• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 I
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• pp.155-160
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• 2001

Actual engineering structure is frequently very complex, and parts of structure are designed independently by different engineers. Also each structure contains so many degree of freedom. For these reason, methods have been developed which permits the structure to be divided into components or substructures, with analysis being done on a small substructure in order to obtain a full structural system. In such case, because of different mesh size among finite element model (FEM) or different matching points among FEM models and experimentally obtained models, their interfacing points may be non-matching. Solving this non-matching problem is useful to other application such as structural dynamic modification or model updating. In this work, virtual node concept is introduced. Lagrange multipliers are used to enforce the interface compatibility constraint, and interface displacement is approximated by polynomial presentation. The governing equation of whole structure is derived using hybrid variational principle. The eigenvalue of whole structure are calculated using the determinant search method. The number of degree of freedom in the eigenvalue problem can be drastically reduced to just the number of interface degree of freedom. Some numerical simulation is performed to show usefulness of synthesis method.

• Earthquakes and Structures
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• 제11권5호
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• pp.809-822
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• 2016

Reinforced concrete buildings constitute the majority of the building stock of Turkey and much of them, do not comply the earthquake codes. Recently there is a great tendency for strengthening to heal their earthquake performance. The performance evaluations are usually executed by the numerical investigations performed in computer packages. However, the numerical models are often far from representing the real behaviour of the existing buildings. In this condition, experimental modal analysis fills a gap to correct the numerical models to be used in further analysis. On the other hand, there have been a few dynamic tests performed on the existing reinforced concrete buildings. Especially forced vibration survey is not preferred due to the inherent difficulties, high cost and probable risk of damage. This study applies both ambient and forced vibration surveys to investigate the dynamic properties of a six-story residential building in Istanbul. Mode shapes, modal frequencies and damping ration were determined. Later on numerical analysis with finite element method was performed. Based on the first three modes of the building, a model updating strategy was employed. The study enabled to compare the results of ambient and forced vibration surveys and check the accuracy of the numerical models used for the performance evaluation of the reinforced concrete buildings.

• Structural Monitoring and Maintenance
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• 제6권2호
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• pp.85-101
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• 2019

The effects of foundation scour depth and riverbed condition on the natural frequencies of a typical cross-river integral abutment bridge have been studied. The conventional operational modal analysis technique has been employed in order to extract the modal properties of the bridge and the results have been used in the Finite Element (FE) model updating procedure. Two tests have been carried out in two different levels of water and wet condition of the riverbed. In the first test, the riverbed was in dry condition for two subsequent years and the level of water was 10 meter lower than the natural riverbed. In the second test, the river was opened to water flow from the upstream dam and the level of water was 2 meter higher than the natural riverbed. The results of these two tests have also been used in order to find to what extend the presence of water flow in the river and saturation of the surrounding soil affect the bridge natural frequencies. Finally, the updated FE model of the bridge has been applied in a series of parametric analyses incorporating the effect of piles' relative scour depth on the bridge natural frequency of the first four vibration modes.

• Structural Engineering and Mechanics
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• 제81권5호
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• pp.617-631
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• 2022

In this paper the viscoelastic responses of four experimental steel-concrete composite beams subjected to highly variable environmental conditions are investigated by means of a finite element (FE) model. Concrete specimens submitted to stepped stress changes are also evaluated to validate the current formulations. Here, two well-known approaches commonly used to solve the viscoelastic constitutive relationship for concrete are employed. The first approach directly solves the integral-type form of the constitutive equation at the macroscopic level, in which aging is included by updating material properties. The second approach is postulated from a rate-type law based on an age-independent Generalized Kelvin rheological model together with Solidification Theory, using a micromechanical based approach. Thus, conceptually both approaches include concrete hardening in two different manners. The aim of this work is to compare and analyze the numerical prediction in terms of long-term deflections of the studied specimens according to both approaches. To accomplish this goal, the performance of several well-known model codes for concrete creep and shrinkage such as ACI 209, CEB-MC90, CEB-MC99, B3, GL 2000 and FIB-2010 are evaluated by means of statistical bias indicators. It is shown that both approaches with minor differences acceptably match the long-term experimental deflection and are able to capture complex oscillatory responses due to variable temperature and relative humidity. Nevertheless, the use of an age-independent scheme as proposed by Solidification Theory may be computationally more advantageous.

