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Airport Pavement Design and Evaluation
Prof. Jie Han, Ph.D., P.E.
The University of Kansas
Outline of Presentation
Introduction
FAA Pavement Design Principles
FAA Flexible Pavement Design
FAA Rigid Pavement Design
FAA Layered Elastic Pavement Design
Introduction
References
• Principles of Pavement Design, Yoder and Witczak (1975)
• Airport Pavement Design and Evaluation, FAA Advisory Circular 150/5320-6D
• Airfield and Highway Pavements, Proceedings of 2006 Airfield and Highway Specialty Conference
• Web seminar “FAA – LEDFAA V1.3 Layered Elastic Flexible Pavement Design for Airfield Pavements”, Rodney N. Joel, FAA
Websites
• http://www.chet-aero.com/download/software.php
• http://www.airtech.tc.faa.gov/naptf/download/index1.asp
• Airport Pavement Structural Design Systemhttp://www.mincad.com.au/apsdsbr.htm
Airfield vs. Highway Pavements
• Repetition of load
• Distribution of traffic
• Geometry of the pavement
Affected by pavement width and type of aircraft
Plan View of Basic Types of Wheel Configuration
a) single trailer-truck unitb) tricycle landing gear with single tiresc) twin-tandem landing geard) double twin-tandem gear
Several Typical Aircrafts
Effect of Standard Deviation of Aircraft Wander on Pavement Damage
Mea
sure
d tr
ansv
erse
cr
ack
freq
uenc
y (%
)
Pred
icte
d tr
ansv
erse
Eq
uiva
lent
DC
-8-6
3F
Stra
in re
petit
ions
(ta
xiw
ay) N
px
103
Flexible Airport Pavement Design
• Corps of Engineering (CBR) method (CBR method): CBR test for subgrade evaluation
• FAA method: field performance data correlated to soil classification, also a CBR method
• Canadian DOT method: plate-bearing tests to evaluate subgrade support/repeated load triaxial tests for full-depth airport pavements
• AI method: theoretically oriented design
Rigid Airport Pavement Design
– PCA method
– Corps of Engineering method
– FAA method: based on the Westergaardanalysis of edge loaded slabs
FAA Pavement Design Principles
FAA Airport Pavement Design
Scope and Design Philosophy
The methods discussed are suitable for aircraft withgross weights of 30,000 lbs (13,000 kg) or more
Design of flexible pavements: CBR method
Design of rigid pavement: jointed edge stress analysis
Layered elastic analysis
Design service life = 20 years
AC 150/5320-6D
Aircraft Considerations
Load (95% main landing gear, 5% nose gear)
Landing gear type and geometry• Single gear aircraft• Dual gear aircraft• Dual tandem gear aircraft• Wide body aircraft – B-747, B-767, DC-10, L-1011
Tire pressure: 75 to 200 psi (515 to 1,380 kPa)
Traffic volume
AC 150/5320-6D
Equivalent Single Wheel Load (ESWL)
AC 150/5320-6D
AC 150/5320-6D
Increased Loading Gear Complexity
Loading Gear Design
Aircraft Grew in Size
Gross Aircraft Weight
Gross Aircraft WeightIn
divi
dual
Whe
el L
oad
(lbs)
Equivalent Single Wheel Load
A New Design Procedure Needed
Efforts for New Design Procedure
Efforts for New Design Procedure
Design Procedure
• Forecast annual departures
• Select design aircraft that requires the thickest pavement
• Transform other aircrafts to equivalent departures of design aircraft
Determination of Design Aircraft
The required pavement thickness for each aircraft typeshould be checked using the appropriate design curve and the forecast number of annual departures for thataircraft
The design aircraft is the aircraft type that produces thegreatest pavement thickness
The design aircraft is not necessarily be the heaviestaircraft in the forecast
Factors for Converting Annual Departures by Aircraft to Equivalent
Annual Departures by Design Aircraft
Conversion of Equivalent Annual Departure of Design Aircraft
R1 – equivalent annual departures of the design aircraft
R2 – annual departures expressed in design aircraft landing gear configuration
W1 – wheel load of the design aircraft
W2 – wheel load of the aircraft being converted
Each wide body as a 300,000-pound dual tandem aircraft
1
221 W
WRlogRlog ⋅=
Example
Aircraft
727-100727-200707-320BDC-9-30CV-880737-200L-1011-100747-100
DualDualDual tandemDualDual tandemdualDual tandemDouble dualtandem
160,000190,500327,000108,000184,500115,500450,000700,000
Gear type Avg. anndepart.
