• 한국구조물진단유지관리공학회 논문집
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• 제22권3호
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• pp.8-15
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• 2018

본 연구에서는 프리스트레스 긴장력의 위치와 크기에 따른 거더의 횡비틀림 안정성 실험을 수행하였다. 거더를 이용한 횡방향 거동 및 안정성 실험은 재료의 비선형성, 초기 기하학적 불완전성, 긴장력의 변화, 하중조건과 지지조건 등 다양한 변수에 의해 예상치 못한 결과를 발생시킬 수 있다. 따라서, 본 연구에서는 프리스트레스 거더 축소 모형 실험안을 제안하여 긴장력에 의한 횡비틀림 안정성을 실험을 수행하였다. 하중 가력조건과 면내 및 면외 지지조건을 만족하며 긴장력을 조절할 수 있는 실험장치를 제안하고 제작하였다. 실험결과 하부 플랜지에 긴장력이 작용하는 경우 횡비틀림 안정성을 증가시켰으며, 최종적으로 긴장력의 위치와 크기에 따라 횡비틀림 안정성을 평가할 수 있는 해석식을 제안하였다.

• Smart Structures and Systems
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• 제18권5호
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• pp.931-953
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• 2016

In this paper, the effects of mass eccentricity of superstructure as well as stiffness eccentricity of isolators on the amplification of seismic responses of base-isolated structures are investigated by using mathematical near-fault pulse models. Superstructures with 3, 6 and 9 stories and aspect ratios equal to 1, 2 and 3 are mounted on a reasonable variety of Triple Concave Friction Pendulum (TCFP) bearings considering different period and damping ratio. Three-dimensional linear superstructure mounted on nonlinear isolators are subjected to simplified pulses including fling step and forward directivity while various pulse period ($T_p$) and Peak Ground Velocity (PGV) amounts as two crucial parameters of these pulses are scrutinized. Maximum isolator displacement and base shear as well as peak superstructure acceleration and drift are selected as the main engineering demand parameters. The results indicate that the torsional intensification of different demand parameters caused by superstructure mass eccentricity is more significant than isolator stiffness eccentricity. The torsion due to mass eccentricity has intensified the base shear of asymmetric 6-story model 2.55 times comparing to symmetric one. In similar circumstances, the isolator displacement and roof acceleration are increased 49 and 116 percent respectively in the presence of mass eccentricity. Furthermore, it is demonstrated that torsional effects of mass eccentricity can force the drift to reach the allowable limit of ASCE 7 standard in the presence of forward directivity pulses.

• 한국자동차공학회논문집
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• 제20권5호
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• pp.65-70
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• 2012

Torque fluctuation of engine generate gear rattle noise of transmission and many researches have been studied to decrease rattle noise by adjusting clutch damper system. So design optimization of clutch system is very important to decrease rattle noise and need knowing clutch dynamic torque at real vehicle driving condition. This makes it possible to measure clutch dynamic torque by using a small-size magnetic sensor. We install a small-size magnetic sensor on the input shaft of the transmission and measure the relative angular displacement between clutch hub and disc plate. We can obtain the clutch torque correspond to the angular displacement in the clutch torsional characteristics test. The object of this research is to measure clutch dynamic torque on real vehicle condition. Therefore, Clutch dynamic torque is very useful for investigating operating range of clutch according to engine torque and predicting the damping performance of torsional vibration on the powertrain.

• Earthquakes and Structures
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• 제13권1호
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• pp.1-8
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• 2017

This article is all about using the MR damper with an external lever system for mitigation torsional and transitional lateral displacements by using of PID control algorithm. The torsional modes are so destructive and can be varied during an earthquake therefore, using a semi-active control system mostly recommended for them. In this paper the corner lateral displacement of each floor obtains and then it equivalents in a solid member and it connects to an MR damper, which relies to a rigid structure to reduce the response. An MR damper is a semi-active control system, which can absorb a lot of energy by injecting current to it. This amount of current is very low and needs low power supply, but it increases the amount of damper force, rather than inactive systems like viscous dampers. This paper will show the appropriate algorithm for current injection into MR damper when the eccentricity of the load is changed by using of Bouc-Wen and Bingham's methods and illustrates the coincidence of them.

• 한국산학기술학회논문지
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• 제18권10호
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• pp.739-744
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• 2017

탄성변형과 피로손상은 카트의 주행성능에 영향을 미치는 것으로 카트 프레임에 영구변형을 유발할 수 있다. 카트프레임은 현가장치와 다른 장치를 포함하지 않으므로 두 가지 변형에 결정적인 영향을 미칠 수 있는 코너주행 시 동적 거동은 비틀림 변형이 원인이 된다. 선회주행 시 카트의 동적 거동을 분석하기 위해 카트의 GPS추적이 실시간으로 이루어지고 카트 프레임에 작용하는 비틀림 응력값을 측정하였다. 레저카트와 레이싱카트의 재료물성치들은 인장실험을 통해 얻었다. 비틀림 응력집중과 프레임 변형은 얻어진 결과 값을 토대로 프레임의 응력해석을 통하여 파악하였다. 개발된 주행분석장치를 이용하여 레저카트와 레이싱카트를 각 조건별로 실차실험을 수행하였고 이를 통한 코너에서 카트의 주행거동을 살펴보았다. 카트가 곡선주행 시 원심력으로 인해 하중이동이 발생하였으며 카트프레임에 비틀림 응력이 발생하였다. 예를 들어 레저카드의 경우, 40 km/h의 속도로 운전할 때 최대 비틀림 피로한도를 측정한 최대 비틀림응력은 230 MPa이며 비틀림 피로한도계수는 0.65를 나타내었다. 뿐만 아니라 카트의 선회 시 운전요소들을 운전측정시스템을 인스톨한 실측장비에서 측정하였으며 카트의 운전거동은 수직변위에 의해 측정하였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2000년도 가을 학술발표회논문집
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• pp.369-376
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• 2000

