UFC 3-260-03
15 Apr 01
used to compute edge stresses for a range of pavement thicknesses and subgrade moduli, k . The maxi-
mum edge stress condition is a free edge with no load transfer. The edge stress is reduced as more load
is transferred across the joint. The 75 percent stress corresponds to a deflection ratio of 0.76, and this
would be for 100 percent of the design load (load factor of 1.00). The condition of 100 percent maximum
stress would occur at a deflection ratio of 0.0 (no load transfer) and would allow for only 75 percent of the
design load (load reduction factor of 0.75). The allowable percent of design load was computed at differ-
ent deflection ratios. Figure 4-11 then provides the procedure for reducing the allowable load determined
at the slab center to account for the load-transfer capabilities at the joint. The load reduction factor falls
between 0.75 and 1.00.
e. Interpretation of WESPAVE Output. A typical WESPAVE output is shown on figure 4-12. The
pavement evaluation is conducted for a specified number of passes of an aircraft. Following are the
results from WESPAVE which must be fully understood and correctly interpreted:
(1) Allowable Load. The load on the critical aircraft that can be supported by the pavement for
the desired number of passes.
(2) Allowable Passes. The number of passes of the critical aircraft at the load that can be
applied to the pavement.
(3) Overlays. The additional pavement thickness required to adequately support the critical
aircraft at a given load for a given number of passes. These thicknesses are to be used for planning only.
A more thorough investigation is required for actual design. For flexible pavements, the overlay is the
required thickness of AC. For rigid pavements, overlays are given for AC, partially bonded PCC (PCC
placed directly on an existing slab), and unbonded PCC (PCC placed on a leveling course or bond
breaker). For composite pavements, the existing AC overlay is considered a bond breaker, and the
partially bonded case is not considered. Overlays are determined using criteria in TI 825-01/AFM
32-1124(I)/NAVFAC DM 21.10, chapter 3, or TM 5-825-2-1/AFM 88-6, chapter 2, section A, and
TM 5-825-3-1/AFM 88-6, chapter 3, section A, for Army and Air Force pavements and in MIL-HDBK-
1021/4 for Navy and Marine Corps pavements.
(4) PCN. PCN is computed for a critical aircraft using the allowable gross aircraft weight and
subgrade strength determined from the evaluation. PCN for Air Force pavements is determined for
50,000 passes of a C-17 Aircraft.
4-14
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