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work is idealized as elastic-plastic with kinematic hardening,
while a linearly elastic constitutive relationship is used for the
spring in the elastic-viscous network. The developed model was
calibrated by Park et al. 2010 using data in Bramel et al. 1999
and Cheung and Cebon 1997.
The developed finite-element model was extensively validated
by Park et al. 2010. This was achieved by comparing model
results to data from two test programs. In particular, force defor-
mation data and strain distributions were computed and compared
to measured test data. Fig. 5 shows an example of a comparison
between the horizontal strain computations from the model andspecimen APJ-1 in Moon et al. 2008. The strains in question are
average surface strains measured from the displacement of small
spikes installed over the surface of the specimen. Clearly, there
is reasonably good correlation between the model and test data.
Fig. 5 shows that not only do the computed strains match reason-
ably well with the experimental measurements, but also the dis-
tribution of strains and the locations of strain concentrations are
well represented.
Loading and Boundary Conditions
The two dominant APJ loading cases considered herein are ther-
mal movement and traffic load. As shown in Fig. 4, traffic load is
applied as a moving traction over the surface of the APJ, which
has two components: normal and shear henceforth designated W
and S. The former is due to the weight of the vehicle while the
latter is caused by the braking or accelerating forces of the ve-
hicle. In this study, an equivalent single axle load ESAL of 80
kN is applied as a moving traffic load. This load is typically used
in pavement design and is not directly associated with the design
truck load in the AASHTO LRFD specifications AASHTO
2004. Moreover, it does not include the effect of impact specified
in AASHTO LRFD AASHTO 2004. The load was selected so as
to match that used in a previous related study as well as pavement
studies the writers are currently undertaking. In essence, however,
the actual value of the load itself does not matter because the
study presented herein is comparative in nature. The tire load is
transformed into a uniformly distributed normal traction W of
0.6375 MPa.
Park et al. 2010 investigated the effect of shear traction on
local demands of APJ by applying shear tractions of S=0, 0.1W,
0.25W the recommended braking force in the AASHTO 2004,
and 0.5W. They showed that the stress and strain demands at
point A significantly rise with the increase of applied shear trac-
tion. In this study, two extreme conditions are selected for further
study: tire load without shear traction S=0 representing passage
of unpowered truck axles; and tire load with maximum shear
traction S=0.5W representing an extreme deceleration of a truck
on the APJ. The fast rate of loading in these cases eliminates
the influence of the time-dependent nature of the APJ materials,
implying that response is linear elastic, i.e., stress and strain de-
mands under traffic loads are linearly proportional to the magni-
tudes of the applied load. The movement of the traffic load is
pided into 18 loading steps, and the location of the traffic load is
assumed to move forward 50 mm each step as shown in Fig. 4.Park et al. 2010 noted that an important factor in simulating
joint movement of APJ is the debonding that occurs at the bottom
boundaries. When thermal movement is applied to an APJ, the
gap plate and concrete deck move in opposite directions, and
consequently the bottom of the joint must debond to accommo-
date motion around the edge of the gap plate. Park et al. 2010