new generation aircraft flexible pavement design challenges

NEW GENERATION AIRCRAFT

FLEXIBLE PAVEMENT DESIGN CHALLENGES

M. ThompsonU of IL @ Urbana-Champaign

A380A380--800 (2006)800 (2006)--Gross Load 1.23 million lbsGross Load 1.23 million lbs

BOEINGBOEING--777 (1995)777 (1995)--Gross Load 632,000 lbsGross Load 632,000 lbs

NEW GENERATION AIRCRAFTNEW GENERATION AIRCRAFT

20051.1B-747-400

21857.9B-777-300ER*

21555.8B-767-400

22553.4B-747-400ER

19762A-380*

22865.3A-340

PRESSURE(psi)

WHEEL LOAD(KIPS)

AIRCRAFT

* DUAL-TRIDEM

787-8 Landing Gear Footprint

Preliminary Data

32 FT 2 IN(9.8 m) TYP

38 FT 1 IN (11.6 M)

74 FT 9 IN (22.8 M)

57.5 IN (1.5 M)

51 IN (1.3 M)

16KG/CM2TIRE PRESSURE221PSIMAIN GEAR

50X20.0R22/34PRINMAIN GEAR TIRE SIZE

KG/CM2TIRE PRESSUREPSINOSE GEAR

40x16.0R16/26PRINNOSE GEAR TIRE SIZE

216,817KILOGRAMSTAXI WEIGHT478,000POUNDSMAX DESIGN787-8UNITSCHARACTERISTI

CS

Preliminary Data

32 FT 2 IN(9.8 m) TYP

38 FT 1 IN (11.6 M)

74 FT 9 IN (22.8 M)

57.5 IN (1.5 M)

51 IN (1.3 M)

MTOW: 482 kips

MAIN GEAR TIRE LOAD: 55.5 kips

MAIN GEAR TIRES: 221 psi

CBR-BASED DESIGN(COE / FAA AC No. 150/5320-6D)

BASED ON ESWL

Is ESWL Adequate for

Dual Tandem & Dual-Tridem ???

Mechanistic-Based Pavement Design Concepts

for NEW GENEREATION AIRCRAFT

Mechanistic-EmpiricalApproach

• Combines the practicality of empirical methods with the technical soundness of mechanistic solutions.

• Uses mechanistic analysis, to determine the pavement response to imposed loads…then applies “empirical” formulations (i.e. “transfer functions”) to determine the development of distress due to the load-induced pavement response.

DESIRABLE M-E DESIGN FEATURES

“Technically Sound”“Technically Sound”“Understandable”“Understandable”“Minimum Inputs”“Minimum Inputs”

“User Friendly”“User Friendly”

M-E IMPLEMENTATION CONCERNS

Airport Agency ResourcesAirport Agency ResourcesInput Data Input Data

Transfer FunctionsTransfer FunctionsCalibration DataCalibration Data

INPUTS• Materials Characterization

– Pavement Materials– Subgrade Soils

• Geometric Layout– Layer thicknesses

• Traffic– Load Levels– Loading Configurations– Number of repetitions

• Environmental– Temperature fluctuations

(daily, monthly)– Moisture conditions

STRUCTURAL MODEL• Linear or Non-linear Multilayered

Elastic models.

TRANSFER FUNCTIONS (FT)

FTCritical

Response

Pavement Distress

(i.e. Damage)

TRANSFER FUNCTIONS (FT)

FTCritical

Response

Pavement Distress

(i.e. Damage)

FINALDESIGN

DESIGNRELIABILITY

OBTAIN CRITICAL RESPONSES• Subgrade Deviator Stress (σD).• Top Subgrade Vertical Strain (εS).• Horizontal Strain (εAC) at the bottom of the

AC layer.

DESIGN ITERATIONS

And/Or

PAVEMENT PERFORMANCE• Cumulative development of distress

STA

RT

Mechanistic-Empirical Approach


AC Layer

Granular BaseLayer

Subgrade

εAC

SSR = σd / quεv

Determine theCritical Responses

εAC : AC FatigueSSR: Subgrade εp

εv : Pavement εp

STRUCTURAL RESPONSES* STRESSES

* STRAINS

* DEFLECTIONS

STRUCTURAL MODEL

STRUCTURAL MODELSTRUCTURAL MODEL

SHOULD ACCOMMODATESHOULD ACCOMMODATE

“MATERIAL PROPERTIES”“MATERIAL PROPERTIES”

Material Characterization

• Resilient Modulus• Pavement Materials:

+ Asphalt Concrete: Temperature, frequency.

