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1. 5 Adjust the thickness of the prescribed layer until structure CDF 1 Increasing thickness decreases CDF Design for overlays on rigid pavements is generally similar in terms of structure definition aircraft list selection and program execution but the LEDFAA User s Manual PAVEMENT THICKNESS DESIGN e 31 AC 150 5320 16 10 22 95 Appendix 2 design procedures require more steps because deterioration of the existing pavement is included More details are given below for design of each of the different types of pavement structure New Flexible and Bituminous Overlay on Flexible Subgrade vertical strain and horizontal strain at the bottom of the top layer are the design criteria for both pavement types With the fixed default asphalt modulus value of 200 000 psi horizontal strain only becomes the dominant criterion when the structure is very deep and is heavily loaded Under these conditions the horizontal strain also has a tendency to increase as the pavement depth increases the opposite of the trend for subgrade strain Overlap of the CDFs can therefore occur and a proper design never realized For these reasons and to save run time the subgrade strain is used to iterate to a subgrade CDF of one Only one evaluation depth needs to be sent to Julea and the run time is approximately halved for deep many layered structures compared to computing subgrade and asphalt strain each time When the subgrade criterion has been satisfied
2. 0 3881x F where Psc 00039x F R S For any given value of R o the computed value of Fsc maintains the number of coverages for SCI 100 constant as Fs varies When the concrete slab is placed on an 8 inch crushed aggregate layer or a 4 inch stabilized layer at 500 000 psi Fs and Fsc both have a value of 1 and the basic failure model is unchanged But if the thickness or quality of the base subbase structure is higher than either of these two conditions Fs decreases and the number of coverages to failure increases The procedure is similar to that used in the design procedure for concrete overlay on rigid pavement as described in reference 3 Failure is defined as the number of coverages for SCI 80 at any given value of R o reference 2 Concrete Overlay on Flexible Pavement When the PCC overlay on flexible layer is placed over an asphalt surface or undefined layer the new rigid pavement design procedure is automatically executed This is analogous to the use of the new PCC design curves in AC 150 5320 6 as described in paragraph 71 of the AC Concrete Overlay on PCC Pavement Two types of concrete overlay on PCC pavement are considered in the program fully unbonded and partially bonded Different interface coefficients between the overlay and the existing pavement are used to simulate the behavior of the different types of structure For the fully unbonded case an interface coefficient of 100 000 is used as required by
3. initial annual departures b percent annual growth Large negative percent annual growth can result in negative aircraft departures before the end of the design life has been reached The program automatically detects this condition if it occurs and assumes zero departures for the aircraft from the time at which the departure rate becomes zero to the end of the design life AIRCRAFT WINDOW e 15 AC 150 5320 16 10 22 95 Appendix 2 Non Standard Aircraft Lists If the design aircraft list does not contain a Boeing 777 or contains only one aircraft the message Non Standard Aircraft List is displayed Clicking on the message displays a longer message explaining why the list is non standard The long message is also displayed in the Design Info text box in the NOTES window Command Buttons Add An aircraft is transferred from the library list to the design list by selecting an aircraft name in the library list and clicking Add The same operation can also be performed by double clicking an aircraft name in the library list Remove An aircraft is removed from the design list by selecting the aircraft name and clicking Remove or by double clicking the aircraft name in the design list Clear List Deletes all aircraft from the design list Save List Saves the data for all of the aircraft in the design list into the data record for the currently selected section in the currently selected job All changes made to a des
4. a final calculation is made to find the asphalt CDF again using only one evaluation depth If the structure is saved after design without making any modifications the section data is marked as being a completed design and the asphalt CDF stored in the JOB file section data record The value of the asphalt CDF can be viewed in the Design Info text box in the NOTES window One consequence of delaying asphalt CDF calculation until after satisfying the subgrade criterion is that the design continues to run after the displayed subgrade CDF has reached its terminal value A message is displayed stating that asphalt CDF is being computed The value of asphalt CDF is displayed when the computation is complete For new flexible design the thickness of the layer next to the subgrade is adjusted to make the subgrade CDF approximately equal to one The current error control is that the design will terminate when CDF is in the range 0 995 to 1 005 If the layer next to the subgrade becomes thinner than its specified minimum thickness the thickness of the layer above is halved or set at its minimum thickness and the procedure continued If the CDF is less than one with both of the adjusted layers at their minimum thicknesses the CDF is displayed and the design terminated This procedure is not intended to optimize a design It is intended only to protect from inappropriate input data For overlay design the thickness of the top layer is adjusted
5. structure so that the design criteria for the particular type of structure are satisfied The structure type is automatically determined from the top two layers and the correct design procedure executed The layer to be adjusted is indicated by the small arrow in the left margin of the picture of the structure Except for new flexible pavements the layer cannot be changed During design the layer being adjusted is highlighted by changing its display color In some cases if a new computed layer thickness is unreasonable such as negative the thickness of an adjacent layer is changed This is only included to prevent unreasonable layer thicknesses and is not intended to try to optimize the design If it occurs the structure should be inspected and changed if necessary followed by a redesign STRUCTURE WINDOW e 11 AC 150 5320 16 Appendix 2 10 22 95 Information on the state of the design is displayed at the bottom of the picture of the structure Details of the design procedures executed by Design Structure for the different pavement structures are given in the Pavement Thickness Design section Interrupt Design When a design is started by clicking Design Structure Save Structure changes to Interrupt Design Clicking this button during design stops the design calculations and leaves the thickness of the layer being adjusted at its value at the time of stopping the design The design can be restarted with the structure as it existe
6. 2 Modulus 2 iC 2 Thick 3 Modulus 3 LC 3 Thick I Modulus I LC I Thick NL Modulus NL iC NL ACName 1 GL 1 Rps 1 SGrowth 1 ACName 2 GL 2 Rps 2 SGrowth 2 ACName J GL J Rps J SGrowth J ACName NA GL NA Rps NA SGrowth NA Blank Line for expansion Blank Line for expansion Next set of section data starting with the name Explanation of JOB File Field Names Format File format identifier Type string current Format3 SectionName section name Type string Date date of completed design Type string Format XX XX XX Time time of completed design Type string Format XX XX XX DateTime date and time of completed design in VB format Type double precision real Field Width 20 Note When a design has not been completed for the section Date 11 01 71 Time 00 00 00 DateTime 26238 LEDFAA User s Manual DATA FILES e 39 AC 150 5320 16 Appendix 2 40 e DATA FILES 10 22 95 em owen om er L Condition index feat 6 ege Pereent gn Li Is RRE for Layer meger o Gross Load for sent meger weu Annual Repetitions for Arrat J integer_ 8 Flexural strength when the layer is PCC Example of a JOB File with 2 Sections Format3 NewFlexible 03 30 95 13 50 38 34790 5768287037 0 000000 20 0 00 100 00 4 3 5 0000 200000 1 8 0000 400000 14 11 2892 47583 6 0 0000 15000 4 DC 10 10 458000 2263 0 000000 B 747
7. The following includes information for making the relationship between the LEDFAA and AC 150 5320 6 layer types and for selecting appropriate layer properties as input data for LEDFAA The requirements and guidelines of AC 150 5320 6 should be followed whenever there is a discrepancy between LEDFAA and the advisory circular For example minimum thicknesses should always be set according to the requirements of the circular for the particular pavement type under design and not the default minimum thicknesses built into LEDFAA References for specific details of the LEDFAA design procedures are 1 Barker W R and W N Brabston Development of a Structural Design Procedure for Flexible Pavements Report No FAA RD 74 199 September 1975 2 Parker F Jr W R Barker R C Gunkel and E C Odom Development of a Structural Design Procedure for Rigid Airport Pavements Report No FAA RD 77 81 April 1977 3 Rollings R S Design of Overlays for Rigid Airport Pavements Report No DOT FAA PM 87 19 April 1988 4 Barker W R and C R Gonzalez Pavement Design by Elastic Layer Theory Subgrade Layers Subgrade modulus values for flexible pavement design can be determined in a number of ways The procedure which will be applicable in most cases is to use available CBR values and substitute in the relationship LEDFAA User s Manual LAYER TYPES e 23 AC 150 5320 16 10 22 95 Appendix 2 E 1 500xCBR psi This method will
8. at the bottom surface of the concrete surfacing layer guards against failure by cracking of the surface layer The computer program iterates on the concrete layer thickness until the CDF reaches a value of 1 0 Once a CDF of 1 0 is achieved the section satisfies the design conditions A design life of 20 years is recommended for airport pavements 15 CONCRETE PAVEMENT SURFACING Concrete pavement surfacing should meet the requirements of FAA Item P 501 The minimum concrete surfacing thickness is 6 inches 152 mm 16 STABILIZED SUBBASE COURSE Bound materials are required for subbase for rigid pavements serving these aircraft Acceptable bound materials are P 304 P 306 P 401 variable stabilized rigid and variable stabilized flexible The minimum thickness of subbase is 4 inches 102 mm More than one layer of subbase may be used i e P 306 over a layer of P 209 Layering must be done so as not to produce a sandwich granular layer between two bound layers section 17 SUBGRADE The subgrade is assumed to be infinite in thickness and is characterized by either a modulus or k value The computer converts k to modulus by using the logarithmic relationship log E 1 415 1 284 log k Subgrade compaction requirements and embankment construction should be in accordance with AC 150 5320 6 and AC 150 5370 10 3 and 2 AC 150 5320 16 10 22 95 18 SEASONAL FROST AND PERMAFROST As with flexible pavements seasonal frost and permafrost e
9. design procedures and with FAA pavement design standards and recommendations The purpose of this section is simply to outline the operation of the program Detailed guidelines for selection are given ina later section These must be read before using the program to design pavements to FAA standards In particular the use of an undefined layer results in a non standard structure Structure properties are changed by clicking on the picture of the structure over the displayed value or setting Instructions are then given for changing the value or setting Layer Type Selection Undefined PCC All P 501 Subgrade Surface Aggregate oO Overlay fully unbonded P 209 Crushed D Overlay partially bonded P 154 Uncrushed Overlay on flexible Asphalt All P 401 Surface Stabilized rigid CH Overlay Variable Stabilized flexible P 301 Soil Cement Base Variable P 304 Cement Treated Base P 401 Asphalt P 306 Econocrete Subbase Figure 4 Layer Types Clicking on the picture in the layer type column displays the selection box shown To change the layer type click the type you want to select followed by OK Certain combinations of layers are not allowed in a structure aggregate on the top for example However the structure is not checked during selection and layers can be changed to anything until End Modify is clicked A complete check of the structure is then made and a message displayed if the str
10. estimated using the relationship Witczak M W Report II Asphalt Mixture Material Characterization University of Maryland May 1989 Log E 153658 0 006447 T 0 00007404 T where E asphalt modulus with units of 105 psi and T asphalt temperature in degrees Fahrenheit Rearranging gives 6 53658 0 006447 T 0 00007404 T E 10 The design procedures executed when an undefined layer is present in one of the top two layers of a pavement structure are summarized below Top Layer Second Layer Design Procedure LEDFAA User s Manual LAYER TYPES e 29 AC 150 5320 16 10 22 95 Appendix 2 Top Layer Second Layer Design Procedure Undefined Asphalt Surface Asphalt Overlay on Flexible Undefined PCC Surface Asphalt Overlay on Rigid Undefined Any Overlay Not valid for design If a structure contains one or more undefined layers the message Non Standard Structure is displayed Clicking on the message displays a longer message explaining why the structure is non standard The long message is also displayed in the Design Info text box in the NOTES window 30 e LAYER TYPES LEDFAA User s Manual 10 22 95 AC 150 5320 16 Appendix 2 PAVEMENT THICKNESS DESIGN General Design Procedure Thickness designs can be made for seven different types of pavement structure 1 New flexible Bituminous overlay on existing flexible New rigid Concrete overlay on existing flexible Unbonded concrete overlay on e
11. in Aggregate Layers 50 ii e Contents LEDFAA User s Manual 10 22 95 AC 150 5320 16 Appendix 2 INTRODUCTION LEDFAA User s Manual LEDFAA is a computer program for airport pavement thickness design It implements layered elastic theory based design procedures developed under the sponsorship of the Federal Aviation Administration FAA for new and overlay design of flexible and rigid pavements The layered elastic procedures as implemented in the program are the FAA airport pavement thickness design standards in Advisory Circular AC 150 5320 16 for pavements intended to serve the Boeing B 777 airplane The core of the program is JULEA a layered elastic computational program implemented in this case as a Microsoft Windows FORTRAN application The remainder of the program is written in Visual Basic and operates under Microsoft Windows JULEA is loaded and executed by LEDFAA when needed and is not visible to the user Design information is entered by means of two graphical screens one for the structure and one for the traffic Default values and ranges for the various input parameters have been set so that the designs produced by LEDFAA are compatible with designs produced by the AC 150 5320 6 design procedures for aircraft up to and including the current generation B 727 DC 8 B 747 DC 10 etc Designs for new generation aircraft starting with the B 777 are not covered by AC 150 5320 6 design procedures LEDFAA includes
