the vertical strain at the top of the subgrade, and
put files and calculates the allowable applications
these relate to rutting damage in the pavement.
predicted by the various models under those con-
They were developed by the Asphalt Institute
ditions. It then divides the design applications by
(1982), the Federal Aviation Administration (Bush
the allowable applications, producing a daily in-
1980), and the Corps of Engineers (U.S. Army
cremental damage value. The incremental values
1987). For rigid pavements, CUMDAM uses the
are summed to produce a cumulative damage value
damage model developed by the Corps of Engi-
and these are printed to individual files for each
neers (U.S. Army 1990), which is based on the
model type. A file summarizing the daily strain
horizontal stress at the base of the PCC.
and deflection information is also produced.
The program assumes that all applications will
affect the point being modeled. That is, the dam-
age is not reduced according to a pass-to-cover-
MN/ROAD PAVEMENT
age algorithm to simulate the lateral wander of the
PERFORMANCE STUDIES
axle within the travel lane.
It is recognized that some of the equations are
Performance predictions using the Mechanistic
being applied outside of the original assumptions
Pavement Design Procedure were conducted in
used in their development; however, they are rep-
three major efforts:
resentative of cumulative damage models currently
Phase 1, conducted in the spring of 1991, in-
available and are used for the initial analysis until
cluded an initial simulation series that modeled
more appropriate equations can be developed.
temperatures from a year close to the mean freez-
The CUMDAM program first reads the strain/
ing index. These boundary conditions were ap-
stress conditions from the daily NELAPAV out-
plied to eight flexible and three rigid sections.
Table 7. Layer composition and thicknesses of pavement structure in test sec-
tions simulated.
Test
Layer 1
Layer 2
Layer 3
Thick †
Section
Comp*
Comp
Thick
Comp
Thick
Flexible
5-yr design
F-1
AC
14.6
(5.75)
CL4
83.8 (33.0)
F-2
AC
14.6
(5.75)
CL6
10.2 (4.0)
CL4
71.1 (28.0)
F-3
AC
14.6
(5.75)
CL5
10.2 (4.0)
CL3
83.8 (33.0)
F-4
AC
22.2
(8.75)
10-yr design
F-14
AC
27.3 (10.75)
F-19
AC
19.7 (7.75)
CL3
71.1 (28.0)
F-21
AC
19.7 (7.75)
CL5
58.4 (23.0)
F-22
AC
19.7 (7.75)
CL6
45.7 (18.0)
Rigid
5-yr design
R-5
PCC
19.7 (7.5)
CL4
7.6 (3.0)
CL3
68.5 (27.0)
R-6
PCC
19.7 (7.5)
CL4
12.7 (5.0)
10-yr design
R-11
PCC
24.1 (9.5)
CL5
12.7 (5.0)
AC--asphalt concrete; PCC--portland cement concrete; CL3--class 3 special;
CL4--class 4 special; CL5--class 5 special; CL6--class 6 special
†Thickness, cm (in.)
14
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