Pei-Yang Lin

A comparative study in the semi-active control of isolated structures

A comparative analytical and experimental study of several algorithms for the control of seismically excited floor- and base-isolated structures is pursued in the current study. A hybrid isolation system that is comprised of a bidirectional roller–pendulum system (RPS) and augmented by controllable magnetorheological (MR) dampers is proposed to reduce the potential for damage to structures and sensitive equipment. Bidirectional motions are intelligently ameliorated in real time by the modulation of MR damper resistance. A Bouc–Wen model is adopted in numerical and experimental trials to predict behavior of the MR dampers. Three contrasting control techniques are examined. They include neural network control, LQR/clipped optimal control with variable gains and fuzzy logic control. Each control scheme is a candidate for mitigating the response of a superstructure to near- and far-field seismic loadings. Minimization of displacement and acceleration responses of the structure are considered in the formulation of each approach to control. Results of the numerical and large-scale experimental efforts reveal that the response of the isolated structure is effectively alleviated by all of the considered control methods, although they do not perform equally well. The LQR/clipped optimal controller with variable gains is superior to the other controllers in 50% of the investigated cases, while the fuzzy logic controller performs well for earthquakes with large accelerations. Neural network control is found to be effective in minimizing the acceleration of the superstructure that is subject to moderate excitation.

Decentralized sliding mode control of a building using MR dampers

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, the El Centro earthquake and Kobe earthquake ground motion data are used as excitations. Further, several decentralized sliding mode control algorithms are developed in this paper specifically for applications of MR dampers in building structures. Various control algorithms are used for the semi-active control studies, including the proposed decentralized sliding mode control (DSMC), LQR control, and passive-on and passive-off control. Each control algorithm is formulated specifically for the use of MR dampers installed in building structures. Additionally, each algorithm uses measurements of the device velocity and device drift for the determination of the control action to ensure that the algorithm can be implemented in a physical structure. The performance of each algorithm is evaluated based on the results of shaking table tests, and the advantages of each algorithm are compared and discussed. The reduction of story drifts and floor accelerations throughout the structure is examined.

Design of dampers for structures based on optimal control theory

SUMMARY The aim of this paper was to propose a design guideline for using visco-elastic dampers for the control of building structures subjected to earthquake loading as well as suspension roof structures subjected to wind loading. The active control algorithm was used to calculate the control forces. Based on the single-mode approach the control forces were transformed to the forces which visco-elastic dampers can provide. Application of the method to the design of the building structure with passive damping devices in the bracing system and to the suspension roof with dampers was studied. Through the application of optimal control theory a systematic design procedure to implement dampers in structures is proposed. Copyright ( 2000 John Wiley & Sons, Ltd.

Structural damage diagnosis based on on-line recursive stochastic subspace identification

This paper presents a recursive stochastic subspace identification (RSSI) technique for on-line and almost real-time structural damage diagnosis using output-only measurements. Through RSSI the time-varying natural frequencies of a system can be identified. To reduce the computation time in conducting LQ decomposition in RSSI, the Givens rotation as well as the matrix operation appending a new data set are derived. The relationship between the size of the Hankel matrix and the data length in each shifting moving window is examined so as to extract the time-varying features of the system without loss of generality and to establish on-line and almost real-time system identification. The result from the RSSI technique can also be applied to structural damage diagnosis. Off-line data-driven stochastic subspace identification was used first to establish the system matrix from the measurements of an undamaged (reference) case. Then the RSSI technique incorporating a Kalman estimator is used to extract the dynamic characteristics of the system through continuous monitoring data. The predicted residual error is defined as a damage feature and through the outlier statistics provides an indicator of damage. Verification of the proposed identification algorithm by using the bridge scouring test data and white noise response data of a reinforced concrete frame structure is conducted.

Semi-active control of torsionally responsive structures

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.

