• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2003.09a
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• pp.467-472
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• 2003

The objective of optimal placement of dampers for a structure is to maximize the effectiveness of the vibration control with the same number of dampers. While many optimal placement methods of linear viscous dampers have been proposed and used, there are only a few methods for MR dampers. Here some optimal location indices for MR dampers are proposed, which are similar to those for linear viscous dampers and show how large the structural responses on each floor we. Every time an additional MR damper is implemented, the optimal location index on each floor is measured, and then the next damper is installed on the floor with the maximum location index. In these sequential procedures, the peak interstory drift, the peak interstory velocity and the absolute acceleration of each floor are selected as the optimal location indeices. Four different earthquakes with various scales are loaded to the 20-story nonlinear benchmark building model (Otori et at. 2000, 2002). Passive On/Off algorithms are used in order to represent the control algorithm of MR dampers.

• Earthquakes and Structures
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• v.18 no.2
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• pp.233-248
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• 2020

In this article, one of the procedures to design viscous dampers proposed in literature is applied to 3D asymmetric-plan buildings, considering different distributions for the damping coefficients, which are assumed to be proportional to specific structural or response parameters. The main purpose was to investigate the effectiveness of different vertical and in-plan distributions of the damping coefficients of nonlinear viscous dampers for the seismic retrofit of existing buildings. For comparison purposes, all the distributions were applied utilizing both a simplified and an extended method for the 3D structures, where the simplified method takes into account only the translation in the seismic direction, and the extended method considers the translations along the two orthogonal directions together with the floor rotations. The proposed distributions were then applied to a typical case study involving an asymmetric-plan six-storey RC building. The effectiveness of the different distributions was examined through time-history analyses, assuming nonlinear behaviour for both the viscous dampers and the structural elements. The results of the nonlinear dynamic analyses were examined in terms of maximum and residual inter-storey drifts, peak floor accelerations and maximum damper forces.

• International Journal of High-Rise Buildings
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• v.8 no.3
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• pp.221-227
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• 2019

In this paper passive seismic retrofit devices for building structures developed by the author in recent years are introduced. The proposed damping devices were developed by slightly modifying the configuration of conventional devices and enhancing their effectiveness. First a seismic retrofit system consisting of a pin-jointed steel frame and rotational friction dampers installed at each corner of the steel frame was developed. Then two types of steel slit dampers were developed; box-type slit damper and multi-slit damper. In addition, hybrid dampers were developed by combining a slit damper and a friction damper connected in parallel. Finally a self-centering system was developed by using preloaded tendons and viscous dampers connected in series. For each retrofit system developed, an appropriate analytical model was developed, and the seismic performance was verified by loading test and earthquake analysis of case study structures. The experimental and analysis results show that the proposed systems can be used efficiently to enhance the seismic performance of building structures.

• Earthquakes and Structures
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• v.6 no.5
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• pp.495-514
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• 2014

The performance of passive control system for the seismic protection of a multi-tower cable-stayed bridge with the application of partially longitudinal constraint system is investigated. The seismic responses of the Jiashao Bridge, a six-tower cable-stayed bridge using the partially longitudinal constraint system are studied under real earthquake ground motions. The effects of the passive control devices including the viscous fluid dampers and elastic cables on the seismic responses of the bridge are examined by taking different values of parameters of the devices. Further, the optimization design principle of passive control system using viscous fluid dampers is presented to determine the optimized parameters of the viscous fluid dampers. The results of the investigations show that the control objective of the multi-tower cable-stayed bridge with the partially longitudinal constraint system is to reduce the base shears and moments of bridge towers longitudinally restricted with the bridge deck. The viscous fluid dampers are found to be more effective than elastic cables in controlling the seismic responses. The optimized parameters for the viscous fluid dampers are determined following the principle that the peak displacement at the end of bridge deck reaches to the maximum value, which can yield maximum reductions in the base shears and moments of bridge towers longitudinally restricted with the bridge deck, with slight increases in the base shears and moments of bridge towers longitudinally unrestricted with the bridge deck.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2000.10a
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• pp.257-264
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• 2000

Nonlinear dynamic time history analysis of a structure with energy dissipation devices is complicated and time consuming. In this regard the nonlinear static analysis is a practical alternative for evaluating the earthquake resisting capacity of a structure. In this study the nonlinear static response of a structure was obtained first, and the equivalent viscous modal damping ratio required to satisfy the performance objective was computed in the capacity spectrum format. Then proper amount of viscous dampers were installed to provide the required damping. Parametric study has been performed for the period of the structure, yield strength, and the stiffness after the first yield. According to the earthquake time history analysis results, the maximum displacement of the model structure with viscous dampers designed in accordance with the proposed method corresponds well with the target displacements that was used in the beginning of the design process.

