Article,
Strengthening Reinforced Concrete Beams Using Fiber Reinforced Polymer (FRP) Laminates
ACI Structural Journal, (September 1999)
Abstract
The behavior of reinforced concrete beams strengthened with various
types of fiber reinforced polymer (FRP) laminates is presented in
this paper. The experimental program included strengthening and testing
14 simply supported rectangular cross section beams. Each beam was
initially loaded above its cracking load. The cracked beams were
strengthened with FRP laminates and then tested until complete failure.
Five available strengthening systems of various types of car-bon/glass
fiber reinforced polymer (CFRP/GFRP) strengthening materials were
used. These materials included two types of CFRP sheets, bi- and
unidirectional GFRP sheets, and CFRP plates. The effects of strengthening
on deflection, failure load and failure mode, strain, and beam ductility
are discussed. In addition, the influence of different numbers of
FRP layers, type of epoxy, and strengthening pattern on the behavior
of beams was examined. The ratio of absorbed energy at failure to
total energy, or energy ratio, was used as a measure of beam ductility.
It is concluded that, in addition to the longitudinal layers, the
fibers oriented in the vertical direction forming a U-shape around
the beam cross section significantly reduce beam deflections and
increase beam load carrying capacity. Furthermore, the presence of
vertical FRP sheets along the entire span length eliminates the potential
for rupture of the longitudinal sheets. The combination of vertical
and horizontal sheets, together with a proper epoxy, can lead to
a doubling of the ultimate load carrying capacity of the beam. However,
all the strengthened beams experienced brittle failure, mandating
a higher factor of safety in design.
