The construction sector
where advanced composite materials have had the most significant
role is in strengthening RC – PC structures. Till few
years ago, the use of FRP was particularly diffused in USA and
Japan, that were the first countries having started research
and fist applications using such materials, in order to find
technological solution more performing with respect to traditional
ones for seismic mitigation.
The use of FRP allows to assure the following advantages:
- High strength and stiffness (up to 10 times more resistant
than steel);
- Considerable lightness with no additional weight impact
on the structure (300/500 gr/m² depending on the material
used);
- Possibility of realizing the installation without interrupting
the use of the structure and with extreme rapidity, drastically
reducing the social costs of the work;
- High durability also in very aggressive environment;
- Possibility of maintaining unaltered the geometry and
volumetry of the structure.
The use of FRP for straightening and retrofitting RC –
PC structures allows answering and solving the following problems:
- Increase of strength capacity for change in use or due
to design code variation;
- Consolidation of degraded structures in order to provide
structural integrity and durability;
- Consolidation of degraded structures in order to provide
structural integrity and durability;
- Design and/or construction mistakes;
Thanks to the recently published design guidelines by the National
Research Council “Guide for design and Construction of
Externally Banded FRP Systems for Strengthening Existing Structures
(CUR-DT 200/2004) the use of such materials in the civil engineering
industry has had a continuous increment, thanks to the establishment
of codes for a sector in continuous development and in need
of design and construction tools for the use of such innovative
materials.
One of the main advantages of this technology is the possibility
of tailoring the design of the member with solutions that could
also be different from the our suggested in the guidelines as
long as their efficiency can be tested and supported by successfully
laboratory tests. Because though all strengthening applications
base their efficiency on the bond between the FRP and the substrate
(see the FRP and the Pultrusion Technologies) it is fundamental
that particular care is given on bond related failure mechanisms.
Such
failure is indeed a fragile type of collapse for FRP straightened
structures and should be avoided and in any case not preceded
the one caused by flexure or shear failure due to rupture of
the composite section.
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