12. major functions in the STARTUP STRUCTURE and AIRCRAFT windows is started by clicking Demonstration The demonstration can be run through all three windows in succession or individual windows can be selected A time delay is inserted between each distinct operation in the demonstration so that the functions occurring can be observed The default delay setting is 2 seconds The delay setting can be changed any time a demonstration specific message box is displayed by clicking Change Delay The demonstration can also be terminated from any of the demonstration specific message boxes by clicking Cancel STARTUP WINDOW e 7 AC 150 5320 16 Appendix 2 Be STARTUP WINDOW 10 22 95 About Displays the application About box giving a brief description of the application and information on the configuration of the computer system Structure Transfers control to the STRUCTURE window Notes Transfers control to the NOTES window This allows incidental section information to be entered and attached to the job file and a summary of the section data to be viewed The NOTES window is described last Exit Closes all files and exits to Windows LEDFAA User s Manual 10 22 95 AC 150 5320 16 Appendix 2 STRUCTURE WINDOW Introduction The STRUCTURE window allows a pavement structure to be modified and designed to carry the load applied by the selected traffic On the left of the window is a list of the sections in th
13. on the section name in the right hand list box or click Structure to transfer to the STRUCTURE window The new flexible pavement structure from the Samples job will be displayed after transfer to the STRUCTURE window But before starting design of the structure information for the traffic mix listed in the introduction to the design examples must be entered in the AIRCRAFT window To do this l 2 Click Aircraft to transfer control to the AIRCRAFT window Click Clear List and answer Yes in the displayed message box All aircraft stored in the new flexible section of the Samples job will be deleted from the table of design aircraft Select one of the aircraft groups in the top left hand list box to display the aircraft contained in that group in the lower left hand Library list box Select the first aircraft in the group to be added to the table of design aircraft by clicking on its name in the library list Transfer the aircraft to the table by clicking Add Double clicking the name will also transfer the aircraft Default values of gross weight annual departures and percent annual growth will be displayed in the table Any of these values can be changed within a specified range by clicking on the number in the table An input box is displayed which also gives the default value and the range within which a new value can be entered Enter the new value and click OK Select the rest of the aircraft to be added to the des
14. provide designs compatible with the current design procedure based on subgrade CBR Resilient modulus and non destructive test NDT data may also be used where the reliability of the measurements is felt to be high Similarly for rigid pavement design where values of foundation modulus k value for the subgrade are available the following relationship can be used logio Esg 1415 1 284 log k or Egg 26k where Esc Resilient modulus of the subgrade psi k Foundation modulus of the subgrade pci Otherwise resilient modulus values from laboratory tests or NDT tests can be used The equations for converting CBR and k to modulus are based on empirical data and were used in the development of the failure models for the layered elastic design procedures The failure models represent the relationship between computed pavement response strain or stress and coverages to failure measured in full scale tests But resilient modulus of the subgrade was not typically measured during the full scale tests most were run before 1974 and the conversions were required to estimate resilient modulus for use in the layered elastic computations of strain and stress CBR was used for flexible pavements and k value for rigid pavements The conversion equations are therefore an integral part of the design procedures when measured values of CBR or k are used for design A consequence of the separate developments is that the conversion fo
15. the layered elastic program JULEA An interface coefficient of 700 is used for the partially bonded concrete overlay based on numerical comparisons between the current design procedures and the layered elastic based design procedures For both cases the maximum tensile stress at the bottom of the overlay is used as the critical response in the calculation of CDF The design starts with a trial overlay thickness selected by the user CDF is calculated for the concrete overlay layer using the same model as that used in new rigid pavement design But the elastic modulus of the existing pavement is assumed to decrease during the period of time when the SCI of the existing pavement is less than 100 The tensile stress of the overlay layer therefore varies during the life of the overlaid pavement and the CDF of the structure must be computed by numerical integration This results in solution times which are typically much longer than those for the other pavement types After the CDF has been calculated the thickness of the overlay is adjusted to bring the next calculated CDF closer to a value of 1 for the correct design life The design is terminated when the calculated value of CDF is in the range 0 995 and 1 005 and the difference between the calculated and desired design life is less than 0 1 year 34 e PAVEMENT THICKNESS DESIGN LEDFAA User s Manual 10 22 95 AC 150 5320 16 Appendix 2 Asphalt Overlay on PCC Pavement LEDFAA User s Manual T
16. these pavements 10 22 95 AC 150 5320 16 10 SUBBASE COURSE Subbases may be aggregate or bound materials The minimum thickness of subbase is 3 inches 76 mm Acceptable aggregate materials are P 209 Crushed Aggregate Base Course P 208 Aggregate Base Course or P 154 Subbase Course Acceptable bound materials are P 401 P 304 P 306 Use of Item P 301 is limited to locations not subject to freeze thaw cycles More than one layer of subbase material may be used i e P 209 over a layer of P 154 Layering must be done so as not to produce a sandwich granular layer between two bound layers section 11 SUBGRADE The subgrade is assumed to be infinite in thickness and is characterized by either a modulus or CBR value The computer program converts CBR to modulus by multiplying by 1500 Subgrade compaction and embankment construction should be in accordance with AC 150 5320 6 Airport Pavement Design and Evaluation and AC 150 5370 10 Standards for Specifying Construction at Airports 12 SEASONAL FROST AND PERMAFROST Seasonal frost and permafrost effects should be considered by applying the techniques in AC 150 5320 6 RIGID PAVEMENT DESIGN 13 SCOPE This section presents FAA standards for the design of rigid pavements intended to serve a mix of traffic which includes the Boeing 777 airplane 14 INTRODUCTION The design process considers one mode of failure for rigid pavement cracking of the concrete slab Limiting horizontal stress
17. to make the subgrade strain CDF equal to one The procedure is also terminated with a message if the top layer becomes thinner than its minimum thickness The failure model used to find the number of coverages to failure for a given vertical strain at the top of the subgrade is 0 000247 0 000245x1oe He Won ese c 1000 O10 a E where C number of coverages to failure 32 e PAVEMENT THICKNESS DESIGN LEDFAA User s Manual 10 22 95 AC 150 5320 16 Appendix 2 EL subgrade modulus psi E vertical strain at the top of the subgrade Subgrade modulus is included in the equation for subgrade failure and has the effect of decreasing the number of coverages to failure for any given strain as the modulus value decreases This is intended reference 1 to simulate the effects of the increasing degree of plasticity generally encountered as soil strength decreases The failure model used to find the number of coverages to failure for a given horizontal strain at the bottom of the surface asphalt layer is log C 2 68 5x log 2 665 log E where C number of coverages to failure E asphalt modulus psi horizontal strain at the bottom of the surface asphalt layer New Rigid Pavement LEDFAA User s Manual Rigid design is the same as for flexible over flexible overlay design except that CDF is calculated using the horizontal stress at the bottom of the PCC layer To make the layere
18. to serve the B 777 Generally speaking existing pavements which currently serve wide body aircraft should be adequate for Boeing 777 traffic 3 BACKGROUND The Boeing 777 airplane is supported by a landing gear arrangement made up of two main gears and a single nose gear The main landing gears are unique in that they have 6 wheels arranged in a tri tandem 3 pairs of wheels in a row configuration The nose gear is composed of a single dual wheel arrangement When the main gear assembly is analyzed using the conventional FAA design methodology the pavement thickness requirements are considered to be unduly conservative This is particularly noticeable for flexible pavements A new airport pavement design methodology was adopted for the Boeing 777 to reduce some of the conservatism experienced with the present method and to phase in a more mechanistic approach The new method is computer based and is code named LEDFAA v1 2 Layered Elastic Design Federal Aviation Administration version 1 2 The methods of design for flexible and rigid pavements and overlays of rigid pavements were originally developed by the U S Army Corps of Engineers Waterways Experiment Station Vicksburg MS and are reported in DOT FAA RD AC 150 5320 16 10 22 95 74 199 DOT FAA RD 77 81 and DOT FAA PM 87 19 respectively See Appendix 1 The new design method uses a general purpose layered elastic analysis procedure code named JULEA developed by Dr Jacob Uzan Technion
19. 200 833000 832 0 000000 B 777 200 B 634500 425 0 000000 NewRigid 11 01 71 00 00 00 26238 0 000000 20 0 00 100 00 4 3 14 0000 700 5 6 0000 700000 17 6 0000 75000 6 0 0000 15000 4 DC 10 10 458000 2263 0 000000 B 747 200 833000 832 0 000000 B 777 200 B 634500 425 0 000000 LEDFAA User s Manual LEDFAA User s Manual AC 150 5320 16 Appendix 2 Layer Codes O Undefined 1 P 401 Asphalt Surface 2 Not Used 3 Not Used 4 Subgrade 5 P 501 PCC Surface 6 P 209 Crushed Aggregate Base Course 7 Variable Stabilized Base rigid 8 P 154 Subbase Course uncrushed aggregate 9 Variable Stabilized Base flexible 10 P 401 Asphalt Overlay 11 P 501 PCC overlay fully unbonded 12 P 501 PCC overlay partially bonded 13 P 501 PCC overlay on flexible 14 P 401 Stabilized Base flexible 15 P 301 Soil Cement Base Course 16 P 304 Cement Treated Base Course 17 P 306 Econocrete Subbase Course NTS File Format NTS files contain user entered information about sections in a job stored as strings The format consists of a sequential list of each section name the length of the notes string for that section followed by the notes string A Visual Basic routine to read the data for a specified section ISECT in a NTS file is as follows NFNo FreeFile Open FileName For Input As NFNo For I 1 To ISect Line Input NFNo S IT Section name Input NFNo Glen Length of Notes
20. 5 Lp 0 75 L 1 when Ly 2 0 75 Lp where Lu number of years of operation of the existing pavement until overlay Ly design life of the existing pavement in years This equation was derived from the empirical relationship between coverages and SCI given in reference 3 But layered elastic stress computations show much lower sensitivity to base material quality than the procedure used in AC 150 5320 6 and a modification was made to the layered elastic failure model to make the two design procedures more compatible The modification essentially increases the percent design life remaining after SCI starts to drop from 100 if the base and subbase layers are of higher quality than an 8 inch aggregate subbase aggregate base thicker than 8 inches or stabilized base thicker than 4 inches The simple LAYER TYPES e 25 AC 150 5320 16 Appendix 2 26 e LAYER TYPES 10 22 95 relationship given above is not valid for such structures and percent CDFU is computed and displayed when Life is clicked in the STRUCTURE window The procedure for computing percent CDFU for a rigid pavement with SCI 100 is as follows Setup the structure based on the original design assumptions 2 Estimate the traffic which has been applied to the pavement and enter into the aircraft design list 3 Set design life to the amount of time the pavement will have been in operation up to the time of overlay 4 Run Life Percent CDFU will be displayed whe
21. AFT Aircraft Load and Traffic Data Input Figure 1 Program Windows and Linkage 4 e OVERVIEW LEDFAA User s Manual 10 22 95 AC 150 5320 16 Appendix 2 STARTUP WINDOW Introduction The startup window has two functions First is to allow selection of either the STRUCTURE or the NOTES window Second is to organize the basic data storage units consisting of Sections embedded in Jobs Jobs are MSDOS ASCII text files containing up to 100 sections All Job files existing in the working directory are listed on the left of the window A special Job file called Samples is initialized within the system and does not exist as an external file It is always available to create new section data This is necessary if no other Job files are present because new structures cannot be created from scratch The Samples structures are also typical of current pavement design practice and are a convenient starting point for design The data in the Samples sections cannot be changed and the structures cannot be designed The sections are provided only for starting new designs Note The normal Windows file dialog boxes are not supported in LEDFAA Backup to floppy disk or other media is therefore not possible directly from the program This was done to simplify the user interface But since job files are MSDOS ASCII files file backup and where necessary deletion can be done using File Manager or from the DOS prompt See the Windo
22. Course is selected for the subbase A B 777 aircraft is included in the mix and the asphalt surfacing also Item P 401 must have a minimum thickness of 5 inches as specified in AC 150 5320 16 Subgrade CBR for the example is 8 Design life is 20 years complying with AC 150 5320 16 The determination and selection of suitable base and subbase thicknesses is discussed below after describing the initial setup of the example 42 e DESIGN EXAMPLES LEDFAA User s Manual 10 22 95 LEDFAA User s Manual AC 150 5320 16 Appendix 2 When LEDFAA is first started the STARTUP window is displayed and if there are no external JOB files a message is displayed stating that there are no job files in the working directory 1 Clear the message by clicking OK and press the New Job command button Enter a name for the new job in the displayed dialog box and click OK Reselect the Samples job by clicking on its name in the left hand list box Click Copy Section to start the procedure for copying from the Samples job to the new job Select the new flexible sample section in the right hand list box by clicking on the NewFlexible section name Copy the selected section to the new job by clicking on the new job file name in the left hand list box and entering in the displayed dialog box the section name to be used in the new job End the copy procedure by clicking End Copy Select the new job file in the left hand list box and double click
