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(Standards Australia 2009), GB50010-2010 (China Building In-
dustry Press 2010), ACI 318-05 (American Concrete Institute
2005), and Eurocode 2 [European Committee for Standardization
(CEN) 2004]) contain a variety of formulas for calculating the com-
pression development lengths. The majority of the experimental
data from which most of these formulas have been developed have
been obtained using lower strength bars.
This paper reports further research in this field. Through a
series of pushout experiments, the compressive bond properties of
500 MPa reinforcing bars in concrete are studied.
Like the tensile anchorage properties of the bar, the factors
influencing bond under compressive conditions can be classified
into four main groups:
1. Influence of concrete on bond: concrete compressive strength,
concrete tensile strength, concrete cover, grading of aggregate,
consistency of fresh concrete, and fibers in concrete.
2. Influence of position of bar on bond: position of bar during
casting, position of bar relative to the nearest flexural crack,
and width of splitting crack along the bar.
3. Influence of reinforcement on bond: relative rib area of bar,
rib pattern of bar (including inclination and shape of ribs),
diameter of bar, coating (epoxy coating for steel bars or sandcoating for nonmetallic bars), corrosion of steel bars, amount
of transverse reinforcement, stress in the reinforcement, and
bar spacing.
4. Influence of load on bond: transverse pressure in anchorage
area, monotonically increasing loading (including influence of
loading rate), long-term loading, cyclic, loading and reversed
cyclic loading.
The final bond strength is also dependent on the embedded
length. All of these parameters influence compressive bond behav-
ior in different ways. In specific cases, careful analysis is required.
However, for any given type of the reinforcing bars and type of
concrete, five of these factors have been found to have significant
influence on the bond strength (Mao et al. 2004; Xu et al. 1994).
This paper addresses the influence of each of these fivemain factors
(strength of the concrete, size of the bar, concrete cover, embedded
length, and transverse reinforcement) on the compressive bond
strength of 500 MPa reinforcing bars. A program of pushout tests
designed to evaluate the influence of each of these factors sepa-
rately is reported. Based on the results, a formula for bond strength
taking into account these factors is proposed.
Experimental Program
The experimental program reported in this paper involved a series
of 99 pushout tests. In each test a length of reinforcing bar was
cast into a cylinder of concrete and then pushed out by a testing
machine. Each cylinder was supported so as to ensure the bar could
be pushed out of the cylinder without interference. Parameters were
varied to determine the influence of strength of the concrete, size of
the bar, concrete cover, embedded length, and transverse reinforce-
ment on the compressive bond strength of 500 MPa reinforcing
bars. The concrete mixes were typical of normal strength Chinese
construction concrete. All the concrete components including
the cement, water, sand, and aggregate were identical, while the
proportions were varied to achieve the various concrete strengths.
The effect of admixtures was not investigated. For each combina-
tion of parameters, three tests were performed.
The reinforcement bars (Li et al. 2010) used all had nominal
yield strength of 500 MPa and the rib pattern shown in Fig. 1.
The bars were embedded in cylinders of concrete with diameters
of 100 or 150 mm, with a single deformed bar in each cylinder.
The bar position was determined by the minimum value of the