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경량골재 콘크리트 기둥의 곡률 및 변위 연성비 평가 Evaluation of Curvature and Displacement Ductility Ratios of Lightweight Aggregate Concrete Columns

https://doi.org/10.4334/JKCI.2022.34.3.235

양근혁(Keun-Hyeok Yang)

The objective of this study is to formulate design models for the curvature and displacement ductility ratios of lightweight aggregate concrete (LWAC) columns. In the nonlinear analysis of the moment-curvature relationship and the lateral load-displacement relationship of the columns, the increase in concrete brittleness due to the decrease in unit weight () of concrete was considered. The curvature ductility ratio of normal-weight concrete (NWC) columns was formulated from a regression analysis using analytical data compiled from the extensive parametric study by the nonlinear analysis procedure. A correction factor was then introduced for the curvature ductility ratio of LWAC to consider the common tendency that the ductility of columns decreases with the decrease in . The curvature ductility ratio model was converted into a displacement ductility ratio from the idealized distribution of curvature along the column length and the equivalent plastic hinge length. The mean and standard deviation of the ratios between predictions and experiments for the displacement ductility ratio are 0.96 and 0.17, respectively, for NWC columns, and 1.08 and 0.16, respectively, for LWAC columns.

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SD600 철근 및 직사각형 나선후프를 사용한 외부접합부의 내진실험 Cyclic Tests of Exterior Joints with SD600 Steel Bars and Rectangular Spiral Hoops

https://doi.org/10.4334/JKCI.2022.34.3.243

엄태성(Tae-Sung Eom) ; 멀무히유발트(Murmu Hiubalt) ; 임종진(Jong-Jin Lim)

In this study, the seismic performance of exterior beam-to-column connections with SD600 beam reinforcements was investigated. Six specimens designed to exhibit beam yield mechanism were tested under cyclic loading. Rectangular spirals were used for shear reinforcement at the beam-column joint where the SD600 beam reinforcements were anchored by 90° standard hooks. Concrete strengths (32.2 and 52.2 MPa), reinforcement yield strengths (442 and 662 MPa), the use of steel fiber concrete were considered as test variables. The tests showed that although the development lengths of SD600 steel bars specified in design codes were not satisfied at the joint with the limited depth, bond slip and anchorage failure did not occur in most specimens. The deformation capacities were larger than 5 % in drift ratio, but in three specimens out of five specimens SD600 steel bars used for beam reinforcements eventually ruptured due to the deficient post-yield hardening behavior. The bond and shear behavior at the joint was improved by the use of higher compressive strength concrete and steel fiber concrete.

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그리드 및 강섬유 보강을 통한 철근콘크리트 벽체의 전자파 차폐 및 충격 성능 향상 Enhancing Electromagnetic Shielding and Impact Resistance of RC Walls through Grid and Steel Fiber Reinforcement

https://doi.org/10.4334/JKCI.2022.34.3.255

이재훈(Jaehoon Lee) ; 윤정우(Jungwoo Youn) ; 최진석(Jin-Seok Choi) ; 윤영수(Youngsoo Yoon)

Electromagnetic interference shielding has received attention for decreasing radiation and electromagnetic waves to protect humans or equipment in design processes. There are several traditional methods to strengthen the shielding performance, such as using conductive paints, conductive fibers, or grids on non-damaged structures. However, few studies have considered the relationship between shielding effectiveness and the damaged area used by hybrid reinforcement methods for improving shielding effectiveness and structural performance. To evaluate the relationship between shielding effectiveness and damaged area, we designed reinforced concrete (RC) walls strengthened by steel fiber, metallic grid/mesh reinforcement, and hybrid reinforcement and created damage area through impact load. The hybrid reinforced specimens had approximately 25.9 times and 2.4 times higher shielding effectiveness than 300 mm thick RC and single-type reinforced specimens. In the relationship between the shielding effectiveness and damaged area, specimens reinforced by metallic mesh exhibited more than 30 dB shielding effectiveness and 150 % free area ratio. Meanwhile, specimens reinforced by metallic mesh and grid exceeded 40 dB shielding effectiveness.

