30 June 2001
10. DESIGN EXAMPLE 1, SINGLE AIRCRAFT.
a. Plain Concrete. This design example is for an airfield taxiway supporting the C-130 aircraft. The
design loading for the C-130 on the taxiway is 70,300 kilograms (155,000 pounds). The design is for the
C-130 aircraft having a single tandem gear with a tire spacing of 1.5 meters (60 inches) c-c, a tire load of
15,820 kilograms (34,875 pounds), a tire contact area of 0.258 m2 (400 in.2), a design traffic of
200,000 passes and a pass to coverage ratio of 4.40. For this example an SCI of 80 is desired at the
end of the design life.
(1) Computations of critical stresses and damages. Several trial concrete slab thicknesses, i.e.,
330, 356, 380, and 405 millimeters (13, 14, 15, and 16 inches) and two thicknesses of granular base and
stabilized base, i.e., 15 and 457 millimeters (6 and 18 inches), were selected for design. The maximum
tensile stresses in each concrete slab were computed using the elastic layered model JULEA.
Equations 19-1, 19-2, and 19-3 were then used to calculate the allowable coverages based on the
calculated stresses and the 4.48-MPa (650-psi) flexural strength of the PCC. The amount of damage is
the ratio of the design passes to the allowable passes. The computed values, together with other
pertinent pavement information, are presented in Tables 19-3 and 19-4 for different base materials. As
an illustration, the determination of values shown in the first line of Table 19-3 is explained. For a
pavement with 330-millimeter (13-inch) PCC and a 15-millimeter (6-inch) base, the maximum stress
under the C-130 aircraft using the computer program JULEA is 2.36 MPa (343 psi). Since an SCI = 80
is desired at the end of the design life, the allowable pass level should be determined from the linear
variation between initial cracking (Co) and complete failure (Cf) (Figure 19-3). From Equation 19-1, the
log Co = 3.50, and from Equation 19-2, the log Cf = 4.12. Interpolating for an SCI = 80, a coverage level
of 4,248 is obtained. The allowable pass level is computed as 4,248 * 4.40 = 18,691. The damage is
calculated as the ratio of 200,000 and 18,691, i.e., 200,000/18,691 = 10.7.
(2) Selection of Concrete Thickness. The results between PCC thickness and damage
presented in Table 19-3 for granular bases and in Table 19-4 for stabilized bases are plotted in
Figure 19-8. The required PCC thicknesses are determined at a damage of 1. The required concrete
thicknesses are 373 millimeters (14.7 inches) and 378 millimeters (14.9 inches) for granular bases of
457 millimeters (18 inches) and 152 millimeters (6 inches), respectively, and are 358 millimeters
(14.1 inches) and 373 millimeters (14.7 inches) for stabilized bases of 457 millimeters (18 inches) and
152 millimeters (6 inches), respectively (thicknesses will be rounded to the nearest 10 millimeters
( inches) for construction). Figure 19-8 shows that in the case of granular base, the increase of the
base thickness from 152 to 457 millimeters (6 to 18 inches) reduces the PCC only 5 millimeters
(2/10 inch). In the case of the stabilized base, the increase of the base thickness from 152 to
457 millimeters (6 to 18 inches) can reduce 13 millimeters ( inch) of PCC. However, an economical
comparison should be made between the 13-millimeter (-inch) reduction in PCC and the 305-millimeter
(12-inch) additional stabilized base to determine the final design.
b. Reinforced Concrete. For reinforced concrete pavements, the increase in effective slab thickness
due to the presence of the steel in the pavement can be determined from the relationship shown in
Figure 19-7. For example, if 0.10 percent reinforcing steel is used for the particular concrete thickness of
381 millimeters (15.0 inches), which was computed in the previous example (see Figure 19-8 for the
case of a 152-millimeter (6-inch) base), the relationship shown in Figure 19-7 indicates that the slab
thickness can be reduced to 381 millimeters 0.9 = 343 millimeters (15 inches 0.9 = 13.5 inches).
c. Frost Action. When frost action needs to be considered in the design, it should first be
determined if the subgrade soil is frost susceptible. A description of frost susceptible soils is given in
Chapter 20. The depth of frost penetration in the region shall be determined to check if the frost action is