CE 452Design of Airfield Pavement I

Slides based on materials prepared by Prof Jie Han, University of Kansas, USA

2

OutlineIntroductionBasic principlesRigid pavement designFAA method

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 unit

b) tricycle landing gear with

single tires

c) twin-tandem landing gear

d) double twin-tandem gear

Several Typical Aircrafts

Effect of Standard Deviation of Aircraft

Wander on Pavement Damage

Measu

red

tra

nsvers

e

cra

ck f

req

uen

cy (

%)

Pre

dic

ted

tra

nsvers

e

Eq

uiv

ale

nt

DC

-8-6

3F

Str

ain

rep

eti

tio

ns

(taxiw

ay)

Np

x 1

03

Rigid Airport Pavement Design

– PCA method

– Corps of Engineering method

– FAA method: based on the Westergaard

analysis of edge loaded slabs

FAA Pavement Design Principles

FAA Airport Pavement Design

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)

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 type

should be checked using the appropriate design curve

and the forecast number of annual departures for that

aircraft

The design aircraft is the aircraft type that produces the

greatest pavement thickness

The design aircraft is not necessarily be the heaviest

aircraft 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

727-100

727-200

707-320B

DC-9-30

CV-880

737-200

L-1011-100

747-100

Dual

Dual

Dual tandem

Dual

Dual tandem

dual

Dual tandem

Double dual

tandem

160,000

190,500

327,000

108,000

184,500

115,500

450,000

700,000

Gear typeAvg. ann

depart.

Max. takeoff

Weight (lbs).

Equiv. dual

gear depart

3760

9080

5185

5800

680

2650

2907

145

Wheel load

(lbs)

Wheel load

Design

aircraft (lbs)

Equiv. ann.

depart. design

aircraft

38,000

45,240

38,830

25,650

21,910

27,430

35,625

35,625

45,240

45,240

45,240

45,240

45,240

45,240

45,240

45,240

1,891

9,080

2,764

682

94

463

1,184

83

3760

9080

3050

5800

400

2650

1710

85

727-200 requires the greatest pavement thickness and thus is the design aircraft

1.7 x 85

Conversion

factor

190,500x0.95/4

45240

35625)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 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. subbase

Types 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 for

most 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 t

op

of

su

bb

as

e(l

b/i

n3)

Effect of Subbase on K- Bank-Run Sand & Gravel (PI<6)

(MN

/m3)

k o

n t

op

of

su

bb

as

e(l

b/i

n3)

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 be

accomplished over an entire slab length and width

Critical and Non- critical Areas

CriticalAircraft speed is low/ aircraft is at rest

e.g. Apron, Taxiway

Non-critical Aircraft speed is high/ aircraft is already partially airborne

E.g. central portion of runway

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 < 5.0

to control transverse cracking

Maximum joint spacing = 60 ft.

Radius of relative stiffness:

" #4/1

2

3

k112

Eh$%

&'(

)

*+!

Dimensions and Spacing of Steel Dowels

Amount of Reinforcement for Reinforced

Concrete Pavements

s

sf

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