23. DAT contains the maximum principal stress at the bottom of the concrete slab for each aircraft in the mix These are interior stresses and are transformed to equivalent edge stresses by LEDFAA before computing CDF The relative magnitudes of the stresses in DAMTMP DAT for different aircraft are therefore not a reliable indication of the relative stress levels used in the design procedure For flexible pavements DAMTMPSG DAT contains the vertical strains at the top of the subgrade and DAMTMP DAT contains the horizontal strains at the bottom of the surface asphalt layer QP ON a If data in any of these files needs to be stored permanently it should be copied to a new file immediately after a design has been completed 38 e DATA FILES LEDFAA User s Manual 10 22 95 AC 150 5320 16 Appendix 2 Storage Files Permanent information for layered elastic design is stored in JOB and NTS files JOB files contain all of the data required by LEDFAA for all of the sections in one job NTS files contain user entered information not needed by LEDFAA but which may be useful in identifying features of the pavement sections tracking design history etc Both are ASCII files and can be read by other applications if necessary JOB File Format 0 1 2 3 4 5 6 0123456789012345678901234567890123456789012345678901234567890 Format SectionName Date Time DateTime ACCDF Life SCIE SCDFU NL NA Thick 1 Modulus 1 LC 1 Thick
24. Q Advisory U S Department of Transportation C i rc u f a r Federal Aviation Administration Subject AIRPORT PAVEMENT DESIGN FOR THE Date 10 22 95 AC No 150 5320 16 BOEING 777 AIRPLANE Initiated by AAS 200 Change 1 PURPOSE The purpose of this advisory circular is to provide thickness design standards for pavements intended to serve the Boeing 777 airplane 2 APPLICATION a New Pavements The guidelines and standards contained herein are recommended by the Federal Aviation Administration FAA and are applicable to the thickness design of airport pavements intended to serve the Boeing 777 airplane Other facets of pavement design are equally important and should be performed in accordance with AC 150 5320 6 Airport Pavement Design and Evaluation Thickness design for pavements not subject to Boeing 777 traffic should be determined using AC 150 5320 6 This program was specifically developed as a pavement design program Traffic is assumed to be composed of a mixture of different aircraft The program is not intended for use as a tool to compare one aircraft with another i e ACN type calculations Attempts to use the program in this fashion will likely lead to erroneous results If only one aircraft is input a warning will appear indicating that the program is designed for a mix of traffic b Existing Pavements The ACN PCN method as described in AC 150 5335 5 is recommended to determine the adequacy of existing pavements
25. String NotesString S Input SLen NFNo Input NFNo SS Get CRLF Next I Close NFNo All data in the notes for section Sect is left in the string NotesString DATA FILES e 41 AC 150 5320 16 10 22 95 Appendix 2 DESIGN EXAMPLES Introduction Four design examples are given new flexible new rigid concrete overlay on rigid and asphalt overlay on rigid In the first 2 examples it is assumed that external job files have not been created and the designs are started from the internal Samples job Examples are also given to illustrate overlay design on composite pavements and the effects of sublayering in aggregate layers All of the design examples have the same traffic mix representing a very heavily loaded pavement as would be found at a major port Aircraft 1 Gross Weight pe 1 Annual Departures _ B 777 200 B 634 500 MD 82 88 150 000 MD 11 621 000 L 1011 496 000 Percent annual growth is assumed to be zero in all of the examples Also layer thickness results are all given to 1 decimal place Rounding would be done before writing the final design specifications New Flexible Design Example The pavement in the new flexible pavement design example is to service aircraft of greater than 100 000 lbs gross weight and must therefore have stabilized base and subbase as specified in AC 150 5320 6 Item P 401 Plant Mix Bituminous Pavement is selected for the base course and Item P 209 Crushed Aggregate Base
26. User s Manual 10 22 95 AC 150 5320 16 Appendix 2 representation of the structure by a lower quality layer type or by the variable stabilized layer type with its modulus value set to less than 500 000 psi Asphalt Overlay on Rigid Design Example Overlays on LEDFAA User s Manual Asphalt overlays on existing rigid pavements are designed in exactly the same way as concrete overlays except that the Asphalt Overlay layer type is selected from the Layer Type Selection box The modulus of the existing PCC surface layer is adjusted during the design and does not have the value reported in the design information from the NOTES window Subbase material substitutions are also appropriate where there is evidence of serious deterioration from field surveys For the same existing pavement and aircraft traffic as used in the concrete overlay design example the final structure from the NOTES window Design Info is The structure is AC Overlay on Rigid Design Life 20 years Pavement Structure Information by Layer Top First No Type Thickness Modulus Poisson s Strength inches psi Ratio R psi 1 P 401 AC Overlay 8 63 200 000 0 35 0 2 PCC Surface 14 00 4 000 000 H E 725 3 P 304 CIB 8 00 500 000 0 20 0 4 P 209 Cr Ag 6 00 30 518 0 35 0 5 Subgrade 0 00 12 152 0 40 0 Total thickness to the top of the subgrade 36 63 inches Composite Pavements Design of overlays on existing rigid pavements which already have an asphalt overlay ca
27. a 20 year predicted life b Concrete Overlays Of Existing Concrete Pavements The design of a concrete overlay of an existing rigid pavement is the most complex type of overlay to be designed Deterioration of the concrete overlay and existing rigid pavement must be considered as well as the degree of bond between the overlay and existing pavement Two degrees of bond are considered and addressed separately 1 Fully Unbonded Concrete Overlay An unbonded concrete overlay of an existing rigid pavement is one in which purposeful steps are taken to eliminate bonding between the overlay and existing pavement Commonly the bond is broken by applying a thin nominal 11 2 inch thick hot mix layer to the existing rigid pavement For this case the interface friction coefficient between the overlay and existing pavement is set to reflect an unbonded condition The interface coefficient is fixed and cannot be changed by the user As with hot mix asphalt overlays an SCI is required to describe the condition of the existing pavement A trial overlay thickness is input and the program iterates until a 20 year service life is predicted The thickness which yields a 20 year service life is the design thickness 2 Partially Bonded Concrete Overlay A partially bonded overlay is one in which no particular effort is made to either eliminate or achieve bond between the concrete overlay and the existing rigid pavement They are normally appropriate for existing r
28. a flexible pavement For rigid pavement design the maximum modulus value of 700 000 psi corresponds to Item P 306 Econocrete Subbase or similar Lower quality materials should be given lower modulus values if the variable type is being used When a variable modulus layer is first created the modulus is automatically set to the minimum value Undefined Layer This layer type is included to allow the use of layers not covered by the most common structural materials and to investigate the effects of using new or otherwise nonstandard materials Properties of the layer type are minimum modulus 1 000 psi maximum modulus 4 000 000 psi Poisson s ratio 0 35 fixed minimum thickness 2 inches There are no restrictions on placement of the undefined layer If an undefined layer is the topmost layer of a pavement structure either the new flexible or an asphalt overlay pavement design procedure is automatically selected depending on the composition of the second layer For flexible pavements and using the Life option this allows for computing estimated asphalt CDF values with asphalt modulus different than the fixed value of 200 000 psi It is very important to recognize that flexible pavement thickness designs made with the top layer modulus value greater than 200 000 psi will result in nonconservative designs compared with the current FAA design procedure The modulus value for asphalt layers as a function of temperature can be
29. an asphalt or undefined layer The modulus of all PCC types is fixed at 4 000 000 psi except for PCC surface when it is part of an overlay structure see below Poisson s ratio is fixed at 0 15 in all cases Flexural strength can be varied in the range 650 to 800 psi PCC modulus is considered to be independent of flexural strength Overlaid rigid pavement designs require the SCI of the existing pavement as an input For unbonded overlays it is assumed that the existing pavement may have suffered serious deterioration before the overlay and SCI can be given values in the range 100 none to negligible structural cracking to 40 For partially bonded overlays it is assumed that the existing pavement is in sound to barely failed condition before the overlay and SCI can be given values in the range 100 none to negligible cracking to 77 slightly worse than the LEDFAA definition of end of design life of SCI 80 Cumulative Damage Factor Used CDFU When SCI 100 for overlay design of an existing rigid pavement an additional input is required to define the amount of life that has been used by the existing pavement up to the time of the overlay The input is in terms of CDF used to first crack CDFU and is equivalent to equation 42 p 98 in reference 3 For aggregate base layers and assuming that traffic on the pavement has been constant over time a good estimate of CDFU can be obtained from L CDFU when L lt 0 7
30. ar track widths will have different pass to coverage ratios in each of the 10 inch strips and may show little cumulative effect on the maximum CDF Removing the aircraft with the lowest stress or strain may then have little effect on the design thickness depending on how close the gear tracks are to each other 22 e CUMULATIVE DAMAGE FACTOR LEDFAA User s Manual 10 22 95 AC 150 5320 16 Appendix 2 LAYER TYPES Introduction and LED References Sixteen layer types are included for building pavement structures Some of the types can be placed at any position in a structure while others can only be placed in specified positions The reason for specifying placement and specifying types is that the design procedure executed by the program is automatically determined by the layer types of the top two surface layers and the presence of aggregate layers Control of default parameter values is also easier when placement is controlled Some flexibility is allowed by the inclusion of an undefined layer type The only restrictions on this type are that Poisson s ratio is fixed at 0 35 and modulus must be in the range 1 000 to 4 000 000 psi Default values and ranges for all layer types are displayed in the Modify Structure data entry dialog boxes However undefined layer types do not meet FAA standards for airport pavement design All layer types except undefined are related in some way to layer types identified or specified in AC 150 5320 6
31. at Haifa Israel 4 RELATED READING MATERIAL Appendix 1 provides a listing of documents containing supplemental material relative to the subject Information on ordering these documents is also provided 5 METRIC UNITS The computer program in its present form does not provide metric dimensions Future revisions will include metric dimensions 6 AVAILABILITY The computer program for airport pavement design for the Boeing 777 airplane is available on the Office of Airport Safety and Standards Electronic Bulletin Board BBS There is no charge to access the bulletin board or download information The bulletin board requirements and parameters are listed below Equipment Requirements Computer with modem Communications software Bulletin Board Parameters Telephone number 202 267 5205 2 lines or 800 224 6287 FAA Corporate BBS Gateway Data Bits 8 Parity N one Stop Bits 1 Baud Rate 300 1200 2400 9600 14400 System Operator Rick Marinelli AAS 100 202 267 7669 Co System Operator Jeffrey Rapol AAS 200 202 267 7474 DAVID L BENNETT Director Office of Airport Safety and Standards 10 22 95 AC 150 5320 16 BACKGROUND 1 INTRODUCTION The Boeing 777 produces an unprecedented airport pavement loading configuration which seems to exceed the capability of the current methods of design Existing methods incorporate some empiricism and have limited capacity for accommodating new gear and wheel arrangements A new method of desig
32. ave the newly created aircraft list and return to the STRUCTURE window with the Back button All of the information for the Samples job structure is correct for this example except for the upper subbase layer the subgrade modulus value the PCC flexural strength and depending on the design engineers judgment the subbase layer thicknesses the Samples job values are 6 inches for each layer Start the design by changing the subbase material 1 Click Modify Structure 2 Click the box containing the name of the material for the upper subbase layer P 306 Econocrete in this case The Layer Type Selection box will be displayed Click on P 304 Cement Treated Base under the heading Stabilized rigid and click OK The box will close and the layer in the pavement change to P 304 The subgrade k value and the PCC flexural strength are both changed by clicking in their respective boxes and entering the new values in the input boxes Clicking End Modify followed by Design Structure causes the thickness of the top layer to be changed until the CDF for tensile stress at the bottom of the surface layer has a value of 1 In this case the surface thickness is 16 0 inches for a CDF of 1 Various design options for subbase thicknesses can be tried with the Design Structure function executed after each change The design in this case was finalized with a Cement Treated Base layer thickness of 8 inches a lower subbase thickness of 6 inches and a su
