• Structural Engineering and Mechanics
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• v.15 no.5
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• pp.513-534
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• 2003

Using fluid dampers to connect adjacent buildings for enhancing their seismic resistant performance has been recently investigated but limited to linear elastic adjacent buildings only. This paper presents a study of inelastic seismic response of adjacent buildings linked by fluid dampers. A nonlinear finite element planar model using plastic beam element is first constructed to simulate two steel frames connected by fluid dampers. Computed linear elastic seismic responses of the two steel frames with and without fluid dampers under moderate seismic events are then compared with the experimental results obtained from shaking table tests. Finally, elastic-plastic seismic responses of the two steel frames with and without fluid dampers are extensively computed, and the fluid damper performance on controlling inelastic seismic response of the two steel frames is assessed. The effects of the fundamental frequency ratio and structural damping ratio of the two steel frames on the damper performance are also examined. The results show that not only in linear elastic stage but also in inelastic stage, the seismic resistant performance of the two steel frames of different fundamental frequencies can be significantly enhanced if they are properly linked by fluid dampers of appropriate parameters.

• Structural Engineering and Mechanics
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• v.55 no.6
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• pp.1261-1278
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• 2015

Due to their low intrinsic damping, stay cables in cable-stayed bridges have often exhibited unanticipated and excessive vibrations which result in increasing maintenance frequency and disruption to normal operations of the entire bridges. Mitigation of undesired cable vibration can be achieved by attaching an external damping device near the anchorage. High Damping Rubber (HDR) dampers have many advantages such as compact size, better aesthetics, easy maintenance, temperature stability, and cost benefits; therefore, they have been widely used to increase cable damping. Although a single damper has been shown to reduce cable vibrations, it is not the most effective method due to geometric constraints. This paper proposes the use of two HDR dampers to improve effectiveness and robustness in suppressing cable vibration. Oscillation parameters of the cable-dampers system were investigated in detail by modeling the stay cable as a taut string and each HDR damper as complex-valued impedance and by using an analytical formulation of the complex eigenvalue problem. The problem of two HDR dampers arbitrarily located along a cable is solved and the solution is discussed. Asymptotic formulas to calculate the damping ratios of the cable with two HDR dampers installed near the anchorage(s) are proposed and compared with the exact solutions. Further, a design example is presented in order to justify the methodology. The results of this study show that when the two HDR dampers are installed close to each other on the same end of the cable, some interaction between the dampers leads to reduced damping ratio. When the dampers are on the opposite ends of the cable, they are effective in increasing damping ratio and can provide better vibration reduction to multiple modes.

• Smart Structures and Systems
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• v.15 no.5
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• pp.1293-1309
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• 2015

3D two adjacent buildings with different heights founded in different kinds of soil connected with viscous dampers groups, with especial arrangement in plane, were investigated. Soil structure interaction for three different kinds of soil (stiff, medium and soft) were modeled as 3D Winkler model to give the realistic behavior of adjacent buildings connected with viscous dampers under various earthquake excitations taking in the account the effect of different kinds of soil beneath the buildings, using SAP2000n to model the whole system. A range of soil properties and soil damping characteristics are chosen which gives broad picture of connected structures system behavior resulted from the influence soil-structure interaction. Its conclusion that the response of connected structures system founded on soft soil are more critical than those founded on stiff soil. The behavior of connected structures is different from those with fixed base bigger by nearly 20%, and the efficiency of viscous dampers connecting the two adjacent buildings is reduced by nearly 25% less than those founded on stiff soil.

• Earthquakes and Structures
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• v.17 no.2
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• pp.143-162
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• 2019

Motivated by a simpler and more compact hybrid active tuned mass damper (ATMD) system with wide frequency spacing (i.e., high robustness) but not reducing the effectiveness using the least number of ATMD units, the active tuned tandem mass dampers (ATTMD) have been proposed to attenuate undesirable oscillations of structures under the ground acceleration. Likewise, it is expected that the frequency spacing of the ATTMD is comparable to that of the active multiple tuned mass dampers (AMTMD) or the multiple tuned mass dampers (MTMD). In accordance with the mode generalised system in the specific vibration mode being controlled (simply referred herein to as the structure), the closed-form expression of the dimensionless displacement variances has been derived for the structure with the attached ATTMD. The criterion for the optimum searching may then be determined as minimization of the dimensionless displacement variances. Employing the gradient-based optimization technique, the effects of varying key parameters on the performance of the ATTMD have been scrutinized in order to probe into its superiority. Meanwhile, for the purpose of a systematic comparison, the optimum results of two active tuned mass dampers (two ATMDs), two tuned mass dampers (two TMDs) without the linking damper, and the TTMD are included into consideration. Subsequent to work in the frequency domain, a real-time Simulink implementation of dynamic analysis of the structure with the ATTMD under earthquakes is carried out to verify the findings of effectiveness and stroke in the frequency domain. Results clearly show that the findings in the time domain support the ones in the frequency domain. The whole work demonstrates that ATTMD outperforms two ATMDs, two TMDs, and TTMD. Thereinto, a wide frequency spacing feature of the ATTMD is its highlight, thus deeming it a high robustness control device. Furthermore, the ATTMD system only needs the linking dashpot, thus embodying its simplicity.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.09a
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• pp.239-246
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• 2002

