• Earthquakes and Structures
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• 제9권3호
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• pp.657-671
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• 2015

The level of ductility is determined by depending on the intended use of the building, the region's seismic characteristics and the type of structural system when buildings are planned by engineers. Major portion of seismic energy is intended to be consumed in the plastic zone in structural systems of high ductility, so the occurrence of damages in load bearing and non-load bearing structural elements is accepted in planning stage under severe earthquakes. However, these damages must be limited among specific values in order not to endanger buildings in terms of the bearing capacity. Isolators placed between the basement and upper structure make buildings behave elastically by reducing the effects of seismic loads and improving seismic performance of building significantly. Thus, damages can be limited among desired values. In this study, the effectiveness of seismic isolation is investigated on both fixed based and seismic isolated models of a hospital building with high ductility level with regard to lateral displacements, internal forces, structural periods and cost of the building. Layered rubber bearings are interposed between the base of the structure and foundation. Earthquake analysis of the building are performed using earthquake records in time domain (Kocaeli, Loma Prieta and Landers). Results obtained from three-dimensional finite element models are presented by graphs and tables in detail. That seismic isolation reduces significantly the destructive effects of earthquakes on structures is seen from the results obtained by seismic analysis.

• Structural Engineering and Mechanics
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• 제66권3호
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• pp.411-421
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• 2018

Although a rubber isolation cushion can reduce the dynamic response of a structure itself, it has little influence on the height of a sloshing wave and even may induce magnification action. Vertical baffles are set into a base-isolated Concrete Rectangular Liquid Storage Structure (CRLSS), and baffles are opened as holes to increase the energy dissipation of the damping. Problems of liquid nonlinear motion caused by baffles are described using the Navier-Stokes equation, and the space model of CRLSS is established considering the Fluid-Solid Interaction (FSI) based on the Finite Element Method (FEM). The dynamic response of an isolated CRLSS with various baffles under an earthquake is analyzed, and the results are compared. The results show that when the baffle number is certain, the greater the number of holes in baffles, the worse the damping effects; when a single baffle with holes is set in juxtaposition and double baffles with holes are formed, although some of the dynamic response will slightly increase, the wallboard strain and the height of the sloshing wave evidently decrease. A configuration with fewer holes in the baffles and a greater number of baffles is more helpful to prevent the occurrence of two failure modes: wallboard leakage and excessive sloshing height.

• Steel and Composite Structures
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• 제34권1호
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• pp.123-139
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• 2020

The tube outward local buckling of Concrete-Filled Steel Tube (CFST) beam under high compression stress is still considered a critical problem, especially for steel tubes with a slender section compared to semi-compact and compact sections. In this study, the flexural performance of stiffened slender cold-formed square tube beams filled with normal concrete was investigated. Fourteen (14) simply supported CFST specimens were tested under static bending loads, stiffened with different shapes and numbers of steel stiffeners that were provided at the inner sides of the tubes. Additional finite element (FE) CFST models were developed to further investigate the influence of using internal stiffeners with varied thickness. The results of tests and FE analyses indicated that the onset of local buckling, that occurs at the top half of the stiffened CFST beam's cross-section at mid-span was substantially restricted to a smaller region. Generally, it was also observed that, due to increased steel area provided by the stiffeners, the bending capacity, flexural stiffness and energy absorption index of the stiffened beams were significantly improved. The average bending capacity and the initial flexural stiffness of the stiffened specimens for the various shapes, single stiffener situations have increased of about 25% and 39%, respectively. These improvements went up to 45% and 60%, for the double stiffeners situations. Moreover, the bending capacity and the flexural stiffness values obtained from the experimental tests and FE analyses validated well with the values computed from equations of the existing standards.

