• Structural Engineering and Mechanics
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• v.71 no.4
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• pp.445-458
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• 2019

This study mainly aims to assess the performance of soil-structure systems designed by direct displacement-based method coupled with strong column-weak beam design concept through various system identification techniques under strong ground motions. To this end, various system identification methods are employed to evaluate the dynamic characteristics of a structure (i.e., modal frequency, system damping, mode shapes, and plastic hinge formation pattern) under a strong seismic excitation considering soil-structure interaction for different site conditions as specified by ASCE 7-10. The scope of the study narrowed down to the code-complying low- to high-rise steel moment resisting frames with various heights (4, 8, 12, 16-story). The comparison of the result of soil-structure systems with fix-based support condition indicates that the modal frequencies of these systems are highly influenced by the structure heights, specifically for the softer soils. This trend is more significant for higher modes of the system which can considerably dominate the response of structures in which the higher modes have more contribution in dynamic response. Amongst all studied modes of the vibration, the damping ratio estimated for the first mode is relatively the closet to the initial assumed damping ratios. Moreover, it was found that fewer plastic hinges are developed in the structure of soil-structure systems with a softer soil which contradicts the general expectation of higher damageability of such structural systems.

• Nuclear Engineering and Technology
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• v.31 no.2
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• pp.214-225
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• 1999

An accurate method is presented for flexural vibrations of sectorial plates having simply supported-free and free-free radial edges, when the circular edge is either clamped or simply supported. The classical Ritz method is employed with two sets of admissible functions assumed for the transverse vibratory displacements. These sets consist of : (1) mathematically complete algebraic-trigonometric polynomials which gurantee convergence to exact frequencies as sufficient terms are retained, and (2) comer functions which account for the bending moment singularities at re-entrant comer of the radial edges having arbitrary edge conditions. Accurate (at least four significant figures) frequencies and normalized contours of the transverse vibratory displacement are presented for the spectra of corner angles [90$^{\circ}$, 180$^{\circ}$(semi-circular), 270$^{\circ}$, 300$^{\circ}$, 330$^{\circ}$, 350$^{\circ}$, 355$^{\circ}$, 360$^{\circ}$ (complete circular)] causing a re-entrant comer of the radial edges. Future solutions drawn from alternative numerical procedures and finite element techniques may be compared with these accurate results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.4
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• pp.35-42
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• 1990

A method for the damage assessment of a structure by an inverse modal perturbation technique is studied. The first few natural frequencies and mode shapes of the damaged structure are assumed to be known. Then, the perturbation equation is formulated for the changes of the modal properties due to the stiffness changes. The stiffness changes due to damages are evaluated, using optimization techniques. Example analyses are carried out for several cases of stick models and a truss model. Results indicate that the present method yields very reasonable estimates for the element stiffness changes.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.10a
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• pp.390-395
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• 2003

Moving flexible structures such as transfer systems in press machine, crane, working table of machine tools have vibration problems because of starting, feeding and stopping. An analysis method is suggested and experimentally studied in order to solve a vibration problem of a moving flexible structure. In this method, the concepts of substructure synthesis method and semi-static displacement including rigid body mode were used. Total deformation of a structure was assumed to be composed of quasi-static and dynamic components. Experimental results from an elementary model of a transfer feeder showed good agreements with computational results.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.2
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• pp.94-101
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• 1996

The equations of motion for a basic industrial robotic system which has a rigid or a flexible arm are derived by Lagrange's equation, respectively. Especially, for the deflection of the flexible arm, the assumed mode method is employed. These equations are highly nonlinear equations with nonlinear coupling between the variables of motion. In order to design the control law for the rigid-arm robot, Hunt-Su's nonlinear transformation method and Marino's feedback equivalence condition are used with linear quadratic regulator(LQR) theory. The control law for the rigid-arm robot is employed to input the desired path and to provide the required nonlinear transformations for the flexible-arm robot to follow. By using the implicit Euler method to solve the nonlinear equations, the comparison of the motions between the flexible and the rigid robots and the effect of flexibility are examined.