Viscoelastic dampers are known effective devices for response reduction under earthquakes and winds. This study addresses how to design the optimum viscoelastic dampers installed at the full scale five-story steel building and novel approach to carry out the experimental work to verify the damper performance. First, an exciter of hybrid mass-type actuator is designed, which can move the building and its mathematical model is derived. The integrated system of building-actuator is experimentally analyzed for mathematical model. Second, convex model is applied for the prediction of required additional damping ratios to reduce responses below a specified target level. Chevron-type viscoelastic dampers are manufactured and installed at the first and second inter-stories, which are optimum places for response reduction. Sine-sweep and white noise excitations, which are generated by the hybrid mass-type actuator, are applied to the full scale building without and with dampers for performance verification. The transfer function of the building with four dampers, two of them installed at each first and second inter-story, are found to be lower than that of the building with two dampers installed at the first inter-story

• Smart Structures and Systems
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• v.18 no.1
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• pp.53-74
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• 2016

This paper presents an experimental study on constructing a tunable secondary suspension for high-speed trains using magneto-rheological fluid dampers (referred to as MR dampers hereafter), in the interest of improving lateral ride comfort. Two types of MR dampers (type-A and type-B) with different control ranges are designed and fabricated. The developed dampers are incorporated into a secondary suspension of a full-scale high-speed train carriage for rolling-vibration tests. The integrated rail vehicle runs at a series of speeds from 40 to 380 km/h and with different current inputs to the MR dampers. The dynamic performance of the two suspension systems and the ride comfort rating of the rail vehicle are evaluated using the accelerations measured during the tests. In this way, the effectiveness of the developed MR dampers for attenuating vibration is assessed. The type-A MR dampers function like a stiffness component, rather than an energy dissipative device, during the tests with different running speeds. While, the type-B MR dampers exhibit significant damping and high current input to the dampers may adversely affect the ride comfort. As part of an ongoing investigation on devising an effective MR secondary suspension for lateral vibration suppression, this preliminary study provides an insight into dynamic behavior of high-speed train secondary suspensions and unique full-scale experimental data for optimal design of MR dampers suitable for high-speed rail applications.

• Structural Monitoring and Maintenance
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• v.10 no.4
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• pp.361-379
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• 2023

In cable structure maintenance, particularly for cable-stayed bridges, cable safety assessment relies on estimating cable tension. Conventionally, in Japan, cable tension is estimated from the natural frequencies of the cable using the higher-order vibration method. In recent years, dampers have been installed on cables to reduce cable vibrations. Because the higher-order vibration method is a method for damper-free cables, the damper must be removed to measure the natural frequencies of a cable without a damper. However, cables on some cable-stayed bridges have two dampers: one on the girder side and another on the tower side. Notably, removing and reinstalling the damper on the tower side are considerably more time- and labor-intensive. This paper introduces a tension estimation method for cables with two dampers, using natural frequencies. The proposed method was validated through numerical simulation and experiment. In the numerical tests, without measurement error in the natural frequencies, the maximum estimation error among 100 models was 3.3%. With measurement error of 2%, the average estimation error was within 5%, with a maximum error of 9%. The proposed method has high accuracy because the higher-order vibration method for a damper-free cable still has an estimation error of 5%. The experimental verification emphasizes the importance of accurate damper modeling, highlighting potential discrepancies between existing damper design formula and actual damper behavior. By revising the damper formula, the proposed method achieved accurate cable tension estimation, with a maximum estimation error of approximately 10%.

• 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.5 no.3
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• pp.261-276
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• 2013

Oil, hysteretic and inertial mass dampers are representatives of passive dampers used for smart enhancement of seismic performance of building structures. Since oil dampers have a nonlinear relief mechanism and hysteretic dampers possess nonlinear restoring-force characteristics, several difficulties arise in the evaluation of buildings including such dampers. The purpose of this paper is to propose a practical method for simultaneous optimal use of such dampers. The optimum design problem is formulated so as to minimize the maximum interstory drift under design earthquakes in terms of a set of damper quantities subject to an equality constraint on the total cost of dampers. The proposed method to solve the optimum design problem is a successive procedure which consists of two steps. The first step is a sensitivity analysis by using nonlinear time-history response analyses, and the second step is a modification of the set of damper quantities based upon the sensitivity analysis. Numerical examples are conducted to demonstrate the effectiveness and validity of the proposed design method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.980-985
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• 2008

This paper presents vehicle road test of a semi-active suspension system equipped with continuously controllable magnetorheological (MR) dampers. As a first step, front and rear MR dampers are designed and manufactured based on the optimized damping force levels and mechanical dimensions required for a commercial middle-sized passenger vehicle. After experimentally evaluating dynamic characteristics of the MR dampers, the test vehicle is prepared for road test by integrating current suppliers, real-time data acquisition system and numerous sensors such as accelerometer and gyroscope. Subsequently, the manufactured four MR dampers (two for front parts and two for rear parts) are incorporated with the test vehicle and a skyhook control algorithm is formulated and realized in the data acquisition system. In order to emphasize practical aspect of the proposed MR suspension system, road tests are undertaken on proving grounds: bump and paved roads. The control responses are evaluated in both time and frequency domains by activating the MR dampers.