UFC 3-260-02
30 June 2001
deep enough to weaken the subgrade soil. When this is the case, the reduced subgrade strength
method shall be used for design. The procedures to determine the PCC thickness using the elastic
layered model are then applied in the same manner as in the first part of this example; the only input
parameter change is the (reduced) subgrade elastic modulus. To check for a lesser thickness
requirement with limited frost penetration procedures, the criteria in Chapter 20 should be used.
11. DESIGN EXAMPLE 2, MIXED AIRCRAFT TRAFFIC. This design example is for type A traffic areas.
The airfield has traffic of 12,500 passes of C-141 (156,500 kilograms (345,000 pounds)), 100 passes of
B-52 (181,450 kilograms (400,000 pounds)), and 25,000 passes of F-15 (30,850 kilograms
(68,000 pounds)), and 12,500 passes of C-17 (1,179,400 kilograms (260,000 pounds)). The
characteristics of the design aircraft are presented in Table 19-5. A 250-millimeter (10-inch) thick
stabilized base layer is used in this example. An SCI = 80 is desired at the end of the design life.
a. Computations of Critical Stresses and Damage. A number of trial concrete slab thicknesses were
selected for design. The maximum tensile stress in each concrete slab under each aircraft loading was
computed using the elastic layered model. Equations 19-1, 19-2, and 19-3 were used to calculate the
allowable coverages based on the calculated stresses and the flexural strength of 4.48 MPa (650 psi) for
the PCC following the same procedure outlined in example 1. The amount of damage is the ratio of the
design or applied passes to the allowable passes. The computed damage for different PCC
Table 19-3
Computation of Cumulative Damage for Selected Pavement Sections, Granular Bases, and C-130
Aircraft
PCC
Base
Maximum
Design
Allowable
Passes1
Thickness, in.
Thickness, in.
Stress, psi
Passes
Damage
(1)
(2)
(3)
(4)
(5)
(6) = (4)/(5)
13
6
343
200,000
18,691
10.7
14
6
309
200,000
64,299
3.11
15
6
280
200,000
232,481
0.86
16
6
255
200,000
894,250
0.22
13
18
336
200,000
23,888
8.37
14
18
303
200,000
80,842
2.47
15
18
275
200,000
290,452
0.69
16
18
251
200,000
1,111,962
0.18
1
Allowable passes are computed using equations 19-1, 19-2, and 19-3 based on the computed
maximum stress shown in column (3), on a selected value of R, and the pass-to-coverage ratio for the
C-130 aircraft.
Conversion Factors: Millimeters = 25.4 inches, Megapascals = 0.006894 psi
19-13
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