The objective of this study is to develop a numerical model of a stay cable interacted with deck, and to examine the
vibration suppression technique of the stayed cable subject to external loading. First, a numerical model based on the
finite difference method and the finite element method has been developed to simulate the effects of the bending
stiffness and its sag-extensibility characteristics of the cable. Accurate vibration mode shapes and modal frequency of
the interaction between stay cable and deck are examined. For the vibration control of cable, a MR-damper is used as
control device. This damper can be achieved either through the passive control strategy or the semi-active control
strategy employing decentralized sliding mode control (DSMC) and maximum energy dissipation (MED) on the staycable.
To verify this study, a scaled-down cable structure is designed and constructed in NCREE, Taiwan. A small
shaker is designed and mounted onto the cable to generate the sinusoid excitation with different amplitudes and
frequencies. Dynamic characteristics of the cable-deck system are identified and the system model is developed for
control purpose. The DSMC algorithm using MR damper was studied to reduce the cable vibration under different
Proc. SPIE. 7292, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2009
KEYWORDS: Numerical simulations, Control systems, Data acquisition, Vibration control, Finite element methods, System identification, Bridges, Feedback control, Control systems design, Performance modeling
This paper presents the numerical simulation and experimental verification of a semi-active cable vibration control
system. The finite-element analysis "ABAQUS" is used to design and simulate the dynamic characteristics of a cable
structure. The system matrixes 'M', 'C' and 'K' of the simplified cable model is then generated from the finite element
model. A 3 kN MR damper, made by Lord co., is connected to the cable to reduce the vibration. Through a systematic
performance test and system identification procedure, the modified Bou-Wen model is generated to represent the
nonlinear behavior of the MR damper. According to the simplified cable model and MR damper model, the LQG with
continuously-optimal control is used to design the semi-active control system. The scaled-down cable structure is design
and builds according to the finite-element model in ABAQUS. Suitable mass and cable force are added to make the cable
vibration more realistic. A small shaker is designed and mounted onto the cable to generate the excitations with different
amplitudes and frequencies. Both passive and semi-active control cases have been tested. Through the numerical
simulation and experimental test results, the semi-active cable vibration control system with MR damper can reduce the
cable vibration well under different kinds of excitations. This investigation demonstrates the feasibility and capabilities
of a cable vibration control system with MR damper.
Critical non-structural equipment, including life-saving equipment in hospitals, circuit breakers, computers, high technology instrumentations, etc., are venerable tostrong earthquakes, and the failure of these equipments may result in a heavy economic loss. In this connection, innovative control systems and strategies are needed for their seismic protections. This paper presents the performance evaluation of passive and semi-active control in the equipment isolation system for earthquake protection. Through shaking table tests of a 3-story steel frame with equipment on the 1<sup>nd</sup> floor, a MR-damper together with a sliding friction pendulum isolation system is placed between the equipment and floor to reduce the vibration of the equipment. Various control algorithms are used for this semi-active control studies, including the decentralized sliding mode control (DSMC) and LQR control. The passive-on and passive-off control of MR damper is used as a reference for the discussion on the control effectiveness.
This paper presents the structural control results of shaking table tests for a steel frame structure in order to evaluate
the performance of a number of proposed semi-active control algorithms using multiple magnetorheological (MR) dampers. The test structure is a six-story steel frame equipped with MR-dampers. Four different cases of damper arrangement in the structure are selected for the control study. In experimental tests, an EL Centro earthquake, a Kobe earthquake and a Chi-Chi earthquake (station TCU067) are used as ground excitations. Various control algorithms are used for this semi-active control studies, including the Decentralized Sliding Mode Control (DSMC), LQR control and passive-on and passive-off control. Each algorithm is formulated specifically for the use of MR-dampers. Additionally, each algorithm uses measurements of the absolute acceleration and the device velocity for the determination of the control action to ensure that the algorithm can be implemented on a physical structure. The performance of each algorithm is evaluated based on the results of shaking table tests, and the advantages of each algorithm is compared and discussed. The reduction of the story drift and acceleration throughout the structure is examined.