• 대한기계학회논문집A
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• 제35권9호
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• pp.983-989
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• 2011

본 연구에서는 경제요소법을 이용한 프레팅 마멸 예측을 위한 수치적 알고리즘을 개발하였다. 반무한체 해석을 통해 사각조각면위의 균일분포하중과 탄성변형량의 관계로부터 접촉 계면의 응력을 계산하였고 Archard wear 모델을 이용해 각 격자의 마멸 깊이를 계산하여 접촉면의 형상을 예측할 수 있는 알고리즘을 제시하였다. 본 연구의 정확성을 검증하기 위해 McColl 등의 연구와 비교하였고 개발된 알고리즘을 구접촉 모델에 확장하여 그 유용성을 확인하였다. 아울러 프레팅 해석의 효율적인 계산을 위해 한 step당 사이클 증가량인 step cycle이 해의 정확성에 미치는 영향을 검토하여 step cycle 설정의 중요성을 제시하였다.

• 국제초고층학회논문집
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• 제4권1호
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• pp.39-44
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• 2015

This paper presents the structural health monitoring (SHM) of Shanghai Tower. In order to provide useful information for safety evaluation and regular maintenance under construction and in-service condition, a comprehensive structural health monitoring (SHM) system is installed in Shanghai Tower, which is composed of a main monitoring station and eleven substations. Structural responses at different construction stages are measured using this SHM system and presented in this study. Meanwhile, a detailed finite element model (FEM) is created and comparison of results between SHM and FEM is carried out. Results indicate that the time-dependent property of concrete creep is of great importance to structural response and the measured data can be used in FEM updating to obtain more accurate FEM models at different construction stages. Therefore, installation of structural health monitoring system in super-tall buildings could be considered as an effective way to assure structural safety during the construction process.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2011년도 정기 학술대회
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• pp.27-31
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• 2011

차량의 대형화 및 고속화, 그리고 기존 교량의 노후화를 고려하였을 때, 교량의 건전성 평가는 매우 중요해지고 있다. 거동을 예측하는데 사용되는 유한요소 모델의 신뢰도는 이상적인 가정과 모델링 오차, 교량의 노후화 등에 의해 실제 거동을 반영하지 못하는 경우가 많다. 유한요소 모델의 신뢰도를 높이기 위해, 실제 교량의 거동을 계측하여, 이를 기반으로 물리적 의미를 가지는 변수들과 지점의 조건을 수정하는 모델의 개선이 주로 행해진다. 이러한 모델 개선은 최적화 기법을 통해 수행된다. 본 연구에서는 목적함수간 가중치에 의한 모델 개선 결과의 영향과 다중 목적 함수 최적화 기법을 통해, 가중치의 영향을 줄이고, 다양한 개선 모델들을 구하는데 적용하였다. 팔곡 3교의 실제 계측 데이터를 이용하여 단일 다중 목적 함수 기반의 모델 개선을 수행하였다. 단일 목적 함수의 경우, 정의되는 목적함수는 주로 고유진동수와 모드 형상에 관한 차이의 가중치 합으로 표현되어 지며, 이러한 가중치에 따라, 모델 개선의 결과에 영향을 가함을 확인하였다. 다중 목적 함수 기반의 모델 개선을 통해, 구해진 모델 개선 결과를 단일 목적 함수 기반 모델 개선의 결과들과 비교하였으며, 모델 개선에 대한 다중 목적 함수 최적화 적용을 분석하였다.

