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Presented to: VI ALACPA Airport Pavements Seminar & IV FAA Workshop
Presented by: David R. Brill, P.E., Ph.D.
Date: 26 October 2009
Federal AviationAdministrationFAA Backcalculation
Software
BAKFAA with LEAF
2Federal AviationAdministration
FAA Backcalculation Software – BAKFAA with LEAFOctober 26, 2009
Opening the Program
Load FWD File
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FAA Backcalculation Software – BAKFAA with LEAFOctober 26, 2009
Readable File Formats
• AASHTO PDDX (Pavement Deflection Data Exchange) (*.ddx)
• Dynatest R80 (*.fwd)• KUAB• JILS (*.txt)
4Federal AviationAdministration
FAA Backcalculation Software – BAKFAA with LEAFOctober 26, 2009
Reading KUAB FWD File
NAPTF CC2 Data
Rigid Pavement Test Item:
–12 in. (30.5 cm) PCC
–10 in. (25.4 cm) P-154 subbase
–CBR 7-8 clay subgrade
5Federal AviationAdministration
FAA Backcalculation Software – BAKFAA with LEAFOctober 26, 2009
Modify Structural LayersEnter seed
values from AC 150/5370-11A (Tables 13,14)
Click on desired test no.
Click on “Backcalculate”
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FAA Backcalculation Software – BAKFAA with LEAFOctober 26, 2009
Backcalculation Results
Click on “Show Output”
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FAA Backcalculation Software – BAKFAA with LEAFOctober 26, 2009
Backcalculation Results
Program minimizes the RMS value of
difference between computed and
measured deflection profiles.
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FAA Backcalculation Software – BAKFAA with LEAFOctober 26, 2009
Example with Dynatest R80 File
Load *.fwd File
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FAA Backcalculation Software – BAKFAA with LEAFOctober 26, 2009
Example with Dynatest R80 File
File type should appear at upper
right.
10Federal AviationAdministration
FAA Backcalculation Software – BAKFAA with LEAFOctober 26, 2009
Example with Dynatest R80 File
Enter the pavement structure with seed values of moduli.
In this case, the asphalt layers are
fixed. Only the subgrade modulus
is changeable.
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FAA Backcalculation Software – BAKFAA with LEAFOctober 26, 2009
Example with Dynatest R80 File
Select an HWD event from the file.
Click “Backcalculate”
12Federal AviationAdministration
FAA Backcalculation Software – BAKFAA with LEAFOctober 26, 2009
Example with Dynatest R80 File
Backcalculatedvalue of subgrade
modulus in psi
Click the “Save Structure” button to save the structure
as a *.str file.
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FAA Backcalculation Software – BAKFAA with LEAFOctober 26, 2009
Backcalculation Results
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FAA Backcalculation Software – BAKFAA with LEAFOctober 26, 2009
Running BAKFAA in Forward Mode(LEAF)
Enter layer structural data
Enter evaluation depth
Click “Select Load and Run
LEAF”
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FAA Backcalculation Software – BAKFAA with LEAFOctober 26, 2009
Running BAKFAA in Forward Mode(LEAF)
Select load from list
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FAA Backcalculation Software – BAKFAA with LEAFOctober 26, 2009
Running BAKFAA in Forward Mode(LEAF)
•Displays LEAF output in a new window.
•Information:–Layer data
–Tire load data
–Stresses, strains and displacements computed for each evaluation point.
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FAA Backcalculation Software – BAKFAA with LEAFOctober 26, 2009
Modifying the External Aircraft File
B-777-200 A56842147.5182N3553780576
-27.5 -5727.5 -57
-27.5 027.5 0
-27.5 5727.5 57
4-244-189189244
627.5 022.0 016.5 011.0 05.5 00.0 0
•Airplane Name
•Gross Weight, lbs.
•Percent gross weight on main gear
•Tire Pressure, psi
•Gear ID Letter (military designation)
•Gear ID Number
•Dual Spacing, inches
•Gear track between inside wheels, inches
•Four-gear spacing, inches
•Tandem spacing, inchesItems in gray must be present, but their values do not affect BAKFAA.
18Federal AviationAdministration
FAA Backcalculation Software – BAKFAA with LEAFOctober 26, 2009
Modifying the External Aircraft File
B-777-200 A56842147.5182N3553780576
-27.5 -5727.5 -57
-27.5 027.5 0
-27.5 5727.5 57
4-244-189189244
627.5 022.0 016.5 011.0 05.5 00.0 0
•Number of tires on evaluation gear
•Tire x and y coordinates, inches
•Number of tire tracks
•Location of tire track, inches
•Number of evaluation points
•Evaluation point x and y coordinates, inches
Items in gray must be present, but their values do not affect BAKFAA.
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FAA Backcalculation Software – BAKFAA with LEAFOctober 26, 2009
Questions
• Contact:Dr. Gordon [email protected]
• Download Files:http://www.airporttech.tc.faa.gov/naptf/download/index1.asp
• Available downloads include BAKFAA and LEAF full source codes (Visual Basic 6.0).
