Geology Reference
In-Depth Information
Dissipaters Based on
Metal Plasticization
of the hosting structure, it is clear that the choice
of dissipater constructive details is critical in
determining the real efficacy of the protective
system. Therefore, the design process presented
here starts from a panel geometry defined through
geometrical parameters. These parameters are
then chosen using an optimization routine hav-
ing the aim of maximizing the energy dissipation
phenomena in the device. For this purpose, a
simple and well-established optimization strategy
has been selected among all the possible strate-
gies developed in the technical literature for the
structural optimization (Kirsch 1993, Spillers and
MacBain 2009).
Metallic systems are relatively simple to con-
struct and it is easy to change their dimensions.
Conceptually, the seismic design of structures
with yielding of steel devices is similar to the
conventional design of buildings based on ductil-
ity with the additional requirement of a limited
number of available devices.
In literature, several metallic systems have
been proposed for their wider development and
use in buildings and structures: lead extrusion
devices, torsion beams, dampers with bending
deformation. A wide variety of different types of
devices have been developed that utilise bending,
shear, or extensional deformation modes into their
plastic range. Important desirable features of these
systems are stable behaviour, long-term reliability,
and generally good resistance to environmental
and temperature factors.
Yielding steel systems represent a sub-group
of the metallic systems (Chan et al., 2009). They
are modelled with different shapes (“X”-shaped,
triangle-shaped, and “U”-shaped) so that the yield-
ing is spread uniformly throughout the material.
The result is a device that is able to sustain repeated
inelastic deformations in a stable manner, avoid-
ing stress concentrations and low cycle fatigue.
A convenient location of these “connections”
is in the diagonal-beam joint. In this case, the
bracing system must be substantially stiffer than
the surrounding structure. The introduction of
such a heavy bracing system into a structure may
be prohibitive unless the system is efficient. The
sizes of these braces and the dissipative capacity
of the device must be calibrated to have the high-
est seismic energy dissipation.
In the following, a new metal dissipater has
been proposed. It is designed to yield under a
shear force and dissipate energy for hysteresis of
the material that composes it. Since the amount
of energy dissipation depends not only by device
dimension and by geometry but also by stiffness
PROPOSAL FOR A NEW
HYSTERETIC DISSIPATOR
Description of the Device
Hysteretic dissipaters for passive seismic protec-
tion of buildings are able to dissipate high amounts
of input energy during an earthquake thanks to
the large plastic behavior of the material utilized
in their manufacturing (Nakashima et al 1994,
Nakashima 1995, Rai et al. 1998, Yamaguchi et
al. 1998, De Matteis et al 2007).
In passive metal devices, the effectiveness of
dissipation depends on two main characteristics:
first, the low value of displacement at which the
hysteresis loops are activated in the material area,
which ensures the protection of structures for
small vibration, and secondly a large plastic field,
which maximizes the energy dissipation. These
two requirements are in conflict, since the use of
a small device allows reducing the load activa-
tion level, but the amount of dissipated energy is
also reduced being proportional to the volume of
material involved in dissipation processes.
In order to satisfy these demands, a new dis-
sipation mechanism has been proposed. The initial
idea was to consider a device where the use of
two different coupled materials could accomplish
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