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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