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Weight held at
200,000 lbs
Gear Type is
Very Important
Increasing Frequency
ACN/PCN System
20
25
30
35
40
45
50
55
1 10 100 1000 10000 100000
Annual Departures (Log Scale)
Required Thickness of Flexible Pavement .
D-200
2D-200
With CBR=5, New Alpha Factors
Constant Weight - Increasing Departures D
2D
Increasing Thickness
D 2D
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Transportation Systems Workshop
April 23, 2008
Federal Aviation
Administration
11
2D landing gears
Constant gross load
of 200,000 lbs
Same gear type
but with different
wheel spacing
Increasing Frequency
ACN/PCN System
Increasing Thickness
20
22
24
26
28
30
32
34
36
38
40
1 10 100 1000 10000 100000
Annual Departures (Log Scale)
Required Thickness of Flexible Pavement .
2D-20-45
2D-20-45
2D-21-46
2D-26-51
2D-30-55
B-767gear 45-56
A330-300gear 55-78
With CBR=5, New Alpha Factors
Constant Weight (200,000 lbs) - Increasing Departures
Changing Wheel Spacing
Which 200k, 2D gear did
you use to generate an
allowable gear load?
12
Transportation Systems Workshop
April 23, 2008
Federal Aviation
Administration
12
ACN – PCN procedure standardizes the
frequency issue by making calculations of
ACN/PCN at 10,000 coverages
(Due to airplane wander, It takes more than one pass
of an airplane to equal a full coverage)
ACN/PCN System - Concept
13
Transportation Systems Workshop
April 23, 2008
Federal Aviation
Administration
13
ACN-PCN Application
• Applies only to pavements with bearing
strengths of 12,500 pounds (5,700 kg) or
greater.
• The method of reporting pavement bearing
strength for pavements of less than 12,500
pounds (5,700 kg) remains unchanged.
14
Transportation Systems Workshop
April 23, 2008
Federal Aviation
Administration
14
• Only intended as a method for airport operators
to evaluate acceptable operations of airplanes
• It provides a load, or damage rating relative to
a specified reference load.
• ACN is not a pavement design procedure.
ACN/PCN System - Limitations
ACN/PCN System - Limitations
Airplanes are represented by only one gear
ACN/PCN System –Flexible Pavement
One Gear versus All Gears (06 alphas)
ACN for single Gear versus all Gears
Airbus A380 - 62,000 lb wheel loads and Boeing B747 - 52,000 lb wheel loads
20
40
60
80
100
120
140
160
180
0 2 4 6 8 10 12 14 16
Subgrade CBR
ACN
B747 - one 4-wheel Gear
B747 - All Gears
A380 - one 4-wheel Gear
A380 - All Gears
17
Transportation Systems Workshop
April 23, 2008
Federal Aviation
Administration
17
• Westergaard solution for loaded elastic plate on
a Winkler foundation
• Interior load (PCA method)
• Concrete working stress = 2.75 MPa (399 psi)
• 4 Subgrade strengths
High (A) = 150 MN/m3 (554 pci )
Medium (B) = 80 MN/m3 (296 pci )
Low (C) = 40 MN/m3 (148 pci )
Ultra low (D) = 20 MN/m3 (74 pci )
ACN/PCN System – Rigid Pavement
18
Transportation Systems Workshop
April 23, 2008
Federal Aviation
Administration
18
• California Bearing Ratio (CBR) Method
• 4 Subgrade Strengths
High (A) = CBR 15
Medium (B) = CBR 10
Low (C) = CBR 6
Ultra low (D) = CBR 3
ACN/PCN System –Flexible Pavement
19
Transportation Systems Workshop
April 23, 2008
Federal Aviation
Administration
19
• A Derived Single Wheel load (DSWL) at
1.25 MPa (181 psi) is computed for each
subgrade.
• Found by equating thickness for DSWL to
design thickness for airplane gear
• ACN = DSWL in kilograms divided by 500
Calculated at maximum main gear loading – i.e. maximum ramp weight and
corresponding maximum center of gravity
ACN/PCN System
20
Transportation Systems Workshop
April 23, 2008
Federal Aviation
Administration
20
Historic Flexible Design Parameter
Derived Single Wheel Load (DSWL)
=
Load at
Max CG DSWL
Equal Deflection
Compute DSWL so
subgrade deflection
is equal
Defined Tire Pressure
181 psi
Airplane Operating
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