Abstract:
Carbon Fibre Reinforced Polymer (CFRP) strengthening technique had been shown
excellent performance in externally strengthening Reinforced Concrete (RC) elements
due to their superior properties compared to the alternatives. A substantial amount of
studies had been done to study the behaviour of externally CFRP strengthened RC
elements. However, as per the authors’ knowledge, while most of the studies have
been focused on the external strengthening of straight RC beams using CFRP, none
of the studies had been focused on strengthening horizontally curved RC beams.
Curved beams innately respond with flexure, shear and especially torsion under outof-plane
loads due to its curvature. Hence, it is important to study the effect of the
additional torsional stress on the CFRP external reinforcement.
A detailed experimental program, a theoretical analysis and a numerical analysis were
conducted in order to reduce the aforementioned research gap. A series of testing was
conducted on beam specimens with 2 m and 4 m radii and externally strengthened
with normal modulus CFRP fabrics to enhance the effects; shear, torsion and their
combination.
From series one experimental results, it was found that the wrapping CFRP fabrics
have enhanced the shear capacity of the curved RC beams by at least 30 % and the
enhancement is higher for beams with lower curvatures. It showed that CFRP
wrapping is a very effective method to enhance the shear capacity of horizontally
curved beams.
The series two experimental results showed that U-socketing of CFRP fabrics for
shear has increased the shear strength by 15.61 kN (16.7 %) and 17.41 kN (18.2 %)
respectively for 2 m and 4 m radius specimens. The main failure mode was crack
induced intermediate debonding of CFRP U-sockets. However, the predicted shear
enhancements according to theoretical investigation are 23.64 kN and 24.51 kN for 2
m and 4 m radius beams respectively. It can be observed that for 2 m and 4 m
specimens recorded respectively 33.97 % and 28.97 % less than the predicted
enhancement by the theoretical study. This can be explained by the additional
torsional stresses contributing to the direct shear stresses which cause to reduce the
shear capacities of RC beams.
The results from numerical models showed excellent agreement with experimental
results which was used to carry out a parametric study. Subsequently, a capacity
reduction factor was defined as the ratio between numerical shear gain and
theoretically predicted shear gain to quantify the effect of torsional stresses on the
shear enhancement of U-socketed CFRP on RC beams with a 1.4 m support distance
which can be used to modify the currently existing analytical model adopted by ACI
440.2R-17 guide to design of FRP as external reinforcement for RC beams.
