Properties and numerical modeling of MR dampers

Among the different strategies available to control engineering vibrations, the semi-active contrai based on Magnetorheological (MR) dampers have become a promising technology to be used in civil engineering structures. The ability of these devices to change the stmctairal behavior without the need of large power sources is a major advantage that can be used to justify their potential application to this engineering branch. This paper reviews the basic concept of MR fluids and provides an insight of MR dampers dynamic behavior and the available numerical procedures to describe the damper response. In the first section an overview ofthe basic properties ofthe MR fluids and the fluid behavior under different flow regimes are presented. Then, a selection of numerical models to simulate MR dampers behavior will be presented based on the available literature

Neuro-fuzzy modeling of a sponge-type MR damper

Numerical modeling of MR dampers based on parametric models constitutes one of the main methodologies to simulate the behavior of this type of devices. However, its highly non-linear nature and also its inherent rheological behavior make this type of numerical modeling harsh and complicated, which hinders the development of simple models capable to cover all aspects associated with the proper numerical simulation of the damper behavior and therefore usually complex parametric models involving several parameters are required to achieve a reliable and accurate representation of its rheological behavior. Hence, non-parametric models represent another feasible approach to simulate the complex non-linear behavior of MR dampers although in this case allowing to obtain a wide-ranging numerical model without the need to define or identify a large number of model parameters. In this context, we attempt to model and predict the response of a sponge-type MR damper using a non-parametric modeling technique based on an Adaptive Neuro-Fuzzy Inference System (ANFIS) model. Initially, the basic structure of this data modeling technique is presented and the main aspects regarding the development of a neuro-fuzzy model for MR dampers are addressed. Then, an ANFIS modeling technique is developed to obtain a non-parametric model for the MR damper. Finally, a comparison between the numerical and experimental results will be presented to validate the selected modeling technique.info:eu-repo/semantics/publishedVersio

Passive control of civil engineering structures

Structural control has been a major research area i n aerospace engineering aimed at solving very complex problems related with analysis and des ign of flexible structures. The efficiency of these strategies to improve the performance of s everal structural systems suggests its potential to reduce damage and control earthquake4i nduced response in civil structures. Therefore, this technology has been well accepted b y structural engineers as a feasible approach to design improved earthquake resistant st ructures. The present paper provide a brief description of each control scheme describing the m ain properties of different anti4seismic solutions and presenting the most relevant developm ents in this area. Control methodologies and devices are highlighted identifying their advan tages and limitations. The main focus of this paper is to present a comprehensive state4of4t he4art of passive control system. Different passive techniques are described and the effectiven ess in mitigating seismic hazard for structures is addressed.The authors gratefully acknowledge the funding by Ministério da Ciência, Tecnologia e Ensino Superior, FCT, Portugal, under grant SFRH/BD/49094/2008

Optimal control of a plan asymmetric structure using magnetorheological dampers

Although building structures can be perceived as a combination of primary frames in two orthogonal directions, they are three-dimensional systems that usually present a very complex dynamic behavior due to irregular geometric configurations, in particular due to plant stiffness or mass eccentricities. This asymmetric geometry results in coupled lateral–torsional motion produced by wind and seismic loading with consequences in the design of lateral and corner columns. A considerable amount of research effort has been devoted to develop structural control systems to reduce the effects of plan asymmetries and to improve the dynamic behavior of these buildings. This paper presents a numerical analysis of a semi-active control system with MR dampers designed to reduce lateral–torsional responses of a plan asymmetric building structure excited by El Centro NS earthquake ground motion. A parametric study comprising passive and semi-active control modes is given to demonstrate the effectiveness of the proposed control system with respect to uncontrolled case. The numerical results prove the efficiency of the semi-active control system and its potential use in mitigating coupled lateral–torsional structural responses.info:eu-repo/semantics/publishedVersio

ANFIS optimized semi-active fuzzy logic controller for magnetorheological dampers

