• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.224-230
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• 1996

In the mechanical systems with large damping, the conventional SDM method developed for no damping systems will lead to an error solution. Here, we introduce a SDM method based on the experimental modal model for large damping systems. The sensitivities of natural frequencies and mode shapes with respect to mass, damping, and stiffness coefficients of structures are used to calculate the position and quantity of modification, and predict the new dynamic characteristics. Through numerical simulation and experiment, the effectiveness of the proposed method is tested.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.859-864
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• 2001

For earthquake resistance design, a response modification factor is used to reduce the design strength and it reflects ductility, reserve strength, redundancy and damping effect. But this factor has not theoretical basis. In this study, two response modification factors are compared and analyzed for shear wall apartment building.; the one is introduced by ATC-19 Procedures, the other is suggested FEMA-273 and ATC-40 through nonlinear static analysis. For the results, ATC-19 procedure gives a reasonable estimation to R factor. But $R_{u}$ by using FEAM-273 and ATC-40 methods is estimated so small in case of a minor or moderate earthquake region. Due to this fact, response modification factor is smaller than suggested load criterion 3.0. So, it needs to decrease wall volume and reduce the global strength and system stiffness for proper ductile behavior matching to domestic load criterion.

• Journal of the Semiconductor & Display Technology
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• v.2 no.2
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• pp.25-30
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• 2003

In the case of a vibration sensitive equipment, it require a vibration free environment to provide its proper function. Especially, lithography and inspection device, which have sub-nanometer class high accuracy and resolution, have come to necessity for producing more improved Giga Class semi conductor wafers. This high technology equipments require very strict environmental vibration criteria in proportion to the accuracy of the manufacturing. In this paper, the dynamic analysis and modal test were performed to evaluate the dynamic properties of the constructing clean room structure. Based on these results, a structural dynamic modification(SDM) were required to satisfiy the vibration allowable limit for pression machine. Therefore, in order to improve the dynamic stiffness of clean room structure, the VSD system which can control the force applied on structure, were adopted and its utility were proved from dynamic test results of the improved structure after a modification work.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.102-106
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• 2003

An experimental modal analysis and dynamic stiffness evaluation of a moving body structure of a high speed machining center are presented in this paper. The natural frequencies and corresponding modes, and dynamic compliance of a moving body structure of high speed machining center are investigated by using F.E.M., hydraulic exciter test, and impulse hammer test. The lowest three natural frequencies were found to be 56.6 Hz, 112.7 Hz, and 142.7 Hz by FEA respectively, while those were 55 Hz, 112 Hz, 131 Hz by experimental analysis. Furthermore, both computed and measured absolute dynamic compliances of the moving body structure in iso-direction showed good agreement especially at the first two mode frequencies. With our experimental data, the dynamic characteristics of the machining center can be exploited to get a new development of structural dynamic design and modification.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1648-1653
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• 2003

This paper predicts the modified proportional damping structural eigenvectors and eigenvalues due to the change in the mass and stiffness of a proportional damping structure by iterative calculation of the sensitivity coefficient using the original dynamic characteristics. The method is applied to examples of a cantilever and 3 degree of freedom lumped mass model by modifing the mass and stiffness. The predicted dynamic characteristics are in good agreement with these from the structural reanalysis using the modified mass and stiffness.

• Steel and Composite Structures
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• v.24 no.2
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• pp.213-226
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• 2017

The behavior of building industry metal sheeting under shear forces has been extensively studied and equations have been developed to predict its shear stiffness. Building design engineers can make use of these equations to design a metal deck form bracing system. Bridge metal deck forms differ from building industry forms by both shape and connection detail. These two factors have implications for using these equations to predict the shear stiffness of deck form systems used in the bridge industry. The conventional eccentric connection of bridge metal deck forms reduces their shear stiffness dramatically. However, recent studies have shown that a simple modification to the connection detail can significantly increase the shear stiffness of bridge metal deck form panels. To the best of the author's knowledge currently there is not a design aid that can be used by bridge engineers to estimate the stiffness of bridge metal deck forms. Therefore, bridge engineers rely on previous test results to predict the stiffness of bridge metal deck forms in bracing applications. In an effort to provide a design aid for bridge design engineers to rely on bridge metal deck forms as a bracing source during construction, cantilever shear frame test results of bridge metal deck forms with and without edge stiffened panels have been compared with the SDI Diaphragm Design Manual and ECCS Diaphragm Stressed Skin Design Manual stiffness expressions used for building industry deck forms. The bridge metal deck form systems utilized in the tests consisted of sheets with thicknesses of 0.75 mm to 1.90 mm, heights of 50 mm to 75 mm and lengths of up to 2.7 m; which are representative of bridge metal deck forms frequently employed in steel bridge constructions. The results indicate that expressions provided in these manuals to predict the shear stiffness of building metal deck form panels can be used to estimate the shear stiffness of bridge metal deck form bracing systems with certain limitations. The SDI Diaphragm Design Manual expressions result in reasonable estimates for sheet thicknesses of 0.75 mm, 0.91 mm, and 1.21 mm and underestimate the shear stiffness of 1.52 and 1.90 mm thick bridge metal deck forms. Whereas, the ECCS Diaphragm Stressed Skin Design Manual expressions significantly underestimate the shear stiffness of bridge metal deck form systems for above mentioned deck thicknesses.