33. c run time library THREED VBX 3 D control library GRID VBX Grid table control library SETUPKIT DLL Setup dynamic link library VER DLL System file version dynamic link library Most of the files on the installation disk are compressed and are expanded during installation If you need to reinstall any of the files you can use the EXPAND EXE program on the installation disk As an example of reinstalling LEDFAA EXE from the a drive transfer to the a drive from the DOS prompt and type EXPAND LEDFAA EX_ DestinationPath LEDFAA EXE LEDFAA User s Manual INSTALLATION 3 AC 150 5320 16 Appendix 2 OVERVIEW 10 22 95 The program consists of five main windows rigidly linked together as shown in the figure The essential windows for pavement design are STARTUP STRUCTURE and AIRCRAFT The NOTES and AIRCRAFT DATA windows are for convenience in entering additional data describing the structure and traffic and for viewing data Operations within a window are executed by clicking the mouse cursor on a command button Command buttons are referred to by showing the button name in bold type For example click the command button called Structure is abbreviated by click Structure NOTES Additional Section Information and Detailed Output Data STARTUP Control and Organization STRUCTURE Structure Data Input and Design AIRCRAFT DATA View Landing Gear Geometry Load and Tire Pressure AIRCR
34. d at the time of interruption by clicking Design Structure again Or the structure can be changed and a new design started from the changed condition During design the structure does not become permanent in the job until the structure is saved see Save Structure Save Structure The structure is saved in the current section data record by clicking Save Structure This cannot be done in modify mode or during design Saving the structure after a design has run to completion marks the section in the data record as being a completed design Clicking Back without having saved the structure causes a message box to be displayed which prompts for the structure to be saved Modifications made to a pavement structure do not become permanent until the data is saved using Save Structure You can therefore try different designs and return to the original structure by canceling the save with the following sequence click Back followed by clicking NO in the displayed message box This transfers control to the STARTUP window Returning to the STRUCTURE window restores the original structure and all changes will have been lost Life Computes the life of the current section in years This function is not required for design but is provided for convenience in computing CDFU and CDF If design for the section has been run to completion the life computed using Life will equal the design life CDF and percent CDFU are computed for new pavement design bas
35. d concrete overlay on an existing rigid pavement 6 Part Bonded on Rigid partially bonded concrete overlay on an existing rigid pavement The sequence for copying a section is 1 Select the job to be copied from by clicking the job name 2 Click Copy Section The caption on the button will change to End Copy 3 Select the section to be copied by clicking the section name in the right hand list box Select the job to be copied to by clicking the job name A dialog box will be displayed asking you to enter the name of the new section The name can have up to 12 characters consisting of alphanumeric hyphen or underscore The old name can be kept provided it does not already exist in the job the section is being copied to Repeat to copy more sections or click End Copy to end copying Copying can be stopped at any time by clicking End Copy Dup Section A section can be duplicated within any job and given a new name First select the job Then select the section and click Dup Section Enter the new name in the displayed dialog box Delete Section To delete a section first select the job Then select the section and click Delete Section The section data is completely deleted from the job file and cannot be recovered Help The Help file is loaded by clicking Help in any of the windows except the AIRCRAFT DATA window or by pressing the F1 key on the keyboard Demonstration An interactive demonstration of the
36. d elastic design procedure compatible with the AC 150 5320 6 procedure which uses 0 75 of the Westergaard edge stress for design an adjustment is made to the calculated layered elastic interior stress to provide an equivalent edge stress Without this adjustment the interior layered elastic stress for a dual wheel landing gear relative to a dual tandem is too low when compared to the Westergaard edge stress for dual wheel relative to dual tandem But for the six wheel B 777 gear and similar the interior stress can be higher than 75 percent of the equivalent edge stress The complete procedure is therefore to compute the interior stress compute 75 percent of the equivalent edge stress and then select the higher of the two as the working stress for design An adjustment is also made to the layered elastic failure model so that the sensitivity of design thickness to base subbase material quality is compatible with that of the AC 150 5320 6 procedure The basic equation used to find the number of coverages to failure C for given concrete strength R and working stress for design o is as given in reference 3 Rr 0 2967 0 3881 0 000039 x SCT log C 0 002269 Two extra coefficients Fs and Fsc have been added to this equation to apply the compensation SCI P 0 2967 F 0 3881 Fee X 0 000039 x SCI log C 0 002269 SCI PAVEMENT THICKNESS DESIGN e 33 AC 150 5320 16 10 22 95 Appendix 2 0392
37. ded for viewing a summary of the design information for the currently selected section and for entering and saving notes on the currently selected section such as size location maintenance history etc On the left of the window is a list of the sections in the currently selected job On the right of the window is a text box which contains either the design information or the notes for the currently selected section The design information is fixed and is taken from the section data record The notes are entered by the user and can contain up to 30 000 characters for each section 5 to 20 pages Text is entered and edited as it would be in the Windows Notepad text editor The ctreertere a New Flexible Dowge Lie 20 renz A dkoga hes net bes completed for Ger coctem Poevement Startam beloeeater by Lape Top Fost Thichonce Fazit Stength mehes Pai Rea DA AC Susteoe 5 09 P AU St ies OC 0 20 3 EZ P 209 Ci Ag 375 Sabgraedn om 3 H 0 n 0 Total theckness tn the top of the zubpade 23 00 inches Aacalt Intermation Groce Wt Boe Asn Ibs Depatees Growth Figure 6 Notes Window Command Buttons Design Info Displays in the NOTES window text box the design information for the currently selected section 18 e NOTES WINDOW LEDFAA User s Manual 10 22 95 LEDFAA User s Manual AC 150 5320 16 Appendix 2 Notes Displays in the NOTES window text box the notes for the currently selected section Copy Copie
38. dulus of the layer below the aggregate layer Aggregate layers can be placed anywhere in the pavement structure except at the top or bottom The following additional restrictions also apply 1 Only one crushed layer and one uncrushed layer may be present in a structure This is for compatibility with the Modulus procedure Sublayering by the Modulus procedure accounts for thick layers and multiple layers of a single aggregate type are not necessary The maximum number of aggregate layers which may be present in a structure is therefore two one of each type 2 If crushed and uncrushed layers are adjacent the crushed layer must be above the uncrushed layer to be compatible with the modulus procedure For efficiency in iterating to a valid thickness design a two stage process is used during design with thick aggregate layers When CDF is outside the range 0 5 to 2 0 the aggregate layers are not sublayered for Julea but are treated as a single layer with modulus equal to the average modulus of what would be the sublayers When CDF is within the range 0 5 to 2 0 full sublayering is used according to the Modulus procedure One consequence of this is that the CDF can increase when sublayering first occurs apparently indicating an error in the procedure The modulus value displayed in the structure table for an aggregate layer is the average value of the sublayer modulus values The only exception is for newly created layers in which cas
39. e 2 Startup Window Delete Job To delete a job file first select the job to be deleted by clicking the job s name in the left hand list box Then click Delete Job A message box will be displayed asking if you want to continue Click Yes to delete the file and close the message box Click No to close the message box without deleting the job Deleting a job will cause all of the information in a job file to be deleted from the disk The only way to restore the information is to immediately run undelete in DOS or Windows Note Whenever as in this case information can be destroyed by an action a message box with a No or Cancel option is displayed to reduce the risk of accidentally destroying the information Copy Section New pavement structures cannot be created from scratch in the STRUCTURE window Instead existing structures in one job are copied to another job or duplicated and renamed within a single job as described below The section list box shows the type of structure for each listed section so that the desired type of structure can be selected before copying without having to check the STRUCTURE window Six types of structure are included 1 New Flexible 2 AC on Flexible asphalt overlay on an existing flexible pavement 3 New Rigid 4 AC on Rigid asphalt overlay on an existing rigid pavement LEDFAA User s Manual 10 22 95 LEDFAA User s Manual AC 150 5320 16 Appendix 2 5 Unbonded on Rigid unbonde
40. e CDFris the CDF for each aircraft type in the mix and Nis the number of aircraft types in the mix Note The same aircraft model with two different gross loads represents two different aircraft types This is because a different pavement load will be applied by each gross load Each failure mode included in the design procedure will have a separate CDF For example in flexible pavement design the thickness is adjusted to make the CDF for subgrade failure equal to 1 An additional computation is then made to find the CDF for asphalt surface cracking If the asphalt CDF CUMULATIVE DAMAGE FACTOR e 21 AC 150 5320 16 10 22 95 Appendix 2 is less than 1 the asphalt is predicted not to fail in cracking before the subgrade fails But if the asphalt CDF is greater than 1 the asphalt is predicted to fail before the subgrade and adjustments should be made to base and subbase layers so that asphalt CDF is less than 1 in the final design In the program implementation CDF is calculated for each 10 inch wide strip along the pavement over a total width of 820 inches Pass to coverage ratio is computed for each strip based on a normally distributed aircraft wander pattern with standard deviation of 30 5 inches equivalent to aircraft operation on a taxiway and used in the above equation for Miner s rule The CDF for design is taken to be the maximum over all 82 strips Even with the same gear geometry therefore aircraft with different main ge
41. e VeneegENA REN ENE AN eNe dE EEEENA EENS SEN VAN 28 Undefined Layer ee ee eege CHEN at 29 PAVEMENT THICKNESS DESIGN ececetceeeceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeneeeeeeeees 31 General Design Procedure oo editota ta siner Een CENK EA E AC ENIA AASER eae 31 New Flexible and Bituminous Overlay on Flexible ow eee 32 New Rigid Pavements assissvessc veevsiesigee teed RE E ERES 33 Concrete Overlay on Flexible Pavement ecceecceeeceeee sererererreres 34 Concrete Overlay on PCC Pavement oo eecceeeccseeeseeee serersresereseeseres 34 Asphalt Overlay on PCC Pavement ceeeeaeeeueeeeneeenees 35 LEDFAA User s Manual Contents el AC 150 5320 16 10 22 95 Appendix 2 RUNNING THE PROGRAM viscsiccsiceiiteiscnientsinieneineetsaninnndsiedieninentinnimedinniens 36 Solution TIMES eege eeh EENS EE EENE AE 36 e e CH 36 Copying to the Clipboard oo eeceseeneeeneeeee EEAO AARE cased 37 IWER 38 COMMUNICATION FES EE 38 Stage Piles d ien gie dagegen eagie Se dachwagtadaeedemedaensadseeise dedackwaradamedemondens 39 DESIGN EXAMPLES aseene erte eebe 42 INUFOMUCHON sereen rerelease indt ree ri dans one D eg ENEE 42 New Flexible Design Example 42 New Rigid Design Example e ta 45 Concrete Overlay on Rigid Design Example ou cceeeeeeeeee ceeeeea es 47 Asphalt Overlay on Rigid Design Example ou cceeeeeeeeee ceeeeee eens 49 Overlays on Composite Pavements sssesseessresesrereressree serseerereseeseeeseee 49 Effects of Sublayering
42. e current job On the right of the window is a table showing the structure with all layers illustrated and the values of all changeable parameter values displayed Clicking a new section name in the list changes the displayed structure to that of the new name LEDFAA Madity and Design Section NewFlexible in Je Samples iS oo es Figure 3 Structure Window Command Buttons LEDFAA User s Manual Modify Structure A structure is modified from the modify mode generally entered by clicking Modify Structure Modify Structure then changes to End Modify and Design Structure changes to Add Delete The only operations allowed until End Modify is clicked are modifications to the structure Alternative ways of entering modify mode are double clicking a section name also changes the displayed structure and double clicking the picture of the structure also starts an associated modification sequence Modifications which can be made to a structure are 1 Change the composition of a layer change layer type STRUCTURE WINDOW e 9 AC 150 5320 16 Appendix 2 10 22 95 Change the thickness of a layer Change the modulus value of a layer except asphalt and PCC Change the flexural strength of a PCC layer Duplicate add an existing layer aa fF bh Delete an existing layer 7 Change the iteration layer for flexible pavement design Layer types and modulus values must be selected for compatibility with the layered elastic
43. e the defaults of 75 000 and 40 000 are LAYER TYPES e 27 AC 150 5320 16 Appendix 2 10 22 95 displayed for crushed and uncrushed respectively These defaults are never used in calculations Sublayering by the Modulus procedure also causes a discontinuity in computed CDF when the number of sublayers changes as the total thickness of an aggregate layer crosses over the threshold during design For example if the thickness of an uncrushed aggregate layer increases from 15 99 inches to 16 01 inches the number of sublayers increases from 2 to 3 and the CDF may jump from a value above 1 to a value below 1 This can result in a condition in which a given combination of structure and traffic does not have a CDF of 1 whatever the thickness of the iteration layer may be and the thickness of the iteration layer changes back and forth across the threshold continuously To stop the continuous iteration the number of sublayers in a structure is fixed when CDF is within the range 0 7 to 1 4 The condition can be detected by running Design Structure again after a design has been completed If the second design gives a different thickness than the first then the condition exists A further consequence is that pavement life computed using Life will not agree with the design life and sudden changes in AC layer CDF may occur for flexible pavements Stabilized Layers 28 e LAYER TYPES Two types of stabilized layers are included classified as s