• 대한기계학회논문집A
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• 제34권8호
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• pp.1105-1111
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• 2010

한국원자력연구원은 전력생산과 해수담수화를 동시에 수행하고 친환경적인 SMART 원자로를 개발하였다. SMART 원자로의 여러 구조물 중에 제어봉 구동 장치(CRDM)는 제어봉의 삽입 량을 조절하여 원자로의 출력을 조정하고 비상시 제어봉을 긴급 삽입하여 원자로를 정지시키기 위한 기기이다. 본 연구의 목적은 제어봉 구동 장치의 구조적 건전성을 확보하기 위해서 동특성해석을 수행하는 것이다. 또한 향후 내진해석에 활용될 단순모델의 활용을 위해 상세모델과의 비교, 검증을 수행하였다. 해석은 유한요소 해석기법을 활용하였고 상용해석 프로그램인 ABAQUS 와 ANSYS V12 를 사용하였다. 유한요소 해석모델은 상세모델인 3-D Solid 모델과 단순모델인 Beam 모델을 작성하여 비교하였고 추가로 단순모델을 오일러 보인 Beam4 요소와 티모센코 보인 Beam188 요소로 작성하여 비교 검토하였다. 향후 SMART 원자로집합체의 단순모델을 작성하여 내진해석 등 다양한 해석에 활용될 계획이므로 단순모델은 상세모델과의 오차를 줄이기 위해서 모델 보정(model updating)이 수행되었다.

• Smart Structures and Systems
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• 제15권3호
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• pp.665-682
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• 2015

Structural identification or St-Id is 'the parametric correlation of structural response characteristics predicted by a mathematical model with analogous characteristics derived from experimental measurements'. This paper describes a St-Id exercise on Humber Bridge that adopted a novel two-stage approach to first calibrate and then validate a mathematical model. This model was then used to predict effects of wind and temperature loads on global static deformation that would be practically impossible to observe. The first stage of the process was an ambient vibration survey in 2008 that used operational modal analysis to estimate a set of modes classified as vertical, torsional or lateral. In the more recent second stage a finite element model (FEM) was developed with an appropriate level of refinement to provide a corresponding set of modal properties. A series of manual adjustments to modal parameters such as cable tension and bearing stiffness resulted in a FEM that produced excellent correspondence for vertical and torsional modes, along with correspondence for the lower frequency lateral modes. In the third stage traffic, wind and temperature data along with deformation measurements from a sparse structural health monitoring system installed in 2011 were compared with equivalent predictions from the partially validated FEM. The match of static response between FEM and SHM data proved good enough for the FEM to be used to predict the un-measurable global deformed shape of the bridge due to vehicle and temperature effects but the FEM had limited capability to reproduce static effects of wind. In addition the FEM was used to show internal forces due to a heavy vehicle to to estimate the worst-case bearing movements under extreme combinations of wind, traffic and temperature loads. The paper shows that in this case, but with limitations, such a two-stage FEM calibration/validation process can be an effective tool for performance prognosis.

• 한국지진공학회논문집
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• 제12권5호
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• pp.57-63
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• 2008

본 연구는 원자력발전소에 설치되는 캐비닛형 전기기기의 동적 진동시험 자료를 이용하여 캐비닛의 지진응답을 예측할 수 있는 기법을 제안하였다. 제안된 기법은 1) 절점질량 이상화 모델에 기반한 등가 지진하중 산정, 2) 진동시험자료에 기반한 캐비닛 구조의 입출력 상태방정식 규명, 3) 산정된 등가지진하중과 규명된 입출력 상태방정식을 사용한 지진응답산정의 과정으로 구성된다. 제안된 기법은 유한요소기법(FEM) 모델 개선(Model Updating)에 기반한 지진응답예측기법에 비하여 모델링 오차가 개입 되지 않는 장점을 가진다. 캐비넷 구조를 이상화한 2차원 프레임 모델과 3차원 상세 모델에 대한 수치검증을 통하여 제안된 기법이 지진응답을 매우 정확하게 예측을 함을 관찰하였고, 측정 노이즈에 대해서도 강인함을 관찰하였다. 추후연구로 실험검증이 요구된다.