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Presented to: VI ALACPA Airport Pavements Seminar & IV FAA Workshop
By: David R. Brill, P.E., Ph.D.
Date: 29 October, 2009
Federal AviationAdministrationFEAFAA Software
Update
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FEAFAA Software UpdateOctober 29, 2009
FEAFAA - Introduction
FINITEELEMENTANALYSIS -FEDERALAVIATIONADMINISTRATION
• Developed by the FAA Airport Technology R&D Branch
• Stand-alone tool for 3D finite element analysis of multiple-slab rigid airport pavements and overlays.
• Use FEAFAA to compute accurate responses of rigid pavement structures to individual aircraft landing gear loads.
• FEAFAA is not intended as a design procedure.
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Acknowledgments
• SRA International Corp.– Dr. Izydor Kawa– Dr. Qiang Wang
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FEAFAA – Major Features
• 9-slab jointed rigid pavement model
• Up to 6 structural layers• Infinite subgrade model• Arbitrary gear loading
capability• Overlay modeling capability• User-defined slab size• Customizable aircraft library
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FEAFAA – Major Revisions (ver. 1.42)
• Pavement Mesh Model– The gear can now be
repositioned anywhere on the surface.
– Uniform 3D mesh.– User-variable mesh size. – Improved mesh boundary
constraints prevent “spurious” stresses from being induced at the slab corners.
“Old” Model with spurious stresses
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FEAFAA – Major Revisions (ver. 1.42)
• Windows Interface– The internal airplane library has
been updated.– The 2D Shell model for slabs is
no longer supported.– Controls allow the user to define
the position of the gear using an x,y coordinate system and a variable gear angle.
– The x-offset is now given relative to the coordinate origin at the edge of the slab (same as mesh coordinate system).
– Interior Load/Edge Load option.
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NIKE3D Finite Element Processor
• FEAFAA drives a modified version of the 3D finite element program NIKE3D, originally developed by the U.S. Department of Energy, Lawrence Livermore National Laboratory (LLNL).– Same program used in FAARFIELD.– The FAA-modified NIKE3D and INGRID mesh
generation programs are distributed in compiled forms under a software sharing agreement between the FAA and LLNL.
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NIKE3D Recent Changes
• Recompiled the NIKE3D processor to remove the size limitation on the output file.
• Corrected an error in the infinite element formulation.
• Improved the contact surface algorithm.– This results in a better solution for cases where
slab/base separation is likely to occur (e.g., on the unloaded side of a joint.).
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FEAFAA 3D Rigid Pavement Mesh
9 Slabs
Up to 6 structural layers
Infinite ElementsMathematically represent a subgrade of infinite depth
Sliding Interface
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Running FEAFAA –1. Airplane Selection Window
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Running FEAFAA –2. Pavement Structure Window
Edge Load (Longitudinal
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Running FEAFAA –2. Pavement Structure Window
Edge Load (Transverse)
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Running FEAFAA –2. Pavement Structure Window
Interior Load
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Running FEAFAA –2. Pavement Structure Window
Skew Load
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Running FEAFAA –3. Joint Modeling Window
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Running FEAFAA –4. 3D Mesh Generation Window
Generates NIKE3D Input File
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Running FEAFAA –4. 3D Mesh Generation Window
Executes NIKE3D Session
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Running FEAFAA –5. NIKE3D Execution Window
• Execution time depends on the problem – 20-30 minutes is typical.
• DOS window will continue to display execution progress.– Session information (screen
display) is written to a file called Nike3d.txt.
– Solution is written to a file called n3dhsp.
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Analyzing FEAFAA Results
• FEAFAA does not include a visual post-processing capability.
• Finite element results can be viewed using commercially available software, e.g., TecPlot or MatLab.
• FEAFAA includes a utility program, NikePlot, that converts the output file to a simple text format readable by TecPlot.
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NikePlot Utility
• Make sure output file n3dhsp is in the same directory as NikePlot1-5.exe.
• Run NikePlot1-5.exe.• Enter the vertical scale
factor when prompted.• NikePlot generates 2
text files:– model_load.dat– model_stress_1.dat
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FEAFAA Example
• Airplane Gear Load– B777-200 Baseline
(6 wheels)– Gross Weight
= 537,000 lbs.– Tire Pressure = 185 psi– Rectangular tire footprint
(PCA)– Gear position:
Longitudinal joint along inside tire edge.
• Pavement Structure– Slab size 20 × 18.75 feet– 14 in. PCC Overlay
• E = 4,000,000 psi– 12 in. Existing PCC
• E = 4,000,000 psi– 8 in. Subbase
• E = 250,000 psi– Subgrade, E = 8,000 psi– No symmetry– Joint: 1.25 in. diameter
dowels @ 15 in. spacing
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FEAFAA Example – Airplane Selection
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FEAFAA Example – Pavement Structure
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FEAFAA Example – Joint Modeling
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FEAFAA Example – 3D Mesh
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FEAFAA Stress ResultsPlotted Using NikePlot Utility and and TecPlotTM
Stress-z Stress-x
Stress-yDetail of Stress-y
Overlay
Base PCC
Compression
Tension
Longitudinal Joint
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FEAFAA Example - Statistics
• Number of Finite Elements = 18,781• Number of Equations = 84,540• Number of Iterations = 32• Total Run Time Charged = 43.07 minutes*
*Intel® Pentium 4® Processor, 3 GHz, 2 MB RAM
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Where to Obtain
• Download FEAFAA from:http://www.airporttech.tc.faa.gov/naptf/download/
• Current version: FEAFAA 1.401• Check back for new updates• More Information: [email protected]
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Current Limitations• Rigid pavement analysis only.• No metric option at this time.• Restricted to 9 slabs.
– Overlay joints must coincide with base slabs. – Joint stiffness is variable, but all joints must have the
same stiffness.
• Gear loading only.– Future versions will introduce combined temperature
and wheel loads.
• FAA is continuing to add improvements.