• 대한기계학회논문집A
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• 제36권1호
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• pp.17-28
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• 2012

본 연구에서는 역해석 방법을 통해, 중심각이 서로 다른 두 삼각뿔 압입자를 이용하는 재료물성 평가법을 제안한다. 자기유사성을 갖는 첨단형 압입자를 사용한 압입시험 전산모사시, 동일 압입깊이에 대해 원뿔형 및 삼각뿔 압입자가 주는 하중-변위 곡선들이 다름을 확인했다. 따라서 삼각뿔형 압입자를 이용한 물성평가는 원뿔형 압입자와 별도로 독립적인 연구가 필수적이다. 먼저 다양한 재료들에 대한 삼각뿔 압입 유한요소해석들로 얻은 하중-변위 곡선들의 특징을 살폈다. 이를 토대로 압입자 반각이 다른 두 삼각뿔 압입자를 이용해 유한요소해석으로 얻은 하중-변위곡선들의 회귀분석으로 재료물성치를 얻는 이중 삼각뿔 압입물성평가 알고리듬을 제시했다. 제안된 물성평가법을 이용하면 다양한 재료에 대해 평균오차 3% 이내로 영률 및 항복강도, 변형경화지수의 예측이 가능하다.

• 대한기계학회논문집A
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• 제35권9호
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• pp.1021-1026
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• 2011

경량화와 강도 관점에서 구조부재에 대한 충돌 문제들은 방위산업, 고속운송수단을 포함한 다양한 분야에서 매우 중요시 되고 있다. 본 연구에서는 수치해석적 기법을 도입하여 알루미늄합금 판재에 대해 충격자의 충돌 조건에 따라 고속충격 환경에서의 파괴거동을 분석하였다. 충격자의 충돌조건은 형상, 속도, 각도의 3 가지 조건을 설정하였으며, 반복적 계산 소요를 줄이기 위하여 실험계획법의 한 종류인 라틴방격법을 도입하였다. 조건 변화에 따른 유한요소해석 결과를 통하여 충격흡수에너지량과 소성변형량을 계산하였으며, 이를 바탕으로 분산분석법을 수행하였고 따라서 각 인자 대한 영향도 평가를 수행할 수 있었다. 결과를 통해 충격흡수에너지 관점에서 충돌속도가 가장 큰 영향을 나타내었으며, 소성변형량 관점에서는 충돌각도가 가장 큰 영향인자로 평가되었다.

• 한국지진공학회논문집
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• 제19권1호
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• pp.29-36
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• 2015

Base isolation is considered as a seismic protective system in the design of next generation Nuclear Power Plants (NPPs). If seismic isolation devices are installed in nuclear power plants then the safety under a seismic load of the power plant may be improved. However, with respect to some equipment, seismic risk may increase because displacement may become greater than before the installation of a seismic isolation device. Therefore, it is estimated to be necessary to select equipment in which the seismic risk increases due to an increase in the displacement by the installation of a seismic isolation device, and to perform research on the seismic performance of each piece of equipment. In this study, modified NRC-BNL benchmark models were used for seismic analysis. The numerical models include representations of isolation devices. In order to validate the numerical piping system model and to define the failure mode, a quasi-static loading test was conducted on the piping components before the analysis procedures. The fragility analysis was performed by using the results of the inelastic seismic response analysis. Inelastic seismic response analysis was carried out by using the shell finite element model of a piping system considering internal pressure. The implicit method was used for the direct integration time history analysis. In addition, the collapse load point was used for the failure mode for the fragility analysis.

• Bulletin of the Korean Chemical Society
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• 제33권6호
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• pp.1839-1844
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• 2012

We have investigated binding between wild-type and mutant Heat Shock Factor (HSF) DNA binding domains (DBDs) with 17-bp HSE containing a central 5'-NGAAN-3' element by equilibrium analytical ultracentrifugation using multi-wavelength technique. Our results indicate that R102 plays critical role in HSE recognition and the interactions are characterized by substantial negative changes of enthalpy (${\Delta}H^0_{\theta}=-9.90{\pm}1.13kcal\;mol^{-1}$) and entropy (${\Delta}S^0_{\theta}=-12.46{\pm}3.77cal\;mol^{-1}K^{-1}$) with free energy change, ${\Delta}G^0_{\theta}$ of $-6.15{\pm}0.03kcal\;mol^{-1}$. N105 plays minor role in the HSE interactions with ${\Delta}H^0_{\theta}$ of $-2.54{\pm}1.65kcal\;mol^{-1}$, ${\Delta}S^0_{\theta}$ of $19.28{\pm}5.50cal\;mol^{-1}K^{-1}$ and ${\Delta}G^0_{\theta}$ of $-8.35{\pm}0.05kcal\;mol^{-1}$, which are similar to those observed for wild-type DBD:HSE interactions (${\Delta}H^0_{\theta}=-3.31{\pm}1.86kcal\;mol^{-1}$, ${\Delta}S^0_{\theta}=17.38{\pm}6.20cal\;mol^{-1}K^{-1}$ and ${\Delta}G^0_{\theta}=-8.55{\pm}0.06kcal\;mol^{-1}$) indicating higher entropy contribution for both wild-type and N105A DBD bindings to the HSE.