Max. takeoffWeight (lbs).
Equiv. dualgear depart
376090805185580068026502907145
Wheel load(lbs)
Wheel loadDesign
aircraft (lbs)
Equiv. ann.depart. design
aircraft
38,00045,24038,83025,65021,91027,43035,62535,625
45,24045,24045,24045,24045,24045,24045,24045,240
1,8919,0802,764682944631,18483
37609080305058004002650171085
727-200 requires the greatest pavement thickness and thus is the design aircraft
1.7 x 85
Conversionfactor
190,500x0.95/4
4524035625)145log(Rlog 1 ⋅=
300,000x0.95/8
Wide body
Total = 16,241
Final design: 16,241 annual departures of a dual wheel aircraft weighing 190,500lbs
Typical Design Section of Runway Pavement
FAA Flexible Pavement Design - CBR Method
Base Course
Minimum CBR value of 80 is assumed for base course
Types of base courses
- Item P-208: aggregate base course- Item P-209: crushed aggregate base course- Item P-211: lime rock base course- Item P-304: cement treated base course- Item P-306: econocrete subbase course- Item P-401: plant mix bituminous pavements
Subbase Course
Minimum CBR value of 20 is for subbase course
Types of subbase courses
- Item P-154: subbase course- Item P-210: cliché base course - Item P-212: shell base course - Item P-213: sand clay base course- Item P-301: soil cement base course
Items P-213 and P-301 are not recommended wherefrost penetration into the subbase is anticipated
Subgarde Compaction Requirements
CBR Design Equations
MWHGL = multiple-wheel, heavy gear load
Alpha Factors – MWHGL Data
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05
Aircraft Traffic Volume Factor, Coverages
Load
Rep
etiti
on F
acto
r, A
lpha
12-Wheel Failure12-Wheel Nonfailure50-kip Single Wheel Failure30-kip Single Wheel Failure30-kip Single Wheel NonfailureDual-Tandem Failure
Alpha = 0.23 log C + 0.15
Single Wheel
Twin Tandem
12 Wheels
Hayhoe (2005)
Selection of Design CBR Value
As a general rule of thumb, the design CBR value shouldbe equal to or less than 85% of all the subgrade CBR values
Corresponds to a design value of one standard deviationbelow the mean value
Design Chart for
Single Wheel Gear
Design Chart for
Dual Wheel Gear
Design Chart for
Dual Tandem
Gear
1-in of the thickness increase should be HMA surfacing
The remaining thickness increases should be proportioned betweenbase and subbase
Pavement Thickness for High Departure Levels
Annual DepartureLevel
Percent of 25,000 DepartureThickness
50,000
100,000
150,000
200,000
104
108
110
112
Minimum Base Course Thickness
Critical and Noncritical Areas
Total critical pavement thickness = T
Noncritical pavement thickness (for base and subbase only)= 0.9T
For variable section of the transition section and thinned edge, the reduction applies only to the base course
0.7T as the minimum for thickness of base can be applied
Example
• A flexible airport pavement to be designed
– Dual gear aircraft– Gross weight of 75,000 lbs– 6,000 annual equivalent departures of the design
aircraft– Design CBR value for subbase = 20– Design CBR value for subgrade = 6
Using SubgradeCBR to find totalpavement thickness (23 in. in this example)
Total Pavement Thickness
Using SubbaseCBR to find: the combined thickness of HMA and base course needed over a 20 CBR subbase is 9.2 in.