Seismic Performance of Vibration Control Device That Generates Power

In a previous paper the authors proposed a semi-active vibration control device (VCD) that generates power. The device utilizes a ball screw, and has inertial and damping forces. The damping coefficient is adjusted by altering resistance at the terminal of the power generator. A small-scale VCD was manufactured for experimental testing. Frequency responses of a small-scale spring mass structure were measured in order to confirm the effects of vibration suppression within a wide range of frequencies. In this paper, as the next step, vibration tests using a benchmark structure with an installed VCD that has a 30 kN capacity are carried out at the National Center for Research on Earthquake Engineering (NCREE) in Taiwan. The benchmark structure has three stories with a 3 m height and a mass of 6 tons at each floor level for a total height and weight of 9 m and 18 tons, respectively. The VCDs are installed between adjacent floors with steel chevron braces. A simple control law that is based on a minimized Lyapunov function and employs bang-bang operation is used as a variable current controller instead of the modifying the resistance level of the VCD. Scaled earthquake motions including the Imperial Valley El Centro north-south component that is normalized to be a peak level of 0.5 m/s2 , are applied to the base of the steel framed structure in the horizontal direction by a shaking table. Experimental responses of each floor for the uncontrolled and controlled cases are compared with analytical responses, and effects of vibration suppression for the large-scale model are discussed quantitatively.Copyright

Inertia Damper Using MR Fluid With Spiraled By-Pass Pipe

Authors develop a unique type damper using MR fluid in order to obtain a series inertia effect for vibration suppression. The damper consists of a cylinder, a piston, and a long by-pass pipe. A rectangular gap is spirally formed at outer side of the cylinder as like a long by-pass pipe, and covered with an outer cylinder by interference fitting. Series inertia effect is caused by quickly movement of the fluid inside the by-pass pipe, and proportional to a length, density, and a ratio of cross sectional areas between the cylinder and the by-pass pipe. It is obvious from former study that not only a resonance frequency can be shifted toward low frequency, but also vibration can be cut off at an anti-resonance frequency by series inertia effect. The test damper is manufactured, and dynamic properties are investigated when it is subjected to sinusoidal wave. Force and Displacement curves are measured, and compared with theoretical results. Seismic vibration tests using 3-story benchmark structure with the damper installed are carried out. The effect of vibration suppression is evaluated, and the validity of the inertia effect is confirmed experimentally.Copyright

Multi-subnet wireless sensing feedback for decentralized ℋ 2 control with information overlapping

This paper studies a time-delayed decentralized structural control strategy that aims to minimize the H2 norm of the closed-loop system. In a decentralized control system, control decisions are made based on data acquired from sensors located in the vicinity of a control device. Due to the non-convexity nature of the optimization problem caused by a decentralized architecture, controller design for decentralized systems remains a major challenge. In this work, a homotopy method is employed to gradually transform a centralized controller into multiple decentralized controllers. Linear matrix inequality (LMI) constraints are adopted in the homotopic transformation to ensure closed-loop control performance. In addition, multiple decentralized control architectures are implemented with a network of wireless sensing and control nodes. The sensor network allows simultaneous operation of multiple wireless subnets. Both the theoretical development and system implementation support the information overlapping between decentralized subnets. For validation, the wireless sensing and control system is installed on a six-story laboratory steel structure controlled by magnetorheological (MR) dampers. Shake-table experiments are conducted to demonstrate the performance of the wireless decentralized control strategies.

Theoretical and experimental study of vibration suppression for stayed cable

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 excitation frequencies.

Vibration Tests of 3-Story Benchmark Structure With Three Semiactive Dampers

In a previous paper the authors developed a semiactive damper that generates electrical power, and carried out vibration tests using a 3-story benchmark structure at NCREE, Taiwan in 2006. At that time, the dampers were installed at 1st and 2nd floors. The damper has a large inertia mass by flywheel and controllable damping force by generator, and a load capacity of 30 kN. In the test, the damper at 1st floor was only controlled by Bang-bang control that was based on Lyapunov function. In this paper as the next step, in order to demonstrate more effectiveness of vibration suppression, the dampers are installed at all floors of the 3-story structure, and vibration tests using the same structure are carried out again in 2008. The control law which is proposed here is based on Lyapunov function or predictive switching control for all of damper at each floor. The structure has 9 m high, 3 m wide, 2 m span, 18 tons total weight. Several earthquake waves normalized to be 150 gal are inputted horizontally to the base by a shaking table, and the seismic responses of each floor are estimated quantitatively. It is obviously from the experimental results that the seismic reductions for acceleration and displacement in case of large inertia mass are much better than the case of small one, but control effect is decreasing. Because seismic reduction can be depended on a balance between inertial force and controllable damping force, and plus the one of the reason is time delay of the damper. At last, we can summarize that the semiactive damper is available for seismic isolation in practical use.Copyright