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