• Smart Structures and Systems
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• 제17권1호
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• pp.149-165
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• 2016

Floods have been known to be one of the main causes of bridge collapse. Contrary to earthquakes, flood events tend to occur repeatedly and more frequently in rainfall areas; flood-induced damage and collapse account for a significant portion of disasters in many countries. Nevertheless, in contrast to extensive research on the seismic fragility analysis for civil infrastructure, relatively little attention has been devoted to the flood-related fragility. The present study proposes a novel methodology for deriving flood fragility curves for bridges. Fragility curves are generally derived by means of structural reliability analysis, and structural failure modes are defined as excessive demands of the displacement ductility of a bridge under increased water pressure resulting from debris accumulation and structural deterioration, which are known to be the primary causes of bridge failures during flood events. Since these bridge failure modes need to be analyzed through sophisticated structural analysis, flood fragility curve derivation that would require repeated finite element analyses may take a long time. To calculate the probability of flood-induced failure of bridges efficiently, in the proposed framework, the first order reliability method (FORM) is employed for reducing the required number of finite element analyses. In addition, two software packages specialized for reliability analysis and finite element analysis, FERUM (Finite Element Reliability Using MATLAB) and ABAQUS, are coupled so that they can exchange their inputs and outputs during structural reliability analysis, and a Python-based interface for FERUM and ABAQUS is newly developed to effectively coordinate the fragility analysis. The proposed framework of flood fragility analysis is applied to an actual reinforced concrete bridge in South Korea to demonstrate the detailed procedure of the approach.

• 한국지반공학회논문집
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• 제18권5호
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• pp.99-108
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• 2002

본 연구에서는 탄성, 탄소성 및 실험을 통해 유도된 비선형-취성-소성 모델을 지하 심부 원형터널의 경우에 적용하여 각 모델에 따른 특성과 추정되는 응력재분배 및 응력교란 범위를 비교하였다. 현지 초기응력의 크기와 주응력차가 커질수록 파괴영 역이 파괴되지 않은 영역에 미치는 응력재분배와 교란의 영향이 증가되기 때문에, 탄소성 또는 탄성 해석의 경우보다 비선형-취성-소성 해석결과에서 응력재분배 및 교란영역, 주응력차와 변위가 더 크게 발생하였다. 따라서 현지 응력 수준과 현지 주응력차가 클 경우, 비선형-취성-소성 해석에 의해 손상영 역의 범위가 더 크게 발생할 것으로 예측되므로 손상해석의 필요성이 증대될 것으로 판단되었다.

• 센서학회지
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• 제24권6호
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• pp.373-378
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• 2015

The structure of the human ear is divided into the outer ear, the middle ear, and the inner ear. The inner ear includes the cochlea that plays a very important role in hearing. Recently, the development of an artificial cochlear device for the hearing impaired with cochlear damage has been actively researched. Research has been carried out on the biomimetic piezoelectric thin film ABM (Artificial Basilar Membrane) in particular. In an effort to improve the frequency separation performance of the existing piezoelectric thin film ABM, this paper presents the design, fabrication, and characterization of the production and performance of a partially etched-type ABM material. $O_2$ plasma etching equipment was used to partially etch a piezoelectric thin film ABM to make it more flexible. The mechanical-behavior characterization of the manufactured partially etched-type ABM showed that the overall separation frequency range shifted to a lower frequency range more suitable for audible frequency bandwidths and it displayed an improved frequency separation performance. In addition, the maximum magnitude of the vibration displacement at the first local resonant frequency was enhanced by three times from 38 nm to 112 nm. It is expected that the newly designed, partially etched-type ABM will improve the issue of cross-talk between nearby electrodes and that the manufactured partially etched-type ABM will be utilized for next-generation ABM research.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2008년도 정보통신설비 학술대회
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• pp.262-267
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• 2008

