• 한국지반공학회논문집
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• 제22권12호
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• pp.89-98
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• 2006

본 논문에서는 지진이 발생한 지역에서 다시 지진이 발생할 경우에 포화된 사질토 지반의 동적거동에 관한 연구를 수행하였다. 반복 직접단순전단시험을 실시하여 느슨한 모래지반에서 간극수압발생량과 재액상화발생여부의 상관관계를 분석하였다. 최초의 전단하중으로 인하여 지반이 원래 가지고 있던 유효수직응력의 약 90%까지 간극수압이 발생하였을 경우 시간 경과에 따라 과잉간극수압이 전부 소산된 이후 다시 전단하중을 가하였을 때 지반의 액상화에 대한 저항력은 증가하였다. 하지만 최초 진동으로 지반이 완전히 액상화되었을 경우에는 다음에 전달되는 전단하중에는 이전보다도 지반이 더욱 조밀해짐에도 불구하고 액상화 저항력은 증가하지 않았다. 이와 같은 실내시험결과를 진동 중에 발생하는 간극수압 변화와 흙의 강성저하를 고려할 수 있는 유효응력모델인 UBCSAND모델에 적용하였으며, 최초 전단하중에서 발생하는 간극수압비에 따라 구성모델의 액상화 저항력을 결정하였다. 이 구성모델을 이용하여 재액상화현상을 연구한 원심모형실험의 결과를 예측하였으며, 계측치와 서로 비교하였다. 국내에서도 일본과 가까운 남부지역에서는 약한 지진이지만 자주 발생하고 있는 시점에서 이와 같은 유효응력모델을 이용한 재액상화 현상에 관한 연구가 절실히 요구되어진다.

• Earthquakes and Structures
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• 제3권1호
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• pp.59-81
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• 2012

A ductility inverse-mapping method for SDOF systems including passive dampers is proposed which enables one to find the maximum acceleration of ground motion for the prescribed maximum response deformation. In the conventional capacity spectrum method, the maximum response deformation is computed through iterative procedures for the prescribed maximum acceleration of ground motion. This is because the equivalent linear model for response evaluation is described in terms of unknown maximum deformation. While successive calculations are needed, no numerically unstable iterative procedure is required in the proposed method. This ductility inverse-mapping method is applied to an SDOF model of bilinear hysteresis. The SDOF models without and with passive dampers (viscous, viscoelastic and hysteretic dampers) are taken into account to investigate the effectiveness of passive dampers for seismic retrofitting of building structures. Since the maximum response deformation is the principal parameter and specified sequentially, the proposed ductility inverse-mapping method is suitable for the implementation of the performance-based design.

• Structural Engineering and Mechanics
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• 제82권2호
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• pp.245-258
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• 2022

Many Structural Health Monitoring (SHM) methods have been proposed for structural damage diagnosis and prognosis. However, SHM for pinched hysteretic structures can be problematic due to the high level of nonlinearity. The model-free hysteresis loop analysis (HLA) has displayed notable robustness and accuracy in identifying damage for full-scaled and scaled test buildings. In this paper, the performance of HLA is compared with seven other SHM methods in identifying lateral elastic stiffness for a six-story numerical building with highly nonlinear pinching behavior. Two successive earthquakes are employed to compare the accuracy and consistency of methods within and between events. Robustness is assessed across sampling rates 50-1000 Hz in noise-free condition and then assessed with 10% root mean square (RMS) noise added to responses at 250 Hz sampling rate. Results confirm HLA is the most robust method to sampling rate and noise. HLA preserves high accuracy even when the sampling rate drops to 50 Hz, where the performance of other methods deteriorates considerably. In noisy conditions, the maximum absolute estimation error is less than 4% for HLA. The overall results show HLA has high robustness and accuracy for an extremely nonlinear, but realistic case compared to a range of leading and recent model-based and model-free methods.

