UFC 3-260-02

30 June 2001

plates and concrete slab as a reaction, to the required total stress level and locked. The total stress

level in the tendons is the sum of the stress needed to provide the design prestress level in the concrete

plus the stress necessary to offset the various losses that will occur. To help reduce cracking in the

concrete during the cure period, a preliminary level of prestress is normally applied at a very early age,

and the final level of prestress applied after several days of curing. Both longitudinal and lateral

prestressing is needed to obtain the desired structural capacity in the pavement.

6.

DESIGN PROCEDURE.

a. General. In the design of prestressed pavements, both thickness and level of prestress will be

unknowns; therefore, their determination, in both the longitudinal and transverse directions, becomes an

iterative process (that is, one is selected and other computed). A normal practice is to compute the

thickness requirements for a range of prestress levels, after which the final selection is made based

upon an economic analysis. A maximum value of design prestress of 400 psi is recommended; and

based upon experience, a design prestress level falling between 100 and 400 psi has been most

economical. The minimum thickness of prestress concrete pavement will be 150 millimeters (6 in.).

b. Design Equation. The design prestress for a given thickness of pavement will be determined as

follows:

&

%

%

(16-1)

where

ds = design prestress required in concrete, psi

P = aircraft gear load, pounds

N = load-repetition factor

B = load-moment factor

w = ratio of multiple-wheel gear load to single-wheel gear load

hp = design thickness of prestressed concrete pavement, inches

R = design flexural strength of concrete, psi

rs = foundation restraint stress, psi

ts = temperature warping stress, psi

Since both ds and hp will be unknown, it is necessary to select values of hp and compute ds. For

guidance, experience has shown that ds levels between 100 and 400 psi are generally economical, and

at these levels hp will be about one-third of the required thickness of plain concrete pavement. The

design gear load P will depend upon the aircraft for which the pavement is being designed. The load-

repetition factor N is a function of the type of design aircraft and the traffic area type. The design aircraft

16-2

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