텐돈의 긴장력 손실에 따른 프리스트레스 콘크리트 격납건물의 거동해석

진재철,전영선,이홍표 충남대학교 산업기술연구소 2000 산업기술연구논문집 Vol.15 No.1

The prestressing force of tendon can be decreased by creep of concrete, shrinkage of concrete and relaxation of steel. In this paper, we describe some primary causes of time-dependent losses of prestressing tendon force. New stress reduction model is proposed to predicit time-dependent losses of prestressing tendon force in accurate way. It should be noted that the proposed model is based on the data, which are accumulated from the in-service inspection of posttensioned cotainment building system. Using the new stress reduction model, we carry out finite element analysis to investigate how the losses of prestressing force effect to the structural behaviour of containment building. From FE analysis with new stress reduction model, concrete creep appears as the primary factor which can influence the reduction of prestressing tendon force. It also appears that the relaxation of steel as the secondary influencing factor and shrinkage of concrete as the tertiary factor.

A PERFORMANCE ASSESSMENT OF A BASE ISOLATION SYSTEM FOR AN EMERGENCY DIESEL GENERATOR IN A NUCLEAR POWER PLANT

Choun, Young-Sun,Kim, Min-Kyu Korean Nuclear Society 2008 Nuclear Engineering and Technology Vol.40 No.4

This study evaluates the performance of a coil spring-viscous damper system for the vibration and seismic isolation of an Emergency Diesel Generator (EDG) by measuring its operational vibration and seismic responses. The vibration performance of a coil spring-viscous damper system was evaluated by the vibration measurements for an identical EDG set with different base systems - one with an anchor bolt system and the other with a coil spring-viscous damper system. The seismic performance of the coil spring-viscous damper system was evaluated by seismic tests with a scaled model of a base-isolated EDG on a shaking table. The effects of EDG base isolation on the fragility curve and core damage frequency in a nuclear power plant were also investigated through a case study.

A Performance Assessment of a Base Isolation System for an Emergency Diesel Generator in a Nuclear Power Plan

Young-Sun Choun,Min-Kyu Kim 한국원자력학회 2008 Nuclear Engineering and Technology Vol.40 No.4

This study evaluates the performance of a coil spring-viscous damper system for the vibration and seismic isolation of an Emergency Diesel Generator (EDG) by measuring its operational vibration and seismic responses. The vibration performance of a coil spring-viscous damper system was evaluated by the vibration measurements for an identical EDG set with different base systems - one with an anchor bolt system and the other with a coil spring-viscous damper system. The seismic performance of the coil spring-viscous damper system was evaluated by seismic tests with a scaled model of a baseisolated EDG on a shaking table. The effects of EDG base isolation on the fragility curve and core damage frequency in a nuclear power plant were also investigated through a case study.

EFFECTS OF MECHANICAL PROPERTY VARIABILITY IN LEAD RUBBER BEARINGS ON THE RESPONSE OF SEISMIC ISOLATION SYSTEM FOR DIFFERENT GROUND MOTIONS

Choun, Young-sun,Park, Junhee,Choi, In-Kil Korean Nuclear Society 2014 Nuclear Engineering and Technology Vol.46 No.5

The effects of variability of the mechanical properties of lead rubber bearings on the response of a seismic isolation system are investigated. Material variability in manufacturing, aging, and operation temperature is assumed, and two variation models of an isolation system are considered. To evaluate the effect of ground motion characteristics on the response, 27 earthquake record sets with different peak A/V ratios were selected, and three components of ground motions were used for a seismic response analysis. The response in an isolation system and a superstructure increases significantly for ground motions with low A/V ratios. The variation in the mechanical properties of isolators results in a significant influence on the shear strains of the isolators and the acceleration response of the superstructure. The variation provisions in the ASCE-4 are reasonable, but more strict variation limits should be given to isolation systems subjected to ground motions having low A/V ratios. For application of seismic isolation systems to safety-related nuclear structures, the variation in the material and mechanical properties of the isolation system should be properly controlled during the manufacturing and aging processes. In addition, special consideration should be given to minimize the accidental torsion caused by the dissimilarity in the stiffness variations of the isolators.

