Enhancement of the Flexural Behavior of CFRP Strengthened RC Beams in Medium and Low Grade Concrete
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Date
2018-10-24
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Abstract
Carbon Fiber Reinforced Polymer (CFRP) has been proved to enhance the flexural strength
of Reinforced Concrete (RC) beams and there is a wide range of application all over the
world. As new strengthening technique Externally Bonded Reinforcement (EBR) FRP has
developed and penetrated the market so quickly, however, its effectiveness on low strength
concrete is questionable and there is also a minimum concrete compressive strength limit on
some deign codes like ACI-2.R-08. The rationale behind this limit is not discussed in the
code and measure that could be taken to improve FRP strengthening techniques at lower
concrete grades is not yet known.
This research assesses different flexural strengthening techniques on medium and low
concrete grades including the minimum limit recommended by ACI. A new CFRP anchorage
technique is also proposed and its performance is compared with other prevailing application
techniques. To do so, RC beams of medium and low concrete strength are casted in the
laboratory and tested with a three point loading then the result is used to validate the concrete
and steel material model on Abaqus non-linear finite element software. Other experimental
results are also used to validate EBR CFRP and end wrapped CFRP strengthened beam
models after different interaction models have been tried on the software.
With the best fitting models validated to represent CFRP strengthened beams, additional
simulation works are done together with section analysis and other analytic manual
calculations. With a one layer 1.4 mm thick SIKA Carbodur E-1014 CFRP Laminate,
remarkable strength and stiffness increment is observed in all concrete grades and application
techniques. However, beams with lower concrete compressive strength close to ACI limit are
found prone to FRP end delamination at their ultimate capacity. More study was done on the
delamination of these low strength beams and the new anchorage technique delayed the
delamination of FRP and increased the ultimate load capacity. The other very important
benefit gained from application of the new anchorage is that it dislocated the delamination
initiation from the end of the FRP to the middle of the beam which is less brittle in nature
compared to the one that initiates at the end of the FRP.
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Keywords
CFRP, RC Beams, Low Grade Concrete, Medium Grade Concrete, Flexural Behavior