• Earthquakes and Structures
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• 제23권1호
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• pp.87-100
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• 2022

Limiting the displacement of seismic isolators causes a pounding phenomenon under severe earthquakes. Therefore, the ASCE 7-16 has provided minimum criteria for the design of the isolated building. In this research the seismic response of isolated buildings by Triple Friction Pendulum Isolator (TFPI) under the impact, expected, and unexpected mass eccentricity was evaluated. Also, the effect of different design parameters on the seismic behavior of structural and nonstructural elements was found. For this, a special steel moment frame structure with a surrounding moat wall was designed according to the criteria, by considering different response modification coefficients (RI), and 20% mass eccentricity in one direction. Then, different values of these parameters and the damping of the base isolation were evaluated. The results show that the structural elements have acceptable behavior after impact, but the nonstructural components are placed in a moderate damage range after impact and the used improved methods could not ameliorate the level of damage. The reduction in the RI and the enhancement of the isolator's damping are beneficial up to a certain point for improving the seismic response after impact. The moat wall reduces torque and maximum absolute acceleration (MAA) due to unexpected enhancement of mass eccentricity. However, drifts of some stories increase. Also, the difference between the response of story drift by expected and unexpected mass eccentricity is less. This indicates that the minimum requirement displacement according to ASCE 7-16 criteria lead to acceptable results under the unexpected enhancement of mass eccentricity.

• 한국구조물진단유지관리공학회 논문집
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• 제15권5호
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• pp.92-100
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• 2011

본 연구는 실제 교량에서 차량 주행에 따른 가속도 계측 자료를 이용하여 교량의 고유진동수를 진동 모드별로 파악한 후, 수치 모델링을 통하여 유도된 동적하중에 따른 6차 모드까지의 고유진동수를 고려하여 처짐을 계산할 수 있는 산정식에 관한 것이다. 처짐 계산식은 모드중첩법에 의한 비감쇠 강제진동 이론을 이용하여 교량을 등속도로 이동하는 동적 주행하중에 의해 발생하는 처짐을 계산할 수 있도록 수치 모델링을 하였으며, 이를 검증하고 자동으로 계산할 수 있도록 하였다. 그리고, 제안된 처짐 계산식을 검증하기 위하여 콘크리트 교량을 대상으로 동적재하시험을 실시하여 처짐을 측정하고 이 값을 본 연구의 처짐 계산식의 결과와 비교하여 정확성 및 타당성 검증을 실시하였다. 이 결과, 본 연구에서 제시하는 처짐 계산식은 고유진동수를 고려하는 진동모드의 차수가 낮은 경우에 비교적 정확한 처짐을 예측하며, 주행속도에 따라서는 적용하는 진동 모드 차수에 의하여 처짐 예측의 정확도가 영향을 받는 것을 확인하였다. 그리고, 주행속도가 비교적 빠른 경우에 한하여 본 연구에서 제시하는 처짐 계산식은 진동 모드에 상관없이 비교적 정확하고 신뢰도가 양호한 계산 결과를 얻을 수 있는 것으로 나타났다.

• Steel and Composite Structures
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• 제27권3호
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• pp.327-335
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• 2018

This paper presents structural assessment of a steel railway bridge for current condition using modal parameter to upgrade finite element modeling in order to gather accurate result. An adequate monitoring, such as acceleration, displacement, strain monitoring, is important tool to understand behavior and to assess structural performance of the structure under surround vibration by means of the dynamic analysis. Evaluation of conditions of an existing steel railway bridge consist of 4 decks, three of them are 14 m, one of them is 9.7 m, was performed with a numerical analysis and a series of dynamic tests. Numerical analysis was performed implementing finite element model of the bridge using SAP2000 software. Dynamic tests were performed by collecting acceleration data caused by surrounding vibrations and dynamic analysis is performed by Operational Modal Analysis (OMA) using collected acceleration data. The acceleration response of the steel bridge is assumed to be governing response quantity for structural assessment and provide valuable information about the current statute of the structure. Modal identification determined based on response of the structure play significant role for upgrading finite element model of the structure and helping structural evaluation. Numerical and experimental dynamic properties are compared and finite element model of the bridge is updated by changing of material properties to reduce the differences between the results. In this paper, an existing steel railway bridge with four spans is evaluated by finite element model improved using operational modal analysis. Structural analysis performed for the bridge both for original and calibrated models, and results are compared. It is demonstrated that differences in natural frequencies are reduced between 0.2% to 5% by calibrating finite element modeling and stiffness properties.

• 한국지진공학회논문집
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• 제20권5호
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• pp.319-329
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• 2016

The Eradi Quake System (EQS) is a seismic isolation bearing system designed to minimize forces and displacements experienced by structures subjected to ground motion. The EQS dissipates seismic energy through friction of Poly Tetra Fluoro Ethylene (PTFE) disk pad. In general, a force-displacement relationship of EQS has post yield stiffness hardening during large inelastic displacement. In this study, seismic responses of seismically isolated nuclear power plant (NPP) subjected to design basis earthquake (DBE) and beyond design basis earthquakes (150% DBE and 167% DBE) are compared considering the post yield stiffness hardening effect of EQS. From the results, it can be observed that if the post-yield stiffness hardening effect of EQS is increased, the displacement response of EQS is reduced, and the acceleration and shear responses of containment structures of NPP is increased.