소형기기의 면진효과 분석을 위한 진동대 실험

전영선(Choun Young Sun),김민규(Kim Min Kyu),최인길(Choi In Kil) 대한토목학회 2003 대한토목학회 학술대회 Vol.2003 No.10

Original Articles : Factors Influencing Corneal Flap Thickness in Laser In Situ Keratomileusis with a Femtosecond Laser

( Chan Young Kim ),( Ji Hye Song ),( Kyoung Sun Na ),( So Hyang Chung ),( Choun Ki Joo ) 대한안과학회 2011 Korean Journal of Ophthalmology Vol.25 No.1

Purpose: To evaluate factors responsible for the variability between intended and achieved corneal-flap thickness during femtosecond laser-assisted laser in situ keratomileusis (LASIK). Methods: A prospective, nonrandomized, case study was performed on 35 eyes of 18 consecutive patients who underwent LASIK surgery using the 60 kHz femtosecond laser microkeratome. Eyes were assigned to three different thickness groups, with 110-, 120-, or 130-μm cut depths. Anterior segment optical coherence tomography was used to assess the morphology of 35 LASIK flaps at postoperative one week postoperatively. The flap thickness was assessed at seven measuring points across each flap. Patient age, preoperative spherical equivalent, manual keratometry, preoperative central pachymetry, and regional variability of the cornea were evaluated to determine where they influenced the achieved corneal flap thickness. Results: Cuttings of all flaps were easily performed without any intraoperative complications. Flap-thickness measurements had a mean of 115.21 ± 4.98 μm (intended thickness, 110 μm), 121.90 ± 5.79 μm (intended, 120 μm), and 134.38 ± 5.04 μm (intended, 130 μm), respectively. There was no significant difference between the 110-μm and 120-μm groups when compared with the 130-μm group (one-way analysis of variance test, p>0.05). Patients` age, preoperative spherical equivalent, manual keratometry, and preoperative central pachymetry did not affect the achieved flap thickness (Pearson correlations test, p>0.05). The reproducibility of flap thickness in the central 1.5-mm radius area was more accurate than that in the peripheral 3.0 to 4.0-mm radius area (paired samples t-test, p<0.05). Conclusions: Femtosecond laser-assisted LASIK is likely to reproduce a reliable thickness of the corneal flap, which is independent of corneal shape factors or refractive status. Future studies should focus on variations in corneal biomechanical factors, which may also play an important role in determining flap thickness.

LASEK, LASIK 후 눈물막의 변화

박영규 ( Young Kyu Park. ),최남영 ( Nam Young Choi ),배선량 ( Sun Ryang Bae ),주천기 ( Choun Ki Joo ) 대한안과학회 2002 대한안과학회지 Vol.43 No.7

유체요소를 이용한 직사각형 유체 저장구조물의 지진해석

金永晳(Young-Surck Kim),金裁民(Jae-Min Kim),田英善(Young-Sun Choun),尹楨邦(Chung-Bang Yun) 한국해양공학회 1992 韓國海洋工學會誌 Vol.6 No.2

In this paper, behavior of rectangular storage structures under earthquake loadings are investigated. Linear sloshing is assumed in this study. The effect of the wall flexibility is considered. Eulerian and Lagrangian approaches are presented. The Eulerian approach is carried out by solving the boundary value problem for the fluid motion. In the Lagrangian approach, the fluid as well as the storage structure is modelled by the finite element method. The fluid region is discretized by using fluid elements. The (1×1)-reduced integration is carried out for constructing the stiffness matrices of the fluid elements. Seismic analysis of the coupled system is carried out by the response spectra method. The numerical results show that the fluid forces on the wall obtained by two approaches are in good agreements. By including the effect of the wall flexibility, the forces due to fluid motion can be increased very significantly.