+ Unbound Granular: “Stress hardening”.

• Subgrade Soils:+ Fine-grained soils: “Stress softening”

+ Granular: “Stress hardening”.

Material CharacterizationAsphalt Concrete Modulus

* Temperature Dependent*Frequency Dependent

* Must consider in M-E Design!!!

21/*17DEC

32/*27NOV

49/1,62042OCT

59/1,00051SEPT

69/61560AUG

72/53062JULY

66/71057JUNE

58/1,04550MAY

46/1,87039APRIL

33/*28MARCH

25/*21FEB

18/*15JAN

MMPT(F)/E (ksi)

MMAT(F)MONTH

CALGARYTemperature Data

MMPT @ 3–inch depth

For: f=10Hz* > 3,000 ksi

“ICM”“ICM”

NCHRP 1NCHRP 1--37A37AENHANCED INTEGRATED ENHANCED INTEGRATED

CLIMATIC MODELCLIMATIC MODEL(Dempsey & Larson)(Dempsey & Larson)

HIRSCH MODEL

“Hirsch Model for Estimating the Modulus of In-Place Asphalt Mixtures”

Christensen - Pellinen - BonaquistAAPT Journal - 2003

INPUTS VMA - VFA - Asphalt “Modulus”

PREDICTIVE EQUATIONS: Modified Hirsch Model

1

*3000,200,4100

1)1(

000,10*3

1001000,200,4*

−

⎥⎥⎥⎥

⎦

⎤

⎢⎢⎢⎢

⎣

⎡

⋅+

−−+⎥

⎦

⎤⎢⎣

⎡⎟⎠

⎞⎜⎝

⎛ ⋅+⎟

⎠

⎞⎜⎝

⎛ −=binder

binder GVFAVMA

VMA

PcVMAVFAGVMAPcE

58.0

58.0

*3650

*320

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛ ⋅+

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛ ⋅+

=

VMA

GVFA

VMA

GVFA

Pcbinder

binder

IG*Ibinder

VMA

VFAvol. properties

dynamic modulus

HIRSCH MODEL

+ G* INPUT (TEMP / FREQ) (ASPHALT MASTER CURVE)

+ G* COMPATIBLE WITH PG GRADE

+ VFA & VMA FROM MIX DESIGN

G* master curve

1

10

100

1000

10000

100000

1000000

10000000

100000000

1.00E-04 1.00E-03 1.00E-02 1.00E-01 1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04

Frequency (Hz)

G* (

Pa)

master curve4.4°C21.1°C37.8°C54.5°C

PG 58-28

GRANULAR MATERIALS

FROM RADA & WITCZAK

From Rada & Witczak

UZAN MODEL (1985)UZAN MODEL (1985)

MMR = K1 ΘK2 (σd) K3

Θ =BULK STRESSΘ = σ1 + σ2 + σ3

MMR = K1 ΘK2 (σd) K3

K1 & K2 MOST IMPORTANT !!K1 & K2 MOST IMPORTANT !!

ERi (ksi) = 0.307 QU (psi) + 0.9

MODULUS CLASSESFINE-GRAINED SOILS

SOIL ERi (ksi) Qu (psi) CBR

STIFF 12.3 33 8MEDIUM 7.7 23 5SOFT 3.0 13 2VERY SOFT 1.0 6 1

ERi (ksi) = 0.42 Qu (psi) - 2

ESTIMATING ESTIMATING EERiRi

EERi Ri (OMC) = 4.46 + 0.098 (%C) + 0.119 (PI)(OMC) = 4.46 + 0.098 (%C) + 0.119 (PI)

EERiRi ((ksiksi) @ 95% T) @ 95% T--9999C C -- %Clay%Clay

E – CBR RELATIONS

COE/FAA: E (psi) = 1,500 CBR

TRL/UK : E (psi) = 2,555 CBR0.64

(CBR: 2 -12)(TRL Report # 1132)

Deviator Stress = ????

STRUCTURAL MODELS

• ELASTIC LAYER PROGRAMS

• FINITE ELEMENT PROGRAMS (2-D / 3-D)

ELASTIC LAYER PROGRAMS

+ LINEAR ELASTIC MATERIALS

+ MODULUS CONSTANT WITHIN THE LAYER

+ NO FAILURE CRITERION

Structural Models• Elastic Layered Programs (ELP)

– All materials linear elastic, homogenous, isotropic (newer versions are improved).