44. ed on the current setting of design life Aircraft Transfers control to the AIRCRAFT window Back Returns control to the STARTUP window 12 e STRUCTURE WINDOW LEDFAA User s Manual 10 22 95 AC 150 5320 16 Appendix 2 LEDFAA User s Manual STRUCTURE WINDOW e 13 AC 150 5320 16 10 22 95 Appendix 2 AIRCRAFT WINDOW Introduction The AIRCRAFT window allows for the creation and modification of an aircraft list for the currently selected section in the currently selected job Other sections or jobs cannot be selected from the AIRCRAFT window If you want to change to another section return to the STRUCTURE window If you want to change to another job return to the STARTUP window Aircraft are selected from a library and placed in a list of design aircraft Except for gross load annual departures and percent annual growth defined below all necessary aircraft information for design is stored internally as part of the library and cannot be changed At the top left of the window is a list of library aircraft groups Selecting one of these groups will display all of the aircraft in that group in the list box located below the aircraft group box he s Modily Aircra tee Section NewFlexible in Jed Samples Figure 5 Aircraft Window At the top right of the window is a table which lists the design aircraft for the currently selected section with associated data Aircraft are transferred from the library list to the design lis
45. ement design examples an overlay layer is added in the STRUCTURE window as follows 1 Click Modify Structure 2 Click Add Delete Layer 3 Click anywhere within the PCC surface layer in the picture of the structure A duplicate of the surface layer will be added to the structure adjacent to the original surface layer 4 Click on the layer material box in the new surface layer while still in modify mode and select Overlay fully unbonded from the Layer Type Selection box under the heading PCC All P 501 After clicking OK to close the Layer Type Selection box the new surface layer will change to an overlay and two additional data entry boxes will appear to the right of the design life box SCI and CDFU percent cumulative damage factor used DESIGN EXAMPLES e 47 AC 150 5320 16 Appendix 2 10 22 95 5 Click on the SCI box and change the value to 70 CDFU will default to a value of 100 CDFU cannot be changed in this example because SCI is less than 100 6 If Life is not already set to 20 click in the Des Life box and enter a value of 20 This will give the pavement a life of 20 years after overlaying 7 Click End Modify to leave the modify mode Run the design by clicking Design Structure Initially the thickness of the overlay layer will change in increments of 4 inches After 2 successive thicknesses have bracketed the correct design thickness the thickness of the overlay layer will iterate to the correct th
46. ength inches psi Ratio R psi 1 P 401 AC Surface 6 00 200 000 0 35 0 2 P 209 Cr Ag 13 00 71 950 O35 0 3 P 154 UnCr Ag 15 91 26 875 0 35 0 4 Subgrade 0 00 13 500 0 35 0 Total thickness to the top of the subgrade 34 91 inches Aircraft Information No Name Gross Wt Annual Annual lbs Departures Growth 1 B 747 400 873 000 4 200 0 00 2 MD 82 88 150 500 16 000 0 00 3 B 777 200 A 537 000 500 0 00 The design was run by setting the subbase as the iteration layer and starting from an arbitrary subbase thickness But running Life after the design was completed gave a life of 18 9 years a subgrade CDF of 1 06 and an asphalt CDF of 0 36 which do not agree with the design information Then without changing any of the properties of the structure or the aircraft mix Design was run again resulting in the following structure The structure is New Flexible Asphalt CDF 0 3543 Design Life 20 years 50 e DESIGN EXAMPLES LEDFAA User s Manual 10 22 95 LEDFAA User s Manual AC 150 5320 16 Appendix 2 Pavement Structure Information by Layer Top First No Type Thickness Modulus Poisson s Strength inches psi Ratio R psi 1 P 401 AC Surface 6 00 200 000 05 35 0 2 P 209 Cr Ag 13 00 70 002 0 35 0 3 P 154 UnCr Ag 16 05 26 471 0 35 0 4 Subgrade 0 00 13 500 0 35 0 Total thickness to the top of the subgrade 35 05 inches From the first to the second design the thickness of the subbase increased from 15 91 to 16 05 inches and cr
47. existing pavement layers requires engineering judgment a Hot Mix Overlay Of An Existing Flexible Pavement A trial thickness of overlay is then selected and the program iterates until a CDF of 1 0 is reached The overlay thickness required to achieve a CDF of 1 0 is the design thickness b Concrete Overlay Of An Existing Flexible Pavement The design of a concrete overlay of an existing flexible pavement is essentially the same as designing a new rigid pavement The existing flexible pavement is characterized by assigning the appropriate thicknesses and moduli of the existing layers A trial thickness of overlay is then selected and the program iterates until a CDF of 1 0 is reached The overlay thickness required to achieve a CDF of 1 0 is the design thickness The design process is relatively simple however the characterization of the existing pavement layers requires engineering judgment The interface between the concrete overlay and the existing flexible surface is assumed to be frictionless 22 OVERLAYS OF EXISTING RIGID PAVEMENTS The design of overlays for an existing rigid pavement is complex because deterioration of the underlying pavement as well as 10 22 95 AC 150 5320 16 deterioration of the overlay must be considered The condition of the existing rigid pavement prior to overlay is important and is expressed in terms of the structural condition index SCI The SCI is derived from the pavement condition index PCI The PCI is a n
48. ffects should be considered by applying the techniques in AC 150 5320 6 19 JOINTING DETAILS Jointing details for rigid pavements are presented in AC 150 5320 6 Airport Pavement Design and Evaluation The limitations on jointing of rigid pavements for wide body aircraft also apply to pavements designed to serve the B 777 OVERLAY DESIGN 20 INTRODUCTION Layered system design permits a direct design approach for overlays The other FAA method relies on an empirically based thickness deficiency approach The layered system design calculates the thickness of overlay required to provide a 20 year life which satisfies the layered elastic failure criteria for limiting stress or strain The 20 year life thickness is defined as the design thickness The design method for overlays of rigid pavement was developed by Dr R S Rollings under an FAA funded research effort as listed in Appendix 1 Overlay pavements are grouped into 4 different types as follows Hot Mix Asphalt Concrete Overlay Hot Mix Asphalt Concrete Overlay Overlay of of Existing Overlay of of Existing Rigid Existing Flexible Flexible Pavement Existing Rigid Pavement Pavement Pavement 21 OVERLAYS OF EXISTING FLEXIBLE PAVEMENTS The design of an overlay for an existing flexible pavement is essentially the same as designing a new pavement The existing flexible pavement is characterized by assigning the appropriate thicknesses and moduli of the existing layers Characterization of the
49. g during turns is expected to be no worse than existing dual tandem gears Item P 401 surfacing should provide adequate surface stability A fixed modulus value for hot mix surfacing is set in the program at 200 000 psi 1380 MPa This modulus value was chosen to produce results which closely matched thickness requirements for pavements designed with the CBR methodology 9 BASE COURSE A minimum 8 inch 203 mm thick stabilized base course is required for pavements serving these aircraft LEDFAA includes two stabilized flexible base options which are designated P 401 and Variable The word flexible is used to indicate that these bases have a higher Poisson s Ratio 0 35 and act as flexible layers as opposed to rigid layers and are not likely to crack P 401 is the standard FAA Item P 401 bituminous base which has a fixed modulus of 400 000 psi 2760 MPa The variable stabilized flexible base can be used to characterize a bound base which does not conform to the properties of P 401 It has a variable modulus ranging from 150 000 to 400 000 psi 1035 to 2760 MPa This modulus range was selected to closely duplicate results from using an equivalency factor range of 1 2 to 1 6 in the CBR method of design Stabilized rigid bases P 304 and P 306 may also be used as base course although they are subject to cracking and can induce reflection cracking in the hot mix asphalt surfacing Item P 301 Soil Cement Base is not acceptable for use as a base course for
50. he design of asphalt overlay on PCC pavement is basically the same as that of the concrete overlay on PCC pavement However the integrated life of the overlaid pavement has two parts 1 the number of years needed to reduce the SCI of the existing pavement from the initial value at the time of overlay to the minimum value at the end of the life of the overlay structure and 2 the number of years needed to cause reflection cracks to propagate through the asphalt overlay the propagation rate is assumed to be one year per inch of overlay thickness PAVEMENT THICKNESS DESIGN e 35 AC 150 5320 16 10 22 95 Appendix 2 RUNNING THE PROGRAM Solution Times The execution time required to design a structure is almost completely dependent on the floating point performance of the computer when performing the layered elastic strain and stress calculations Execution time is roughly proportional to the total number of design wheels for all of the aircraft in the design list and is proportional to a small power of the number of layers in the structure The inner loop in JULEA consumes almost all of the solution time The next most important factor is disk access time but this mainly affects the response of Windows when performing other tasks while a design is in progress and not the total solution time The most effective strategy for reducing solution times is to use an abbreviated aircraft list consisting of the most damaging aircraft to
51. ickness This process will take considerably longer than in the new pavement designs From the NOTES window Design Info the final structure is The structure is Unbonded PCC Overlay on Rigid Design Life 20 years Pavement Structure Information by Layer Top First No Type Thickness Modulus Poisson s Strength inches psi Ratio R psi 1 PCC Overlay Unbond TOY 22 4 000 000 0 15 700 2 PCC Surface 14 00 4 000 000 0 15 725 3 P 304 CIB 8 00 500 000 0 20 0 4 P 209 Cr Ag 6 00 30 518 0 35 0 5 Subgrade 0 00 12 152 0 40 0 Total thickness to the top of the subgrade 38 22 inches In the output from the NOTES window the modulus of the PCC surface layer of the existing structure is given as 4 000 000 psi But this is not the value used during design when the SCI of the layer is less than 100 The value used is calculated from the relationship given in reference 3 E E yy X 0 02 0 064 x SCI pui 0 00584 x SCT where SClrxist SCI of the existing PCC layer as it deteriorates during the life of the overlaid structure Erast modulus of the existing PCC layer at SCIzxust E100 modulus of the existing PCC layer when its SCI is 100 4 000 000 psi in this case The modulus of the CTB layer is also set at its default value of 500 000 psi which is appropriate for design of new structures But if from field surveys the layer is known to be seriously deteriorated it can be replaced in the 48 e DESIGN EXAMPLES LEDFAA
52. igid pavements which are in good condition i e when the SCI is 77 or greater For this case the interface coefficient is set to reflect a small degree of friction between the overlay and base pavement This coefficient is fixed and cannot be changed by the user An SCI for the existing pavement is required A trial overlay thickness is input and the program iterates until a 20 year service life is predicted The thickness which yields a 20 year service life is the design thickness 10 22 95 AC 150 5320 16 Appendix 1 APPENDIX 1 RELATED READING MATERIAL 1 The latest issuance of the following free publications may be obtained from the Department of Transportation Utilization and Storage Section M 443 2 Washington D C 20591 Advisory Circular 00 2 updated triannually contains the listing of all current issuances of these circulars and changes thereto a AC 00 2 Federal Register Advisory Circular Checklist and Status of Federal Aviation Regulations 2 The following advisory circulars which can be found in AC 00 2 may be obtained from the Superintendent of Documents U S Government Printing Office Washington D C 20402 Use the Superintendent of Documents stock number when ordering along with the AC number and title Send a check or money order in the amount listed for each document No c o d orders are accepted a AC 150 5335 5 Standardized Method of Reporting Airport Pavement Strength PCN dated June 15 1983 and Change 1 da
53. ign aircraft table from the group one at a time and change the default data values as required If a mistake is made and the wrong aircraft added to the table the aircraft can be removed by selecting its name and clicking Remove or by double clicking its name DESIGN EXAMPLES e 43 AC 150 5320 16 10 22 95 Appendix 2 7 Repeat the process for each group until all aircraft in the traffic mix have been added to the table Note that the L 1011 in this example is contained in the Other Commercial group 8 Click Save List and answer OK to the displayed message 9 Click Back to return to the STRUCTURE window Suitable base and subbase thicknesses can now be determined by running design cases However there is no explicitly defined procedure for doing this and judgment is required on the part of the design engineer to make a selection within two limiting cases The first case is to select the minimum base course thickness of 8 inches as specified in AC 150 5320 16 for B 777 service and run a design 1 The new flexible structure in the Samples job has the correct base and subbase materials for this example the base thickness is set at 8 inches and the surface thickness is set at 5 inches All that has to be done before running the design is to change the subgrade modulus by clicking Modify Structure and clicking the CBR box Enter a value of 8 in the displayed input box and click OK Click End Modify Make sure that the arrow
