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isolator. Another example of hybrid control system
is a combination of passive isolation bearings
with some passive energy dissipating devices.
Additional damping in these systems enhances
control performance of them particularly in near
field earthquakes.
The main objective of this chapter is to find
the optimal values of the base isolation system as
a kind of passive control device, and that of the
STMD system as a kind of semi-active control
device using genetic algorithms (GAs) and fuzzy
logic to simultaneously minimize the buildings'
selected responses. A comprehensive literature
review of these systems is provided in the main
relevant sections of each system.
optimal values of the design parameters, moreover
in semi-active control device the damping ratio
is regulated by a fuzzy logic controller.
The main objective of this chapter is multi-
objective optimization design of control devices
to reduce the structural vibrations excited by the
earthquake. In past decades, the use of evolution-
ary algorithms is considered by many researchers
in different optimization fields (Schaffer 1985;
Fonseca & Fleming 1993; Srinivas & Deb 1994;
Zitzler & Thiele 1998; Knowles & Corne 1999).
Genetic algorithms (GAs) are effective search
methods in very large and wide space that even-
tually lead to the orientation towards finding an
optimal answer. They can be used for solving
a variety of optimization problems that are not
well suited for standard optimization algorithms
including problems in which the objective function
is discontinuous, non-differentiable, stochastic
or highly nonlinear (Pourzeynali & Mousanejad,
2010; Pourzeynali & Zarif 2008).
AIMS AND SCOPE OF
THE CHAPTER
In the present chapter, STMD system with variable
viscous damper as a kind of semi-active control
device; and base-isolation, and TMD systems as
two kinds of passive control devices are studied.
In this regard, a realistic ten story building mod-
eled as a 2-D frame is selected to represent the
results of use of the base-isolation systems; and
a realistic twelve story building modeled as a
3-D frame is selected to simulate the response of
the building with STMD/TMD systems against
earthquake excitations. The parameters of these
devices have been optimally designed by multi-
objective genetic algorithms and fuzzy logic
utilizing the well known MATLAB software. The
results of use of base isolation systems, and those
of the STMD/TMD control devices are provided
in next sections. In order to study the performance
of the base isolation systems, 18 worldwide strong
ground motion accelerogrames, and to show the
effectiveness of STMD/TMD control devices,
7 earthquake accelerogrames are selected, for
which the detail descriptions will be provided in
the future sections of the chapter. In both control
systems, genetic algorithm (GA) is used to find the
ASSUMPTIONS
The following simplified assumptions are made in
the analyses (Matsagar & Jangid, 2003; Matsagar
& Jangid, 2004):
•
The main building is assumed to remain
within the elastic limit during the earth-
quake excitation. As the control systems
reduce the building response to a relatively
low value, therefore this assumption would
be reasonable.
•
To study the effect of base-isolation sys-
tems, the building is modeled as a shear
type frame having one lateral degree
of freedom at each story level (lumped
mass and rigid floor assumption), while
in STMD/TMD systems, the building is
modeled as a 3D frame having 3 degrees
of freedom, two translational and one tor-
sional, in each story level.
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