For the general loading condition and boundary condition, it is very difficult to obtain closed-form solutions for buckling loads and natural frequencies of thin-walled structures because its behaviour is very complex due to the coupling effect of bending and torsional behaviour. Consequently most of previous finite element formulations introduced approximate displacement fields using shape functions as Hermitian polynomials, isoparametric interpoation function, and so on. The purpose of this study is to calculate the exact displacement field of a thin-walled straight beam element with the non-symmetric cross section and present a consistent derivation of the exact dynamic stiffness matrix. An exact dynamic element stiffness matrix is established from Vlasov's coupled differential equations for a uniform beam element of non-symmetric thin-walled cross section. This numerical technique is accomplished via a generalized linear eigenvalue problem by introducing 14 displacement parameters and a system of linear algebraic equations with complex matrices. The natural frequencies are evaluated for the non-symmetric thin-walled straight beam structure, and the results are compared with available solutions in order to verify validity and accuracy of the proposed procedures.

• Structural Engineering and Mechanics
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• 제26권3호
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• pp.297-313
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• 2007

A preliminary performance-based seismic design methodology is proposed. The top yield displacement of the system is computed from these of the components, which are assumed constant. Besides, a simple procedure to evaluate the top yield displacement of frames is developed. Seismic demands are represented in the form of yield point spectra. The methodology is general, conceptually transparent, uses simple calculations based on first principles and is applicable to asymmetric systems. To consider a specific situation two earthquake levels, occasional and rare are considered. The advantage of an arbitrary assignment of strength to the different components to reduce eccentricities and improved the torsional response of the system is addressed. The methodology is applied to an asymmetric five story building, and the results are verified by push-over analysis and non linear dynamic analysis.

• Structural Engineering and Mechanics
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• 제52권4호
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• pp.787-813
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• 2014

Starting with Hamilton's variational principle, the governing field equations for the steady state response of thin-walled beams under harmonic forces are derived. The formulation captures shear deformation effects due to bending and warping, translational and rotary inertia effects and as well as torsional flexural coupling effects due to the cross section mono-symmetry. The equations of motion consist of four coupled differential equations in the unknown displacement field variables. A general closed form solution is then developed for the coupled system of equations. The solution is subsequently used to develop a family of shape functions which exactly satisfy the homogeneous form of the governing field equations. A super-convergent finite element is then formulated based on the exact shape functions. Key features of the element developed include its ability to (a) isolate the steady state response component of the response to make the solution amenable to fatigue design, (b) capture coupling effects arising as a result of section mono-symmetry, (c) eliminate spatial discretization arising in commonly used finite elements, (d) avoiding shear locking phenomena, and (e) eliminate the need for time discretization. The results based on the present solution are found to be in excellent agreement with those based on finite element solutions at a small fraction of the computational and modelling cost involved.

• 한국강구조학회 논문집
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• 제14권1호
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• pp.31-40
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• 2002

적층된 박벽 복합재료 보의 자유 진동에 관한 연구를 수행하였다. 박벽 C형강 복합재료의 동적 거동에 적용 가능한 일반적인 해석 모델을 개발하였다. 이 모델은 classical lamination theory를 기초로 두고 있으며, 임의의 적층 상태의 구성 즉, 대칭뿐만 아니라 비대칭의 적층 상태, 그리고 다양한 경계조건에 따른 휨과 비틀림 형상의 연계(coupling)을 설명하였다. 변위를 기반으로 한 일차원 유한 요소 모델은 박벽 복합재료 보의 고유 진동수와 그에 대응하는 진동 모드를 예측하기 위해 개발되었다. 운동방정식은 Hamiton의 원리로부터 유도되었으며, 수치적인 결과는 박벽 복합재 보에서 복합재료의 진동수와 모드 형상에 대해 적층각, 계수비, 그리고 경계조건의 영향을 얻을 수 있었다.

• 한국소음진동공학회논문집
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• 제21권2호
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• pp.169-177
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• 2011

In this paper, the natural frequency of a cracked cantilever L-beams with a coupled bending and torsional vibrations is investigate by theory and experiment. In addition, a method for detection of crack in a cantilever L-beams is presented based on natural frequency measurements. The governing differential equations of a cracked L-beam are derived via Hamilton's principle. The two coupled governing differential equations are reduced to one sixth order ordinary differential equation in terms of the flexural displacement. Futher, the dynamic transfer matrix method is used for calculation of a exact natural frequencies of L-beams. The crack is assumed to be in the first mode of fracture and to be always opened during vibrations. In this study, the differences between the actual and predicted positions and sizes of crack are less than about 10 % and 39.5 % respectively.