JEC COMPOSITES MAGAZINE - Issue #111 - March 2017 - Special JEC World - o - 101

Seismic retrofitting of reinforced concrete structures using FRP: French guidelines

Guideline description
The document contains five chapters with
detailed design examples, case studies and
FRP detailing.
Chapter 2
Retrofitting examples were provided by
the companies participating in the working
group to qualitatively present the principles of retrofitting with adhesive-bonded
composites, FRP localisation and application methods. Case studies are provided in
Appendix 2. These documents, which mainly
come from product suppliers and installers,
do not explicitly address the dimensioning of
the reinforcements applied but describe real-life retrofitting examples considered to be
representative. They include many cases relating to reinforced concrete and prestressed
concrete buildings (shopping malls, production facilities, administrative buildings, skyscrapers, etc.), bridges (often old) as well as
examples of applications in masonry and civil
engineering structures (industrial stacks).
The retrofitting context is often that of seismic upgrading and/or repairs (even though
the case studies proposed are more limited
in the second case) that have to be carried
out as a result of the repair or reinforcement
of structural components to withstand static
and/or service loading.

fabric wrapping. Industrial stacks are among
the vertical elements that can be retrofitted
to enhance flexural strength using FRP strips
placed inside or outside the structure. The
retrofitting of column/beam joints, as well as
horizontal elements in relation to flexure, is
also the subject of several case studies. It can
be observed that these reinforcements can be
anchored to the structure in certain cases.
Finally, several case studies show that FRP
retrofitting is not the only possible solution
to strengthen the structure with regards to
seismic loading. To meet the requirements of
this type of loading, a combination of several
retrofitting techniques can be used, including
FRP reinforcement. Thus, certain structures
are reinforced by combining sprayed concrete,
additional prestressing, earthquake protection
systems and FRPs.
Chapter 3: analysing the seismic risk of
existing civil engineering works
This chapter deals with the methods used to
analyse the seismic risk of existing civil engineering works. It includes analysis methods
and modelling methods using the different
approaches defined in paragraph 3.2.3. To
validate the retrofitting process, the reinforced
structure has to be analysed. Effective simulation of the reinforcement is essential. For example, if the strength of the structural member
is increased, the composite strips are incorporated into the model as section reinforcements
modelled with a linear behaviour until failure.
They are assigned a high strength and modulus of elasticity corresponding to their real
characteristics. The increase in ductility can be
induced by the confinement effect on the constitutive law of concrete in compression. The
materials are taken into consideration in the
models via their static constitutive laws.
No111 March 2017

/ jec composites magazine

Feature Construction

In this context, in France, seismic upgrading
is simply recommended for bridges while it
is compulsory for buildings. In the examples
proposed, the aim of structural reinforcements is to offset inadequate detailing in
terms of dynamic loading (overlap or length
of rebar anchorage, quantity of reinforcements required for shear or flexural strengthening, etc.), to reinforce the structure for a
new purpose or configuration, or to repair a
structure damaged by a previous earthquake.
The examples provided show that the currently applied reinforcement materials are
often carbon-fibre-based FRPs and that the
most frequently reinforced structural component is the column, which is often wrapped
with a fabric, generally applied continuously. However, confinement is sometimes
completed with flexural strengthening or
strengthening designed to offset inadequate
detailing (overlap or anchorage lengths). This
is achieved by placing FRP strips under the

Fig. 2: FRP strangthening effect on RC wall Under cyclic
loading

Chapter 4: FRP design
This chapter presents the different FRP reinforcement solutions with respect to the normal force, flexure, confinement and shear
force. Since Eurocode 8-3 is entirely devoted
to the retrofitting of existing buildings, it is
not intended for civil engineering structures.
However, in the absence of any other regulations and considering that the behaviour of
a bridge pier is similar to that of a building
column, the EC8-3 rules will be assumed to
be applicable to civil engineering structures
in this document. The field of application of
these recommendations covers the design of
reinforced concrete components that need
to be repaired or reinforced using composite
materials (based on carbon, glass or aramid
fibres). The design methods presented refer
to the Eurocode 8 regulations and lie within
their framework. The structural component
on which the FRP is to be installed has to be
sound and free of any pathologies that could
reduce the capacity of its surface to lastingly
transfer forces to the composite. It is therefore essential to assess the state of repair of
the concrete material. Given the different
reinforcement procedures and in order to
ensure a reliable, lasting retrofitting result,
it is recommended to consult chapters I,
III and IV of the AGFC's guidelines [10],
respectively entitled «Recommendations
concerning the characterisation of composite
materials used to repair concrete structures»,
«Recommendations concerning in situ implementation of composite materials for reinforcement» and «Recommendations concerning
in situ inspection of composite materials for
reinforcement», in addition to standards NF
P 95101 and NF EN 1504. First, it is important to conduct a global analysis of the structure in accordance with the provisions of
Eurocode 8 and the guidelines for assessing
existing structures in relation to earthquakes.
However, since seismic analysis is too complex a field to be addressed in detail in this
document, this chapter will only provide
elements relating to the detailing of composites for seismic retrofitting (accidental ULS
(ultimate limit state) load conditions). It
should be ensured that the structure is verified not only for ULS but also for SLS (serviceability limit state) load conditions and
that the construction phasing is taken into
account in relation to the SLS.

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Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #111 - March 2017 - Special JEC World - o