• Structural Engineering and Mechanics
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• 제74권4호
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• pp.481-494
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• 2020

In this paper, a probability-based procedure to evaluate the performance of existing RC structures exposed to seismic and fire actions is presented. The procedure is demonstrated with reference to an existing old school building, located in Italy. The vulnerability assessment of the building highlights deficiencies under both static and seismic loads. Retrofit operations are designed to achieve the seismic safety. The idea of the work consists in assessing the performance of the existing and retrofitted building in terms of both the seismic and fire resistance. The seismic retrofit and fire resistance upgrading follow different paths, depending on the specific configuration of the building. A good seismic retrofit does not entail an improving of the fire resistance and vice versa. The goal of the current work is to study the variation of response due to the uncertainties considered in records/fire curves selection and to carry out the assessment of the studied RC structure by obtaining fragility curves under the effect of different records/temperature. The results show the fragility curves before and after retrofit operations and both in terms of seismic performance and fire resistance performance, measuring the percent improving for the different limit states.

• 한국농공학회논문집
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• 제56권2호
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• pp.11-23
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• 2014

The impact and adaption on agricultural water resources considering climate change is significant for reservoirs. The change in rainfall patterns and hydrologic factors due to climate change increases the uncertainty of agricultural water supply and demand. The quantitative evaluation method of uncertainty based on agricultural water resource management under future climate conditions is a major concern. Therefore, it is necessary to improve the vulnerability management technique for agricultural water supply based on a probabilistic and stochastic risk evaluation theory. The objective of this study was to analyse the uncertainty of water resources under future climate change using probability distribution function of water supply in agricultural reservoir and demand in irrigation district. The uncertainty of future water resources in agricultural reservoirs was estimated using the time-specific analysis of histograms and probability distributions parameter, for example the location and the scale parameter. According to the uncertainty analysis, the future agricultural water supply and demand in reservoir tends to increase the uncertainty by the low consistency of the results. Thus, it is recommended to prepare a resonable decision making on water supply strategies in terms of using climate change scenarios that reflect different future development conditions.

• 국제강구조저널
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• 제18권4호
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• pp.1325-1335
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• 2018

This study dealt with investigating the seismic performance of the smart and shape memory alloy (SMA) and magnets plus rubber-spring (MRS) dampers and their effects on the seismic resistance of multiple-span simply supported bridges. The rubber springs in the MRS dampers were pre-compressed. For this aim, a set of experimental works was performed together with developing nonlinear analytical models to investigate dynamic responses of the bridges subjected to earthquakes. Fragility analysis and probabilistic assessment were conducted to assess the seismic performance for the overall bridge system. Fragility curves were then generated for each model and were compared with those of as-built. Results showed dampers could increase the seismic capacity of bridges. Furthermore, from system fragility curves, use of damper models reduced the seismic vulnerability in comparison to the as-built bridge model. Although the SMA damper showed the best seismic performance, the MRS damper was the most appropriate one for the bridge in that the combination of magnetic friction and pre-compressed rubber springs was cheaper than the shape memory alloy, and had the similar capability of the damper.

• 국제강구조저널
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• 제18권4호
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• pp.1200-1209
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• 2018

In this study, a probabilistic framework of the damage assessment of pipelines subjected to extreme hazard scenario was developed to mitigate the risk and enhance design reliability. Nonlinear 3D finite element models of T-joint systems were developed based on experimental tests with respect to leakage detection of black iron piping systems, and a damage assessment analysis of the vulnerability of their components according to nominal pipe size, coupling type, and wall thickness under seismic wave propagations was performed. The analysis results showed the 2-inch schedule 40 threaded T-joint system to be more fragile than the others with respect to the nominal pipe sizes. As for the coupling types, the data indicated that the probability of failure of the threaded T-joint coupling was significantly higher than that of the grooved type. Finally, the seismic capacity of the schedule 40 wall thickness was weaker than that of schedule 10 in the 4-inch grooved coupling, due to the difference in the prohibition of energy dissipation. Therefore, this assessment can contribute to the damage detection and financial losses due to failure of the joint piping system in a liquid pipeline, prior to the decision-making.

