french institute of science and technology for transport ... - Ifsttar

esearch orientation r_durability, hazards and nuisances
Reducing the seismic vulnerability
of existing constructions
Reducing the seismic vulnerability of existing
constructions is vitally importantles structures
Columns undergoing
testing at the IFSTTAR
structures laboratory
in Paris.
Reducing the seismic vulnerability of existing constructions
is vitally important.
The use of bonded composites has become one of the
standard techniques for strengthening reinforced concrete
structures, in particular because they have many qualities and
are simple to use. Carbon fibre based composites provide effective
strengthening, acting as external reinforcing bars. However,
we still lack knowledge about the behaviour of structures
that have been reinforced in this way when they are subjected
to external stresses (impacts, explosions or earthquakes).
This observation was responsible for a major research project
at IFSTTAR (1) which set out to undertake experimental studies
of the behaviour of reinforced concrete columns that have
been strengthened with bonded composites and subjected
to seismic-type stresses. The strengthening materials that are
currently on the market were provided and installed by the
project’s industrial partners (Freyssinet International et Cie and
Vinci Construction France).
To operate with these systems, an innovative anchorage system
was developed and validated by experiments at the Autun
Département Laboratoire (CETE de Lyon).
The columns were tested at the IFSTTAR structures laboratory
in Paris. The reinforcement was bonded to the test
specimens in a number of configurations in order to conduct
a multicriteria evaluation of the effects of each of them. The
performance of the tested reinforcement systems was confirmed,
and in particular it was demonstrated that the new
anchorage system considerably increases the effectiveness
of flexural strengthening.
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(1) In the framework of the ANR-INPERMISE project and work on
Raphaëlle Sadone’s doctoral thesis.
@ CONTACT
marc.quiertant@ifsttar.fr
Shear forces in
heterogeneous plates
A new theory
Gaining a detailed understanding of the effect of shear
forces in heterogeneous plates poses many difficulties.
Although Reissner’s theory for homogeneous plates
dates from 1945, it is still awaiting satisfactory extension to
heterogenous plates. Consequently, when we study stratified
carbon fibre plates we are forced to use more complex models
that are of little use to engineers.
By taking up Reissner’s work again, but applying it to a
heterogeneous plate, we have shown that this model is not
able to describe the effects of shear forces. In particular, the
inclusion of additional variables is required. We have called
the new model the Bending-Gradient model as it makes
use of all the components of the gradient of the bending
moment while the shear force only considers its divergence.
Mechanical interpretation is nevertheless straightforward.
In the case of a homogeneous plate, the bending-gradient
model corresponds simply to Reissner’s original model However,
much better results were obtained when the model was
applied to stratifi ed plates under very general conditions. In
annual report 2011 ifsttar.fr