가 내리는 국지성 집중호우가 빈번히 발생하고 이로 인한 침수피해가 증가하고 있다. 국지성 집중호우로 인한 피해를 예방하기 위하여 기상청이 제공하는 지역 앙상블 예측시스템(Local ENsemble prediction System, LENS)과 관측자료와 동네예보 자료를 활용한 기계학습과 확률 매칭(Probability Matching, PM) 기법을 이용하여 수문학적 정량강우예측정보(Hydrological Quantative Precipitation Forecast, HQPF)을 개발하였다. 국지성 집중호우로 인한 침수피해 대비를 위한 호우 영향정보로 HQPF를 생산하고 있지만, 낮은 강우강도에 대하여 과대예측하는 경향이 나타났다. 본 연구에서는 HQPF의 예측정확도 향상과 과대예측 성향을 개선하기 위하여 머신러닝 학습자료 기간확대, 앙상블 기법 분석 및 확률매칭(PM) 기법 프로세스 변경을 통하여 HQPF 개선하였다. 개선된 HQPF의 예측성능을 평가하기 위해 2021년 8월 27일 ~ 2021년 9월 3일 장마전선으로 인한 호우 사례를 대상으로 예측성능 검증을 수행하였다. 10 mm 이하의 강우에 대하여 예측정확도가 크게 향상되었고, 관측과 유사한 발생가능성 및 강우영역을 예측하는 등 과대예측 성향이 개선되었음을 확인하였다.

• Structural Monitoring and Maintenance
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• 제2권4호
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• pp.319-338
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• 2015

The electro-mechanical impedance (EMI) technique makes use of surface-bonded lead zirconate titanate (PZT) patches as impedance transducers measuring impedance variations monitored on host structural components. The present experimental work further evaluate an alternative to the conventional EMI technique which performs measurements of the variations in the output voltage of PZT transducers rather than computing electromechanical impedance (or admittance) itself. This paper further evaluates a variant of the EMI approach presented in a previous work of the present authors, suitable, for low-cost concrete structures monitoring applications making use of a credit card-sized Raspberry Pi single board computer as core hardware unit. This monitoring approach is also deployed by introducing a new damage identification index based on the ratio between the area of the 2-D error ellipse of specific probability of EMI-based measurements containment over that of the 2-D error circle of equivalent probability. Experimental results of damages occurring in concrete cubic and beam specimens are investigated under increasing loading conditions. Results illustrate that the proposed technique is an efficient approach for identification and early detection of damage in concrete structures.

• 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.

• Structural Engineering and Mechanics
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• 제56권4호
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• pp.569-588
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• 2015

A comprehensive methodology is proposed for design of metallic dampers in seismic retrofit of earthquake-damaged frame structures. It is assumed that the metallic dampers remain elastic and only provide stiffness during frequent earthquake (i.e., earthquake with a 63% probability of exceedance in 50-year service period), while in precautionary earthquake (i.e., earthquake with a 10% probability of exceedance in 50-year service period), the metallic dampers yield before the main frame and dissipate most of the seismic energy to either prevent or minimize structural damages. Therefore by converting multi-story frame to an equivalent single-degree-of-freedom system, the added stiffness provided by metallic dampers is designed to control elastic story drifts within code-based demand under frequent earthquake, and the added damping with the combination of added stiffness influences is obtained to control structural stress within performance-based target under precautionary earthquake. With the equivalent added damping ratio, the expected damping forces provided by metallic dampers can be calculated to carry out the configuration and design of metallic dampers along with supporting braces. Based on a detailed example for retrofit of an earthquake-damaged reinforced concrete frame by using metallic dampers, the proposed design procedure is demonstrated to be simple and practical, which can not only meet current China's design codes but also be used in retrofit design of earthquake-damaged frame with metallic damper for reaching desirable performance objective.

• 콘크리트학회논문집
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• 제20권1호
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• pp.13-22
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• 2008

다공성 시스템 내부 동결체의 생성과 성장은 온도경사와 화학적 에너지뿐만 아니라 열 물리학적 영향과 이동 물질에 의해서도 영향을 받는다. 더욱이 융해 화학물질의 확산율은 반복적인 동경융해 환경 하에서 매우 높은 값을 나타낸다. 결과적으로 콘크리트구조물의 열화는 해양환경과, 높은 고도 및 북쪽 지방에서 특히 크게 발생된다. 그러나 균열 성장과 누적된 손상에 의한 열화를 동반한 동결융해의 특성은 실험을 통해서 추정하기가 곤란하다. 이러한 손상을 예측하기 위해서 응답면기법 (RSM)을 이용한 회귀분석법을 사용하였다. 콘크리트구조물에서 반복되는 동결융해로 인한 열화의 주요 변수인 물-시멘트비, 연행공기, 동결융해의 반복 횟수 등은 응답면기법의 한계상태방정식을 구성하는데 중요한 입력 변수로 사용되었다. 누적변형률, 상대동탄성계수, 또는 등가 소성변형과 같은 주요한 열화 변수에 대한 회귀방정식은 열화된 구조물의 성능을 평가할 수 있다. 300번의 동결융해 반복 후의 상대동탄성계수와 잔류변형의 결과는 실험 결과와 매우 유사한 경향을 나타내었다. 응답면기법의 결과는 설계 시 한계값에 대한 초과 확률을 예측하는데 사용되어질 수 있다. 그러므로 개발된 예측 기법을 활용하여 반복적인 동결융해에 의해서 누적 손상을 받는 콘크리트구조물의 생애주기 관리에 사용될 수 있다.