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강섬유 혼입률 및 압축강도 변수를 고려한 이방향 RC슬래브의 충격저항성능 Impact Resistance of Two-Way RC Slabs considering Steel Fiber Volume Fraction and Compressive Strength

https://doi.org/10.4334/JKCI.2022.34.3.265

손진수(Jin-Su Son) ; 이진영(Jin-Young Lee)

To investigate impact resistance of two way RC slabs, slabs (1,600 mm×1,600 mm×105 mm) were fabricated and tested using drop-weight impact testing machine. Two volume fractions (0, 2 vol%) and concrete compressive strengths (25, 45, 60, 100, 140, 180 MPa) were considered as the variables. To evaluate the impact resistance of the slabs, failure modes, impact and reaction force, and deflection were measured and the energy dissipating capacity was derived from the force-deflection relationships. As a result, it was found that addition of steel fibers enhanced impact resistance of two way RC slabs in load carrying capacity, energy dissipating capacity, and displacement. Furthermore, steel fiber reinforced concrete specimens of 140, and 180 MPa showed significantly larger energy dissipating capacity in comparison with the others.

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비상관 지반운동이 작용하는 원자력 시설의 불규칙진동이론을 이용한 추계학적 지진응답 해석 Earthquake Response Analysis of a Nuclear Facility Subjected to Incoherent Seismic Waves Using the Random Vibration Theory

https://doi.org/10.4334/JKCI.2022.34.3.275

이진호(Jin Ho Lee)

In this study, an earthquake response analysis for a nuclear facility with a rigid foundation is proposed based on the random-vibration-theory (RVT) methodology when the system is subjected to incoherent seismic waves. Using a coherency function of the seismic waves, the power spectral density (PSD) matrix for 6 degrees-of-freedom motions of the rigid foundation is calculated. The PSD function for pseudo-acceleration of an equipment, which is installed on one floor of the structure, is derived. The spectral acceleration or in-structure response spectrum (ISRS) of the equipment is estimated using a peak factor for a random motion. The proposed RVT methodology is applied to nuclear power plant structures to calculate ISRS when coherent seismic waves are applied to the system. The accuracy of the proposed approach is verified by comparing its results with those from the response-history methodology. It is demonstrated that incoherent seismic waves can reduce ISRS of structures at high frequencies.

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다층 쉘요소와 보-트러스 모델을 이용한 원자력발전소 격납건물의 비선형 동적해석 Nonlinear Dynamic Analyses of Reactor Containment Building Using Multi-Layer Shell Model and Beam-Truss Model

https://doi.org/10.4334/JKCI.2022.34.3.283

비덱 투사(Bidhek Thusa) ; 삼다니 아자드(Md Samdani Azad) ; 두이두안 응웬(Duy-Duan Nguyen) ; 이태형(Tae-Hyung Lee)

The objective of this study is to investigate linear and nonlinear analysis schemes for evaluating seismic performance of a reactor containment building (RCB) in the advanced power reactor 1400 nuclear power plant (NPP). Two structural modeling schemes, the multi-layer shell model (MLSM) and beam-truss model (BTM), are developed to simulate the seismic behaviors of RCB. A full three-dimensional finite element model is additionally constructed to verify the numerical modeling schemes used. A set of input ground motions with response spectra compatible with US NRC 1.60 design spectrum is generated to perform linear and nonlinear time-history analyses. The floor response spectra and floor displacements are obtained at different elevations of the structure since those are critical outputs for evaluating seismic behaviors of RCB and secondary components. The results show that the difference in seismic responses between linear and nonlinear analyses becomes larger as earthquake intensity increases. The linear analysis underestimates floor displacement while it overestimates floor acceleration. BTM and MLSM are good options for seismic performance evaluation of NPP structures by nonlinear time-history analyses.