• 대한원격탐사학회지
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• 제34권5호
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• pp.721-738
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• 2018

이 연구의 목적은 확률모델의 2가지 방법인 Frequency Ratio(FR), Evidential Belief Functions(EBF) 모델을 사용하여 산사태 취약성을 작성하고 강릉시 사천면과 주문진읍에서의 결과 비교를 통해 각 지역에 적합한 모델을 선정하는 것이다. 사천면에서 762개, 주문진읍에서 548개의 산사태 위치를 항공 사진의 해석을 기반으로 작성되었다. 각각의 산사태 지점 중 절반을 모델링을 위해 무작위로 선택하였고 남은 산사태 지점은 검증 목적으로 사용하였다. 지형 요소, 수문 요소, 산림입지토양도(1:5,000), 임상도(1:5,000), 지질도(1:25,000)와 같은 5가지 범주로 분류된 20가지의 산사태 유발 요소가 연구에서 산사태 취약성 작성을 위해 고려되었다. 산사태 발생과 산사태 유발 요소 사이의 관계는 FR, EBF 모델을 사용하여 분석되었다. 그 후, 2 가지 모델을 AUC(curve under area) 방법을 사용하여 검증하였다. 검증 결과에 따르면 주문진읍에서 FR모델(AUC = 81.2%)이 EBF 모델(AUC = 78.9%)에 비해 정확도가 높았다. 사천면 지역에서는 EBF 모델(AUC = 83.6%)이 FR모델(AUC = 81.6%)보다 정확도가 높게 나타났다. 검증 결과 FR 모델과 EBF 모델은 정확도 80% 내외로 높은 정확도를 가지고 있음을 나타낸다.

• 한국지진공학회논문집
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• 제14권3호
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• pp.59-68
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• 2010

기존 구조물의 내진보강을 경제적으로 수행 위해서는 내진성능을 보다 정확하게 평가하는 것이 필요하다. 우리나라 도로교의 내진성능은 "기존교량의 내진성 평가 요령"에 의해 평가되고 있으며, 이는 이를 활용할 당시 기술자의 기술수준을 고려하여 비교적 간단한 방법이 채택되었다. 최근에는 입력지진의 불확실성을 고려하여 내진성능을 확률적으로 평가하는 연구가 많이 수행되고 있다. 일반적으로 구조물은 지반의 영향을 무시하고 모델화되거나 때로는 지반을 탄성스프링으로 모델화하여 응답에 대한 지반의 영향을 고려하고 있다. 그러나 지반도 지진시 비선형특성을 나타내므로 교량의 응답특성을 보다 정확하게 평가하기 위해서는 이를 고려할 필요가 있다. 본 연구에서는 지진세기에 따른 지반의 비선형성을 등가의 선형스프링으로 모델화하여 6경간연속교를 대상으로 하여 지진해석을 수행하였으며, 교각의 파괴 및 낙교에 대한 지진취약도의 특성변화를 확률적으로 평가하였다.

• 한국수자원학회논문집
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• 제46권8호
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• pp.795-805
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• 2013

가뭄은 중요한 자연재해의 하나로서 수자원 관리 부분에서 매우 중요한 인자이다. 본 연구에서는 대한민국의 55개 기상청 관측소를 대상으로 SPI 지수에 따른 가뭄기간과 가뭄심도를 정의하고, 코풀라 이론을 이용하여 두 가뭄변수의 결합 확률 분포를 유도하였다. 또한 이를 이용하여 가뭄의 발생양상을 고찰하고 가뭄의 재현기간으로 제시하였으며, 대한민국을 대상으로 가뭄의 공간적 분포를 분석하였다. 연구에서 도출된 가뭄의 재현기간별 SPI 지수로부터 대한민국의 충청도의 공주 및 충주 인근, 강원도의 원주, 인제, 정선, 태백 등의 지역이 상대적으로 가뭄에 취약한 것으로 도출되었다.

