• Journal of the Earthquake Engineering Society of Korea
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• v.21 no.5
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• pp.227-236
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• 2017

This study reviews concepts, theories and formulas included in standards on soil-structure interaction and also shows practical example of application for engineers. Real structures are 3 dimensional and multi degree of freedom but they are often idealized to single degree of freedom for convenience. In this study, detailed procedures to calculate soil spring constants and damping coefficients and method to model soil-structure system are explained. Additionally, case studies to judge fixed base condition and evaluation of applicability of simple analysis method based on response spectra are performed.

• Earthquakes and Structures
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• v.4 no.1
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• pp.109-132
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• 2013

Current codes incorporate simplified methods for the prediction of acceleration demands on secondary structural and non-structural elements at different levels of a building. While the use of simple analysis methods should be advocated, damage to both secondary structural and non-structural elements in recent earthquakes have highlighted the need for improved design procedures for such elements. In order to take a step towards the formation of accurate but simplified methods of predicting floor spectra, this work examines the floor spectra on elastic and inelastic single-degree of freedom systems subject to accelerograms of varying seismic intensity. After identifying the factors that appear to affect the shape and intensity of acceleration demands on secondary structural and non-structural elements, a new series of calibrated equations are proposed to predict floor spectra on single degree of freedom supporting structures. The approach uses concepts of dynamics and inelasticity to define the shape and intensity of the floor spectra at different levels of damping. The results of non-linear time-history analyses of a series of single-degree of freedom supporting structures indicate that the new methodology is very promising. Future research will aim to extend the methodology to multi-degree of freedom supporting structures and run additional verification studies.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.3
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• pp.21-28
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• 2008

To evaluate the seismic performance of multi-degree of freedom(MDF) systems, repeated nonlinear response history analyses are often conducted, which require extensive computational efforts. To reduce the amount of computation required, equivalent single degree of freedom(SDF) systems representing complex multi-degree of freedom(MDF) systems have been developed. For the equivalent SDF systems, bilinear models and trilinear models have been most commonly used. In these models, the P-$\Delta$ effect due to gravity loads during earthquakes can be accounted for by assigning negative stiffness after elastic range. This study evaluates the adequacy of equivalent SDF systems having these hysteretic models to predict the actual response of steel moment resisting frames(SMRF). For this purpose, this study conducts cyclic pushover analysis, nonlinear time history analysis and incremental dynamic analysis(IDA) for SAC-Los Angeles 9-story buildings using nonlinear MDF models(exact) and equivalent SDF models(approximate). In addition, this study considers the strength limited model.

• Journal of Industrial Technology
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• v.25 no.A
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• pp.23-30
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• 2005

The capacity spectrum method(CSM) can be used for the evaluation of inelastic maximum response of structures and has been recently used in the seismic design using the incorporation of pushover analysis and response spectrum method. To efficiently evaluate seismic performance of multi-degree-of freedom(MDOF) bridge structures, it is important that the equivalent response of MDOF bridge structures should be calculated. To calculate the equivalent response of MDOF system, equivalent responses are obtained by using Song method, Fajfar method and Calvi method. Also, those responses are applied to CSM method and seismic performance of bridge according to the ESDOF method are compared and evaluated straightforwardly.

• Wind and Structures
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• v.7 no.3
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• pp.203-214
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• 2004

This paper describes a method for developing a multi-degree-of freedom aero-elasto-plastic model of a base-isolated mid-rise building. The horizontal stiffness of isolators is modeled by several tension springs and the vertical support is performed by air pressure from a compressor. A lead damper and a steel damper are modeled by a U-shaped lead line and an aluminum line. With this model, the frequency ratio of torsional vibration to sway vibration, and plastic displacements of isolation materials can be changed easily when needed. The results of isolation material tests and free vibration tests show that this model provides the object performance. The peak displacement factors are about 4.5 regardless of wind speed in wind tunnel tests, but their gust response factor decreases with increment of wind speed.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.838-839
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• 2011

The spherical motor is very valuable actuator, because the motor can operate as multi-degree of freedom rotation. Especially, the motor is useful machine for robot's joint by reason of high efficiency, compact size, high power, precise control, etc. These characteristics of spherical motor have to require continuously research. Therefore, in this paper, two different types of spherical motor are compared and double-airgap spherical motor as novel stucture is introduced.

• Steel and Composite Structures
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• v.25 no.4
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• pp.497-503
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• 2017

In this paper, nonlinear vibration of multi-degree of freedom systems are studied. It has been tried to develop the mathematical model of systems by second-order nonlinear partial differential equations. The masses are connected with linear and nonlinear springs in series. A great effort has been done to solve the nonlinear governing equations analytically. A new analytical method called Variational Iteration Method (VIM) is proposed and successfully applied to the problem. The linear and nonlinear frequencies are obtained and the results are compared with numerical solutions. The first order of Variational Iteration Method (VIM) leads us to high accurate solution.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2003.04a
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• pp.19-26
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• 2003

In energy-based design, the structures are generally transformed into equivalent SDOF systems to obtain the input and the dissipated energy. In this study the energy demands in multi-story structures were compared with that of equivalent single degree of freedom systems to validate the transformation method. Three-, eight-, and twenty-story steel moment-resisting frames and buckling restrained braced frames are compared with those of equivalent single degree of freedom systems. Sixty earthquake ground motions recorded in different soil conditions were used to compute the input and hysteretic energy demands in model structures. According to the analysis results, in 3 and 8-story structures the hysteretic energy demands computed in the equivalent SDOF structures are compatible with those computed in the original MDOF structures, while in the 20-story structures the transformed equivalent structures underestimated the hysteretic energy demands.

• International Journal of Aeronautical and Space Sciences
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• v.11 no.2
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• pp.69-79
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• 2010

This paper describes the experimental framework for the control system design and validation of a rotorcraft unmanned aerial vehicle (UAV). Our approach follows the general procedure of nonlinear modeling, linear controller design, nonlinear simulation and flight test but uses an indoor-installed multi-camera system, which can provide full 6-degree of freedom (DOF) navigation information with high accuracy, to overcome the limitation of an outdoor flight experiment. In addition, a 3-DOF flying mill is used for the performance validation of the attitude control, which considers the characteristics of the multi-rotor type rotorcraft UAV. Our framework is applied to the design and mathematical modeling of the control system for a quad-rotor UAV, which was selected as the test-bed vehicle, and the controller design using the classical proportional-integral-derivative control method is explained. The experimental results showed that the proposed approach can be viewed as a successful tool in developing the controller of new rotorcraft UAVs with reduced cost and time.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.9
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• pp.5452-5459
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• 2014

A resonance linear electric generator in a vehicle suspension is a system that performs self-electric generation by collecting the vibration energy when a vehicle runs on a road, and takes the resonance phenomenon to derive large electric generation from slight road surface vibrations. In this paper, the motions of an armature in three different electric generator structures were simulated and the actual generation quantity was calculated and compared with these results. Furthermore, when the vehicle runs on the road, the design improvement for a multi-degree of freedom electric generator was conducted to make the resonance respond to various excitation frequencies, and the change in the resonance points and generation quantity were identified.