In this paper, we report on the development of a neuro-fuzzy controller for magnetorheological dampers using an Adaptive Neuro-Fuzzy Inference System or ANFIS. Fuzzy logic based controllers are capable to deal with non-linear or uncertain systems, which make them particularly well suited for civil engineering applications. The main objective is to develop a semi-active control system with a MR damper to reduce the response of a three degrees-of-freedom (DOFs) building structure. The control system is designed using ANFIS to optimize the fuzzy inference rule of a simple fuzzy logic controller. The results show that the proposed semi-active neuro-fuzzy based controller is effective in reducing the response of structural system.info:eu-repo/semantics/publishedVersio

Vibration control of civil engineering structures using magneto-rheological dampers

Recent developments in civil engineenng stmctures design and constmction allowed the creation of slender and flexible stmctures such as towers, high-rise buildings and long span bridges. The structural properties of these stmctures, namely the low damping capability makes them vulnerable to strong wind or earthquake actions. In recent decades various control systems based on passive, active, semi-active and hybrid devices have been proposed and different control strategies were developed and implemented for structural vibration control. Among these, lhe semi-active based control hás become an important altemative to passive and active control methods as a result of its ability to gather some of the advantages of the passive control such as the reliability of these systems with the adaptability of the active control

Seismic performance of metallic braced frames by pushover analyses

A preliminary investigation is presented on a pushover analysis used for the seismic performance of metallic braced frames equipped with diagonal X-bracing and K-bracing systems. Three steel frames were analysed corresponding to 3, 6 and 10 floor regular buildings. The frames were modelled in the MIDAS/Civil finite element software and in the analyses nonlinear static methods were used to obtain the pushover curve. The principal objective of this article is to compare the evaluation of the structural performances of these buildings with respect to the proposed N2-method, and so also of the consequent convenience of using pushover methodology for the seismic analysis of structures

A parametric study of the non-linear geometric behaviour and carrying capacity of 3D asymmetric steel frames

Non-linear P-delta behaviour of three-dimensional frames with plan and elevation asymmetries is studied, using a parametric variation of geometry in plan and a stiffness variation along the height. Some behavioural aspects of a calibration frame have been addressed to ascertain the importance of the nodal rigidity, modelled with laminar elements of the type shell with implicit formulation of thick plate or modelled with elastic stiff springs, in the study and modelling of the geometric nonlinearity and stability of such calibration frame. Eurocode 3 criteria for second order analyses is briefly addressed in connection with the 2D frame classification with respect to sway behaviour; however for 3D structures the calculated carrying capacity is independent of this classification. So a parametric study of the critical load factor of asymmetric three-dimensional frames, un-braced and braced, permits to characterize their carrying capacity with respect to overall structural stability

Seismic response reduction of building structures using a semi-active control system based on a brain emotional learning controller

The present paper investigates the effectiveness of a bio-inspired semi-active controller to reduce seismic-induced vibrations in building structures. The control system is based on the use of a MR damper in combination with the so-called Brain emotional learning based intelligent controller (BELBIC), which is an intelligent controller based on the model of Limbic system of brain. A general case for a three degrees of freedom building structure excited by the El Centro earthquake will be used to demonstrate how a semi-active control system comprising a MR damper in a non-collocated configuration can reduce the structural response under seismic loading. Hence, the key objective of this study will be to evaluate and verify the efficiency of a MR damper in controlling the level of vibrations in a three degrees of freedom building structure by means of a BEL controller. A comparison between uncontrolled and controlled structural responses are used to validate the performance and efficiency of the proposed semi-active controller.info:eu-repo/semantics/publishedVersio

Estudo preliminar sobre o desempenho sísmico de pórticos metálicos contraventados a partir de análises estáticas não-lineares (PUSHOVER)

Neste artigo apresenta-se uma investigação preliminar sobre o uso de métodos de análise pushover no dimensionamento de pórticos com elementos de contraventamento (diagonais metálicas). Para este efeito foram analisados três pórticos metálicos de aço com 3, 6 e 10 pisos. Os pórticos foram modelados através do programa de elementos finitos MIDAS/Civil e nas análises foram usados métodos não-lineares estáticos de pushover. O objectivo principal consiste na avaliação comparativa dos desempenhos estruturais, e portanto também na consequente conveniência do uso deste método “pushover” na análise sísmica de estruturas