• Coupled systems mechanics
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• 제2권1호
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• pp.111-126
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• 2013

The structural design requirements of an offshore platform subjected to wave induced forces and moments in the jacket can play a major role in the design of the offshore structures. For an economic and reliable design; good estimation of wave loadings are essential. A nonlinear response analysis of a fixed offshore platform under structural and wave loading is presented, the structure is discretized using the finite element method, wave plus current kinematics (velocity and acceleration fields) are generated using 5th order Stokes wave theory, the wave force acting on the member is calculated using Morison's equation. Hydrodynamic loading on horizontal and vertical tubular members and the dynamic response of fixed offshore structure together with the distribution of displacement, axial force and bending moment along the leg are investigated for regular and extreme conditions, where the structure should keep production capability in conditions of the 1-yr return period wave and must be able to survive the 100-yr return period storm conditions. The result of the study shows that the nonlinear response investigation is quite crucial for safe design and operation of offshore platform.

• 한국기계가공학회지
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• 제9권3호
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• pp.35-41
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• 2010

In this study, a mode analysis of uncoupled system was discussed using FRF. The eigen-mode range of FRF analysis is consistent with conventional FFT in spectrum. Also, the numerical response of second order uncoupled system was obtained using the Runge-Kutta Gill method. The displacement, velocity and acceleration response were calculated after numerical analysis and its response was used for the calculation of FRF for uncoupled system. Using the separated and mixed response of 1st and 2nd mode in example, its FRF was analysed for the prediction of the uncoupled systems and its mode shape was calculated by solving the eigen problem.

• 한국공간구조학회논문집
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• 제16권3호
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• pp.59-66
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• 2016

This study analyze the dynamic response property of latticed domes according to natural frequency ratio of substructure. Through eigenvalue analysis, it is was confirmed that the half-open angle $30^{\circ}$ and $45^{\circ}$ dominate vibration mode of the vertical direction and the half-open angle $60^{\circ}$ and $90^{\circ}$ dominate vibration mode of the horizontal direction. Through the dynamic response analysis, it is was confirmed that the first frequency about total structure largely appears about the vertical and the horizontal direction regardless of half-open angle.

• 융합정보논문지
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• 제11권9호
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• pp.130-137
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• 2021

주파수를 갖는 외부 가진력에 의하여 강제 진동의 특성을 가진력의 진폭과 주파수에 따라 그 특성을 분석하였다. 변위, 속도 및 가속도를 얻기 위해 수치해석을 수행하여 주파수 응답을 얻었고 특히 주파수 영역에서 시스템 고유진동수와 가진 주파수의 발생 위치를 밝히고자 각각의 FRF의 분석을 하였다. 외부 가진에 의한 진동모델에서 변위, 속도 및 가속도의 거동과 주파수 응답함수에서 고유진동 주파수와 주변의 가진 모드 분포도 파워 스펙트럼과 실수부와 허수부의 FRF 에서 나타났으며 각 모드 특성도 구하였다. 진동의 응답은 가진 신호의 크기와 주파수를 주어 정현파의 가진력으로 외부 가진력을 근사화 하였고 이런 가진력에 의하여 발생하는 모드를 구별할 수 있었다. 상당 질량, 감쇠 및 강성을 변화시켜 수치 분석 후 외부 가진력에 의한 강제 진동 응답 특성을 체계적으로 분석하였다.

• 한국지진공학회논문집
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• 제14권1호
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• pp.1-9
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• 2010

실제 구조요소나 구조시스템의 비선형응답은 단순화된 형태의 분할선형 이력모델 보다는 완만한 곡선이력모델로 나타내는 것이 보다 정확하다. 본 논문에서는 완만한 곡선이력거동을 적용한 일정연성도 비탄성 응답스펙트럼을 작성하는 방법을 제시하였다. 가속도, 변위 및 입력에너지에 대한 비탄성 응답스펙트럼에 대한 곡선형이력거동의 완만한 정도의 영향을 평가하였다. 해석결과로부터 곡선형이력거동의 완만도가 증가할수록 비탄성 응답스펙트럼은 감소하는 경향을 나타냄을 알 수 있었다.

• International Journal of Automotive Technology
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• 제7권7호
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• pp.769-776
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• 2006

A mathematical model is developed in this paper to define the interaction between the occupant and vehicle passenger compartment and to predict the occupant dynamic response during a sudden impulse load. Two different types of occupants are considered in this study, child and adult occupants. The occupants are considered as lumped masses connected to the child seat and vehicle's body masses by means of restraint systems. In addition, the occupant restraint characteristics of seat belt and airbag are represented by stiffness and damping elements. To obtain the dynamic response of the occupant, the equations of motion of the occupants during vehicle collisions are developed and analytically solved. The occupant's acceleration and relative displacement are used as injury criteria to interpret the results. It is demonstrated from the numerical simulations that the dynamic response and injury criteria are easily captured and analyzed. It is also shown that the mathematical models are flexible, useful in optimization studies and it can be used at initial design stage.