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TECHNICAL PAPER

π
IN-SITU -ANCHOR FOR

FIBER-REINFORCED

POLYMER U-WRAPS USED

FOR STRENGTHENING SHEAR

DEFICIENT REINFORCED

CONCRETE BEAMS A. GHANI RAZAQPUR*,

CLINTON D’SOUZA

Abstract because the top surface of beams is often attached to the slab
and is inaccessible. U-wrap and side-bonded configurations
An in-situ carbon fiber-reinforced polymer (CFRP) π-anchor is are alternatives, but they are not as effective because of their
developed for CFRP U-wraps used to strengthen reinforced limited bond length, which precipitates premature debonding
concrete beams in shear. Fourteen beams were tested, and a and prevents them from developing their strength. This is a
segment of some beams was diagonally pre-cracked at 30 or major problem as it reduces the efficiency of the FRP and leads
45° inclination. The cracked segment was not provided with to higher cost. Using the experimental data in NCHRP Report
internal stirrups but strengthened by surface bonded CFRP full 678 , Belarbi and Acun presented an extensive review of the
[3]
[2]
wraps or U-wraps. The U-wraps fitted with the new anchor fully failure modes of beams externally strengthened in shear with
restored the beam strength. In a beam with a 30° diagonal crack, FRP laminates. They reported no debonding in fully wrapped
the U-wraps with the π-anchor increased the beam strength 74% beams, debonding in 83% of U-wrapped beams and in 92% of
more than the strength of the companion beam with twice the side- bonded beams.
U-wrap but without anchor.
To solve the problem of premature debonding for U-wrapped
Keywords: Anchor, Concrete beam, FRP, Retrofit, Shear. and side-bonded configurations, many anchorage systems have
been proposed and tested [4-12] . Presently, the main anchorage
1. INTRODUCTION systems consist of horizontal FRP strips, FRP spike anchors, and
metallic anchors.
Damage to internal steel reinforcement in reinforced concrete
structures due to corrosion or fatigue is a major problem in The strip anchor comprises horizontal FRP strips bonded to the
aging infrastructure. Since it is not economical to replace all FRP U-wrap or side bonded laminates at their free ends. This
damaged reinforced or deficient concrete structures at the anchorage system requires the least amount of labour compared
same time, strengthening them provides a practical solution. to others, however, there are conflicting reports regarding its
Fiber-reinforced polymer (FRP) composites have been used in effectiveness. Schnerch [13] used it for shear strengthening of full
construction to externally strengthen concrete structures for the scale prestressed concrete I-girders and reinforced concrete
past 25 years. Their high resistance to corrosion, high strength T-beams and reported that it did not delay debonding of the
to weight ratio, and minimal labour requirements make them an external FRP shear reinforcement nor it increased the shear
attractive choice for strengthening . capacity of the strengthened beam. On the other hand, Al-
[1]
Mahaidi and Kalfat [10] reported that in their tests conducted on
For shear strengthening, the FRP laminate or fabric can be beams with U-wrap and side-bonded shear reinforcement, it
wrapped around the entire cross-section of the beam (fully delayed debonding and increased the beam shear capacity.
wrapped), bonded to the beam sides and bottom (U-wrapped),
or only to the sides (side bonded). Full wrapping is the most FRP spike anchors consist of resin impregnated fiber roving
effective configuration as it can fully develop its strength, which is inserted through the FRP wrap at its free ends and
provided failure at the cross-section corners can be averted. inserted into pre-drilled holes in the concrete. The fibers at the
Despite the advantage of full wrap, it is usually impractical protruding end of the roving are splayed onto the exposed

THE INDIAN CONCRETE JOURNAL | OCTOBER 2020 7
*Corresponding author : A. Ghani Razaqpur, Email: razaqpu@mcmaster.ca