• Earthquakes and Structures
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• v.18 no.3
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• pp.313-320
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• 2020

The usage of conventional tuned mass damper (TMD) was proved as an effective method for passive mitigating vortex-induced vibration (VIV) of a bridge deck. Although a variety of linear TMD systems have been so far utilized for vibration control of suspension bridges, a sensitive TMD mechanism to wind spectrum frequency is lacking. Here, we introduce a bistable tuned mass damper (BTMD) mechanism which has an exceptional sensitivity to a broadband input of vortex shedding velocity for suppressing VIV in suspension bridge deck. By use of the Monte Carlo simulation, performance of the nonlinear BTMD is shown to be more efficient than the conventional linear TMD under two different wind load excitations of harmonic (sinusoidal) and broadband input of vortex shedding. Consequently, an appropriate algorithm is proposed to optimize the design parameters of the nonlinear BTMD for Kap Shui Mun Bridge, and then the BTMD system is localized for the interior deck of the suspension bridge.

• Structural Engineering and Mechanics
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• v.83 no.1
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• pp.31-43
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• 2022

A nonlinear gas-spring tuned mass damper is proposed to mitigate the seismic responses of the multi-degree-of-freedom (MDOF) structure, in which the nine-story benchmark model is selected as the controlled object. The nonlinear mechanical properties of the gas-spring are investigated through theoretical analysis and experiments, and the damper's control parameters are designed. The control performance and damping mechanism of the proposed damper attached to the MDOF structure are systematically studied, and its reliability is also explored by parameter sensitivity analysis. The results illustrate that the nonlinear gas-spring TMD can transfer the primary structure's vibration energy from the lower to the higher modes, and consume energy through its own relative movement. The proposed damper has excellent "Reconciling Control Performance", which not only has a comparable control effect as the linear TMD, but also has certain advantages in working stroke. Furthermore, the control parameters of the gas-spring TMD can be determined according to the external excitation amplitude and the gas-spring's initial volume.

• Earthquakes and Structures
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• v.24 no.4
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• pp.247-258
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• 2023

Multiple pounding tuned rolling mass damper (MPTRMD) distributed in the cavity of voided slabs is proposed to passively control multi-story frame structures, which disperses the mass of the oscillator to multiple dampers so that the control device can be miniaturized without affecting the vibration control performance. The mechanism and the differential motion equations of the MPTRMD-controlled multi-degree-of-freedom system are derived based on the Lagrange principle. Afterward, this advanced RMD is applied to a simplified 20-floor steel frame to evaluate the seismic control performance in the numerical analysis. A four-storey frame structure equipped with MPTRMD is then taken for a shaking table test to verify its effectiveness of control performance. The pounding mechanism has been detailed studied numerically and experimentally as well. The numerical and experimental results show that the proposed damper is practically promising not only for its prominent control performance but also for its lightweight and space-saving. Additionally, the pounding mechanism influenced by the variable impact parameters exhibits a balance between the two effects of motional limitations and energy dissipation.

• International Journal of High-Rise Buildings
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• v.5 no.3
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• pp.167-176
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• 2016

This paper describes a large tuned mass damper (TMD) developed as an effective seismic control device for an existing highrise building. To realize this system, two challenges needed to be overcome. One was how to support a huge mass that has to move in any direction, and the second was how to control mass displacement that reaches up to two meters. A simple pendulum mechanism with strong wires was adopted to solve the first problem. As a solution to the important latter problem, we developed a high-function oil damper with a unique hydraulic circuit. When the mass velocity reaches a certain value, which was predetermined by considering the permissible displacement, the damper automatically and drastically increases its damping coefficient and limits the mass velocity. This velocity limit function can effectively and stably control the mass displacement without any external power. This paper first examines the requirements of the TMD using a simple model and clarifies the constitution of the actual TMD system. Then the seismic upgrading project of an existing high-rise building is outlined, and the developed TMD system and the results of performance tests are described. Finally, control effects for design earthquakes are demonstrated through response analyses and construction progress is introduced.

