UFC 3-260-02
30 June 2001
(4) Number of Aircraft Passes. Forecast the total number of passes (not coverages) of each
aircraft that is expected to use the pavement feature over its design life. The "number of passes" is
normally the number of departures. The exception to this is in touchdown areas on runways where the
impact due to aircraft performing touch-and-go operations will cause pavement damage. On pavements
that are to be used for touch-and-go operations, add the expected number of touch-and-go operations
over the design life to the number of departures to arrive at the design traffic passes. Minimum pass
levels for design are given in Chapter 4.
(5) Primary or Secondary Traffic Area. Guidance on determining if the pavement feature is a
primary or secondary traffic area is given in Chapter 4.
g. Thickness design procedure for a single design aircraft. Use Figures 12-19 to 12-23 to
determine the concrete slab thickness for single-design aircraft. This procedure will provide the required
slab thickness for a specified type of aircraft when the flexural strength, k value, gear load, tire pressure
for single-wheel gear aircraft, number of passes, and type of design traffic area are specified. The
design chart for aircraft with single wheel gear is shown in Figure 12-19 and is used by entering the
design flexural strength and the tire load and projecting as shown by the dashed example lines until the
required slab thickness is obtained. The design charts shown in Figures 12-20 through 12-23 are also
entered with the design concrete flexural strength and projecting as shown by the dashed example lines
until the required slab thickness is obtained. The calculated slab thickness is then rounded to obtain the
design thickness.
h. Thickness Design Procedure for Mixed Traffic. When an airfield pavement will be loaded by two
or more aircraft, the combined damage caused by the aircraft mix must be used in the design. The
required slab thickness may be determined for a mix of aircraft types using Miner's damage hypothesis
and data on forecasted operations of different aircraft types operating at the facility. The slab thickness
design for mixed traffic is an iterative procedure in which the designer selects a trial slab thickness that is
normally the thickness required for the most critical aircraft using the feature plus 25 millimeters (1 inch).
The designer then computes the proportion of the fatigue life of the pavement consumed as the sum of
the individual damage contributions of the forecasted volume of each aircraft type, and subsequently
varies the slab thickness until less than 100 percent of the fatigue life of the pavement is consumed by
the forecasted mix of traffic. This procedure is described in the following sections and is facilitated by
the use of a table for computations as shown in Table 12-3.
(1) Required Inputs. The specific aircraft types and their design gear load (typically 95 percent
of the maximum gross departure gear load) are entered in columns 1 and 2 of Table 12-3. The
projected number of passes (departures) over the selected design period are entered in column 3 of
Table 12-3. Divide the projected passes by the appropriate pass-coverage ratio from Table 12-4 to
obtain projected coverages for each aircraft. If the forecasted number of passes is not available, use the
minimum pass levels given in Chapter 4. Use the pass-coverage ratios given for primary (channelized)
traffic areas when designing for runway ends, primary taxiways, and aprons. Use the pass-coverage
ratios given for secondary (unchannelized) traffic areas when designing for other areas. Enter the pass-
coverage ratio selected for each aircraft in column 4 of Table 12-3, and the number of coverages
computed in column 5. The other required inputs are the concrete flexural strength, the effective k value
on top of the base, and the tire pressure for each single wheel aircraft, which should be recorded in the
spaces provided at the top of Table 12-3.
(2) Determination of interior flexural stresses. Select a trial slab thickness and record it in the
space provided for the iteration being performed. For the initial trial, use the required thickness for the
expected critical aircraft (determined from Figures 12-19 through 12-23) plus 25 millimeters (1 inch).
12-9
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