• 한국안전학회지
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• 제27권6호
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• pp.172-177
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• 2012

In areas around Deoksan Li and Deokjeon Li, Inje Eup, Inje Gun, located between $38^{\circ}2^{\prime}55^{{\prime}{\prime}}N$ and $38^{\circ}5^{\prime}50^{{\prime}{\prime}}N$ in latitude and $128^{\circ}11^{\prime}20^{{\prime}{\prime}}E$ and $128^{\circ}18^{\prime}20^{{\prime}{\prime}}E$ in longitude, large-sized avalanche disasters occurred due to Typhoon Ewiniar in 2006. As a result, 29 people were dead or missing, along with a total of 37.25 billion won of financial loss(Gangwon Province, 2006). To evaluate such landslide and debris flow risk areas and their vulnerability, this study applied a technique called 'Weight of Evidence' based on GIS. Especially based on the overlay analysis of aerial images before the occurrence of landslides and debris flows in 2005 and after 2006, this study extracted 475 damage-occurrence areas in a shape of point, and established a DB by using such factors as topography, hydrologic, soil and forest physiognomy through GIS. For the prediction diagram of debris flow and landslide risk areas, this study calculated W+ and W-, the weighted values of each factor of Weight Evidence, while overlaying the weighted values of factors. Besides, the diagram showed about 76% in prediction accuracy, and it was also found to have a relatively high correlationship with the areas where such natural disasters actually occurred.

• Smart Structures and Systems
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• 제24권1호
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• pp.127-139
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• 2019

Residual drifts after an earthquake can incur huge repair costs and might need to replace the infrastructure because of its non-reparability. Proper functioning of bridges is also essential in the aftermath of an earthquake. In order to mitigate pounding and unseating damage of bridges subjected to earthquakes, a self-adaptive Ni-Ti shape memory alloy (SMA)-cable-based frictional sliding bearing (SMAFSB) is proposed considering self-adaptive centering, high energy dissipation, better fatigue, and corrosion resistance from SMA-cable component. The developed novel bearing is associated with the properties of modularity, replaceability, and earthquake isolation capacity, which could reduce the repair time and increase the resilience of highway bridges. To evaluate the super-elasticity of the SMA-cable, pseudo-static tests and numerical simulation on the SMA-cable specimens with a diameter of 7 mm are conducted and one dimensional (1D) constitutive hysteretic model of the SMAFSB is developed considering the effects of gap, self-centering, and high energy dissipation. Two types of the SMAFSB (i.e., movable and fixed SMAFSBs) are applied to a two-span continuous reinforced concrete (RC) bridge. The seismic vulnerabilities of the RC bridge, utilizing movable SMAFSB with the constant gap size of 60 mm and the fixed SMAFSBs with different gap sizes (e.g., 0, 30, and 60 mm), are assessed at component and system levels, respectively. It can be observed that the fixed SMAFSB with a gap of 30 mm gained the most retrofitting effect among the three cases.

• Structural Engineering and Mechanics
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• 제76권6호
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• pp.751-763
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• 2020

Available records of recent earthquakes show that near-field earthquakes have different characteristics than far-field earthquakes. In general, most of these unique characteristics of near-fault records can be attributed to their forward directivity. This phenomenon causes the records of ground motion normal to the fault to entail pulses with long periods in the velocity time history. The energy of the earthquake is almost accumulated in these pulses causing large displacements and, accordingly, severe damages in the building. Damage to structures caused by past earthquakes raises the need to assess the chance of future earthquake damage. There are a variety of methods to evaluate building seismic vulnerabilities with different computational cost and accuracy. In the meantime, fragility curves, which defines the possibility of structural damage as a function of ground motion characteristics and design parameters, are more common. These curves express the percentage of probability that the structural response will exceed the allowable performance limit at different seismic intensities. This study aims to obtain the fragility curve for low- and mid-rise structures of reinforced concrete moment frames by incremental dynamic analysis (IDA). These frames were exposed to an ensemble of 18 ground motions (nine records near-faults and nine records far-faults). Finally, after the analysis, their fragility curves are obtained using the limit states provided by HAZUS-MH 2.1. The result shows the near-fault earthquakes can drastically influence the fragility curves of the 6-story building while it has a minimal impact on those of the 3-story building.