• Wind and Structures
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• v.30 no.6
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• pp.663-678
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• 2020

Robust semi-active vibration control of wind turbines using tuned mass dampers (TMDs) is a promising technique. This study investigates a 1.5 megawatt wind turbine controlled by eight different types of tuned mass damper systems of equal mass: a passive TMD, a semi-active varying-spring TMD, a semi-active varying-damper TMD, a semi-active varying-damper-and-spring TMD, as well as these four damper systems paired with an additional smaller passive TMD near the mid-point of the tower. The mechanism and controllers for each of these TMD systems are explained, such as employing magnetorheological dampers for the varying-damper TMD cases. The turbine is modelled as a lumped-mass 3D finite element model. The uncontrolled and controlled turbines are subjected to loading and operational cases including service wind loads on operational turbines, seismic loading with service wind on operational turbines, and high-intensity storm wind loads on parked turbines. The displacement and acceleration responses of the tower at the first and second mode shape maxima were used as the performance indicators. Ultimately, it was found that while all the semi-active TMD systems outperformed the passive systems, it was the semi-active varying-damper-and-spring system that was found to be the most effective overall - capable of controlling vibrations about as effectively with only half the mass as a passive TMD. It was also shown that by reducing the mass of the TMD and adding a second smaller TMD below, the vibrations near the mid-point could be greatly reduced at the cost of slightly increased vibrations at the tower top.

• Smart Structures and Systems
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• v.13 no.2
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• pp.203-217
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• 2014

Due to the shift in paradigm from passive control to adaptive control, smart tuned mass dampers (STMDs) have received considerable attention for vibration control in tall buildings and bridges. STMDs are superior to tuned mass dampers (TMDs) in reducing the response of the primary structure. Unlike TMDs, STMDs are capable of accommodating the changes in primary structure properties, due to damage or deterioration, by tuning in real time based on a local feedback. In this paper, a novel adaptive-length pendulum (ALP) damper is developed and experimentally verified. Length of the pendulum is adjusted in real time using a shape memory alloy (SMA) wire actuator. This can be achieved in two ways i) by changing the amount of current in the SMA wire actuator or ii) by changing the effective length of current carrying SMA wire. Using an instantaneous frequency tracking algorithm, the dominant frequency of the structure can be tracked from a local feedback signal, then the length of pendulum is adjusted to match the dominant frequency. Effectiveness of the proposed ALP-STMD mechanism, combined with the STFT frequency tracking control algorithm, is verified experimentally on a prototype two-storey shear frame. It has been observed through experimental studies that the ALP-STMD absorbs most of the input energy associated in the vicinity of tuned frequency of the pendulum damper. The reduction of storey displacements up to 80 % when subjected to forced excitation (harmonic and chirp-signal) and a faster decay rate during free vibration is observed in the experiments.

• Smart Structures and Systems
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• v.15 no.6
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• pp.1625-1642
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• 2015

We propose an electrically self-reliant structural health monitoring (SHM) system that is able to wirelessly transmit sensing data using electrical power generated by vibration without the need for additional external power sources. The provision of reliable electricity to wireless SHM systems is a highly important issue that has often been ignored, and to expand the applicability of various wireless SHM innovations, it will be necessary to develop comprehensive wireless SHM devices including stable electricity sources. In light of this need, we propose a new, highly efficient vibration-powered generator based on a tuned-mass-damper (TMD) mechanism that is quite suitable for vibration-based SHM. The charging time of the TMD generator is shorter than that of conventional generators based on the impedance matching method, and the proposed TMD generator can harvest 16 times the amount of energy that a conventional generator can. The charging time of an SHM wireless transmitter is quantitatively formulated. We conduct wireless monitoring experiments to validate a wireless SHM system composed of a self-reliant SHM and a vibration-powered TMD generator.