54. ign list must be saved or discarded before returning to the STRUCTURE window The Save operation permanently changes the aircraft data stored in the section data record Save to Float An independent floating list of aircraft is provided to allow an existing list to be transferred easily to a different section Clicking Save to Float transfers the current design list and aircraft data to the floating list replacing the existing floating list The new floating list will remain available until the next Save to Float operation or the program is terminated The floating list is displayed in the list box at the bottom right of the window and is always empty when the program starts Add Float Adds the aircraft in the floating list to the current design list up to the maximum of 20 aircraft 16 e AIRCRAFT WINDOW LEDFAA User s Manual 10 22 95 AC 150 5320 16 Appendix 2 View Gear Transfers control to the AIRCRAFT DATA window discussed under separate heading Back Returns control to the STRUCTURE window If changes have been made to the design list and the list has not been saved a message box is displayed requesting that the changes be saved or discarded or that the Back operation be canceled Control cannot return to the STRUCTURE window until the changes have been saved or discarded LEDFAA User s Manual AIRCRAFT WINDOW e 17 AC 150 5320 16 10 22 95 Appendix 2 NOTES WINDOW Introduction The NOTES window is provi
55. ion Administration Office of Airport Safety and Standards AAS 1 Federal Aviation Administration Washington D C 10 22 95 AC 150 5320 16 Appendix 2 INTRODUCTION visisicccinisiscsvsssseneiecaieceisinvennsstadecnssdsienniasniereuedunscainnniaansicadauniens 1 INSTALLATION jisctessccsccescecietesesusecesecatedesesveecuseeviususeewiecuseewiusuieewtecuneceneduaeeenedes 3 SAA ETEA A a EEEE EEEE EE EE ENEE EENEG 4 STARTUP WIND E 5 Introduction oinor e E EE E E E Reeg geen 5 Command Buttons 37 EEN E e CRITS 5 STRUCTURE WINDOW sisicisicsissniiccivesicetiianssedivencesivarsiasivedsiniaverivadavenccadivarns 9 Introduction EE 9 Command Buttons ENER dE ioy e E e y a eia 9 AIRCRAFT WINDOW ugereegt UE 14 Introduction EE 14 Non Standard Aircraft Lists esesssssesrssereersee srrsossossroscoseroseseerseessee 16 Command ButtOns 30 ictevsccivewes deed egen EE SEA E E seven EEN S 16 NOTES WINDOW EN 18 Introduction EE 18 Command Buttons oi ase E A ilove tated EAEE LADATA 18 AIRCRAFT DATA WINDOW eessen 20 CUMULATIVE DAMAGE FACTOR cccsssesseeeeeeeeeeeeeseeneeeeeeeeeseeeeeneseseeenees 21 Baden 23 Introduction and LED References oo cieeeeeeceeeceneeeeeeeee cueeeeaeeeaeeeaeeeeuees 23 S bgrade Layers arrani in o EE ENEEEN AE SEANCE EEENN ENEE REENEN 23 Asphalt Layers edd RER sed Riedie devin tice RL eis 24 Concrete Layers soes ieta EC chelsea ins AE ENEE aes 25 Agregate LAV ee ef A ege ee EE Cetin tatteds ER Stabilized Layers su
56. ltiple aircraft mixes The program is also primarily intended for use in designing airport pavements according to a standard procedure It is not intended to be used to compare the damaging effects of different aircraft by running single aircraft designs or CDF computations i e ACN type calculations LEDFAA User s Manual 10 22 95 AC 150 5320 16 Appendix 2 INSTALLATION Installation of LEDFAA is started by inserting the distribution diskette in an available diskette drive usually a or b Then from Windows Program Manager select Run from the File menu Type in a setup or b setup and press Enter on the keyboard You will be asked to enter a working directory The default is C LEDFAA If this is OK click continue The directory will be created if it does not already exist If you want to use a different directory type in the name with full path The remainder of the setup is automatic A new program group will be created called LEDFAA LEDFAA is run by double clicking the LEDFAA icon in the program group The icon can be dragged into a different group such as applications and the LEDFAA group deleted if you wish The following files are installed by setup Directory LEDFAA or user determined directory LEDFAA EXE Visual Basic I O and design program JULEAWW EXE Julea compiled as a Windows application LEDFAA HLP Help file Directory WINDOWS SETUP 1 EXE Setup executable Directory WINDOWS SYSTEM VBRUN300 DLL Visual Basi
57. maximum of 20 aircraft can be analyzed Solution times are a function of the number of aircraft in the mix The design procedure described herein deals with mixed traffic differently than previous methods There is no need to determine a design aircraft The program calculates the damaging effects of each aircraft in the traffic mix The damaging effects of all aircraft are summed in accordance with Miner s Law When the cumulative damage factor CDF sums to a value of 1 0 the design conditions have been satisfied b Boeing 777 In addition to the requirement for mixed traffic Boeing 777 aircraft must be in the mixture If a 777 airplane is not in the traffic mix a warning will appear on the screen and on the printout 5 PAVEMENT CONSIDERATIONS a Design Life The FAA design standard for pavements is based on a 20 year design life The computer program is capable of considering other design life time frames Use of a design life other than 20 years constitutes a deviation from standards and will require FAA approval 1 and 2 AC 150 5320 16 10 22 95 b Design Reliability The reliability of this method of design should be approximately the same as the reliability of the CBR method of pavement design c Materials Pavement materials are characterized by thickness elastic moduli and Poisson s ratio Layer thicknesses can be varied at will except where minimum thicknesses are required Elastic moduli are either fixed or variable dependi
58. n based on layered elastic analysis has been developed to calculate design thicknesses for pavements for the Boeing 777 The new design method is computationally intense and is thus in the form of a computer program 2 COMPUTER PROGRAM The computer program operates under Microsoft Windows The core program JULEA is a Microsoft Windows FORTRAN application The remainder of the program is written in Visual Basic 3 HARDWARE AND SOFTWARE REQUIREMENTS In order to achieve reasonable solution times an IBM compatible computer with a 486 or Pentium central processing unit CPU and a math co processor is recommended Windows 3 1 is the required software These requirements are intended to be compatible with the in house capabilities of most consulting firms The program will operate with a 386 CPU and a math co processor however solution times may be objectionably long 4 AIRCRAFT CONSIDERATIONS A wide variety of aircraft with pertinent pavement design characteristics are stored in the program library The designer has some latitude in selecting aircraft parameters a Mixed Traffic The computer program was developed and calibrated specifically to analyze a mixture of different aircraft If a single aircraft is used for design a warning will appear in the Aircraft Window indicating the program was intended for use with a mixture of different aircraft types Nearly any traffic mix can be developed from the aircraft in the program library A
59. n decreases the subgrade CDF from 1 06 to 0 98 7 5 percent but decreases the asphalt CDF by a much larger relative amount from 0 35 to 0 19 51 percent 2 Changing the base material to variable stabilized at 150 000 psi on the second design decreases the subgrade CDF to 0 28 and decreases the asphalt CDF to 0 003 a negligible amount 52 e DESIGN EXAMPLES LEDFAA User s Manual
60. n of the design procedures and program structure is not possible within the confines of a user s manual and these descriptions can be found in other publications The main intent of the user s manual is INTRODUCTION e 1 AC 150 5320 16 Appendix 2 2 e INTRODUCTION 10 22 95 to provide sufficient information for operating the program selecting input data values and interpreting the output data Installation of the program is described first followed by descriptions of the various parts of the program and its operation Information is then given on the structure data input requirements and how they relate to the design procedures Final sections provide a short discussion on program running times with possible strategies for decreasing design time for a given design case a description of the structure of external data files so that interested users can access the files and incorporate the data in other applications if desired anda selection of design examples The relationship between the layered elastic design procedures and the AC 150 5320 6 design procedures is not discussed in the manual However it should be pointed out that the traffic and failure models are fundamentally different and comparisons between the two sets of procedures are only valid when considering multiple aircraft traffic mixes Single aircraft comparisons misleadingly indicate a degree of conservatism with the LED procedures which is not present for typical mu
61. n the computation is completed Values of percent CDFU greater than 100 indicate that the procedure predicts that the SCI of the pavement should be less than 100 A value of 100 should then be entered for percent CDFU as input data for the overlay design However since the computation of percent CDFU will be based on estimated structure properties and traffic the value is likely to be unreliable An alternative procedure is to run Design Structure for the original structure with design life set to the actual design life Then repeat the steps given above and use the new value of percent CDFU If it is suspected that the pavement has been subjected to more or heavier traffic than assumed in the Life computation percent CDFU should be increased from the computed value Setting percent CDFU to 100 will give the most conservative design For both partially bonded and fully unbonded concrete overlays the modulus of the base pavement is varied as a function of SCI of the base pavement when SCI is less than 100 according to the relationships given in reference 3 The computation is automatic and transparent to the user Structure Condition Index SCI The ranges of the SCI inputs correspond to specific ranges of the factors cp and cr used in overlay design by the AC 150 5320 6 method For a concrete overlay on rigid pavement the following taken from reference 3 can be used to relate the c factor in the current FAA procedure with SCI required f
62. ng on the material The permissible range of variability for elastic moduli is fixed to ensure reasonable values Poisson s ratio for all material is fixed Materials are identified with their corresponding FAA specification designations for example crushed stone base course is identified as Item P 209 The list of materials contains an undefined layer with variable properties If an undefined layer is used a warning will appear in the Structure Window stating that a non standard material has been selected and its use in the structure will require FAA approval FLEXIBLE PAVEMENT DESIGN 6 SCOPE This section presents FAA standards for the design of flexible pavements intended to serve a mix of traffic which includes the Boeing 777 airplane 7 INTRODUCTION The design process considers two modes of failure for flexible pavement vertical strain in the subgrade and horizontal strain in the asphalt layer Limiting vertical strain in the subgrade is intended to preclude failure by subgrade rutting Limiting horizontal strain at the bottom surface of the asphalt surfacing layer guards against failure by cracking of the asphalt surface layer 8 HOT MIX ASPHALT SURFACING Hot mix asphalt surfacing should meet the requirements of FAA Item P 401 A minimum thickness of 5 inches 127 mm of hot mix surfacing is required for traffic mixes which include the Boeing 777 The landing gear of the 777 is articulated rear dual wheels are steerable thus scrubbin
63. nnot be done directly using LEDFAA because a PCC surface layer cannot be placed further down than the second layer in a structure One method of representing such a structure is to replace the PCC layer in the existing pavement with an undefined layer or a variable stabilized layer The modulus of the substitute layer can be selected based on the design engineers judgment of the SCI of the existing PCC layer and application of the equation for PCC layer modulus given in the concrete overlay design example DESIGN EXAMPLES e 49 AC 150 5320 16 10 22 95 Appendix 2 Effects of Sublayering in Aggregate Layers As discussed in the section on aggregate layers sublayering of aggregate layers is included in the design procedures The maximum sublayer thicknesses are 8 inches for uncrushed aggregate and 10 inches for crushed aggregate except when the number of layers is fixed to avoid continuous iteration The following example illustrates the effects of the sublayering caused by changes in effective stiffness of an aggregate layer when the number of sublayers changes The example structure has a 6 inch thick asphalt surface layer over aggregate base and subbase layers and a 9 CBR subgrade modulus of 13 500 psi Aircraft in the mix are B 747 400 MD 80 82 and B 777 200 A The structure is New Flexible Asphalt CDF 0 3096 Design Life 20 years Pavement Structure Information by Layer Top First No Type Thickness Modulus Poisson s Str
64. on the left of the structure points to the subbase and click Design Structure 4 Wait until the program has changed the subbase thickness to give a CDF of 1 for vertical strain in the subgrade and computed the asphalt surface CDF In this case the design subbase thickness is 21 1 inches and asphalt CDF is negligible The second limiting case is to assume that the base course must protect a subbase having a CBR of 20 To do this 1 Remove the subbase from the structure by clicking Modify Structure followed by Add Delete Layer the caption on the Design Structure button changes to Add Delete Layer in modify mode Click anywhere within the subbase and select delete in the displayed box Alternatively return to the STARTUP window duplicate the section with another name use the new section for temporary working and return to the first section for final design Change the subgrade CBR to 20 Click End Modify followed by Design Structure The thickness of the base will be changed until the CDF for vertical strain in the 20 CBR subgrade has a value of 1 In this case the revised base thickness is 8 3 inches A base thickness of 8 inches is therefore not quite sufficient for the design But increasing the base thickness decreases the total pavement thickness for a subgrade CBR of 1 and adjustments to the base course thickness can be made at the judgment of the engineer provided that the minimum requirements are satisfied Fo
65. opied by right clicking on the picture RUNNING THE PROGRAM e 37 AC 150 5320 16 10 22 95 Appendix 2 DATA FILES Communication Files Information is passed to and from JULEA in the following data files JULEA STR JULEA LOA JULEADAT OUT JULEASG OUT DAMTMP DAT 6 DAMTMPSG DAT JULEA STR and JULEA LOA are structure and aircraft data files written by LEDFAA for input to JULEA each time JULEA is executed They are ASCII files in exactly the same format as used in the LEDNEW collection of programs The data can be examined in a text editor if more detail is required than given in the LEDFAA windows JULEADAT OUT and JULEASG OUT are ASCII files written by JULEA and have exactly the same format as used in the LEDNEW collection of programs They contain all of the structure aircraft stress and strain data read or produced by JULEA Stresses and strains are given for each evaluation point for each aircraft in the traffic mix Principal and octahedral stresses are included For rigid pavements only JULEADAT OUT is written For flexible pavements JULEASG OUT contains the data for stresses and strains computed at the top of the subgrade and JULEADAT OUT contains the data for stresses and strains computed at the bottom of the asphalt layer The files are overwritten each time JULEA is executed DAMTMP DAT and DAMTMPSG DAT are written by JULEA and contain the stresses or strains used by LEDFAA to compute CDF For rigid pavements DAMTMP
