UFC 3-260-02
30 June 2001
(
(16-9)
The maximum difference in temperature between the top and bottom of the prestressed concrete
pavement is estimated to be about 6, 7, and 8 degrees for the 6-, 7-, and 8-inch pavements,
respectively, with resulting temperature warping stresses of 46, 65, and 75 psi, respectively. The design
prestressing required in the concrete is then determined by the following equation:
&
%
%
(16-10)
For hp values of 6, 7, and 8 inches, the design prestress ds in the longitudinal direction will be 853, 492,
and 253 psi, respectively, and in the transverse direction the values of ds will be 761, 391, and 151 psi,
respectively. Plotting these values, as shown in Figure 16-6, permits the selection of various
thicknesses and prestressing levels that will support the design loading condition. Experience has
shown that ds levels between 100 and 400 psi are most practicable; therefore, from Figure 16-6, a
provide a satisfactory pavement. With a slab length of 400 feet, 25 slabs and thus 24 joints will be
required for the 10,000-foot-long taxiway. In actual design, several combinations of k, hp, slab length,
etc., should be considered, and the final selection should be based on an economic study considering all
aspects of material and construction costs.
c. Prestressed Tendon Design. Plastic-encased stranded wire having an ultimate strength fF of
240,000 psi is selected for the prestressed tendons. The stranded wire tendon will be finally anchored at
a stress not to exceed 0.7fF or 168,000 psi. The required area of steel in the longitudinal and transverse
directions to achieve the design prestressing level in the concrete and allowing for the various tendon
stress losses will be
(16-11)
(16-12)
Several combinations of wire diameter and spacing will yield the required cross-sectional area of steel
for the stressing tendons. For example, if in the longitudinal direction, a spacing of four times the
prestressed concrete pavement thickness (30 inches) is selected, then 30 tendons will be required, each
having a cross-sectional area of 0.58 square inch and diameter of 0.86 inch. Therefore, a
7/8-inch-diameter tendon could be selected. Selection of a tendon that is greater or less than that
required may require the final anchor stress to be revised. If, in the transverse direction, a spacing of
five times the prestressed concrete pavement thickness (37.5 inches) is selected, then 128 tendons
16-8
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