• Journal of Korean Association for Spatial Structures
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• v.6 no.3 s.21
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• pp.59-67
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• 2006

A conventional passive TMD is only effective when it is tuned properly. In many practical applications, inevitable off-tuning of a TMD occurs because the mass in a building floor could change by moving furnishings, people gathering, etc. when TMDs are offtuned, TMDs their effectiveness is sharply reduced. Moreover, the off-tuned nTMDs can excessively amplify the vibration levels of the primary structures. This paper discusses the application of a new class of MR damper, for the reduction of floor vibrations due to machine and human movements. The STMD introduced uses a MR damper called to semi-active damper to achieve reduction in the floor vibration. Here, the STMD and the groundhook algorithm are applied to a single degree of freedom system representative of building floors. The performance or the STMD is compared to that or the equivalent passive TMD. In addition, the effects of off-tuning due to variations in the mass of the floor system. Comparison of the results demonstrates the efficiency and robustness or STMD with respect to equivalent TMD.

• Journal of Korean Association for Spatial Structures
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• v.21 no.1
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• pp.79-86
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• 2021

Control performance of a smart tuned mass damper (TMD) mainly depends on control algorithms. A lot of control strategies have been proposed for semi-active control devices. Recently, machine learning begins to be applied to development of vibration control algorithm. In this study, a reinforcement learning among machine learning techniques was employed to develop a semi-active control algorithm for a smart TMD. The smart TMD was composed of magnetorheological damper in this study. For this purpose, an 11-story building structure with a smart TMD was selected to construct a reinforcement learning environment. A time history analysis of the example structure subject to earthquake excitation was conducted in the reinforcement learning procedure. Deep Q-network (DQN) among various reinforcement learning algorithms was used to make a learning agent. The command voltage sent to the MR damper is determined by the action produced by the DQN. Parametric studies on hyper-parameters of DQN were performed by numerical simulations. After appropriate training iteration of the DQN model with proper hyper-parameters, the DQN model for control of seismic responses of the example structure with smart TMD was developed. The developed DQN model can effectively control smart TMD to reduce seismic responses of the example structure.

• Journal of Korean Association for Spatial Structures
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• v.17 no.3
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• pp.107-115
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• 2017

In this paper, a structural design method of a smart tuned mass damper (TMD) for a retractable-roof spatial structure under earthquake excitation was proposed. For this purpose, a retractable-roof spatial structure was simplified to a single degree of freedom (SDOF) model. Dynamic characteristics of a retractable-roof spatial structure is changed based on opened or closed roof condition. This condition was considered in the numerical simulation. A magnetorheological (MR) damper was used to compose a smart TMD and a displacement based ground-hook control algorithm was used to control the smart TMD. The control effectiveness of a smart TMD under harmonic and earthquake excitation were evaluated in comparison with a conventional passive TMD. The vibration control robustness of a smart TMD and a passive TMD were compared along with the variation of natural period of a simplified structure. Dynamic responses of a smart TMD and passive TMD under resonant harmonic excitation and earthquake load were compared by varying mass ratio of TMD to total mass of the simplified structure. The design procedure proposed in this study is expected to be used for preliminary design of a smart TMD for a retractable-roof spatial structure.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.26 no.1
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• pp.69-77
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• 2013

When structural design of a tall building is conducted, reduction of wind-induced lateral displacement is one of the most important problem. For this purpose, additional dampers and vibration control devices are generally considered. In this process, control performance of additional devices are usually investigated for optimal design without variation of characteristics of a structure. In this study, multi-objective integrated optimization of structure-smart control device is conducted and possibility of reduction of structural resources of a tall building with additional smart damping device has been investigated. To this end, a 60-story diagrid building structure is used as an example structure and artificial wind loads are used for evaluation of wind-induced responses. An MR damper is added to the conventional TMD to develop a smart TMD. Because dynamic responses and the amount of structural material and additional smart damping devices are required to be reduced, a multi-objective genetic algorithm is employed in this study. After numerical simulation, various optimal designs that can satisfy control performance requirement can be obtained by appropriately reducing the amount of structural material and additional smart damping device.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.2 s.54
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• pp.57-68
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• 2007

The mega frame system is becoming popular for the design and construction of skyscrapers because this system exhibits structural efficiency by allowing high rigidity of the structure while minimizing the amount of structural materials to be used. Since the mega frame system is usually adopted for super high-rise buildings, the comfort of occupants may be main concerns in the practical application of this system. For the enhancement of the serviceability of mega frame structures, a semi-active tuned mass damper (STMD) is developed in this study. To this end, a Magnetorheological (MR) damper is employed replacing passive damper as a semi-active damper to improve the control effect of a conventional TMD. Since a conventional finite element model of mega frame structures has significant numbers of DOFs, numerical simulation for investigation of control performances of a STMD is impossible by using the full-order model. Therefore, a reduced-order system using minimal DOFs, which can accurately represent the dynamic behavior of a mega frame structure, is proposed in this study through the matrix condensation technique To improve the efficiency of the matrix condensation technique, multi-level matrix condensation technique is proposed using the structural characteristics of mega frame structures. The efficiency and accuracy of the reduced-order control proposed in this study and the control performance of a STMD were verified using example structures.

