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at the mercy of the nature as one concern that still
remains is that no structure can be built to with
stand all possible loads. The uncertainty in future
loadings and few fold increase in cost of construc-
tion never allow the engineers to design and built
a structure that can withstand all possible loading
conditions. The best alternative is to supplement
structures with added devices such that they can
take care of any unforeseen events and loadings.
For an example, recent earthquake followed by a
tsunami in Japan (11
th
March 2011) has not only
devastated but wiped out cities. Strict building
codes and added damping to the structures have
saved Japan from wider destructions as noted
in various international newspapers worldwide
(Glanz and Onishi, 2011; Ross, 2011).
Seismic base isolation is an old, widely accept-
ed and implemented structural mechanism due to
its robustness and ease in deployment. Following
the Northridge earthquake (1994), and Kobe earth-
quake (1995), the interest of structural engineers
in understanding near-source ground motions has
enhanced (Soong and Spencer, 2002). Documents
published after these earthquakes emphasized the
issue of large base displacements because of the
use of none or little isolation damping (of viscous
type only) prior to these events. More recent studies
have investigated analytically and experimentally,
the efficiency of various dissipative mechanisms to
protect seismic isolated structures from recorded
near source long period, pulse-type, high-velocity
ground motions. Consequently, hybrid isolation
systems, seismic base isolation supplemented
with active/semi-active damping mechanisms,
have become the focus of current research trend
in structural vibration control.
The recent focus on hybrid mechanism is to
augment base isolation devices with semi-active
magnetorheological (MR) dampers for efficient
structural vibration control. MR dampers provide
hysteretic damping and can operate with battery
power (Dyke et al., 1996; Ali and Ramaswamy,
2008a).
The use of MR damper as a semi-active device
involves two steps:
1. Development of a model to describe the MR
damper hysteretic behaviour
2. Development of a proper nonlinear control
algorithm to monitor MR damper current /
voltage supply
The present chapter deals with the develop-
ment of nonlinear control strategies to use with
MR damper for base isolated buildings. The
chapter unfolds in two interlinked areas. First
an intelligent fuzzy logic control (FLC) scheme
is developed to monitor the MR damper voltage
input. The FLC is optimized using micro genetic
algorithm. An experimental study is undertaken
to access the efficacy of the optimal FLC in real
time and to verify the numerical studies. Next the
chapter provides insight to two newly developed
model based nonlinear control techniques, viz, a
dynamic inversion based MR damper monitoring
and an integrator backstepping based MR damper
monitoring. These two control algorithms are
studied through numerical simulations.
The chapter is organized as follows: the next
section provides a comprehensive review of lit-
erature on nonlinear control schemes to monitor
MR damper for structural applications. Next, de-
velopment of an optimal FLC using micro genetic
algorithm is shown in details. A novel geometric
scheme is developed to optimize the FLC such
that a few optimization variables are required.
Experimental study carried out to access the ef-
ficiency of the FLC is detailed next. The chapter
then introduces the nonlinear control schemes.
The mostly used clipped optimal control scheme is
discussed. Emphasis is given to recently developed
backstepping and dynamic inversion based control
schemes. Results of numerical simulations of the
nonlinear algorithms are provided and discussed
thereafter. Finally the chapter concludes with a
future direction of research.
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