concrete cover required. The length of the cylinders varied with
the embedded length of the rebar. Both the bottom and the top
surfaces of the specimens before tests can be seen from Fig. 2.
The specimens were cast in smooth cylindrical molds in the same
orientation that they were tested (Fig. 3). The bottom surfaces of
the molds were smooth, ensuring that the bottom surface of the
specimens were consistently smooth where they were in contact
with the metal pad (item 5 in Fig. 4).To investigate the influence of the five main factors on the
ultimate compressive bond strength, five series of specimens were
designed, AT for strength of the concrete, BT for size of the bar, CT
for concrete cover, DT for embedded length, and ET for transverse
reinforcement. The details of the specimens are provided in Table 1.
A sketch of a pushout specimen is provided in Fig. 3. The com-
pressive force was applied to the end of the 20-mm length of
bar protruding from the top of the specimen (the load end). The
bars protruded 90 mm from the bottom of the specimen to allow
connection of the displacement sensors (the free end). Because the
bottom of the cylinders rested on a bearing plate, the bars weredebonded from the concrete cylinder for a length of 5d from the
bottom of the cylinders (where d is the bar diameter) using a plastic
tube in order to reduce any influence of the disturbed stress zone
close to the bearing plate.
The test setup is shown in Fig. 4. A flat metal plate with a thick-
ness of 8 mm was placed on the top of the reinforcing bar in order to
apply the load to the bar evenly. The slip of the bar relative to the
concrete at the load end and the free end were measured to high
resolution with the testing machine and two laser displacement
sensors (LDSs) [Keyence (Japan) LB-72/LB-12]. On the free end,
two LDSs were clamped to the rebar using magnets in order to
measure the relative displacement between the bar and the base of
the cylinder. They were diametrically opposed to each other in
order to compensate for any rotation of the bar. The relative dis-
placement between the base of the concrete and the load end of
the reinforcing bar was measured by the testing machine.
The tests were performed using a Baldwin loading machine with
a capacity of 200 kN, and a data acquisition system (DAQ) was
used to collect the data. Each specimen was placed vertically on
the bearing plate and a compressive force was applied at the top
extremity end of the bar, which can be seen from Fig. 5.
All the tests were carried out in displacement control mode.
The load was measured with the electronic load cell of the machine.
Output from the testing machine and the two LDSs was recordedthrough the automatic data acquisition system. The load rate for the
specimens was proportional to the square of the bar diameter, and
was calculated by the formula VF ¼ 0.03d2
, where VF is the load
rate in units of kilonewtons per minute and d is the diameter of the
bar in millimeters.
The loading process was continued until either (1) the enclosing
concrete split, or (2) slippage of approximately 20 mm had oc-
curred at the load end.
Observed Phenomena and Analysis
Failure Modes
Two types of failure modes were observed: (1) pushout failure
when adequate confinement was present, and (2) splitting failure
with a sudden drop of bond stress when the concrete cover split
along the reinforcing bar. A few of the specimens with longer em-
bedded length or with stirrups exhibited the damage characteristics
of bar yield. Photographs of some of the specimens after testing are
provided in Fig. 6.
Compressive Force-Slip Curve
After processing the data acquired from each test, the force-slip 钢筋在混凝土中的受压英文文献和中文翻译(3):http://www.youerw.com/fanyi/lunwen_13898.html