• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.53-56
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• 2008

본 연구는 주거용 고층 건물에서 폭넓게 사용되고 있는 플랫 플레이트 구조에서 장방형 기둥-슬래브 접합부를 대상으로 실시한 6개의 실험결과를 분석한 것이다. 연구의 목적은 지진하중과 같이 반복적으로 작용하는 횡하중에 대하여 기둥 단면의 형상비(${\beta}$c=$c_1/c_2$)에 따른 접합부의 이력거동을 비교 평가 하는 것이다. 기둥 형상비는 $b_o$가 일정해 지도록 0.33${\sim}$3($c_1/c_2$=1/3, 1/1, 3/1)으로 선정하였다. 슬래브 휨철근비는 1.0%, 1.5%로 변화시켰으며, 중력전단력비($V_g/V_c$) 등 접합부의 이력거동에 영향을 줄 수 있는 다른 영향인자들은 일정한 조건으로 계획하여 기둥 형상비의 영향을 고찰할 수 있도록 하였다. 실험을 통해서 뚫림전단파괴 양상과 균열 패턴, 접합부의 강성, 변형능력 등을 변수에 따라 분석하였다.

• 한국통신학회논문지
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• 제39C권3호
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• pp.239-246
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• 2014

무선 센서 네트워크에서 가장 중요한 이슈는 에너지 소모이다. 초저전력 통신을 위해서, 동기 주기에 따른 클럭 편차 에러에 대한 실험 결과를 이용하여, 지연 조건이 크지 않으며 모니터링 간격이 큰 분야에 적합한 새로운 MAC (Medium Access Control) 프로토콜을 디자인하였다. 제안 방식은 전송 패킷이 발생할 때 동기를 수행하는 방식이며, 동기 주기에 따라 그에 맞는 동기 에러에 대한 크기를 예측할 수 있다. 따라서 제안 방식은 기존 프로토콜들이 낮은 충격 계수 환경만을 지원하는 것과 달리, 초저 충격 계수 환경까지 지원할 수 있기 때문에 트래픽이 매우 낮은 초저전력, 높은 수명을 요구하는 분야에 사용될 수 있다. 제안 프로토콜의 성능을 평가하기 위해서 테스트베드를 구현하였으며, 관련 프로토콜들과 성능을 비교 하였고, 이를 통해 SCP-MAC 대비 80% 정도 에너지 소모량을 줄일 수 있음을 보였다. 제안 프로토콜은 매우 긴 네트워크 수명을 필요로 하며 지연 조건이 강하지 않은 무선 모니터링 분야 등에 큰 기여를 할 것으로 기대한다.

• Structural Engineering and Mechanics
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• 제31권2호
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• pp.163-180
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• 2009

In the design of tall reinforced concrete (R/C) buildings, the serviceability stiffness criteria in terms of maximum lateral displacement and inter-story drift must be satisfied to prevent large second-order P-delta effects. To accurately assess the lateral deflection and stiffness of tall R/C structures, cracked members in these structures need to be identified and their effective member flexural stiffness determined. In addition, the implementation of the geometric nonlinearity in the analysis can be significant for an accurate prediction of lateral deflection of the structure, particularly in the case of tall R/C building under lateral loading. It can therefore be important to consider the cracking effect together with the geometric nonlinearity in the analysis in order to obtain more accurate results. In the present study, a computer program based on the iterative procedure has been developed for the three dimensional analysis of reinforced concrete frames with cracked beam and column elements. Probability-based effective stiffness model is used for the effective flexural stiffness of a cracked member. In the analysis, the geometric nonlinearity due to the interaction of axial force and bending moment and the displacements of joints are also taken into account. The analytical procedure has been demonstrated through the application of R/C frame examples in which its accuracy and efficiency in comparison with experimental and other analytical results are verified. The effectiveness of the analytical procedure is also illustrated through a practical four story R/C frame example. The iterative procedure provides equally good and consistent prediction of lateral deflection and effective flexural member stiffness. The proposed analytical procedure is efficient from the viewpoints of computational effort and convergence rate.