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알칼리-실리카 반응에 의한 콘크리트 손상을 고려한 원전 격납구조물의 지진취약도 평가 Seismic Fragility Analysis on Nuclear Containment Structure considering the Material Degradation

https://doi.org/10.4334/JKCI.2022.34.3.291

김찬영(Chan-Young Kim) ; 신명수(Myoung-Su Shin)

This study focuses on conducting fragility analysis and estimating the change in fragility curve and the structural capacity due to the alkali-silica reaction (ASR) by using nonlinear seismic analysis. The shell element and nonlinear concrete constitutive model of Opensees have been adopted to conduct the nonlinear seismic analysis. As a result, the HCLPF of the containment structure is estimated as 1.407 g, and it is comparatively higher than the value reported by previous researches which use a lumped mass model. In addition, the median capacity of the containment structure is about 2.704 g when it is under the effects of ASR corresponding to the median longitudinal expansion of 0.013 %. Consequently, the median capacity of the containment structure is decreased about 17.5 % with the aforementioned level of alkali-silica reaction.

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지반운동의 파형특성변화 지표에 따른 원전 격납건물의 지진응답 Seismic Response of a NPP Containment Building Analyzed Using Ground Motion Records with Different Indices of Wave Characteristic Changes

https://doi.org/10.4334/JKCI.2022.34.3.299

전성하(Seong-Ha Jeon) ; 신동현(Dong-Hyun Shin) ; 박지훈(Ji-Hun Park)

A procedure to select ground motions with less change in wave form characteristics, which result from spectral matching of recorded accelerograms, is developed for input ground motion sets that match a target response spectrum for probabilistic seismic performance evaluation of nuclear power plant structures. For this purpose, indices that comprehensively evaluate various wave characteristics is proposed. Using the proposed procedure and indices, ground motion sets with different wave characteristic changes are determined. Probabilistic seismic performance evaluation of a nuclear power plant containment building is conducted using those ground motion sets. Influence of change in wave form characteristics by spectral matching is investigated for probabilistic seismic characteristics.

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형상비가 낮은 플랜지형 원전 벽체의 전단강도 평가 모델 Shear Strength Model for Flanged Squat Walls in Nuclear Power Plants

https://doi.org/10.4334/JKCI.2022.34.3.311

김주형(Ju-Hyung Kim) ; 이유상(Yousang Lee) ; 박홍근(Hong-Gun Park)

A numerical shear strength model was proposed for seismic design and performance evaluation of RC walls in nuclear power plants. Given that NPP walls are integrated with cross walls, the proposed model focused on the shear strength contribution of flanges, particularly in squat walls. Based on the experimental studies of flanged walls, web and flanges were replaced by equivalent shear panels and the response of each panel was analyzed using modified compression field theory. Shear stress in the web induces axial tension and compression in the flange walls, which results in different shear strength contributions of the flanges. The shear strength contribution of compression flanges was greater than that of tension flanges due to the axial load effect. The accuracy of the proposed model was verified based on existing test results of squat walls with boundary elements. The model showed uniform accuracy predictions for various design parameters.

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원전 구조물 내 설치된 앵커의 지진취약도 평가 Seismic Fragility Analysis of Anchorage Failure in Nuclear Power Plant Structure

https://doi.org/10.4334/JKCI.2022.34.3.321

이유상(Yousang Lee) ; 김주형(Ju-Hyung Kim) ; 박홍근(Hong-Gun Park)

Floor response spectrum (FRS) is commonly used for the evaluation of equipment installed in nuclear power plant. In conventional practice, FRS representing the entire floor responses are simplified using a lumped-mass stick model (LMSM). However, actual responses at different locations may show significant variation, which may have a substantial influence on the seismic fragility of the equipment. In the present study, FRS at different slab locations were calculated using a 3-D finite element model, and the results were compared. The results showed that significant variance exists even in a floor. Based on the result, seismic fragility analysis of anchorage failure was performed to show variance of High Confidence of Low Probability of Failure (HCLPF), considering the location-dependent variability of FRS.

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