Subbase thickness = 23-9.2 =13.8 in. (14-in)
SubbaseThickness
Thickness of HMA surface (critical area) =4 in.
Thickness of base course = 9.2-4 = 5.2 in (6-in).
Thickness of subbase course = 14in.
Thickness should be rounded off to even increments
Design Pavement Sections
Notes on Frost Effects and Stabilized Materials
• The thickness determined from these design charts are for untreated granular bases and subbases
• Frost effects and stabilized materials must be handled separately
Stabilized Base and Subbase
• Required for new pavements and jet aircraft weighting 100,000 lbs or more
• Subbase and base equivalency factors– Standard for granular/stabilized subbase is Item P-
154 with CBR of 20– Standard for granular/stabilized base is Item P-209,
crushed aggregate base course with CBR of 80
• Min. total pavement thickness calculated ≥ that required by a 20 CBR subgrade from design curve
Frost Effect• Thicker subbase courses • Determine soil frost group
• Determine the depth of frost penetration• Frost protection (complete, limited, reduced subgrade
strength)
Design Air Freezing Indices
3500
2500
1500
750
250
50
Unit: degree days Fo
Depth of Frost Penetration
Air freezing index, degree days Fo
(Degree days Co)
Fros
t pen
etra
tion
inch
es
Met
ers
0 1000 2000 30000
20
40
60
80
100
120
140
160
600
40.8
FAA Rigid Pavement Design
Principles of Rigid Airport Pavement Design
Based on Westergaard analysis of edge loaded slabs (modified to simulate a jointed edge condition)
Determine k value for rigid pavement
Concrete flexural strength
Gross weight of design aircraft
Annual departures of design aircraft
Subbase Requirements
A minimum thickness of 4 in. subbaseTypes of subbase courses
- Item P-154: subbase course- Item P-208: aggregate base course- Item P-209: crushed aggregate base course- Item P-211: lime rock base course - Item P-304: cement treated base course- Item P-306: econocrete subbase course - Item P-401: plant mix bituminous pavements
Stabilized subbase (aircraft weight > 100,000 lbs)- Item P-304: cement treated base course- Item P-306: econocrete subbase course- Item P-401: plant mix bituminous pavements
Exceptions for No Subbase
Concrete Flexural Strength
Design strength of 600 to 650 psi is recommended formost airfield applications
Strength at 28 days
5% less than the test strength used for thickness design
Effect of Subbase on K- Well-Graded Crushed Aggregate
(MN
/m3 )
K o
n to
p of
sub
base
(lb/in
3 )
Effect of Subbase on K- Bank-Run Sand & Gravel (PI<6)
(MN
/m3 )
k on
top
of s
ubba
se(lb
/in3 )
Effect of Subbase
on K- Stabilized
Subbase
Design Curves – Single Wheel Gear
Gross weight of design aircraft
Design Curves – Dual Wheel Gear
Design Curves – Dual Tandem Gear
Critical and Noncritical Areas
Total critical pavement thickness = T
Noncritical pavement thickness (for concrete slab thickness)= 0.9T
For variable section of the transition section and thinned edge, the reduction applies only to the concrete slab thickness
The change in thickness for the transitions should beaccomplished over an entire slab length and width
Design Example
• Dual tandem aircraft: gross weight = 350,000 lbs, annual equivalent departures =6000 (including 1200 of B-747 weighing 780,000 lbs)
• Subgrade k =100pci with poor drainage, frost penetration =18 in.
• Primary runway, 100% frost protection
• Subgrade soil is CL
• MR = 650 psi
Stabilized subbase required
Design Steps
• Several thickness of subbase thickness should be tried => most economical section
• Assume P-304 (cement treated base course) to be used
• Trial thickness of subbase = 6 in.
