Semiactive control devices have received significant attention in recent years because they offer the adaptability of active control devices without requiring the associated large power sources. Magnetorheological (MR) dampers are semiactive control devices that use MR fluids to produce controllable dampers. They potentially offer highly reliable operation and can be viewed as fail-safe in that they become passive dampers should the control hardware malfunction. To develop control algorithms that take full advantage of the unique features of the MR damper, models must be developed that can adequately characterize the damper's intrinsic nonlinear behavior. Following a review of several idealized mechanical models for controllable fluid dampers, a new model is proposed that can effectively portray the behavior of a typical MR damper. Comparison with experimental results for a prototype damper indicates that the model is accurate over a wide range of operating conditions and is adequate for control design an...

Phenomenological model for magnetorheological dampers

Estimation of Small Failure Probabilities in High Dimensions by Subset Simulation

Control of civil engineering structures for earthquake hazard mitigation represents a relatively new area of research that is growing rapidly. Control systems for these structures have unique requirements and constraints. For example, during a severe seismic event, the external power to a structure may be severed, rendering control schemes relying on large external power supplies ineffective. Magnetorheological (MR) dampers are a new class of devices that mesh well with the requirements and constraints of seismic applications, including having very low power requirements. This paper proposes a clipped-optimal control strategy based on acceleration feedback for controlling MR dampers to reduce structural responses due to seismic loads. A numerical example, employing a newly developed model that accurately portrays the salient characteristics of the MR dampers, is presented to illustrate the effectiveness of the approach.

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Modeling and Control of Magnetorheological Dampers for Seismic Response Reduction

This paper presents the description, calibration and application of relatively simple hysteretic models that include strength and stiffness deterioration properties, features that are critical for demand predictions as a structural system approaches collapse. Three of the basic hysteretic models used in seismic demand evaluation are modified to include deterioration properties: bilinear, peak-oriented, and pinching. The modified models include most of the sources of deterioration: i.e. various modes of cyclic deterioration and softening of the post-yielding stiffness, and also account for a residual strength after deterioration. The models incorporate an energy-based deterioration parameter that controls four cyclic deterioration modes: basic strength, post-capping strength, unloading stiffness, and accelerated reloading stiffness deterioration. Calibration of the hysteretic models on steel, plywood, and reinforced-concrete components demonstrates that the proposed models are capable of simulating the main characteristics that influence deterioration. An application of a peak-oriented deterioration model in the seismic evaluation of single-degree-of-freedom (SDOF) systems is illustrated. The advantages of using deteriorating hysteretic models for obtaining the response of highly inelastic systems are discussed. Copyright © 2005 John Wiley & Sons, Ltd.

Hysteretic models that incorporate strength and stiffness deterioration

Past, present and future of nonlinear system identification in structural dynamics

Based on a Markov-vector formulation and a Galerkin solution procedure, a new method of modeling and solution of a large class of hysteretic systems (softening or hardening, narrow or wide-band) under random excitation is proposed. The excitation is modeled as a filtered Gaussian shot noise allowing one to take the nonstationarity and spectral content of the excitation into consideration. The solutions include time histories of joint density, moments of all order, and threshold crossing rate; for the stationary case, autocorrelation, spectral density, and first passage time probability are also obtained. Comparison of results of numerical example with Monte-Carlo solutions indicates that the proposed method is a powerful and efficient tool.

Method for Random Vibration of Hysteretic Systems

A differential equation model for hysteretic systems with strength, stiffness or combined degradation is presented. Solution under white noise, Kanai filtered white noise and temporally modulated filtered white noise is obtained by equivalent linearization, without recourse to the Krylov-Bogoliubov approximation typically required for hysteretic systems. Resulting zero time lag covariance response matrices agree well with simulated solutions at all excitation levels. First passage predictions are nonconservative, because of the non-Gaussian character of the response.

Random vibration of hysteretic degrading systems

A random vibration method is developed for the response analysis of hysteretic structural systems under stochastic two-dimensional earthquake excitations. The biaxial hysteretic restoring force is modelled by coupled non-linear differential equations; the response statistics are obtained using the equivalent linearization technique. The validity of the proposed model is appraised using available biaxial loading tests of reinforced concrete columns. A parametric study was performed to examine the significance of the effects of biaxial interaction under earthquake excitations. A practical method to evaluate the extreme response statistics is also presented.

Random vibration of hysteretic systems under bi-directional ground motions

An approximate method for nonstationary solution of nonlinear systems under random excitation is presented. The nonlinearities in the restoring force are polynomial type. The excitation is either shot noise or filtered shot noise. The solution is based on a Markov-vector approach. The unsteady Fokker-Planck-Kolmogorov equation for the nonlinear system is solved approximately by a Galerkin method where a time-dependent Hermite-series expansion is used and the equation is reduced to a system of first-order ordinary differential equations. The method is illustrated by numerical examples on a damped Duffing oscillator and a Ramsberg-Osgood yielding system. Comparison of results obtained herein with exact stationary solution and Monte Carlo results indicates that the proposed method is powerful and efficient for study of nonlinear systems.

Approximate Method for Nonlinear Random Vibration

The performance-based seismic design of steel special moment-resisting frame (SMRF) structures is formulated as a multiobjective optimization problem, in which conflicting design criteria that respectively reflect the present capital investment and the future seismic risk are treated simultaneously as separate objectives other than stringent constraints. Specifically, the initial construction expenses are accounted for by the steel material weight as well as by the number of different standard steel section types, the latter roughly quantifying the degree of design complexity related additional construction cost; the seismic risk is considered in terms of maximum interstory drift demands at two hazard levels with exceedance probabilities being 50% and 2% in 50 years, respectively. The present formulation allows structural engineers to find an optimized design solution by explicitly striving for a desirable compromise between the initial investment and seismic performance. Member sizing for code-compliant design of a planar five-story four-bay SMRF is presented as an application example using the proposed procedure that is automated by a multiobjective genetic algorithm. Copyright © 2004 John Wiley & Sons, Ltd.

Yi-Kwei Wen

Papers

Method for Random Vibration of Hysteretic Systems

Random vibration of hysteretic degrading systems

Random vibration of hysteretic systems under bi-directional ground motions

Approximate Method for Nonlinear Random Vibration

Multiobjective optimization for performance‐based seismic design of steel moment frame structures