Recently, landslides frequently occur on natural slope and/or man-made cut slope during periods of intense rainfall. With a rapidly increasing population on or near steep terrain, landslides have become one of the most significant natural hazards. Thus, it is necessary to protect people from landslides and to minimize the damage of houses, roads and other facilities. To accomplish this goal, many landslide monitoring systems have been developed throughout the world. In this paper, a simple landslide detection system that enables people to escape the endangered area is introduced. The system is focused on the debris flows which happen frequently during periods of intense rainfall. The system is based on the wireless sensor network (WSN) that is composed of wireless sensor nodes, gateway, and remote server system. Wireless sensor nodes and gateway are deployed by commercially available Microstrain G-Link products. Five wireless sensor nodes and one gateway are installed at the test slope for detecting ground movement. The acceleration and inclination data of test slope can be obtained, which provides a potential to detect landslide. In addition, thresholds to determine whether the test slope is stable or not are suggested by a series of numerical simulations, using geotechnical analysis software package. It is obtained that the alarm should be issued if the x-direction displacement of sensor node is greater than 20mili-meters and the inclination of sensor node is greater than 3 degrees. It is expected that the landslide detection method using wireless senor network can provide early warning where landslides are prone to occur.

• 한국구조물진단유지관리공학회 논문집
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• 제22권2호
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• pp.16-25
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• 2018

콘크리트는 장기수명이 요구되는 구조물에 적합한 건설재료로 내구성이 우수하지만 장기간 지하수에 노출되어 발생하는 칼슘용출 현상에 대한 이해 및 이에 따른 RC 부재의 휨 거동 특성을 평가할 필요가 있다. 실험결과에 따르면, 광물질 혼화재는 RC 부재의 장기강도 개선에 효과적이지만, 칼슘용출이 발생하면 RC 부재의 항복하중 및 휨 강성이 감소하고 중립축깊이와 처짐량이 증가하는 것으로 나타났다. 따라서 칼슘용출에 의한 열화는 RC 부재의 성능 저하를 유발하므로 칼슘용출 환경에 노출되는 지하구조물에 광물질 혼화재가 적용될 경우에는, 광물질 혼화재 종류에 따른 최적 혼입 비율이 마련되어야할 것으로 사료된다.

• 토지주택연구
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• 제8권3호
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• pp.181-187
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• 2017

To proactively respond to internal and external changes such as the recent demographic change and rising demand for diversified housing types, this study investigated the framed-structure free plan public house model proposed by the LH to look at the seismic performance of framed-structure apartment according to damper system use through non-linear analysis. The effectiveness thereof was also examined in terms of performance and economy. As a result, the proposed damper system application method to framed-structure free plan public house model was found to meet the performance requirements of the present earthquake-resistant design (KBC2016) and effective to apply to designs. The max response displacement and max response acceleration were compared based on the nonlinear analysis. As a result, the building with damper system showed better earthquake resistance performance than earthquake-resistant structure thanks to the damper system, although the base shear of earthquake-resistant system was reduced by 20% in design. The damper system is expected to help reduce building damage while ensuring excellent earthquake resistance performance. In addition, the framework quantities of earthquake-resistant structure and structure with damping system were compared. As a result, columns were found to reduce concrete amount by about 3.9% and rebar, by about 7.3%. Walls showed about 12.6% reduction in concrete and about 10.7% in rebar. In terms of cost, framework construction cost including formwork and foundation expenses was expected to drop by about 5~6%.

• 한국구조물진단유지관리공학회 논문집
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• 제7권4호
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• pp.191-199
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• 2003

대부분 강구조 및 철근콘크리트 구조물은 탄소성 거동에 의해 극한강도가 지배된다. 비록 평상시에는 탄성 범위를 초과하는 진폭(振幅)이 발생하지 않지만 심각한 폭발이나 지진하중과 같은 극단적인 경우가 발생할 때, 엔지니어는 구조물에 영구적인 손상을 줄 수 있는 상황들을 접하게 된다. 이러한 상태 평가를 위해 본 연구는 폭발 등의 극한하중에 특성에 의해 발생되는 구조물의 동적거동을 분석하였다. 그리고 본 연구는 극한진동 특성을 분석하기 위해 비선형 유한요소프로그램(ATENA2D, FRANC2DL)을 사용하였다. 본 연구의 해석결과, 평상시와 횡하중시의 균열은 발생 위치와 양태가 매우 다르게 나타났다. 또한, 초기 손상균열이 있는 RC라멘의 보에 단면형상과 기하학적 형상비 변화를 고려하여 균열각의 변화를 분석하였으며 이를 통해 동적 횡하중 작용에 의한 피해여부를 판단할 수 있었다.