• Steel and Composite Structures
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• v.33 no.5
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• pp.681-697
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• 2019

This paper numerically assesses the initial stiffness and moment capacity of stainless steel composite bolted joints with concrete-filled circular tubular (CFCT) columns. By comparing with existing design codes including EN 1993-1-8 and AS/NZS 2327, a modified component method was proposed to better predict the flexural performance of joints involving circular columns and curved endplates. The modification was verified with independent experimental results. A wide range of finite element models were then developed to investigate the elastic deformations of column face in bending which contribute to the corresponding stiffness coefficient. A new design formula defining the stiffness coefficient of circular column face in bending was proposed through regression analysis. Results suggest that a factor for the stiffness coefficient of endplate in bending should be reduced to 0.68, and more contribution of prying forces needs to be considered. The modified component method and proposed formula are able to estimate the structural behaviour with reasonable accuracy. They are expected to be incorporated into the current design provisions as supplementary for beam-to-CFCT column joints.

• Earthquakes and Structures
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• v.7 no.6
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• pp.1283-1301
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• 2014

Ground motion modification is extensively used in seismic design of civil infrastructure, especially where few or no recorded ground motions representative of the design scenario are available. A site in Los Angeles, California is used as a study site and 28 ground motions consistent with the design earthquake scenario are selected. The suite of 28 ground motions is scaled and modified in the time domain (TD) and frequency domain (FD) before being used as input to a bilinear SDOF system. The median structural responses to the suites of scaled, TD-modified, and FD-modified motions, along with ratios of he modified-to-scaled responses, are investigated for SDOF systems with different periods, strength ratios, and post-yield stiffness ratios. Overall, little difference (less than 20%) is observed in the peak structural accelerations, velocities, and displacements; displacement ductility; and absolute accelerations caused by the TD-modified and FD-modified motions when compared to the responses caused by the scaled motions. The energy absorbed by the system when the modified motions are used as input is more than 20% greater than when scaled motions are used as input. The observed trends in the structural response are predominantly the result of changes in the ground motion characteristics caused by modification.

• Steel and Composite Structures
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• v.19 no.6
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• pp.1449-1466
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• 2015

Mixed structures consist of two parts: a lower part and an upper part. The lower part is usually made of concrete while the upper part is made of steel. Analyzing these structures is complicated and code-based design of them has many associated problems. In this research, the seismic behavior of mixed structures which have reinforced concrete frames and shear walls in their lower storeys and steel frames with bracing in their upper storeys were studied. For this purpose, seventeen structures in three groups of 5, 9 and 15 storey structures with different numbers of concrete and steel storeys were designed. Static pushover analysis, linear dynamic analysis and incremental dynamic analysis (IDA) using 15 earthquake records were performed by OpenSees software. Seismic parameters such as period, response modification factor and ductility factor were then obtained for the mixed (hybrid) structures using more than 4600 nonlinear dynamic analysis and used in the regression analysis for achieving proper formula. Finally, some formulas, effective in designing such structures, are presented for the mentioned parameters. According to the results obtained from this research, the response modification factor values of mixed structures are lower compared to those of steel or concrete ones with the same heights. This fact might be due to the irregularities of stiffness, mass, etc., at different heights of the structure. It should be mentioned that for the first time, the performance and seismic response of such structures were studied against real earthquake accelerations using nonlinear dynamic analysis, andresponse modification factor was obtained by IDA.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.693-696
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• 2007

In this paper, vibration sources of an electric forklift are identified and the forklift vibrations are reduced by structural modification by using the finite element analysis. From some experiments, it is also found that resonances occur because the natural frequencies of the forklift exist in usual driving speed range. To vibration sources of the electric forklift, the modeling is designed by using a commercial 3D CAD program CATIA and the finite element model is designed by a using finite element analysis program ANSYS which can perform modal analysis of flexible mode. To shift the natural frequencies out side the driving speed range, the frame part, the connection parts between main body and loader are modified to increase stiffness. It is verified that considerable amount of vibration are reduced by the structural modification.