• 한국지진공학회논문집
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• 제2권2호
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• pp.13-22
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• 1998

본 연구는 지진격리장치의 일종인 마찰 단진자 시스템(FPS)의 교량에의 적용에 관한 연구이다. FPS에 의하여 지진 격리된 교량과 지진 격리되지 않은 교량의 지진하중 작용시의 응답을 비교하기 위하여 축소모델 교량을 이용한 진동대 실험을 수행하였다. 연구결과, 본 장치를 설치한 경우 지진하중에 대한 지지능력이 향상하는 것으로 나타났다. 또한, 활동면 곡류반경에 의해 조절이 가능한 F.P.S 베어링의 강성은 입력된 kwlsfur의 강도와는 무관하며, 활동면의 마찰계수에 따라 속도가 변화하여 약진시에는 활동면에서의 속도가 작으므로 강진시와 비교하여 지진하중에 의하여 발생하는 마찰력도 감소하게 되었다. 한편 F.P.S 베어링의 마찰특성은 반복된 실험에서도 변화하지 않았고, 영구변형은 약적으로도 작았을 뿐만 아니라 누적되지도 않았다.

• Earthquakes and Structures
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• 제25권2호
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• pp.125-134
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• 2023

In the present work, a new global damage index is proposed for the seismic performance and failure analysis of concrete gravity dams. Unlike the existing indices of concrete structures, this index doesn't need scaling with an ultimate or an upper value. For this purpose, the Beni-Haroun dam in north-eastern Algeria, is considered as a case study, for which an average seismic capacity curve is first evaluated by performing several incremental dynamic analyses. The seismic performance point of the dam is then determined using the N2 method, considering multiple modes and taking into account the stiffness degradation. The seismic demand is obtained from the design spectrum of the Algerian seismic regulations. A series of recorded and artificial accelerograms are used as dynamic loads to evaluate the nonlinear responses of the dam. The nonlinear behaviour of the concrete mass is modelled by using continuum damage mechanics, where material damage is represented by a scalar field damage variable. This modelling, which is suitable for cyclic loading, uses only a single damage parameter to describe the stiffness degradation of the concrete. The hydrodynamic and the sediment pressures are included in the analyses. The obtained results show that the proposed damage index faithfully describes the successive brittle failures of the dam which increase with increasing applied ground accelerations. It is found that minor damage can occur for ground accelerations less than 0.3 g, and complete failure can be caused by accelerations greater than 0.45 g.

• 대한인간공학회지
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• 제32권1호
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• pp.117-124
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• 2013

Objective: This paper presents additional considerations related to organization and safety culture extracted from recent human error incidents in Korea, such as station blackout(i.e., SBO) in Kori#1. Background: Safety culture has been already highlighted as a major cause of human errors after 1986 Chernobyl accident. After Fukushima accident in Japan, the public acceptance for nuclear energy has taken its toll. Organizational characteristics and culture became elucidated as a major contributor again. Therefore many nuclear countries are re-evaluating their safety culture, and discussing any preparedness and its improvement. On top of that, there was an SBO in 2012 in the Kori#1. Korean public feels frustrated due to the similar human errors causing to a catastrophe like Fukushima accident. Method: This paper reassesses Japan's incidents, and revisits Korea's recent incidents. It focuses on the analysis of the hazards rather than the causes of human errors, the derivation of countermeasures, and their implementation. The preceding incidents and conclusions from Japanese experience are also re-analyzed. The Fukushima accident was an SBO due to the natural disaster such as earthquakes and a successive tsunami. Unlike the Fukushima accident, the Kori#1 incident itself was simple and restored without any loss and radioactive release. However, the fact that the incident was deliberately concealed led to massive distrust. Moreover, the continued violation of rules and organized concealment of the accident are serious signs of a new distorted type of human errors, blatantly revealing the cultural and fundamental weakness of the current organization. Result: We should learn from Japanese experiences who had taken pride in its safety technology and fairly high confidence in safety culture. Japan's first criticality accident in JCO facility splashed cold water on that confidence. It has turned out to be a typical case revealing the problems in the organization and safety culture. Since Japan has failed to gain lessons and countermeasure, the issue persists to the Fukushima incident. Conclusion: Safety culture is not a specific independent element, which makes it difficult to either evaluate it properly or establish countermeasures from the lessons. It may continue to expose similar human errors such as concealment of incident and manipulation of bad data. Application: Not only will this work establish the course of research for organization and safety culture, but this work will also contribute to the revitalization of Korea's nuclear industry from the disappointment after the export contract to UAE.