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Abstract: Few studies on the anchorage of reinforcing bars under the compressive conditions have been undertaken. This paper reports the results of 99 pushout tests done to investigate the compressive bond anchorage properties of 500 MPa steel bars in concrete. The precise slip values have been measured using a laser displacement sensor with high resolution, allowing the complete force-slip curves to be obtained.The influence of concrete strength, bar diameter, concrete cover, embedded length, and transverse reinforcement on the bond properties under compressive conditions is investigated. A new formula for calculating the compressive bond strength for 500 MPa reinforcing bars in concrete is proposed based on the test results. DOI: 10.1061/(ASCE)ST.1943-541X.0000793. © 2013 American Society of Civil Engineers.21614
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Author keywords: 500 MPa steel bars; Pushout; Compressive bond strength; Force-slip; Concrete and masonry structures.
Introduction
Bond in reinforced concrete refers to the adhesion between a
reinforcing bar and the surrounding concrete. The bond between
the reinforcing bar and concrete ensures strain compatibility (the
strain at any point in the bar is equal to that in the adjoining
concrete) and thus composite action of the concrete and steel.
A reinforcing bar must be embedded sufficiently far in the con-
crete to transmit the force within it to the concrete through
the bond.
Bond in reinforced concrete is achieved through the following
mechanisms: chemical adhesion due to the products of hydration,
frictional resistance due to the surface roughness of the reinforce-
ment and the grip exerted by the concrete shrinkage and mechanical
interlock due to the ribs provided on deformed bars. The contri-
bution of each of these processes to the overall bond strength is
complicated because at high steel strains there will be partial local
slip between the steel and the concrete, and the bond strength
will be provided by mechanical interaction between the bar and
the concrete rather than through chemical bond. The relative
strain between the steel and the concrete will vary throughout
the embedment length, and so the relative contributions of chemi-
cal and mechanical processes to the bond strength will also vary
throughout the embedment length. Consequently, experimental
studies on bond strength have not attempted to isolate the
contribution of each process to the bond strength, but have simply
evaluated the total bond strength experimentally.
Abrams (1913) undertook tests to determine the bond be-
tween concrete and iron bars as early as 1876. Although more than130 years have passed since then, bond research still continues.
Because the majority of reinforcing bars are used in tension and
the development length for tension is a critical design issue, many
researchers [including Li et al. (2011b, 2012), Mao et al. (2004),
Esfahani and Rangan (2000), Haskett et al. (2008), Nilson (1972),
Mirza and Houde. (1979), Song and Zhao (1987), Ichinose et al.
(2004), Wang (2009), and Xu et al. (1994)] have studied tensile
bond-slip models and have determined the factors that influence
tensile bond. However, few researchers have studied compressive
bond properties of reinforcing bars. Li et al. (2011a) have proposed
a model for compressive bond-slip relationship of 500 MPa rein-
forcing bars based on test results.
Embedded bars subject to compression cause splitting of the
cover in a different way to embedded bars subject to tensile
forces (Concrete Institute of Australia 2007) because the three-
dimensional stress state of the concrete is different. In the first
case, concrete is in compression in the direction parallel to the bar,
while in the second case concrete is in tension parallel to the
bar. Consequently, international codes (such as AS3600-2009