Table 6. Cumulative damage models used.
A. Flexible Pavement Horizontal Strain Criteria
1) The Asphalt Institute (MS-1, 1982):
[Ea -0.854 ]
-3.291
Na = 18.4 C (4.325 10 -3 ) ε t
where Na
=
number of load applications to 45% cracking
a function of the volume of the voids and the volume of asphalt, 10z
C
=
z
=
4.84 [(Vb/Vv + Vb) 0.69]
Vb
=
volume of the asphalt, percent (11%)
Vv
=
volume of the voids, percent (5%)
εt
=
tensile strain at the bottom of the asphalt layer, in./in.
modulus of the asphalt layer, lb/in.2
Ea
=
2) Witczak (1972) (i.e., Asphalt Institute MS-11):
d
Na = abq (1 / ε t )c
1.86351 1017
where a
=
b
=
1.01996
c
=
4.995
d
=
1.45
pavement temperature, F
q
=
3) The Corps of Engineers (U.S. Army 1988):
Na = 10(2.68-5 log
ε t -2.66 log Ea )
4) Coetzee and Connor (1990):
Na = a ε tb Eac
where when Ea ≥ 1,500,000 lb/in.2: a, b, c = 3.364 106, 7.370, 4.470
and when Ea < 1,500,000 lb/in.2: a, b, c = 6.565 106, 5.764, 3.640
B. Flexible Pavement Subgrade Strain Criteria
1) The Asphalt Institute (1982):
Ns = 10[1 / m (log l - log ε v )]
where Ns
=
allowable traffic based on subgrade strain
m
=
a constant (0.25)
a constant (2.8 102)
l
=
εv
=
vertical strain at the top of the subgrade, in./in.
2) The Corps of Engineers (U.S. Army 1987):
Ns = 10000 ( A / ε v ) B
where A = 0.000247 + 0.00245 log Es
B = 0.0658 Es0.559
Es = subgrade resilient modulus, lb/in.2
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