Tee Beams
FRP laminates were applied to reinforced concrete beams in varying amounts and in
different configurations. A T-section was selected as being the one most suitable
for use in the study, since it provides a large surface area for application of
the laminates, as well as a relatively large compressive resistance area of the
flange. A total of sixteen beams were tested.
FRP fabric was applied over the entire stem of a beam from center-to-center of supports.
These specimens are referred to as ”fully wrapped? In two beams, the FRP laminates
were applied only to the bottom surface of the stem (“partially wrapped?. Concrete
having a nominal compressive strength of 5,000 PSI was used in all specimens.
The MAS2000 Fiber Wrap System is composed of unidirectional carbon material formed
by weaving individual yarns into a fabric that has a manufacturer’s reported ultimate
tensile strength of 530 KSI and an elastic modulus of 33,500 KSI. The sheets created
during the weaving process result in a 0.5 mm thick material with individual yarn
density of 0.43/mm. Each individual yarn has a cross-sectional area of pure carbon
equal to 0.45 mm2 [700 x 10-6 in2].
In order to achieve maximum bond, a thixotropic type epoxy adhesive was used to
attach the fabric to the beams. This adhesive has been developed after years of
testing and has been shown to provide the required bond between concrete and carbon
fiber. The mixed adhesive has a viscosity of approximately 1400 CPS, which is sufficient
to provide complete wet-out of the fabric.
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Failure Mode For Partial Wrap |
All members were subjected to two-point loading up to failure. Deflections were
measured at the supports, load points and mid-span using linear variable displacement
transducers (LVDT). Strains were monitored at load points and mid-span using electrical
resistance strain gauge transducers.
For fully wrapped specimens (one to four layers), an increase in flexural strength
up to 70 % was observed. The strength increase diminished with increasing number
of layers beyond two layers. This was attributed to the fact that crushing of concrete
in the compression zone occurred before the full utilization of the tensile strength
of the fabric in the tension zone. The load deformation curves were linear and followed
a similar path up to the yield stress point of the internal steel reinforcement.
Beyond this yield point, the slope of the curves varied depending on the number
of FRP layers. All load deformation lines were bilinear regardless of the number
of layers of fabric.
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Splitting Failure Mode For Uni-Directional Materials |
Ductility was reduced with the increase in the amount of FRP. The partially wrapped
specimens exhibited less ductility and strength than the corresponding fully wrapped
specimens. Furthermore, the partially wrapped specimens exhibited a very undesirable
mode of failure.
As the applied load increased, a horizontal crack developed at the level of internal
steel reinforcement, followed soon afterward with the delamination of concrete in
the bottom portion of the beam, and failure. This brittle mode of failure indicates
that the use of partial wrapping is not an efficient way of strengthening and rehabilitation.
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