UFC 3-260-02

30 June 2001

pass level is divided by the aircraft pass per coverage factor to determine the design number of stress

repetitions, which are in turn used in Figure 16-1 to obtain N. The load-moment factor B and ratio of

multiple-wheel load to single-wheel load w are determined from Figures 16-2 and 16-3, respectively, by

entering with a value of A/R2 (note that for the light-load and Class I airfields, w is 1.0 for all values of

A/R2). A is the contact area in square inches of a tire in the main gear of the design aircraft, and R is

computed by

(16-2)

R

&

where

R = radius of relative stiffness, inches

E = the modulus of elasticity of concrete (a value of 4,000,000 psi is normally used)

hp = design thickness of prestressed concrete pavement, inches

= Poisson's ratio

k = modulus of subgrade reaction, pci

c. Foundation Restraint Stress. The subgrade restraint stress rs is a function of the coefficient of

sliding friction between the pavement and underlying foundation and the length or width of the

prestressed concrete slab and is determined by

D

D

(16-3)

where

rs = foundation restraint stress, psi

Cf = coefficient of sliding friction

L = length of prestressed concrete slab, feet

W = width of prestressed concrete slab, feet

D = density of concrete, lb/ft3

Experience has shown that for a prestressed concrete pavement constructed with sand and

polyethylene sheet bond-breaking medium on the surface of the prepared foundation, a value of Cf of

0.60 is representative. This value can be reduced, with a subsequent reduction in the design prestress

level, through the selection of materials with lower coefficients of friction and through careful preparation

of the foundation layer.

16-3

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