• 한국지진공학회논문집
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• 제23권6호
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• pp.311-319
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• 2019

The number of aged bridges is increasing so that bridges over 30 years old account for about 11% of all bridges. Consequently, the development of a seismic performance evaluation method that considers the effects of ageing is essential for a seismic retrofitting process for improvement of the seismic safety of existing old bridges. Assessment of the damage situation of bridges after the recent earthquakes in Korea has been limited to the bearings, anchor, and concrete mortar on piers. The purpose of this study is to evaluate the seismic responses of PSC box girder bridges by considering the ageing effect of rubber bearings (RBs) and lead-rubber bearings (LRBs). The modification factor proposed by AASHTO is used to take into account the ageing effect in the bearings. PSC box girder bridges with RBs and LRBs were 3D modeled and analyzed with the OpenSEES program. In order to evaluate the ageing effect of RBs and LRBs, 40 near fault and 40 far field records were used as the input earthquakes. When considering the effect of ageing, the displacement responses and shear forces of bridge bearings (RBs and LRBs) were found to increase mostly under the analytical conditions. It was shown that the effect of ageing is greater in the case of RBs than in the case of LRBs.

• Advances in concrete construction
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• 제8권3호
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• pp.173-185
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• 2019

This article presents a comparative study of the effect of steel layouts on the seismic behavior of transition steel-concrete composite connections, both experimental and analytical investigations of concrete filled steel tube-reinforced concrete (CFST-RC) and steel reinforecd concrete-reinforced concrete (SRC-RC) structures were conducted. The steel-concrete composite connections were subjected to combined constant axial load and lateral cyclic displacements. Tests were carried out on four full-scale connections extracted from a real project engineering with different levels of axial force. The effect of steel layouts on the mechanical behavior of the transition connections was evaluated by failure modes, hysteretic behavior, backbone curves, displacement ductility, energy dissipation capacity and stiffness degradation. Test results showed that different steel layouts led to significantly different failure modes. For CFST-RC transition specimens, the circular cracks of the concrete at the RC column base was followed by steel yielding at the bottom of the CFST column. While uncoordinated deformation could be observed between SRC and RC columns in SRC-RC transition specimens, the crushing and peeling damage of unconfined concrete at the SRC column base was more serious. The existences of I-shape steel and steel tube avoided the pinching phenomenon on the hysteresis curve, which was different from the hysteresis curve of the general reinforced concrete column. The hysteresis loops were spindle-shaped, indicating excellent seismic performance for these transition composite connections. The average values of equivalent viscous damping coefficients of the four specimens are 0.123, 0.186 and 0.304 corresponding to the yielding point, peak point and ultimate point, respectively. Those values demonstrate that the transition steel-concrete composite connections have great energy dissipating capacity. Based on the experimental research, a high-fidelity ABAQUS model was established to further study the influence of concrete strength, steel grade and longitudinal reinforcement ratio on the mechanical behavior of transition composite connections.

• Nuclear Engineering and Technology
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• 제53권9호
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• pp.2937-2952
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• 2021

A typical three-dimensional finite element model for a fuel assembly is established, which is composed of 16 monolithic U-10Mo fuel plates and Al alloy frame. The distribution and evolution results of temperature, displacement and stresses/strains in all the parts are numerically obtained and analyzed with a self-developed code of FUELTM. The simulation results indicate that (1) the out-of-plane displacements of Al alloy side plates are mainly attributed to the bending deformations; (2) enhanced out-of-plane displacements appear in fuel plates adjacent to the outside Al plates, which results from the occurred bending deformations due to the applied constraints of outside Al plates; (3) an intense interaction of fuel foil with the cladding occurs near the foil edge, which appears more heavily in the fuel plates adjacent to the outside Al plates. The maximum first principal stresses in the fuel foil are similar for all the fuel plates and appear near the fuel foil edge; while, the through-thickness creep strains of fuel foil in the fuel plate near the central region of fuel assembly are larger, and the induced creep damage might weaken the fuel skeleton strength and raise the fuel failure risk.