• Earthquakes and Structures
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• 제13권5호
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• pp.485-496
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• 2017

The behavior of 8 steel reinforced high-strength concrete (SRHSC) columns, which comprised of four identical columns with cross-shaped steel and other four identical columns with square steel tube, was investigated experimentally under cyclic uniaxial and biaxial loading independently. The influence of steel configuration and loading path on the global behavior of SRHSC columns in terms of failure process, hysteretic characteristics, stiffness degradation and ductility were investigated and discussed, as well as stress level of the longitudinal and transverse reinforcing bars and steel. The research results indicate that with a same steel ratio deformation capacity of steel reinforced concrete columns with a square steel tube is better than the one with a cross-shaped steel. Loading path affects hysteretic characteristics of the specimens significantly. Under asymmetrical loading path, hysteretic characteristics of the specimens are also asymmetry. Compared with specimens under unidirectional loading, specimens subjected to bidirectional loading have poor carrying capacity, fast stiffness degradation, small yielding displacement, poor ductility and small ultimate failure drift. It also demonstrates that loading paths affect the deformation capacity or deformation performance significantly. Longitudinal reinforcement yielding occurs before the peak load is attained, while steel yielding occurs at the peak load. During later displacement loading, strain of longitudinal and transverse reinforcing bars and steel of specimens under biaxial loading increased faster than those of specimens subjected to unidirectional loading. Therefore, the bidirectional loading path has great influence on the seismic performance such as carrying capacity and deformation performance, which should be paid more attentions in structure design.

• 한국구조물진단유지관리공학회 논문집
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• 제24권1호
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• pp.116-124
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• 2020

코어 위치변화에 따른 횡력저항성능 분석을 위하여, 대칭 평면형 20층 건물을 대상으로 3차원 구조해석을 수행하였다. 중심 코어, 1축 편심 코어, 2축 편심 코어로 구분하여 4가지 해석모델을 구성하고, 고유치해석, 풍하중 해석, 지진하중 해석을 수행하였다. 중심 코어 건물에서는 비틀림이 발생하지 않았으나, 편심 코어의 배치에 따라 휨과 비틀림이 복합적으로 발생하였으며 횡력저항성능이 저하되었다. 코어의 편심 배치에 따른 풍하중 크기의 변화는 작으나, 최대 횡변위는 코어의 편심 배치에 의하여 크게 증가하는 것으로 확인되었다. 또한, 편심 코어의 경우 횡방향 강성의 저하로 인하여 중심 코어에 비해 지진하중이 다소 감소하였으나, 비틀림의 영향으로 최대 층간변위비는 크게 증가하는 것으로 확인되었다. 이러한 결과들을 바탕으로 코어의 위치에 따른 구조거동을 확인하고, 계획 및 설계 단계에서 코어 배치의 가이드라인으로 활용할 수 있다.

• 한국해양공학회지
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• 제31권2호
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• pp.81-90
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• 2017

The 1MW OTEC (Ocean Thermal Energy Conversion) platform was designed for application in equatorial seas. In this study, the OTEC platform was investigated using numerical and experimental methods. An octagon-shaped OTEC platform was investigated using the Ocean Engineering Basin of KRISO. These experiments included various tests of regular waves, irregular waves and irregular waves with current (wave+current). The responses of the platform in regular waves showed good agreement between the numerical and experimental results, including the motion RAO, wave run up, and mean drift force. The peak period of heave and pitch motions were observed around 0.5 rad/s, and the effect of the total reflection was found under short wave conditions. The standard deviation (STD) of the platform motion was checked in irregular waves of equatorial and Hawaiian seas. The STD of the pitch was less than $4^{\circ}$ different from the operability requirement under equatorial conditions and the surge STD of the wave frequency showed good agreement between the numerical and experimental results. The STD values of the surge and pitch were increased 66.6% and 92.8% by the current effects in irregular waves, but the pitch STD was less than $4^{\circ}$ under equatorial conditions. This study showed that the STD of the surge was affected by spring effects. Thus, the watch circle of the platform and tension of the mooring lines must be evaluated for a specific design in the future.