• 한국가스학회지
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• 제7권2호
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• pp.33-41
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• 2003

LPG는 사용, 저장, 생산 과정뿐만 아니라 이송 중에도 많은 잠재위험(Hazard)을 갖고있다. 소규모의 수요처일 경우, LPG 용기를 적재한 차량에 의해 지역 사업자에 의하여 배달된다. 만약 도심지역에 가스용기를 적재한 차량에 폭발사고가 발생한다면 주변지역에 재산 피해뿐 아니라 상당한 인명피해를 초래할 것이다 본 연구에서는 LPG 누출 사례연구를 통하여 가스용기를 이용한 LPG의 운반 중에 사고의 원인이 되는 잠재위험을 확인한 후 사고발생 시나리오를 작성하고 발생 가능성과 피해결과를 예측하는 위험성(risk)의 정량적 분석을 하였다. 본 연구에서는 위험분석 프로그램을 Excel과 Visual Basic으로 프로그래밍 하여, ETA(Event Tree Analysis)법으로 LPG 운반도중 발생할 수 있는 사고의 빈도수를 구한 뒤, 이를 바탕으로 폭발로 인한 피해 범위 및 피해정도를 도출하였다. UVCE의 경우, 가스용기에서 누출되어 증발된 LPG에 대하여 사고현장주변에서 10m 이내에서는 심각한 구조적 손상을 보이며, 150m 이상에서도 유리가 파열되는 심각한 손상확률을 보였다. 그리고 TNT 상당법으로 Probit 결과, 10분간 누출되었을 때 40m 지점에서 유리창의 $75\%$가 깨졌으며, 20m 지점에서 $16\%$, 40m 지점에서는 $10\%$의 구조적 손상을 보였다.

• Earthquakes and Structures
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• 제20권3호
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• pp.279-293
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• 2021

Most of the existing seismic codes for RC buildings consider only a scenario earthquake for analysis, often characterized by the response spectrum at the specified location. However, any real earthquake event often involves occurrences of multiple earthquakes within a few hours or days, possessing similar or even higher energy than the first earthquake. This critically impairs the rehabilitation measures thereby resulting in the accumulation of structural damages for subsequent earthquakes after the first earthquake. Also, the existing seismic provisions account for the non-linear response of an RC building frame implicitly by specifying a constant response modification factor (R) in a linear elastic design. However, the 'R' specified does not address the changes in structural configurations of RC moment-resisting frames (RC MRFs) viz., building height, number of bays present, bay width, irregularities arising out of mass and stiffness changes, etc. resulting in changed dynamic characteristics of the structural system. Hence, there is an imperative need to assess the seismic performance under sequential earthquake ground motions, considering the adequacy of code-specified 'R' in the representation of dynamic characteristics of RC buildings. Therefore, the present research is focused on the evaluation of the non-linear response of medium-rise 3D RC MRFs with and without vertical irregularities under bi-directional sequential earthquake ground motions using non-linear dynamic analysis. It is evident from the results that collapse probability increases, and 'R' reduces significantly for various RC MRFs subjected to sequential earthquakes, pronouncing the vulnerability and inadequacy of estimation of design base shear by code-specified 'R' under sequential earthquakes.

• Wind and Structures
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• 제21권1호
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• pp.1-23
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• 2015

Wind tunnel testing of a low-rise building with openings (holes) of different sizes and shapes on a roof corner is conducted to measure the internal and external pressures from the building model. Detailed analysis of the testing data is carried out to investigate the characteristics of the internal and external pressures of the building with different openings' configurations. Superimposition of the internal and external pressures makes the emergence of positive net pressures on the roof. The internal pressures demonstrate an overall uniform distribution. The probability density function (PDF) of the internal pressures is close to the Gaussian distribution. Compared with the PDF of the external pressures, the non-Gaussian characteristics of the net pressures weakened. The internal pressures exhibit strong correlation in frequency domain. There appear two humps in the spectra of the internal pressures, which correspond to the Helmholtz frequency and vortex shedding frequency, respectively. But, the peak for the vortex shedding frequency is offset for the net pressures. Furthermore, the internal pressure characteristics indirectly reflect that the length of the front edge enhances the development of the conical vortices.The objective of this study aims to further understanding of the characteristics of internal, external and net pressures for low-rise buildings in an effort to reduce wind damages to residential buildings.

• Geomechanics and Engineering
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• 제20권5호
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• pp.447-459
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• 2020

Based on the literature statistical method, the paper publication status of the isolated working face and the distribution of the rockburst coal mine were obtained. The numerical simulation method is used to study the stress distribution law of working face under different mining range. In addition, based on the similar material simulation test, the overlying strata failure modes and the deformation characteristics of coal pillars during the mining process of the isolated working face with thick-hard key strata are analyzed. The research shows that, under the influence of the key strata, the overlying strata formation above the isolated working face is a long arm T-type spatial structure. With the mining of the isolated working face, a series of damages occur in the coal pillars, causing the key strata to break and inducing the rockburst occurs. Combined with the mechanism of rockburst induced by the dynamic and static combined load, the source of dynamic and static load on the isolated working face is analyzed, and the rockburst monitoring methods and the prevention and control measures are proposed. Through the above research, the occurrence probability of rockburst can be effectively reduced, which is of great significance for the safe mining of deep coal mines.