• International journal of steel structures
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• v.18 no.5
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• pp.1598-1606
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• 2018

An integrated optimal structural design method for a diagrid structure and control device was developed. A multi-objective genetic algorithm was used and a 60-story diagrid building structure was developed as an example structure. Artificial wind and earthquake loads were generated to assess the wind-induced and seismic responses. A smart tuned mass damper (TMD) was used as a structural control system and an MR (magnetorheological) damper was employed to develop a smart TMD (STMD). The multi-objective genetic algorithm used five objectives including a reduction of the dynamic responses, additional stiffness and damping, mass of STMD, capacity of the MR damper for the integrated optimization of a diagrid structure and a STMD. From the proposed method, integrated optimal designs for the diagrid structure and STMD were obtained. The numerical simulation also showed that the STMD provided good control performance for reducing the wind-induced and seismic responses of a tall diagrid building structure.

• Journal of Korean Association for Spatial Structures
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• v.15 no.2
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• pp.105-112
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• 2015

A shared tuned mass damper (STMD) was proposed in previous research for reduction of dynamic responses of the adjacent buildings subjected to earthquake loads. A single STMD can provide similar control performance in comparison with two traditional TMDs. In previous research, a passive damper was used to connect the STMD with adjacent buildings. In this study, a smart magnetorheological (MR) damper was used instead of a passive damper to compose an adaptive smart STMD (ASTMD). Control performance of the ASTMD was investigated by numerical analyses. For this purpose, two 8-story buildings were used as example structures. Multi-input multi-output (MIMO) fuzzy logic controller (FLC) was used to control the command voltages sent to two MR dampers. The MIMO FLC was optimized by a multi-objective genetic algorithm. Numerical analyses showed that the ASTMD can effectively control dynamic responses of adjacent buildings subjected to earthquake excitations in comparison with a passive STMD.

• Journal of Korean Association for Spatial Structures
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• v.22 no.2
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• pp.39-46
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• 2022

Recently, machine learning is widely used to solve optimization problems in various engineering fields. In this study, machine learning is applied to development of a control algorithm for a smart control device for reduction of seismic responses. For this purpose, Deep Q-network (DQN) out of reinforcement learning algorithms was employed to develop control algorithm. A single degree of freedom (SDOF) structure with a smart tuned mass damper (TMD) was used as an example structure. A smart TMD system was composed of MR (magnetorheological) damper instead of passive damper. Reward design of reinforcement learning mainly affects the control performance of the smart TMD. Various hyper-parameters were investigated to optimize the control performance of DQN-based control algorithm. Usually, decrease of the time step for numerical simulation is desirable to increase the accuracy of simulation results. However, the numerical simulation results presented that decrease of the time step for reward calculation might decrease the control performance of DQN-based control algorithm. Therefore, a proper time step for reward calculation should be selected in a DQN training process.

• Journal of Korean Association for Spatial Structures
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• v.22 no.3
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• pp.49-56
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• 2022

Tuned mass damper (TMD) is widely used to reduce dynamic responses of structures subjected to earthquake loads. A smart tuned mass damper (STMD) was proposed to increase control performance of a traditional passive TMD. A lot of research was conducted to investigate the control performance of a STMD based on analytical method. Experimental study of evaluation of control performance of a STMD was not widely conducted to date. Therefore, seismic response reduction capacity of a STMD was experimentally investigated in this study. For this purpose, a STMD was manufactured using an MR (magnetorheological) damper. A simple structure presenting dynamic characteristics of spacial roof structure was made as a test structure. A STMD was made to control vertical responses of the test structure. Two artificial ground motions and a resonance harmonic load were selected as experimental seismic excitations. Shaking table test was conducted to evaluate control performance of a STMD. Control algorithms are one of main factors affect control performance of a STMD. In this study, a groundhook algorithm that is a traditional semi-active control algorithm was selected. And fuzzy logic controller (FLC) was used to control a STMD. The FLC was optimized by multi-objective genetic algorithm. The experimental results presented that the TMD can effectively reduce seismic responses of the example structures subjected to various excitations. It was also experimentally shown that the STMD can more effectively reduce seismic responses of the example structures conpared to the passive TMD.

• Earthquakes and Structures
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• v.4 no.1
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• pp.63-84
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• 2013

A semi-active mass damping (SMD) system with magnetorheological (MR) dampers focusing on low- and mid-rise buildings is proposed in this paper. The main purpose of this study is to integrate the reliable characteristics of the traditional tuned mass damper (TMD) and the superior performance of the active mass damper (AMD) to the new system. In addition, the commonly seen solution of deploying dense seismic dampers throughout the structure nowadays to protect the main structure is also expected to switch to the developed SMD system on the roof with a similar reduction performance. In order to demonstrate this concept, a full-size three-story steel building representing a typical mid-rise building was used as the benchmark structure to verify its performance in real life. A numerical model with the interpolation technique integrated was first established to accurately predict the behavior of the MR dampers. The success of the method was proven through a performance test of the designated MR damper used in this research. With the support of the MR damper model, a specific control algorithm using a continuous-optimal control concept was then developed to protect the main structure while the response of the semi-active mass damper is discarded. The theoretical analysis and the experimental verification from a shaking table test both demonstrated the superior mitigation ability of the method. The proposed SMD system has been demonstrated to be readily implemented in practice.