• Structural Engineering and Mechanics
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• v.86 no.4
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• pp.573-587
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• 2023

A conventional tuned mass damper (TMD) provides a passive control option to suppress the structures' wind- or earthquake-induced vibrations. However, excessive displacements of the TMD raise concerns in the practical implementation. Therefore, this study proposes a novel TMD designed for and deployed on a high-rise sightseeing tower. The device consists of an integrated two-way slide rail mount and an eddy current damper (ECD) with a stroke control mechanism. This stroke control mechanism allows the damping coefficient to automatically increase when the stroke reaches a predetermined value, preventing excessive damper displacements during large earthquakes. The corresponding two-stage damping parameters are designed with a variable-thickness copper plate to enable the TMD stroke within a specified range. Thus, this study discusses the detailed design schemes of the device components in TMD. The designed two-stage damping parameters are also numerically verified, and the structural responses with/without the TMD are compared. As seen in the results, the proposed TMD yields effective control authority to limit the acceleration response within a comfort level. In addition, this TMD resolves the spatial availability for the damper movement in high-rise buildings by the controllable damping mechanism.

• Structural Engineering and Mechanics
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• v.72 no.6
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• pp.747-762
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• 2019

Based on the ball-screw mechanism, a tuned viscous mass damper (TVMD) has been proposed, which has functions of amplifying physical mass of the system and frequency tuning. Considering the sensitivity of a single TVMD's effectiveness to frequency mistuning like that of the conventional tuned mass damper (TMD) and according to the concept of the conventional multiple tuned mass damper (MTMD), in the present paper, multiple tuned mass viscous dampers (MTVMD) consisting of many tuned mass dampers (TVMD) with a uniform distribution of natural frequencies are considered for attenuating undesirable vibration of a structure. The MTVMD is manufactured by keeping the stiffness and damping constant and varying the mass associated with the lead of the ball-screw type inerter element in the damper. The structure is represented by its mode-generalized system in a specific vibration mode controlled using the mode reduced-order method. Modal properties and fundamental characteristics of the MTVMD-structure system are investigated analytically with the parameters, i.e., the frequency band, the average damping ratio, the tuning frequency ratio, the total number of TVMD and the total mass ratio. It is found that there exists an optimum set of the parameters that makes the frequency response curve of the structure flattened with smaller amplitudes in a wider input frequency range. The effectiveness and robustness of the MTVMD are also discussed in comparison with those of the usual single TVMD (STVMD) and the results shows that the MTVMD is more effective and robust with the same level of total mass.

• Earthquakes and Structures
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• v.12 no.4
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• pp.425-436
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• 2017

Vibration control using a tuned mass damper (TMD) is an effective technique that has been verified using analytical methods and experiments. It has been applied in mechanical, automotive, and structural applications. However, the damping of a TMD cannot be adjusted in real time. An excessive mass damper stroke may be introduced when the mass damper is subjected to a seismic excitation whose frequency content is within its operation range. The semi-active tuned mass damper (SATMD) has been proposed to solve this problem. The parameters of an SATMD can be adjusted in real time based on the measured structural responses and an appropriate control law. In this study, a stiffness-controllable TMD, called a leverage-type stiffness-controllable mass damper (LSCMD), is proposed and fabricated to verify its feasibility. The LSCMD contains a simple leverage mechanism and its stiffness can be altered by adjusting the pivot position. To determine the pivot position of the LSCMD in real time, a discrete-time direct output-feedback active control law that considers delay time is implemented. Moreover, an identification test for the transfer function of the pivot driving and control systems is proposed. The identification results demonstrate the target displacement can be achieved by the pivot displacement in 0-2 Hz range and the control delay time is about 0.1 s. A shaking-table test has been conducted to verify the theory and feasibility of the LSCMD. The comparisons of experimental and theoretical results of the LSCMD system show good consistency. It is shown that dynamic behavior of the LSCMD can be simulated correctly by the theoretical model and that the stiffness can be properly adjusted by the pivot position. Comparisons of experimental results of the LSCMD and passive TMD show the LSCMD with less demand on the mass damper stroke than that for the passive TMD.