• Journal of Institute of Control, Robotics and Systems
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• v.6 no.5
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• pp.356-366
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• 2000

In this paper, a nonlinear $H_2/H_\infty/LTR$ control for the flexible inverted pendulum of a parallel type with Coulomb friction is presented. The dynamic equation for this system is derived by the Hamilton's principle and assumed-mode method. This hard nonlinear system can be modeled by a the quasi-linear state space model using the REF method. It is shown that the $H_2/H_\infty$ control can be applied to the nonlinear controller design of the system having Coulomb frictions if the proper LTR conditions are satisfied. In order to present the usefulness of the suggested control method, the nonlinear $H_2/H_\infty/LTR$ controller is designed to control the Position of the end point of the flexible inverted pendulum that has Coulomb frictions present in actuator parts. The results are given via computer simulations.

• Transactions of the Korean Society of Automotive Engineers
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• v.2 no.4
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• pp.18-26
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• 1994

The buckling characteristics of I - shaped columns which are composed of thin web and equal upper/lower flange plates are generally classified into the local and global modes. In this paper, its local buckling problem has been formulated on the basis of the assumed buckling modes using the finite element method for beams and plates. The effects of local bucklings are studied for various size rations and end conditions of I-shaped columns. The calculated results are comparatively well consistent with values obtained from the existing studies. The global buckling characteristics calculated by the present method are in good agreement with the classical rigid web solution

• Journal of the Korea Institute of Military Science and Technology
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• v.8 no.1 s.20
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• pp.81-91
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• 2005

It is well known that the natural frequencies of the pipe come to be lower as internal fluid velocity and pressure increase, and the pipe will be unstable if the fluid velocity is higher than critical velocity. But even if the velocity of the fluid below the critical velocity, resonance will be caused by pulsation of the fluid. So the effects of pulsating fluid in pipe should be also taken into consideration for better analysis. The research of the vibration of piping system due to a fluid pulsation has been studied by many people. But most of them are dealt with determining the boundary between stable and unstable region without analyzing forced response in the stable region. In this study, not only stability analysis but also forced response analysis, which is caused by harmonically excited fluid especially, is conducted. In order to analyze the system numerically, the descretized equation is formulated by using FEM(Finite Element Method). And the results of this method are compared with those of AMM(Assumed Mode Method) which were used by many researcher earlier.

• Earthquakes and Structures
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• v.8 no.1
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• pp.205-224
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• 2015

A new method for designing moment resisting concrete frames failing in a global mode is presented in this paper. Starting from the analysis of the typical collapse mechanisms of frames subjected to horizontal forces, the method is based on the application of the kinematic theorem of plastic collapse. The beam section properties are assumed to be known quantities, because they are designed to resist vertical loads. As a consequence, the unknowns of the design problem are the column sections. They are determined by means of design conditions expressing that the kinematically admissible multiplier of the horizontal forces corresponding to the global mechanism has to be the smallest among all kinematically admissible multipliers. In addition, the proposed design method includes the influence of second-order effects. In particular, second-order effects can play an important role in the seismic design and can be accounted for by means of the mechanism equilibrium curves of the analysed collapse mechanism. The practical application of the proposed methodology is herein presented with reference to the design of a multi-storey frame whose pattern of yielding is validated by means of push-over analysis.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.17 no.6
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• pp.124-129
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• 2018

A non-linear vibration isolation system which is composed of a non-linear spring and a linear damper was proposed in past research. When the support of the isolation system is excited harmonically, the response component of the isolation system mass at the excitation frequency has been calculated approximately using the harmonic balance method. The response was approximated by a single mode, and the result was compared with a numerical result which is assumed as an accurate one. Next, the response was approximated by two modes, and the result was compared with the former one.