stands for Fiber Reinforced Polymers and it is used
to indicate a wide category of composite materials which constitute the
frontier of current construction technology. They ... are costitued of
polymers matrix where unidirectional or multiaxial fabrics are imbibbed.
Their use in aeronautic
construction continues with great success. The revolutionary Centurion
aircraft is taking its first experimental flights; it combines lightness
of weight with aerodynamic efficiency, and like its predecessor Pathfinder,
its structure is entirely made of composite materials (carbon fiber and
kevlar) coated in protective film. The Centurion can reach the stratosphere
with extremely low-powered engines.
In civilian constructions, FRPs are been used with promising results in
three main areas:
1) structures wholly made of composite (beams, panels, outer shells)
2) strengthening of traditional materials such as reinforced concrete,
walls and timber
3) reinforcement of existing structural elements of different typologies
The first category is dominated by pultruded profiles, light, resistant
and sufficiently stiff; their use is typically envisaged for structural
The main efforts currently aim at solving connection problems. As concerns
other plate or shell-type elements, the classical evolution of application
in the field of aircraft, ship and automobile constructions can be now
found in the first examples of composite civil constructions. The first
bridges and housing units entirely made of composite are appeared.
The second category is dominated by bars and meshes obtained with different
technologies. These are used to strengthen reinforced concrete beams and
masonry walls, or structurally to co-operate with wood. Prestressing is
particularly interesting for the high strength/longitudinal modulus of
composites cables or bars. Anchorage problems are principal research task
Prestressed and cable stayed bridges are already in use in different parts
of the world.
The third category is the fastest growing. Reinforcing deteriorated structures
offers the most possibilities for use.
The rapidity of interventions and the great efficiency have convinced
many designers to choose this path. The cost is not high compared to traditional
technologies both in terms of execution time and construction difficulties.
In seismic areas, the improvement of the structural behaviour of existing
structures is often surprisingly effective.
The high "resistance/weight" ratio must be kept in mind, which
is "a must" for structures subjected to seismic action. In this
context, wrapping technology, with composites prepared on site, represents
a real structural engineering revolution. In fact the columns confinement,
the bending and shear beams strengthening are achieved easily and effectively
by bonding structural elements with resin-impregnated fabrics. Resins
constitute the matrix of the composite, while the fabric's fibres vary
in nature: carbon, aramide, glass, polivyniialcohol or other mineral fibers.
By dosing layers and
morphologies of the composite, it is possible to obtain considerable improvements
in resistance and ductility The applications development of this sector
is progressing rapidly whereas the methodologies for calculating are not
completely organized and collected in codes of recommendations. In particular,
reinforced concrete beams shear strengthening is being researched as concerns
the schematization of calculations and applications morphologies. In the
quasi-totality of these intervention, the reinforcement is external, therefore
the transfer of actions from the composite to the original structure takes
place on the external film of the reinforced element. In reinforced concrete
beams, the external concrete thickness which must be able to transmit
the above-mentioned actions is known as "steel cover".
Before each intervention it is necessary to evaluate the consistency of
the support, and only if it is considered adequate, can the application
be carried out. The methodologies of Non Destructive Testing are a useful
tool for acquiring elements of judgement.