• Structural Engineering and Mechanics
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• 제76권3호
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• pp.279-291
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• 2020

The seismic design of conventional frame structures is meant to enhance plastic deformations at beam ends and prevent yielding in columns. To this end, columns are made stronger than beams. Yet yielding in columns cannot be avoided with the column-to-beam strength ratios (about 1.3) prescribed by seismic codes. Preventing plastic deformations in columns calls for ratios close to 4, which is not feasible for economic reasons. Furthermore, material properties and the rearrangement of geometric shapes inevitably make the distribution of damage among stories uneven. Damage in the i-th story can be characterized as the accumulated plastic strain energy (W_pi) normalized by the product of the story shear force (Q_yi) and drift (δ_yi) at yielding. Past studies showed that the distribution of the plastic strain energy dissipation demand, W_pi/ΣW_pj, can be evaluated from the deviation of Q_yi with respect to an "optimum value" that would make the ratio W_pi/(Q_yiδ_yi) -i.e. the damage- equal in all stories. This paper investigates how the soil type and ductility demand affect the optimum lateral strength distribution. New optimum lateral strength distributions are put forth and compared with others proposed in the literature.

• 대한조선학회논문집
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• 제31권4호
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• pp.66-72
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• 1994

선박의 조종성능을 정확히 평가하기 위해서 지난 약 10년간 각종모형시험이 수행되었다. 그러나 수학모델에 나타나는 변수들은 너무 다양하고, 복잡한 특성을 나타내기 때문에 아직까지 설계분야에 직접 사용할 수 있는 유용한 형태가 구축되지 않았다. 본 연구에서는, 이 수학모델에서 가장 중요한 변수인 프로펠러에서의 유효반류계수($1-{\omega}_P$)와, 유효타각 $\delta_R(\beta_R)$)을 회류수조에서 조사하였다. 모델은 설계속도와 저속에서 각각 실험이 이루어졌고, 흘수 또한 만재상태와 밸러스트상태에서 실시되었다. 프로펠러 추력과 타직압력은 주어진 사항각과 프로펠러 회전수에서 측정되었다. 이 추력은 유효유입속도나 유입방향의 해석에 사용된다.

• 한국환경복원기술학회지
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• 제24권2호
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• pp.103-114
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• 2021

The purpose of this study is to provide basic data for habitat restoration by implementing a series of processes of capturing and translocating Kaloula borealis and managing them in artificial breeding facilities. The study site in Samcheon, Jeonju-si, Jeollabuk-do was a waste landfill site in the past, and Kaloula borealis was found during the Samcheon Ecological River Restoration Project around March 2018. To restore the habitat, a plan was established to capture, translocate, artificially breed, and release Kaloula borealis at the site. The capture methods of adult Kaloula borealis were pitfall trap and drift fence, direct capture, and deep barrels. During 2018-2019, 86 adults of Kaloula borealis were captured and translocated to artificial breeding facilities. VIE-tagging was inserted under the skin for monitoring. For artificial breeding, Gryllus bimaculatus with oyster powder and vegetables were regularly supplied to feed Kaloula borealis. At the end of October 2020, 150 young Kaloula borealis raised in artificial breeding facilities were found not entering hibernation, so they were managed in a separate artificial breeding facility. Some young and adult Kaloula borealis currently hibernating will be scheduled to be continuously managed in artificial breeding facilities and released to the restored habitat in the spring of 2021.

• Steel and Composite Structures
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• 제30권4호
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• pp.365-382
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• 2019

In steel frame-tube structures (SFTSs) the application of flexural beam is not suitable for the beam with span-to-depth ratio lower than five because the plastic hinges at beam-ends can not be developed properly. This can lead to lower ductility and energy dissipation capacity of the SFTS. To address this problem, a replaceable shear link, acting as a ductile fuse at the mid length of deep beams, is proposed. SFTS with replaceable shear links (SFTS-RSLs) dissipate seismic energy through shear deformation of the link. In order to evaluate this proposal, buildings were designed to compare the seismic performance of SFTS-RSLs and SFTSs. Several sub-structures were selected from the design buildings and finite element models (FEMs) were established to study their hysteretic behavior. Static pushover and dynamic analyses were undertaken in comparing seismic performance of the FEMs for each building. The results indicated that the SFTS-RSL and SFTS had similar initial lateral stiffness. Compared with SFTS, SFTS-RSL had lower yield strength and maximum strength, but higher ductility and energy dissipation capacity. During earthquakes, SFTS-RSL had lower interstory drift, maximum base shear force and story shear force compared with the SFTS. Placing a shear link at the beam mid-span did not increase shear lag effects for the structure. The SFTS-RSL concentrates plasticity on the shear link. Other structural components remain elastic during seismic loading. It is expected that the SFTS-RSL will be a reliable dual resistant system. It offers the benefit of being able to repair the structure by replacing damaged shear links after earthquakes.