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Preparing the installation of
the SMA devices.
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September
1997: five earthquakes shook the Italian regions of Umbria and Marche. Some
20 kilometres from the epicentre, the Basilica of St Francis of Assisi was
one of the victims. Clouds of dust invaded the nave, whole sections of the
frescoes by Giotto and Cimabue were reduced to rubble, and a gaping hole,
like a pool of light, appeared where the tympanum had once been. More than
a million tourists and pilgrims visit the site annually, with even more
expected for the year 2000.
Shape
memory alloys
September 1998: the Italian Ministry of Culture and the European Commission
organised a three-day meeting, an opportunity for European experts in
the field of research for the protection and restoration of cultural heritage
to come together for an exchange of views. Among the research projects
presented , Istech(1) proposed a technology based
on a nickel and titanium alloy belonging to the SMA, or shape memory alloy,
family.
"The principal
benefit of this material is its ability to disperse the energy produced
by movement. For example, it can dissipate some of the shock waves coming
up from the ground during an earthquake," explains Giorgio Croci, a professor
at "La Sapienza" University (Rome), who is in charge of the restoration
work in Assisi. "Our SMA devices offer the advantage of being calibrated
for a specific level of seismic activity up to which they behave according
to their unique characteristics. Above this design level, they provide
the required rigidity using traditional steel bars. This double guarantee
makes them very reliable," confirms the project's scientific coordinator,
Maria Gabriella Castellano of FIP Industriale.(2)
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Seismic protection using shape
memory alloys (SMAs): a world 'first' applied to the Assisi tympanum.
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Supporting
tests
September 1999: the scars at the Basilica are beginning to heal. "We chose
different restoration methods depending on the architectural elements
to be repaired and the damage incurred," points out Giorgio Croci. "For
the tympanum, and its connection with the roof, we opted for the SMA system,
whose properties are particularly suited to this part of the basilica,
which was badly damaged and quite fragile."
Before being
chosen for Assisi, this innovative technology had to prove its worth.
Tests were carried out in the ELSA laboratory at the Joint Research Centre
in Ispra (I). Simulations on life-size masonry walls showed that, at the
same seismic intensity, non-reinforced walls are seriously damaged or
collapse, while walls fitted with the SMA systems suffer no damage at
all. Digital analyses and additional tests carried out by ENEA (Bologna)
showed that structures protected in this way increase their resistance
to earthquakes by at least 50%. Finally, before starting work on the basilica's
tympanum, the restorers installed four SMA devices in the tower of the
San Giorgio de San Martino church in Rio, a victim of another earthquake.
(1)
Istech (Development of Innovative Techniques for the Improvement of Stability
of Cultural Heritage, in particular Seismic Protection), was supported
by the Environment and Climate programme (Fourth Framework Programme),
and brings together six partners: FIP Industriale (I), ENEA - Ente per
le Nuove Tecnologie, l'Energia e l'Ambiente (I), Università degli Studi
di Roma "La Sapienza" (I), Aristotle University - Thessaloniki (GR), Instituto
Superior Tecnico - Lisbon (PT), ELSA - European Laboratory for Structural
Assessment - JRC (I).
(2) FIP is also at the origin of two other types of seismic protection
device, developed under the REEDS project (Brite-EuRam programme), one
of which is also being installed in St Francis' Basilica in Assisi.
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