66. or input in LEDFAA c 0 076 SCI 100 1 073 L 93 2 c 71 Asphalt overlays on rigid pavements also require the input of a value for SCI of the existing pavement The range is 100 to 50 The following taken from reference 3 can be used to relate the c factor in the current FAA procedure with SCI required for input in LEDFAA SCI 100c 25 0 75 lt c lt 1 The range for cis specified in AC 150 5320 6 Note that the relationship is not valid when SCI is between 75 and 100 LEDFAA User s Manual 10 22 95 AC 150 5320 16 Appendix 2 Aggregate Layers LEDFAA User s Manual Crushed Aggregate Crushed Aggregate in LEDFAA corresponds to Item P 209 Crushed Aggregate Base Course The modulus of crushed aggregate layers is computed automatically and cannot be changed manually Uncrushed Aggregate Uncrushed Aggregate in LEDFAA corresponds to Item P 154 Subbase Course The modulus of uncrushed aggregate layers is computed automatically and cannot be changed manually Modulus Values of Aggregate Layers The modulus values of aggregate layers are calculated automatically The WES Modulus procedure included with LEDNEW is followed with sublayering performed automatically maximum sublayer thicknesses are 8 inches for uncrushed aggregate and 10 inches for crushed aggregate The modulus values of the sublayers decrease with increasing depth of a sublayer within the aggregate layer and are also dependent on the mo
67. ossed the threshold for sublayering from 2 sublayers to 3 The modulus values of both aggregate layers also changed as did the asphalt CDF The changes in the structure are summarized in the table below with the sublayer modulus values included read from the JULEADAT OUT file Property Designi 1 Design All of the values given are for the structure at the end of design except where noted that they were obtained after running Life For the first design the subbase has 3 sublayers instead of the 2 required by its thickness of less than 16 inches This is because during the final stages of design the number of sublayers was fixed when the thickness of the subbase was greater than 16 inches Then when Life was run the correct number of 2 sublayers was created and the life computations made for a slightly different structure Also when the second design was run the structure started with the correct number of 3 sublayers the number of sublayers was fixed at 3 and the design completed with 3 sublayers and a thickness of less than 16 inches If the number of layers had not been fixed at some stage the design would have cycled back and forth across the threshold DESIGN EXAMPLES e 51 AC 150 5320 16 10 22 95 Appendix 2 thickness of 16 inches with CDF values of 1 06 and 0 94 repeated endlessly Two other interesting aspects of this example are 1 Removing the MD 82 from the aircraft list and running Life on the second desig
68. produce a first approximation to the pavement design The full aircraft design list can then be used to finalize the design Thick aggregate layers increase the solution time more than would be expected because of the sublayering used to represent variation of modulus with depth Thin concrete overlays on rigid pavements have the longest solution times of all the structure types Options A batch option has been included in the program so that a number of time consuming designs can be executed unattended The option is activated by double clicking anywhere on the gray background of the structure window A check box appears which when clicked changes the caption of the Life button to Batch The first section to be designed is then selected and Batch clicked Each section in the list starting at the one selected to the last will then in turn be designed and the results stored in the JOB file The already designed and saving structure messages are suppressed However if any other message such as minimum thickness for a layer is displayed the batch job will halt until the message is cleared The results can be viewed in the NOTES window after the batch job has finished An additional option called No AC CDF is included to disable the computation of asphalt surface CDF at the end of a flexible pavement design This option is most effective during initial design of pavement sections with thick aggregate layers and many ai
69. r CBR to modulus should not be used when designing a rigid pavement based on measurements of CBR The recommended method is to convert the CBR value to k using any preferred method and then use the equation given above for converting from the intermediate k value to modulus This will almost certainly not give the same modulus as the direct CBR relationship but considering the empirical nature of the relationships the lack of correspondence is to be expected Details of the development of the conversion equations is given in references 1 and 2 Asphalt Layers Two types of asphalt layers are included asphalt surface and asphalt overlay Both have the same properties with modulus fixed at 200 000 psi and Poisson s ratio fixed at 0 35 The asphalt overlay type can be placed over asphalt surface or PCC surface types The asphalt surface type can only be placed on the top of a structure or under an asphalt overlay 24 e LAYER TYPES LEDFAA User s Manual 10 22 95 AC 150 5320 16 Appendix 2 Concrete Layers LEDFAA User s Manual Four types of concrete layers are included PCC surface PCC unbonded overlay on a rigid pavement PCC partially bonded overlay on a PCC pavement and PCC overlay on a flexible pavement The PCC surface type can be placed on the top of the structure for new designs or next to the top for overlays The overlay types can only be placed on the top of the structure PCC overlay on flexible pavement can be placed on
70. r this example a base thickness of 10 inches was finally selected Giving after a final design run a subbase thickness of 18 2 inches and a total pavement thickness of 33 2 inches From the NOTES window Design Info button the design information for the final design is 44 e DESIGN EXAMPLES LEDFAA User s Manual 10 22 95 AC 150 5320 16 Appendix 2 The structure is New Flexible Asphalt CDF 0 0000 Design Life 20 years Pavement Structure Information by Layer Top First No Type Thickness Modulus Poisson s Strength inches psi Ratio R psi 1 P 401 AC Surface 5 00 200 000 0 35 0 2 P 401 St flex 10 00 400 000 0 35 0 3 P 209 Cr Ag 18 17 50 845 O35 0 4 Subgrade 0 00 12 000 0435 0 Total thickness to the top of the subgrade 33 17 inches Aircraft Information No Name Gross Wt Annual Annual lbs Departures Growth 1 B 737 400 150 000 360 0 00 2 B 747 400 873 000 4 200 0 00 3 B 75 250 000 360 0 00 4 B 767 200 335 000 720 0 00 D B 777 200 B 634 500 720 0 00 6 MD 82 88 150 000 600 0 00 7 DC 10 30 583 000 360 0 00 8 DC 10 30 Belly 583 000 360 0 00 9 MD 11 621 000 700 0 00 10 MD 11 Belly 621 000 700 0 00 11 L 1011 496 000 320 0 00 Note that the wing gear and the belly gear for the DC 10 30 and MD 11 are treated as separate aircraft in the design procedure Also the thickness of the subgrade is given as 0 00 inches whereas the assumption in the layered elastic representation of the structure i
71. rcraft in the design list If a lengthy design computation is underway a second instance of LEDFAA can be started from Program Manager and section data edited Design computation is only allowed from the first instance of the program because JULEA cannot be run from two programs at once Alternatively any other application can be run from Windows while a design is in progress The 36 e RUNNING THE PROGRAM LEDFAA User s Manual 10 22 95 AC 150 5320 16 Appendix 2 elapsed time window will always remain on top of the desktop so that the progress of the design can be monitored Copying to the Clipboard LEDFAA User s Manual In addition to copying the design and notes information to the clipboard from the NOTES window any of the program windows can be copied to the clipboard as a bitmap using the Windows Alt PrintScreen function The bitmap can then be pasted into another application and printed or saved First make sure that the window to be copied is the active window by clicking the mouse within the window area Then hold down the Alt key and press the PrintScreen key If the window is not copied to the clipboard check your computer documentation for the equivalent function The picture of the structure in the STRUCTURE window can also be copied to the clipboard by placing the mouse pointer within the area of the picture and clicking the right mouse button Similarly the picture of the gear layout in the AIRCRAFT DATA window can be c
72. rface thickness of 15 8 inches The final design information from the NOTES window Design Info button is given below for the structure only the aircraft information is the same as in the new flexible example The structure is New Rigid Design Life 20 years 46 e DESIGN EXAMPLES LEDFAA User s Manual 10 22 95 AC 150 5320 16 Appendix 2 Pavement Structure Information by Layer Top First No Type Thickness Modulus Poisson s Strength inches psi Ratio R psi 1 PCC Surface 15 79 4 000 000 0 15 725 2 P 304 CIB 8 00 500 000 0 20 0 3 P 209 Cr Ag 6 00 30 518 0435 0 4 Subgrade 0 00 12 152 0 40 0 Total thickness to the top of the subgrade 29 79 inches Concrete Overlay on Rigid Design Example LEDFAA User s Manual Design of an overlay on a rigid pavement normally starts with an existing pavement structure having a known SCI In the design example an unbonded overlay is to be applied over an existing rigid pavement which has an SCI of 70 The same traffic mix as used in the new pavement design examples is to be applied for 20 years after overlaying The properties of the existing structure are No Type Thickness Modulus Poisson s Strength inches psi Ratio R psi 1 PCC Surface 14 00 4 000 000 0 15 725 2 P 304 CIB 8 00 500 000 0 20 0 3 P 209 Cr Ag 6 00 30 518 0 35 0 4 Subgrade 0 00 12 152 0 40 0 After setting up the structure to match the information above and setting the traffic information as described in the new pav
73. s that the subgrade is infinitely thick New Rigid Design Example LEDFAA User s Manual The new rigid design example uses the same traffic mix as the new flexible design example and the pavement for the new rigid design example must therefore have a stabilized subbase course to satisfy the requirements of AC 150 5320 6 A 2 layer subbase has been selected with Item P 304 Cement Treated Base at the top and Item P 209 Crushed Aggregate Base Course below Subgrade k value is 120 pci and the surface is Item P 501 Portland DESIGN EXAMPLES e 45 AC 150 5320 16 10 22 95 Appendix 2 Cement Concrete Pavement with a design flexural strength of 725 psi Design life is 20 years The design can be started by copying the NewRigid section in the Samples job to the same job file as used in the new flexible example Since the aircraft mix is the same as in the flexible example some time can be saved by using the floating aircraft list 1 Select the NewFlexible design example while in the STRUCTURE window and transfer to the AIRCRAFT window by clicking Aircraft 2 Click Save to Float to copy all of the aircraft in the design aircraft list to the Float Aircraft list 3 Click Back to return to the STRUCTURE window and select the NewRigid section 4 Goto the AIRCRAFT window and clear the design aircraft list with the Clear List command button 5 Click Add Float to copy the aircraft in the float list to the design aircraft list 6 S
74. s the design information and the notes from the NOTES window to the Windows clipboard The text can then be pasted into another application such as a text editor or word processor Print Prints the design information and the notes from the NOTES window to the currently selected default Windows printer Save Saves the notes for the currently selected section in the NTS file for the currently selected job Each JOB file has a corresponding NTS file When initialized the notes for a section contain only the section name unless the section was created using Copy Section in the STARTUP window in which case the old notes are copied into the new section NOTES WINDOW e 19 AC 150 5320 16 10 22 95 Appendix 2 AIRCRAFT DATA WINDOW The AIRCRAFT DATA window primarily shows the main gear layout for the aircraft currently selected in the design list The gear layout and the tire contact patches are drawn to scale An image of the picture can be copied to the clipboard by clicking the right mouse button on the picture An image of the window is printed by clicking Print Gross load can also be changed by clicking the Gross Load data display box LEDFAA Aimat Data for Sectee NewFicSdic ia Joh Semetes Figure 7 Aircraft Landing Gear Data 20 e AIRCRAFT DATA WINDOW LEDFAA User s Manual 10 22 95 AC 150 5320 16 Appendix 2 CUMULATIVE DAMAGE FACTOR LEDFAA User s Manual Cumulative damage factor CDF is the amount of the struc
75. t by selecting an aircraft in the library list by clicking the name once and clicking Add or by double clicking the aircraft name in the library list Aircraft are removed from the design list by selecting an aircraft in the design list by clicking the name once and clicking Remove or by double clicking the aircraft name in the design list Values in the first three data columns of the design aircraft list table gross load annual departures and percent annual growth can be changed by 14 e AIRCRAFT WINDOW LEDFAA User s Manual 10 22 95 LEDFAA User s Manual AC 150 5320 16 Appendix 2 clicking on the value to be changed An input box is displayed which gives instructions and the allowed ranges for data entry Scrolling the table columns to the left shows columns for total lifetime departures tire pressure percent gross load on the design gear dual wheel spacing tandem wheel spacing tire contact width and tire contact length None of these can be changed For all aircraft in the library the fraction of the gross load carried by the main gear has been set at 95 percent to make the LEDFAA design procedures compatible with those of AC 150 5320 6 The tire contact lengths and widths are those used in the calculation of pass to coverage ratio for the aircraft An elliptical contact patch is assumed with its area equal to the tire load divided by the tire pressure In contrast circular tire contact patches are used in JULEA beca
