UFC 3-260-02

30 June 2001

established criteria for the design of reinforced pavements is shown in Figure 19-7. Assuming that the

proposed elastic layer design procedure can result in adequate thicknesses of unreinforced pavement,

application of the criterion illustrated in Figure 19-7 will result in adequate thicknesses of reinforced

pavements.

9. DESIGN EXAMPLES. Design examples are given illustrating various layer elastic design

procedures. The first example illustrates the procedure for selecting a concrete thickness for an airfield

designed for a single aircraft. This design example considers the cases of unreinforced concrete slabs.

The second example is for an airfield subject to mixed traffic. Overlay designs are given in the last

example. The designed concrete pavements are for a type A or primary traffic area. The steps in

designing a rigid pavement using the elastic layered method are to establish input data, compute critical

stresses, and complete final design.

a. Input Data Required for the Design.

(1) Modulus values and Poisson's ratios of the PCC, bonded and nonbonded granular

materials, and subgrade soil. For the purpose of this design example, the following values are assumed

in the computation.

EPCC and PCC = 27,580 MPa (4,000,000 psi) and 0.2, respectively

Ebound and bound = 1,034 MPa (150,000 psi) and 0.2, respectively (stabilized base)

Eunbound and unbound = 207 MPa (30,000 psi) and 0.3, respectively (granular base)

Esubgrade and subgrade = 42 MPa (6,000 psi) and 0.4, respectively

(2) Flexural strength of the PCC. A value of 4.48 MPa (650 psi) is assumed.

(3) Aircraft parameters. The characteristics of the design aircraft and other traffic data required

in design are wheel load, number and spacing of wheels in an assembly, tire contact pressure, design

life, design traffic, design coverage level, and pass-to-coverage ratio for the particular aircraft.

(4) Limiting stress criteria. Equation 19-1 and 19-2 are used to determine the allowable

coverages based on the computed critical stresses induced by the design aircraft.

b. Computation of Critical Stresses. The critical tensile stress in the trial concrete section is

computed using the JULEA elastic layered model based on the design aircraft loading and the material

properties of each component layer. The interface conditions between layers are such that frictional

constraints do not exist between the PCC slab and the base layer and that frictional constraint is

developed between the base layer and subgrade soil. Several concrete trial sections are needed for

each design. A nearly optimum concrete slab thickness should first be selected, and concrete

thicknesses less and greater than the optimum value are then selected. Computations should also be

made for different thickness of base-course materials.

c. Final Design. The accumulated damage for each trial concrete section is computed based on the

design and the allowable coverages. The final concrete slab thickness is selected as that thickness

having an accumulated damage of 1.

19-11

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