UFC 3-260-02

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

19-12

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