• 한국전산구조공학회논문집
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• 제25권4호
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• pp.293-300
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• 2012

본 논문에서는 직교이방성 적층평판에서의 균열생성 및 전파로 이루어진 층간분리해석을 다룬다. 기존의 p-유한요소가 가지고 있는 요소의 강건성을 균열진전해석에 적용하여, 균열진전시 모델링을 재구성하지 않고, 균열 선단부에 해당되는 꼭지점 모드의 위치만을 이동하도록 하여, 요소망을 단순화시켰다. 이와 같은 층간분리해석에 대해서 이 논문에서의 주요 목적은 다음 두 가지이다. 첫째, 적층복합 재료의 층간분리해석 시, 일반적인 유한요소 모델과 비교하여 매우 간단한 요소망을 가지는 모델을 제안하는 것이다. 모델의 타당성을 평가하기 위해 적층 복합재료로 구성된 이중 외팔보 해석을 통하여, 기존 참고문헌 값과의 비교를 수행하였다. 둘째, 제안된 모델을 내부균열을 갖는 적층평판의 층간분리해석에 적용하여 여러 가지 거동 양상에 대한 평가이다. 이와 같은 목적을 수행하기 위하여 로바토 형상함수를 이용한 완전층별요소가 고려되었으며, 선형탄성파괴역학에 기초한 3차원 가상균열닫힘법을 이용하여 에너지 방출률을 산정하였다.

• Corrosion Science and Technology
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• 제3권5호
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• pp.216-221
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• 2004

The operating experience showed that the fatigue is one of the major piping failure mechanisms in nuclear power plants (NPPs). The pressure and/or temperature loading transients, the vibration, and the mechanical cyclic loading during the plant operation may induce the fatigue failure in the nuclear piping. Recently, many fatigue piping failure occurred at the socket weld area have been widely reported. Many failure cases showed that the gap requirement between the pipe and fitting in the socket weld was not satisfied though the ASME Code Sec. III requires 1/16 inch gap in the socket weld. The ASME Code OM also limits the vibration level of the piping system, but some failure cases showed the limitation was not satisfied during the plant operation. In this paper, the fatigue behavior of the socket weld in the nuclear piping was estimated by using the three dimensional finite element method. The results are as follows. (1) The socket weld is susceptible to the vibration if the vibration levels exceed the requirement in the ASME Code OM. (2) The effect of the pressure or temperature transient load on the socket weld in NPPs is not significant because of the very low frequency of the transient during the plant lifetime operation. (3) 'No gap' is very risky to the socket weld integrity for the specific systems having the vibration condition to exceed the requirement in the ASME OM Code and/or the transient loading condition. (4) The reduction of the weld leg size from $1.09*t_1$ to $0.75*t_1$ can affect severely on the socket weld integrity.

• 대한화학회지
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• 제28권5호
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• pp.293-301
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• 1984

단일 희석법을 이용한 X-선형광분광법으로 주석, 슬랙중 $Ta_2O_5$와 $Nb_2O_5$, $ZrO_2$등을 정량분석하였다. 이 방법은 표준 검정 곡선을 직선으로 되게끔 수학적으로 보정하는 것이다. 시료의 조성과 비슷한 한개의 합성표준시료와 분석시료를 무수물의 $Li_2B_4O_7$으로 묽혀서 각각 시료가 1%, 2%, 3%되게 한다. 묽힌 시료들을 $1150^{\circ}C$에서 30분간 용융하여 유리화된 구슬을 만든 다음, 곱게 갈아서, 다시 유압기로 압축하여 분석시편을 만든다. 이 시편을 사용하여 X-선 세기를 측정하고, 원소의 특성 X-선 세기에 관한 J. Scherman의 식으로부터 유도한 식에 대입하여 분석 결과를 계산했다. 이들 분석결과들을 표준검정곡선법으로 얻은 기준값과 잘 일치하며, 결과에 대한 재현성도 좋음을 보여 주었다.