76. tabilized flexible and stabilized rigid The classifications are derived from the fact that the modulus values correspond to current procedure AC 150 5320 6 equivalencies when comparing designs made by current and LED procedures Variable modulus types are provided as well as fixed modulus types corresponding to standard material items Property values are Type Poisson s Ratio Stabilized flexible Variable Minimum 150 000 Variable Maximum 400 000 P 401 Asphalt 400 000 Stabilized rigid Variable Minimum 250 000 Variable Maximum 700 000 P 301 Soil Cement Base 250 000 P 304 Cement Treated Base 500 000 P 306 Econocrete Subbase 700 000 Because the modulus values were determined on the basis of producing thickness designs comparable with the current design procedures typical laboratory test data for stabilized materials should not be used in preparing input data for LEDFAA designs Instead the material recommendations and equivalencies given in AC 150 5320 6 should be followed and related to the modulus values as follows LEDFAA User s Manual 10 22 95 AC 150 5320 16 Appendix 2 For flexible pavement design the minimum modulus value of 150 000 psi corresponds to a base course equivalency factor of 1 2 and the maximum value of 400 000 psi corresponds to a base course equivalency factor of 1 6 paragraph 36 b in AC 150 5320 6 The choice of base course modulus value can have a significant effect on total thickness of
77. ted March 6 1987 b AC 150 5370 10A Standards for Specifying Construction of Airports dated February 17 1989 c AC 150 5320 6C Airport Pavement Design and Evaluation dated December 7 1978 3 Copies of the following reports may be obtained from the National Technical Information Service 5285 Port Royal Road Springfield VA 22161 a DOT FAA RD 74 199 Development of a Structural Design Procedure for Flexible Airport Pavements November 1974 b DOT FAA RD 77 81 Development of a Structural Design Procedure for Rigid Airport Pavements April 1979 c DOT FAA PM 87 19 Design of Overlays for Rigid Airport Pavements April 1988 4 Copies of ASTM standards may be obtained from the American Society of Testing and Materials 1916 Race Street Philadelphia PA 19103 1 and 2 10 22 95 AC 150 5320 16 Appendix 2 APPENDIX 2 USERS MANUAL This appendix contains the users manual for LEDFAA It provides detailed information on proper execution of the computer program LEDFAA v1 2 Note that this design method is considered to be an FAA standard only if a mixture of traffic is considered and the Boeing 777 airplane is a part of that mixture 1 and 2 10 22 95 AC 150 5320 16 Appendix 2 LEDFAA User s Manual Federal Aviation Administration Airport Pavement Design October 1995 AC 150 5320 16 10 22 95 Appendix 2 A computer program for layered elastic based airport pavement design Developed by the Federal Aviat
78. ted in the Design Info text box in the NOTES window Input data for overlay structures also includes the structural condition index SCJ of the existing pavement before overlay and under some conditions the Cumulative Damage Factor Used CDFU of the existing pavement CDFU is related to the remaining life of the existing pavement Recommendations for selecting appropriate values of SCI and CDFU are given in the discussion of concrete layers in the Layer Types section The small arrow in the left margin of the picture of the structure indicates the layer which will be adjusted during design see below The position of the arrow can only be changed when the structure is a new flexible pavement Clicking in the margin to the left of any layer except for the top or bottom layers will select that layer as the adjustment layer for design Add Delete Layers can be added or deleted using Add Delete After clicking the button you must select a layer in the picture of the structure A box is displayed requesting the selection of Add or Delete Selecting Add duplicates the selected layer The properties of the layer can then be changed as desired Selecting Delete completely removes the selected layer from the structure End Modify Terminates the modify mode No functions other than structure modifications can be executed while the modify mode is active Design Structure Clicking this button adjusts the thickness of one of the layers of the
79. the necessary information for thickness design when B 777 aircraft are included in the aircraft mix Apart from the procedures being implemented as a computer program instead of as nomographs the main change in pavement design from the user s perspective is that the design aircraft concept has been replaced by design for fatigue failure expressed in terms of a cumulative damage factor CDF using Miner s rule Also the major material property of the pavement layers is now uniformly expressed as an elastic modulus instead of the previous CBR California Bearing Ratio for flexible pavements or k value for rigid pavements Formulas for transforming CBR and k values to modulus values are provided where appropriate in the documentation Automatic conversion is provided in the program It should also be borne in mind that although layered elastic based procedures are normally considered to be mechanistic and more rational than the previous procedures a considerable amount of engineering judgment is still required Designs produced by LEDFAA should comply with the detailed requirements and recommendations of AC 150 5320 16 and AC 150 5320 6 The program does not automatically satisfy all of these requirements and the recommendations in the ACs should be followed in the selection of input parameters It is the designer s responsibility to use the program and the advisory circulars in conjunction with each other A complete descriptio
80. tion factor ratings Cp and Cy a Hot Mix Asphalt Overlays Of Existing Rigid Pavements The design process for hot mix overlays of rigid pavements considers two conditions for the existing rigid pavement to be overlaid The SCI of the existing pavement may be equal to or less than 100 1 Structural Condition Index Less Than 100 The most likely situation is one in which the existing pavement is exhibiting some structural distress i e the SCI is less than 100 If the SCI is less than 100 the overlay and base pavement deteriorate at a given rate until failure is reached An overlay thickness is assumed and the program iterates on the thickness of overlay until a 20 year life is predicted A 20 year predicted life satisfies the design 2 Structural Condition Index Equal to 100 An existing pavement with an SCI of 100 may require an overlay to strengthen the pavement in order to accept heavier aircraft If the SCI of the base pavement is equal to 100 an additional input is required CDFU cumulative damage factor used which estimates the amount of pavement life used up prior to overlay The program assumes the base pavement will deteriorate at one rate while the SCI is 5 and 2 AC 150 5320 16 10 22 95 equal to 100 and at a different rate after the SCI drops below 100 As before a trial overlay thickness is input and the program iterates on that thickness until a 20 year life is predicted The design thickness is that which provides
81. tural fatigue life of a pavement which has been used up It is expressed as the ratio of applied load repetitions to allowable load repetitions to failure or for one aircraft and constant annual departures CDF number of applied load repetitions number of allowable repetitions to failure annual departures x life in years pass coverage ratio x coverages to failure applied coverages coverages to failure When CDF 1 the pavement will have used up all of its fatigue life When CDF lt 1 the pavement will have some life remaining and the value of CDF will give the fraction of the life used When CDF gt 1 all of the fatigue life will have been used up and the pavement will have failed Note In these definitions failure means failure in a particular structural failure mode according to the assumptions and definitions on which the design procedures are based A value of CDF greater than one does not necessarily mean that the pavement will no longer support traffic but that it will have failed according to the definition of failure used in the design procedure and within the constraints of uncertainties in material property assumptions etc Nevertheless the thickness design is based on the assumption that failure occurs when CDF 1 Multiple aircraft types are accounted for by using Miner s Rule instead of the design aircraft concept as in the current procedures or CDF CDF CDF2 CDFn Wher
82. ucture is not valid for design The reason for disallowing the structure is given in the message You cannot leave modify mode until the structure is valid for design When the displayed value of a layer thickness or layer modulus is clicked an input box is displayed giving instructions on changing the value In some cases the modulus value cannot be changed manually and a description is given of how the program assigns the value automatically Note The thickness of the bottom layer is assumed to be infinite and cannot be assigned a value The thickness display column in the bottom 10 e STRUCTURE WINDOW LEDFAA User s Manual 10 22 95 LEDFAA User s Manual AC 150 5320 16 Appendix 2 layer is therefore used to display either the CBR or the k value corresponding to the modulus value of the bottom layer CBR for flexible pavements and k value for rigid pavements The conversion factors used are given in the section Layer Types If the value in either of the two columns is changed the value in the other column changes automatically Design life in years is displayed at the top of the picture of the structure and can be given any value within the range 1 to 50 years However the standard design life is 20 years If the design life of a section is different than 20 years the message Non Standard Life is displayed Clicking on the message displays a longer message explaining why the life is non standard A warning message is also prin
83. umerical rating indicating the operational condition of an airport pavement based on visual survey The scale ranges from a high of 100 to a low of 0 with 100 representing a pavement in excellent condition The PCI is measured using ASTM standard test method D 5340 Standard Test Method for Airport Pavement Condition Index Survey For rigid pavements 15 different types of distress are considered in measuring the PCI These distress types all reduce the PCI of a pavement depending on their severity and relative effect on performance Not all distress types are indicative of structural distress Rollings has identified 6 distress types that are indicative of the structural condition of the pavement The 6 distress types are listed in Table 1 TABLE 1 RIGID PAVEMENT DISTRESS TYPES USED TO CALCULATE THE STRUCTURAL CONDITION INDEX SCI Corner Break Longitudinal Transverse Diagonal Cracking Shattered Slab Shrinkage Cracks cracking partial width of slab Spalling Joint Spalling Corner Used only to describe a load induced crack that extends only part way across a slab The SCI does not include conventional shrinkage cracks due to curing problems To illustrate an SCI of 80 is consistent with the current FAA definition of initial failure of a rigid pavement i e 50 of the slabs in the traffic area exhibiting initial structural cracking The SCI allows a more precise and reproducible rating of a pavement s condition than previous FAA condi
84. use the layered elastic model is axisymmetric Aircraft with dual wheel belly gear DC 10 30 MD 11 and A 340 are treated as two aircraft for design a two gear dual tandem aircraft and a single gear dual wheel aircraft For example adding a DC 10 30 to the design list places the two aircraft for design in the list automatically and removing one of the two aircraft from the design list removes the other automatically The data for the two aircraft is also tied changing the data for one changes the data for the other automatically A maximum of 20 aircraft can be included in the design list The library list contains aircraft representative of the most common commercial and military aircraft Substitutions can be made for aircraft not in the list either by a similar aircraft or from the Generic group list Data for the Generic group is from AC 150 5320 6 Annual departures is defined as the aircraft departure rate in departures per year The displayed value is the annual departures for the selected aircraft at the start of the pavement s design life Percent annual growth is defined as the percent change in annual departures per year over the design life of the pavement Negative values represent a decrease in annual departures The total number of departures for the selected aircraft over the design life of the pavement is given by the equation vu E 200 kant where N total departures L pavement design life a
85. ws or DOS manual for file management procedures All job files have the extension JOB Section data consists of pavement structure properties aircraft names and gross loads and annual departures and growth for each aircraft Details of the required information are given when the data entry windows are discussed Jobs are listed in the list box on the left of the window All sections in the selected job are listed in the right hand list box Scroll bars will appear if there are too many jobs or sections to fit in the boxes The operations associated with each of the command buttons on the STARTUP window are briefly described under separate headings Command Buttons LEDFAA User s Manual New Job New jobs are created by clicking New Job A dialog box will then appear requesting that a name be entered for the new job The name can have up to 8 characters Normal letters and numbers are allowed together with hyphen and underscore _ Clicking OK or pressing Enter on the keyboard will accept the name create the file and close the dialog box Clicking Cancel will close the dialog box without creating a new file When first created job files are completely empty But new sections cannot be STARTUP WINDOW e 5 AC 150 5320 16 Appendix 2 6 e STARTUP WINDOW 10 22 95 created from scratch Instead old sections are moved and renamed using Dup Section or Copy Section LEDFAA Layered Elastic Aepon Pavement Design Figur
86. xisting rigid Partially bonded concrete overlay on existing rigid NOONAN Bituminous overlay on existing rigid New flexible bituminous overlay on flexible and new rigid pavements are designed with the following general procedure 1 Create a structure a design aircraft list and set the design life 2 Click Design Structure in the STRUCTURE window This causes the thickness of a prescribed layer to be automatically adjusted by the program until the design criteria are satisfied 3 Inspect the structure when the design program has stopped running and if necessary manually adjust the thickness of other layers in the structure and click Design Structure again Repeat until the thickness design is satisfactory 4 Click Save Structure This permanently saves all the information for the new structure in the job file and marks the section as being a completed design The automatic adjustment of the thickness of the prescribed layer in step 2 is done as follows 1 Calculate the maximum stress or strain at a layer interface in the structure for each aircraft in the design list 2 Calculate the allowable number of aircraft departures to failure for each aircraft based on a defined relationship between allowable departures and stress or strain 3 Find the ratio of actual departures to allowable departures for each aircraft This is the CDF for each aircraft Add the aircraft CDFs together to find the CDF for the structure

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