• 2D “Axi-symmetric” Non-linear Finite Element:– Can incorporate a wide range of material models,

more specifically “Stress dependent” models.– Results for Single Wheel Loads (in theory)

• 3D Non-Linear Finite Element:– Same as 2D but can apply Multiple Wheel Loads.

Structural Models: ILLIPAVE

• Analysis for Single Wheel Load (SWL)…Uses superposition to extend results to MWL.

• “Stress dependent” material models for Coarse and Fine Grained soils.

• Mohr-Coulomb Failure criteria.• 32-bit application, run-time ~5-30 sec for

typical pavement geometry.• Up to 7000 elements can be used.• User-friendly GUI input software for Windows.

ILLI-PAVE: 2D FEM

Surface

Base

Subgrade

Subbase

AxisOf

Revolution

Surface

Base

Subgrade

Subbase

AxisOf

RevolutionSurface

Base

Subbase

Subgrade

Results for Single Wheel LoadsResults for Single Wheel Loads

Structural Models: 2D FE• 3D Non-linear FEMs are very inefficient even

with computing power today…

• Consider the possibility of using 2D Non-linear FEMs with superposition to extend the single wheel results to multiple wheel.

• Must validate the Principle of Superposition for“Engineering” purposes.

ILLIPAVE MODEL

* “Stress dependent” material models for Granular Materials and Fine Grained soils.

*Mohr-Coulomb Failure Criteria.* Analysis for Single Wheel Load (SWL)* SUPERPOSITION to extend results to

MWL.

MULTIPLE WHEEL SOLUTION

Chou & Ledbetter (1973)MWHGL TESTS @ WES

SUPERPOSITION WORKS for

FLEXIBLE PAVEMENTS !!

SUPERPOSITION Studies USCOE Study 1973 (Examples…)

Section #1 Section #2

-0.05

0

0.05

0.10

0.15

0.20

0.25

0.30 4 6 1080 2

-0.02

0.02

0.04

0.06

0.08

0

4 6 1080 2Ver

tical

def

lect

ion,

10-3

inch

es

Offset, FT

SUPERPOSITION Studies USCOE Study 1973 (Examples…)

Section #1 Section #2

-404 6 1080

-20

0

20

40

60

80

2-20

0

20

40

60

80

Ver

tical

Stre

ss, l

b/in

2

Offset, FT4 6 1080 2

Horizontal Stress(Radial or Tangential)

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0.0 5.0 10.0 15.0 20.0 25.0 30.0

Superposed Response, psi

Act

ual R

espo

nse,

psi

Rebound Response

Vertical Stress

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0Superposed Response, psi

Actu

al R

espo

nse,

psi Rebound Response

Vertical Stress

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0Superposed Response, psi

Actu

al R

espo

nse,


Vertical Stress

0.0

10.0

20.0

30.0

40.0

50.0

0.0 10.0 20.0 30.0 40.0 50.0Superposed Response, psi

Actu

al R

espo

nse,



0.0

5.0

10.0

15.0

20.0

0.0 5.0 10.0 15.0 20.0

Superposed Response, psi

Act

ual R

espo

nse,

psi

Rebound Response


0.0

5.0

10.0

15.0

20.0

0.0 5.0 10.0 15.0 20.0

Superposed Response, psiA

ctua

l Res

pons

e, p

si

Rebound Response

MFC Section HFS Section HFC Section

Equality Line

Upper/Lower Bounds(2-psi or 10%)

FAA NAPTF Study FAA NAPTF Study 2001 2001 –– UofUof ILILFAA Airport Technology Transfer Conference FAA Airport Technology Transfer Conference -- 20022002

SOLUTION FOR MULTIPLE WHEELSILLI-PAVE + Superposition

ILLIILLI--PAVEPAVE++

SuperpositionSuperposition

( ) ( )( ) ( )

( )

αττ

αττ

αασστ

σσ

ασασσ

ασασσ

cos

sin

cossin

cossin

sincos

22

22

⋅=

⋅=

⋅⋅−=

=

⋅+⋅=

⋅+⋅=

rzxz

rzyz

ttrrxy

zzzz

ttrryy

ttrrxx

α

r σrr, σtt, σzz, τrz

X

Y


AC Layer

Granular BaseLayer

Subgrade

εAC

SSR = σd / quεv

Determine theCritical Responses

εAC : AC FatigueSSR: Subgrade εp

εv : Pavement εp

CONCEPTS FOR DEVELOPING A M-E BASED ACN PROCEDURE

FOR NEW GENERATION AIRCRAFT2006 ISAP

Quebec City, Canada

Thompson & Gomez-Ramirez (U of IL)