Slab Thickness
• 16.6 in. round off to 17 in.
• 17 + 6 =23 in. > 18 in. (frost depth)
• Wide body aircraft did not control slab thickness but to be considered in establishment of jointing requirements and design of drainage structures
Rigid Pavement Joint Types and Details
Recommended Maximum Joint Spacing- Rigid Pavement without Stabilized Subbase
Recommended Maximum Joint Spacing- Rigid Pavement with Stabilized Subbase
Joint spacing (unit: in.)/radius of relative stiffness < 5.0to control transverse cracking
Maximum joint spacing = 60 ft.
Radius of relative stiffness:
( )4/1
2
3
k112Eh
⎥⎦
⎤⎢⎣
⎡ν−
=l
Dimensions and Spacing of Steel Dowels
Amount of Reinforcement for Reinforced Concrete Pavements
ss f
LtL7.3A =
where As = area of steel per foot of width or length (in2)L = length or width of slab, ft.T = thickness of slab, in.fs = allowable tensile stress in steel, psi, 2/3 yield strength
Minimum percentage of steel reinforcement = 0.05%to the area of concrete per unit length or width
Allowable Strengths of Various Grades of Reinforcing Steel
Allowable
Dimensions and Unit Weights of Deformed Steel Reinforcing Bars
Sectional Areas of Welded Fabric
Jointing of Reinforced Rigid Pavements
Spreadsheet Programs
• F806FAA for flexible pavement design
• F805FAA for rigid pavement design
FAA Layered Elastic Pavement Design
LEDFAA –Layered Elastic Design
• Heavier load + complex multiple-wheel, multiple truck landing gear systems
• Complex wheel load interactions with pavement structures– B-777 or Airbus A-380 (TDT)– B-777: 2 six-wheel main landing gears (TDT: 3 pairs
of wheels in a row) + a single nose gear (single dual wheel) to support gross weight up to 535,000 lbs
• Compatible with conventional FAA design• Landing gear configuration and layered pavement
structures can be modeled directly
Flexible Pavement Failure Modes
Layered Elastic Method vs. CBR Method
LEDFAA V1.3 Default Values
LEDFAA V1.3
Cumulative Damage Factor (CDF) for Traffic Model
Cumulative Damage Factor (CDF) for Traffic Model
Cumulative Damage Factor (CDF) for Traffic Model
Cumulative Damage Factor (CDF) for Traffic Model
Sample Aircraft Traffic Mix CDF Contribution
Sample Aircraft Traffic Mix CDF Contribution
Large Aircraft Traffic Mix Gear Locations
No More Design Aircraft in LEDFAA
From CBR Method to LEDFAA
• Nomographs => computer program• ‘design aircraft’ => ‘cumulative damage factor’ using
Miner’s rule for fatigue failure design• CBR or k-value => elastic modulus
• LEDFAA design should comply with detailed requirements and recommendations from Advisory Circular
• Should follow Advisory Circular recommendations in selection of input parameters
Flexible Airport Pavement Design
• Two modes of failures – Vertical strain in the subgrade– Horizontal strain in asphalt layer
• For traffic mixture including aircraft with triple dual tandem (TDT) gears– Min. thickness =5 in. of hot mix surfacing– Min. thickness =5 in. of stabilized base (not containing
TDT, 6 in.)– P-301 soil cement base not acceptable– Min. thickness =3 in. of subbase base– Subgrade: E=1500*CBR
Rigid Airport Pavement Design
• One mode of failure (cracking of concrete slab)– Limiting horizontal stress at the bottom surface of the
concrete slab
• For traffic mixture including aircraft with TDT gears– Min. thickness =6 in. of concrete surfacing– Min. thickness =4 in. of stabilized subbase (bound
materials)– Subgrade : logE=1.415+1.284logk
Design Software
• LEDFAA 1.3