30 June 2001
Determine the flexural stress at the bottom of the slab caused by each particular aircraft gear for the
interior loading position, using Figures 12-24 through 12-20. For each single wheel gear aircraft, enter
Figure 12-24 with the trial slab thickness, tire load, and tire pressure, move either up or down to the base
effective k value and continue horizontally to the flexural stress. For each of the multiwheel gear aircraft
types listed, enter the appropriate Figures 12-25 through 12-28 with the trial slab thickness, project a
horizontal line left to the effective k value, move either up or down to the design gear load, and continue
horizontally to the flexural stress. Record the stress values in column 6 of Table 12-3.
(3) Fatigue life consumption. The stress-strength ratio recorded for each aircraft in column 7 of
Table 12-3 is the flexural stress in column 6 divided by the design concrete flexural strength. Select from
Table 12-2 the allowable number of coverages corresponding to the stress-strength ratio computed for
each aircraft type, and record the allowable number of coverages in column 8 of Table 12-3. For each
aircraft type, divide the projected number of coverages in column 5 by the allowable number of
coverages in column 8 to determine the portion of fatigue life consumed by the forecasted volume of
each aircraft type and record in column 9. The sum of the values in column 9 is the total damage, the
proportion of total fatigue life of the slab consumed by the forecasted volumes of the aircraft types listed.
If this number is considerably less than 1.00 (100 percent), indicating that the slab has considerable
remaining fatigue life at the end of the design period not consumed by the forecasted mix of traffic, then
the trial slab thickness may be reduced in the next iteration. If the total damage is greater than 1.00
(100 percent), indicating that the fatigue life of the slab will be consumed by lower traffic volumes than
those projected over the design period, then the trial slab thickness must be increased in the next
iteration. The process of selecting a slab thickness, determining the flexural stress, and calculating the
fatigue life consumption is repeated until the slab thickness which corresponds to an acceptable value
for damage (less than 1.00 or 100 percent) is determined.
i. Minimum Thickness. The minimum allowable new concrete pavement thickness is
200 millimeters (8 inches) in primary and secondary traffic areas and 100 millimeters (4 inches) in blast
protective areas not subject to aircraft loading. For helicopter and basic training fields the minimum
thickness in primary and secondary traffic areas is 150 millimeters (6 inches).
DESIGN EXAMPLES FOR NAVY AND MARINE CORPS PLAIN CONCRETE PAVEMENTS.
a. Thickness Design for a Single Aircraft. It is desired to design a plain rigid pavement for the
Aircraft = C-141
Design gear load = 70,300 kilograms (155,000 pounds)
Design flexural strength = 4.48 MPa (650 psi)
Effective k value at top of base course = 54 kPa/mm (200 pci)
Total departures over 20-year design life = 25,000
Traffic area = primary taxiway (channelized traffic)
Using Figure 12-22, the required slab thickness is 340 millimeters (13.4 inches). This thickness would
then be rounded upward to 350 millimeters (14.0 inches).
b. Thickness Design for Mixed Traffic. A new runway is to be designed to serve frequent
operations of C-141, C-130, C-17, and C-5A aircraft. In addition to these aircraft, the new facility will be
used by F-14 and P-3 aircraft. The runway is located in a warm climatic region where frost penetration
does not need to be considered in the design process. Use the following general design procedure
when designing the rigid pavement for this runway.