Gervais & Roginski(Boeing)

20051.1B-747-400(REF)

21857.9B-777-300ER*

21555.8B-767-400

22553.4B-747-400ER

19762A-380*

22865.3A-340

PRESSURE(psi)

WHEEL LOAD(KIPS)

AIRCRAFT

* DUAL-TRIDEM

ICAO Subgrade

" Representative" CBR QU (psi) ERi (ksi)

A 15 68 21

B 10 45 15

C 6 27 9

D 3 14 5

ICAO SUBGRADESC = QU/2 PHI = 0°

GRANULAR LAYERS

TGRAN = BASE + SUBBASE

MR (psi) = 5,000 (THETA)0.5

C = 0 PHI = 45°

10 -507.5 - 10A (CBR-15)15-505A (CBR-15)15-607.5 -10B (CBR-1020-605B (CBR-10)20-705C (CBR-6)30-705C (CBR-6)

40-1007.5 & 10D (CBR-3)50-1005D (CBR-3)

GRANULAR(INCHES)

AC(INCHES)

ICAOSUBGRADE

PAVEMENT PARAMETERS

SINGLE WHEEL RESPONSES* Surface Def. (0-72 ins)

* AC Surface Strain* AC Base Strain

* GB Dev. Stress (top/middle)* Subgrade Dev. Stress

(Top / 1&2 Radii)* Subgrade Vertical Strain

(Top / 1&2 Radii)

MULTIPLE WHEEL RESPONSES(GRID: 1/4 Dual & 1/4 Axle)

* Max. Surface Def. * Max. AC Surface Strain

* Max. AC Base Strain* Max. GB Dev. Stress (top/middle)

* Max. Subgrade Dev. Stress(Top / 1&2 Radii)

* Max. Subgrade Vertical Strain(Top / 1&2 Radii)

ILLIPAVE Analysis Results-1

26 -132 -1

52

-124

-126 -133

-161

-121

-180-160-140-120-100-80-60-40-20

0A340M A340B A380M A380W B747-

400ERB767-400 B777-300 B747-400

Aircraft Type

Def

lect

ion,

mils

MLG--Surface DMax

AC Surface Thickness: 10-in -- Modulus: 500-ksiGB Thickness: 40-in -- SG Eri: 5-ksi

ILLIPAVE Analysis Results47

4

470

443

442

433

435

423

406

360

380

400

420

440

460

480

A340M A340B A380M A380W B747-400ER

B767-400 B777-300 B747-400

Aircraft Type

Mic

rost

rain

MLG--Max AC Surface Strain


ILLIPAVE Analysis Results7.

6

8.2

8.0

7.8

8.5

8.9 9.

0

8.2

6.5

7

7.5

8

8.5

9

9.5

A340M A340B A380M A380W B747-400ER

B767-400 B777-300 B747-400

Aircraft Type

Stre

ss, p

si

MLG--Deviator Stress @ Top of Subgrade Layer



54

0.59

0.57

0.56

0.61

0.63 0.

64

0.59

0.480.500.520.540.560.580.600.620.640.66

A340M A340B A380M A380W B747-400ER

B767-400 B777-300 B747-400

Aircraft Type

SSR

MLG--Subgrade Stress Ratio (SSR)


ILLIPAVE Analysis Results-9

74

-111

4

-105

7

-973

-104

9 -111

5

-112

8

-998

-1150

-1100

-1050

-1000

-950

-900

-850A340M A340B A380M A380W B747-

400ERB767-400 B777-300 B747-400

Aircraft Type

Mic

rost

rain

MLG--Vertical Strain @ Top of Subgrade Layer



03 1.09

1.25

1.02 1.04 1.

10

1.32

1.00

1.17

1.16

1.09

1.09

1.07

1.07

1.04

1.00

0

0.2

0.4

0.6

0.8

1

1.2

1.4

A340M A340B A380M A380W B747-400ER B767-400ER B777-300ER B747-400Aircraft Type

Rat

io W

RT

B74

7-40

0

MLG--Surface DMax MLG--Max AC Surface Strain



93 1.00

0.98

0.95 1.

03 1.08 1.10

1.00

0.98

1.12

1.06

0.98 1.

