Geology Reference
In-Depth Information
The requirements that a mechanism of passive
control of the seismic response should guarantee
are listed below:
antees of avoiding damage to the non-structural
elements during a severe earthquake, so even the
restoration of the principal elements could be dif-
ficult. Therefore, in the last thirty years several
energy dissipation and base isolation systems have
been proposed to localise non-linear behaviour in
certain pre-defined areas of a structure.
•
After the seismic event, the structure must
return to its original position (high defor-
mations must not be permitted).
•
The daily life of the people living in the
structure must not be altered during the
checking and restoration phases.
Concept of Energy Dissipation
•
Utilising mechanisms of this type the ini-
tial cost of construction and of the struc-
tural reinforcing of the existing building
should be reduced.
Energy dissipation systems are able to localise
the ductility demand in some “weak” points able
to dissipate energy in a stable form and which
may be easy to repair. The energy dissipation
concept may be understood because of the modern
tendency toward seismic-resistant design. In this
case, the “weak” points correspond to mechani-
cal elements, which dissipate energy in a stable
form. In the event of a severe earthquake, and if
the devices are damaged, they may be replaced
without disturbing the use of the building.
In antiseismic design the mechanical elements
that are able to dissipate energy are called energy
dissipative devices (EDDs); this modern approach
to seismic resistant design is now spreading and
widening, also thanks to the development of de-
vices obtained by using innovative materials or
materials traditionally utilized for different use.
EDDs are inserted into a structure so that when
it vibrates, they deform and dissipate energy. After
the biggest earthquakes, such devices can be eas-
ily replaced. In this way, they do not require any
major structural flexibility in the system, since the
damage (permanent deformation) is concentrated
in the device. In this way, the other structural ele-
ments remain elastic.
There are many systems with the objective of
dissipating the seismic energy and some of them
have been utilised in buildings and bridges (Jara
et al 1992, Hanson et al. 1992).
In general, the significant reduction of struc-
tural response to severe earthquakes utilizing
energy dissipaters depends on their number, po-
sition in the building, the type of dissipater and
•
The mechanical properties of the devices
must not vary substantially with time.
•
Maintenance and inspection must not be
required except after the occurrence of a
severe earthquake; in this case, the opera-
tions requested should be simple.
To accomplish all these requirements, a
complicated device is not useful, while a simple,
economic device with stable behaviour under
seismic action is preferable.
The traditional seismic design takes into ac-
count that some structural elements enter the
inelastic range of behaviour, and the hysteretic
energy involved will contribute to reducing the
value of the demand of responses during a destruc-
tive earthquake. In fact, the conventional design
of seismic-resistant structures is based on the
concept of ductility and structural redundancy.
The forces induced by a severe earthquake are sig-
nificantly reduced as a function of both concepts,
connected with the energy dissipation capacity of
the structural elements (Bozzo and Barbat, 1995).
A seismic resistant rational design guarantees that
for a certain global structural ductility demand the
ductility capacity of the elements is not exceeded.
Due to uncertainties with non-linear analysis is
difficult to estimate precisely the local ductility
demands in each section of a structure. Moreover,
the traditional building design offers few guar-
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