U-Wrapped Configuration Variation on Shear Strengthening of RC Beam by Carbon Fiber Reinforced Polymer Fabric

Abstract

The demand to upgrade deficient structural members has grown over
the years. According to experimental and numerical publications in this
area, the application of fiber-reinforced polymer (FRP) to strengthen
reinforce concrete (RC) elements in shear is an effective means.
Strengthening RC beams with carbon FRP has several advantages over
the steel plate strengthening method, for instance, ease of application,
weight to high strength ratio, and durability. This paper studies the
effect of U-wrapped configuration variation on the shear strengthening
of RC beams by carbon FRP fabrics. Three shear strengthening Uwrapped configurations of CFRP fabric were studied: 200 g/m2 and
300 g/m2 of CFRP fabric strips of 100 mm by 400 mm applied as Uwrapped, spaced 250 mm center to center as a model of the prototype;
200g/m2 and 300 g/m2 of CFRP fabric measured 250 mm by 367 mm
applied as U-wrapped in the shear spans from the bottom of the beam
as a model of the prototype; 200 g/m2 and 300 g/m2 CFRP fabric strips
of 300mm by 400mm applied as strip U-wrapped, spaced 375 mm
center to center as a model of the prototype. Thirteen (13) RC beams
(100 x 150 x 1100 mm) with flexural internal reinforcement (As =2Φ10
mm), compression reinforcement (AS =2Φ8 mm) and shear
reinforcement (Asv =Φ6 mm @ 220 mm c/c). The beams were
strengthened in shear as described above with bond thickness of 2 mm,
4 mm, and 6 mm. All the beam samples were subjected to two-point
load application to examine the CFRP contribution to shear strength.
The beams strengthened by U-wrapped CFRP fabrics improved the
shear capacity of the control beam by 40%. The U-wrap
configurations, which were designed to simulate the conventional
method of shear reinforcement placement along the longitudinal axis
of the beam, provided the best results compared to the other U-wrap
configurations. The CFRP fabric to bond thickness ratio should not be
more than 0.069. According to ACI 440 2R 17, a complete-wrapping
configuration provides the best result in terms of increasing the shear
strength of the strengthened RC beams. However, the study proves that
in the absence of complete-wrapped configurations, U-wrap
configurations simulating the conventional shear reinforcement
placement along the horizontal axis can also be employed effectively.
Bond thickness was also observed to have a significant impact on the
shear strength of RC beams.