LEDFAA 1.3 - Computer Program for Airport Pavement Thickness Design

LEDFAA 1.3 is a 32-bit version and requires Windows 95/98, NT, or later.

Setup requires the files:

Setup.exe
Setup.lst
LEDFAA1.cab
LEDFAA2.cab

Copy all of the files into a directory on a hard disk. Then run setup.exe. Setup can also be run from the distribution disk.

The Alternate SG check box allows a flexible pavement design (or Life) to be run based on the vertical strain at the top of
the layer below the arrow on the left side of the pavement structure. The procedure is: 1) get into the Structure window, 2) check the Alternate SG box at the bottom left of the structure, 3) press the Modify button, 4) click to the left of the picture of the structure (in the margin) to move the arrow so that it sits to the left of the layer above the layer where the vertical strain criterion will be applied, 5) return to design mode, 6) if a design is run then the layer pointed to by the arrow will change thickness to satisfy the strain criterion in the layer below, 7) if Life is run then the life for the strain criterion in the layer below will be calculated.

See the help file under Running the Program - Options for information on Batch, No AC CDF, and No Out Files.

LEDFAA 1.3 includes the Airbus A340-500 and A340-600 aircraft in the aircraft library. The same methodology is used as for other aircraft with two wing gear and one belly gear (MD-11 and A340-200 for example) except that the A340-500/600 has a dual-tandem belly gear instead of a dual-wheel belly gear. The methodology is for the A340-500/600 to be split into two separate aircraft for design; one with the two wing gear and the other with the one belly gear. The two aircraft (for design) are shown separately in the aircraft list.

LEDFAA 1.3 includes the Airbus A380-800 and A380-800F aircraft in the aircraft library. Inclusion of these aircraft required changes to the design methodology implemented in version 1.2 because of the different number of wheels in the wing and body gears (four in the wing and six in the body). The main difference is in the flexible design procedure as follows:

1. Vertical strain at the top of the subgrade is computed at multiple points with all of the wheels in the main gear contributing to the computed strain (16 wheels for the B-747 and 20 wheels for the A-380). In version 1.2, subgrade strain is computed for the B-747 with four wheels, representing only one of the gears, contributing to the computed strain.
2. Response under the wing and body gears is evenly split into two areas. The maximum response in the wing gear area is used to compute the pass-to-coverage ratios and cumulative damage factors (CDF) for the wing gears. The maximum response in the body gear area is used to compute pass-to-coverage ratios and CDFs for the body gears. These two sets of CDF values are then added to the CDFs calculated for all of the other aircraft in the mix and the result used in the normal thickness design procedure.

The design procedure for rigid pavement design is unchanged from that in LEDFAA 1.2. The difference between the number of wheels in the wing and body gears of the A-380 is accommodated by treating the aircraft as two different aircraft in the design mix. One of the design mix aircraft is a dual tandem with the same configuration as the A-380 wing gears and the other is a dual-tridem with the same configuration as the body gears of the A-380. The separation into two design mix aircraft is transparent to the user.

A number of other changes have been made to the program either for ease of use or for improved functionality. These changes include:

1. Replacement of the layered elastic computational program Julea with the internally prepared program Leaf.
2. A full 32-bit implementation which is compatible with all current Microsoft PC operating systems.
3. The default setting for data output files (*.out) is for them not to be written. Double click on the gray area of the Structure Window and uncheck "No Out Files" for the data files to be written to the working directory. (The default setting is not described in the help file.)

LEDFAA 1.3 is an interim release of the computer program, FAArfield, now in preparation. FAArfield includes a 3-D FEM model for rigid pavement response calculations. The flexible design procedure will remain unchanged from LEDFAA 1.3 except that the failure model parameters may be adjusted as a result of the compatibility study now underway. Any changes in the flexible design parameters will result in minor differences in computed design thicknesses.

A beta version of FAArfield (called FEDFAA) will be released in September, 2003, for public evaluation and review. Three workshops are also planned to accompany the review process. The workshops will be held in Atlanta, GA, Chicago, IL, and Seattle, WA.