Performance of Reinforced Concrete T-Girders Strengthened in Shear
with Carbon Fiber-Reinforced Polymer Fabric
ACI Structural Journal, 99 (3):
335--343 (May 2002)Abstract
This paper presents results of an experimental investigation on the
performance of 20 ft long reinforced concrete (RC) T-girders strengthened
in shear using epoxy-bonded bidirectional carbon fiber-reinforced
polymer (CFRP) fabric. The main objective of the study was to evaluate
and gain insight into the effectiveness of shear strengthening of
large-scale girders with externally bonded CFRP under a low shear
span condition. The study considered four series of tests corresponding
to the following four stirrup spacings: 5.5, 8, 16, and 24 in. Each
series of girders included control specimens with no CFRP wrap and
specimens retrofitted in shear with one, two, and three layers of
CFRP wrap. Results showed that for unwrapped specimens, the values
for nominal shear predicted by ACI underestimated, by 40 to 80%,
the shear resistance of beams developing arch action, such as those
considered in this study. For wrapped specimens, the maximum shear
force as well as the midspan deflection generally increased with
the number of CFRP layers. The optimum number of layers to achieve
the maximum gain in shear resistance was found to depend on the internal
shear steel reinforcement provided. The effective CFRP strain used
to calculate the contribution of the CFRP to the shear capacity was
correlated to the total shear reinforcement ratio consisting of steel
stirrups and CFRP wrap. Retrofitting RC girders in shear with CFRP
wrap also increased the ductility. The experimental evidence indicates
that an optimum combination of CFRP layers and steel stirrups exists
for a maximum increase in ductility.