The mitigation of torsional responses in structures using semi-active devices is pursued in the current study. Multiple
magnetorheological (MR) dampers are employed for real-time control of response of a benchmark structure to
earthquake excitations. MR damper resistance levels are intelligently managed by a global fuzzy logic controller (FLC).
The FLC is generated using a controlled-elitist genetic algorithm (GA). Development of an optimal FLC is expedited by
a discretized search space of fuzzy logic membership functions. To enable robust control a training excitation is created
using the RSPMatch2005 algorithm which modifies historic ground records in the time-domain by wavelet operations.
Both numerical and large-scale experimental efforts are undertaken to validate the proposed control system. Results
show the GA-optimized FLC performs superior to passive operation in 42% of considered cases.
Proc. SPIE. 6932, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2008
KEYWORDS: Mathematical modeling, Control systems, Electroluminescence, Earthquakes, Near field, System identification, Adaptive control, Optical isolators, Fuzzy logic, Voltage controlled current source
This paper presents the performance evaluation of a semi-active controlled floor isolation system for earthquake
reduction. The floor isolation system consists of a rolling pendulum system and a semi-active controlled MR damper.
The modified Bouc-Wen model is used to represent the behavior of the MR damper. A serious of performance test of the
MR damper is made and been used for system identification. Two contrasting control methods including LQR with
continuous-optimal control and Fuzzy Logic control are experimentally investigated as potential algorithms and
comparisons are made from the results. Unlike the clipped-optimal control, LQR with continuous-optimal control can
output the continuous command voltage to control the MR damper, and get smoother control effect. A three-story steel
structure with the floor isolation system on the 2nd floor is tested on the shake table. Scaled historical near- and far-field
seismic records are employed to examine controller performance with respect to frequency content and PGA level.
Experimental results show that both control algorithms can suppress the acceleration of the isolated floor during small
and large PGA levels, and alleviate both displacement and acceleration simultaneously in larger, near-field events. Both
control algorithms are adaptive and robust to various intensity of excitation. This investigation demonstrates the
feasibility and capabilities of a smart semi-active controlled floor-isolation system.
This study examines the potential use of wireless communication and embedded computing technologies within realtime
structural control applications. Based on the implementation of the prototype WiSSCon system in a three story steel
test structure with significant eccentricity, the centralized control architecture is implemented to mitigate the lateral and
torsional response of the test structure using two MR dampers installed in the first story. During the test, a large
earthquake time history is applied (El Centro earthquake) at the structure base using a shaking table. Three major
performance attributes of the wireless control system were examined: (1) validation of the reliability of wireless
communications for real-time structural control applications, (2) validation of a modified exponential damper model
embedded in the wireless sensors to operate the MR dampers, and (3) exploration of control effectiveness when using
WiSSCon in a centralized architectural configuration.
An extensive program of full-scale ambient vibration testing has been conducted to measure the dynamic response of a 240 meter cable-stayed bridge - Gi-Lu Bridge in Nan-Tou County, Taiwan. A MEMS-based wireless sensor system and a traditional microcomputer-based system were used to collect and analyze ambient vibration data. A total of four bridge modal frequencies and associated mode shapes were identified for cables and the deck structure within the frequency range of 0~2Hz. The experimental data clearly indicated the occurrence of many closely spaced modal frequencies. Most of the deck modes were found to be associated with the cable modes, implying a considerable interaction between the deck and cables. The results of the ambient vibration survey were compared to modal frequencies and mode shapes computed using three-dimensional finite element modeling of the bridge. For most modes, the analytical and the experimental modal frequencies and mode shapes compare quite well. Based on the findings of this study, a linear elastic finite element model for deck structures and beam element with P-Delta effect for the cables appear to be capable of capturing much of the complex dynamic behavior of the bridge with good accuracy.