철근콘크리트 격납건물의 비선형 해석을 위한 쉘 유한요소

전영선,이홍표,Choun Young-Sun,Lee Hong-Pyo 한국전산구조공학회 2006 한국전산구조공학회논문집 Vol.19 No.1

격납건물은 원자로 사고발생시 방사능물질의 외부 유출을 막는 최후의 방벽이므로 가동 중 원전의 격납건물에 대한 안전성평가는 반드시 수행되어야 된다. 이러한 맥락에서 이 논문은 원전 격납건물의 비선형해석을 위해 탄소성 모델을 바탕으로 개발된 8절점 가변형도 쉘 요소와 이를 이용한 구조물의 비선형해석에 대하여 기술하였다. 비선형해석을 위해 콘크리트의 압축거동에 Drucker-Prager 파괴기준을 적용하였고 파괴포락선의 형상을 결정짓는 재료매개변수는 이축응력 실험으로부터 도출하였다. 개발된 쉘 유한요소는 퇴화 고체기법과 횡 전단변형도를 고려하기 위하여 Reissner-Mindlin(RM)가정을 도입하였고 쉘의 두께가 얇거나, 즉 종횡비가 작거나, 균일하지 않은 유한요소망을 사용할 경우 구조물의 강성이 과대하게 평가되는 묶임현상(locking phenomenon)을 제거하기 위해 본 논문에서는 가변형도법을 도입하였다. 개발된 철근콘크리트 쉘 요소의 성능검증을 위해서 벤치마크 테스트를 수행하였고 그 결과 이 논문에서 도출한 유한요소해석 결과는 실험결과와 잘 일치 하였다 It is absolutely essential that safety assessment of the containment buildings during service life because containment buildings are last barrier to protect radioactive substance due to the accidents. Therefore, this study describes an enhanced degenerated shell finite element(FE) which has been developed for nonlinear FE analysis of reinforced concrete(RC) containment buildings with elasto-plastic material model. For the purpose of the material nonlinear analysis, Drucker-Prager failure criteria is adapted in compression region and material parameters which determine the shape of the failure envelop are derived from biaxial stress tests. Reissner-Mindlin(RM) assumptions are adopted to develop the degenerated shell FE so that transverse shear deformation effects is considered. However, it is found that there are serious defects such as locking phenomena in RM degenerated shell FE since the stiffness matrix has been overestimated in some situations. Therefore, shell formulation is provided in this paper with emphasis on the terms related to the stiffness matrix based on assumed strain method. Finally, the performance of the present shell element to analysis RC containment buildings is tested and demonstrated with several numerical examples. From the numerical tests, the present results show a good agreement with experimental data or other numerical results.

Reevaluation of Seismic Fragility Parameters of Nuclear Power Plant Components Considering Uniform Hazard Spectrum

Park, In-Kil,Choun, Young-Sun,Seo, Jeong-Moon,Yun, Kwan-Hee Korean Nuclear Society 2002 Nuclear Engineering and Technology Vol.34 No.6

The Seismic probabilistic risk assessment (SPRA) or seismic margin assessment (SMA) have been used for the seismic safety evaluation of nuclear power plant structures and equipments. For the SPRA or SMA, the reference response spectrum should be defined. The site-specific median spectrum has been generally used for the seismic fragility analysis of structures and equipments in a Korean nuclear power plant Since the site-specific spectrum has been developed based on the peak ground motion parameter, the site-specific response spectrum does not represent the same probability of exceedance over the entire frequency range of interest. The uniform hazard spectrum is more appropriate to be used in seismic probabilistic risk assessment than the site- specific spectrum. A method for modifying the seismic fragility parameters that are calculated based on the site-specific median spectrum is described. This simple method was developed to incorporate the effects of the uniform hazard spectrum. The seismic fragility parameters of typical NPP components are modified using the uniform hazard spectrum. The modification factor is used to modify the original fragility parameters. An example uniform hazard spectrum is developed using the available seismic hazard data for the Korean nuclear power plant (NPP) site. This uniform hazard spectrum is used for the modification of fragility parameters.