• Earthquakes and Structures
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• v.18 no.5
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• pp.609-623
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• 2020

This paper presents a displacement-based seismic design procedure for new structures with fluid viscous dampers and/or for existing structures, where these devices are required as a retrofit measure and damage control. To consider the non-proportional damping produced by these devices in a conventional modal spectral analysis, the effect of the fluid viscous dampers is approximated as the sum of a proportional damping matrix and a complementary matrix which is representative of non-proportional damping matrix. To illustrate the application of this procedure and evaluate the performance of structures designed with the procedure proposed, five regular plane frames: 8, 12, 17, 20 and 25-storey, and an 8-storey building are designed. The seismic demands used for design and validation were the records obtained at the SCT site during the 1985 Michoacan earthquake, and that of the 2017 Morelos - Puebla earthquake obtained at the Culhuacan site, both stations located on soft soil sites. To validate the procedure proposed, the performances and damage distributions used as design targets were compared with the corresponding results from the nonlinear step-by-step analyses of the designed structures subjected to the same seismic demands.

• Journal of KSNVE
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• v.5 no.2
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• pp.225-234
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• 1995

In this study, first, transformation process of damping ratios, whose are evaluated in active control analysis, into damping matrix resulting from installed viscous dampers is illustrated. Then, a method is followed to maximize the effect of response reduction, which leads to optimum locations and size of viscous dampers using sensitivity analysis. Highly coupled nonlinearity between damping ratios and dampers makes it hard to find the optimal size of dampers. Therefore, the nonlinearity is transformed to linear problem with small increments of damping ratios and the size of dampers can be found. However, there are many cases for the size of dampers satisfying the small increment of damping ratios, so it is necessary to select minimum size using optimization technique. To determine optimum locations of dampers, dampers are assumed to be installed between the different stories and their locations are selected corresponding corresponding to the degree of damping size. Numerical examples for the frame structure and the shear wall structure show that optimum locations and size of dampers are different form each other depending on the characteristics of modal responses of the structures. The proposed method in this study can be applied to get optimum locations of active controller in the active control.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.6
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• pp.569-574
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• 2009

The paper presents the influences of the external damping and the tip mass on dynamic stability of a vertical cantilevered pipe conveying fluid. In general, real pipe systems may have some valves and attached mechanical parts, which can be regarded as attached lumped masses and support-dampers. The support-dampers can be assumed as viscous dampers. The equations of motion are derived by energy expressions using extended Hamilton's principle, and some numerical results using Galerkin's method are presented. Critical flow velocities and stability maps of the pipe with external dampers and tip mass are obtained for various tip mass ratios, external damping coefficients and positions of the viscous dampers.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.465-468
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• 2005

The paper deals with the influences of external damping and tip mass on dynamic stability of a vertical cantilevered pipe conveying fluid. In general, real pipe systems may have some valves and attached parts, which can be regarded as attached lumped masses and support-dampers. The support-dampers can be assumed as viscous dampers. The equations of motion are derived by energy expressions using extended Hamilton's principle, and some numerical results using Galerkin's method are presented. Critical flow velocities and stability maps of the pipe with external dampers and tip mass are obtained for various tip mass ratios, external damping coefficients and positions of the viscous dampers.

• Earthquakes and Structures
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• v.13 no.4
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• pp.337-351
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• 2017

In the present study a capacity spectrum method based on constant ductility inelastic spectra to estimate the seismic performance of structures equipped with elastic viscous dampers is presented. As the definition of the structures' effective damping, due to the damping system, is necessary, an alternative method to specify the effective damping ratio ${\xi}eff$ is presented. Moreover, damping reduction factors (B) are introduced to generate high damping elastic demand spectra. Given the elastic spectra for damping ratio ${\xi}eff$, the performance point of the structure can be obtained by relationships that relate the strength demand reduction factor (R) with the ductility demand factor (${\mu}$). As such expressions that link the above quantities, known as R - ${\mu}$ - Τ relationships, for different damping levels are presented. Moreover, corrective factors (Bv) for the pseudo-velocity spectra calculation are reported for different levels of damping and ductility in order to calculate with accuracy the values of the viscous dampers velocities. Finally, to evaluate the results of the proposed method, the whole process is applied to a four-storey reinforced concrete frame structure and to a six-storey steel structure, both equipped with elastic viscous dampers.