05 1.12

1.13

1.00

0

0.2

0.4

0.6

0.8

1

1.2

A340M A340B A380M A380W B747-400ER B767-400ER B777-300ER B747-400Aircraft Type

Rat

io W

RT

B74

7-40

0

MLG--Deviator Stress @ Top of Subgrade LayerMLG--Vertical Strain @ Top of Subgrade Layer


TRANSFER FUNCTIONS(RESPONSES – DISTRESS)

CRITICAL FACTORS!!!

FLEXIBLE PAVEMENT DISTRESSES

• HMA FATIGUE

• RUTTING:

+ HMA (MATL. SELECTION / MIX DESIGN)

+ GRANULAR BASE/SUBBASE

+ SUBGRADE

SUBGRADE TRANSFER FUNCTIONS

•SUBGRADE VERTICAL STRAIN

•SUBGRADE STRESS RATIO (SSR)(SSR= DEV STRESS / QU)

VERTICAL STRAIN CRITERIA εε= L (1/N)m

0.40.2531.5*10-2TRL/1132 (85%)

0.251.8*10-295%0.252.1*10-285%0.252.8*10-250%

SHELL0.50.2231.05*10-2AIRD (INS)mLAGENCY

WES / TOWNSEND & CHISOLM / 1976

Vicksburg ”BUCKSHOT CLAY”

(CH)

Transfer Functions:Subgrade Rutting-

Vertical Strain Design Criteria1.5

1.0

0.90.8

0.7

0.61,000 2,000 5,000 10,000 20,000VE

RTI

CA

L C

OM

PRES

SIVE

ST

RA

IN A

T TO

PO

F SU

BG

RA

DE,

εv

10-3

ANNUAL STRAIN REPETITIONS

(20 YEAR LIFE)

EESS = 30,000 PSI= 30,000 PSI

15,00015,000

9,0009,000

3,0003,000

COE / FAA LEDFAA

FAAFAA SUBGRADE STRAIN CRITERIA

(Revised)

C = (0.004 / εv )8.1 Coverages < 12,100

C = (0.002428 / εv )14.21 Coverages > 12,100

C - Coverages

εv - Subgrade Vertical Compressive Strain

Transfer Functions:Subgrade Rutting-SSR

Influence of SSR on Permanent Deformation

0.00

0.02

0.04

0.06

0.08

1 201 401 601 801 1001

Load Applications

Perm

anen

t Str

ain

1.00 SSR

0.75

0.50

0.25

qu = 28 psiγd = 98 pcfw = 26 %

UNSTABLE!!!UNSTABLE!!!

STABLE BehaviorSTABLE Behavior

BejaranoBejarano & Thompson (2001)& Thompson (2001)DuPontDuPont ClayClay


Permanent Deformation vs. SSR

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.00 0.25 0.50 0.75 1.00Subgrade Stress Ratio

p afte

r N=1

000

20.0% CSSC23.0%24.5%23.0% DPC26.0%28.5%30.5%

BejaranoBejarano & Thompson (2001)& Thompson (2001)

SUBGRADE RUTTING ALGORITHM

LOG εP = A + b (LOG N)

εP = ANb

“Development of a Simplified M-E Design Procedure for Low-Volume Flexible Roads”

Zhao & DennisUniversity of ArkansasTRR # 1989 – Vol. 1

Subgrade Stress Ratio (SSR) / A

Subgrade Stress Ratio (SSR) / b


Damage Potential… Low/Acceptable Limited High SSR… 0.5 / 0.6 0.6 to 0.75 > 0.75

SSR General GuidelinesSSR General Guidelines

GRANULAR LAYER RUTTING

* COE – NOT A CRITERION* FAA / LEDFAA - NOT A CRITERION

INDIRECT ACCOMODATION: MINIMUM HMA SURFACE THICKNESS

STABILIZED BASE - > 100 KIPS

GRANULAR BASE

• Minimum HMA Surface ThicknessFAA

4-5 ins. / Critical3-4 ins. / Noncritical

(Base CBR - 80)

• S. African “F”

South African Mechanistic Approach

Stress Based Safety Factor FMaterial Shear Strength / Shear Stress

F = [σ3 ∗ φterm + cterm] / [σ1 - σ3]where:

φterm = [tan2(45 + φ/2) - 1]cterm = 2 * C * tan(45 + φ/2)φ - friction angle, degreesC - cohesion, psi

GRANULAR BASE RATIO

FOR PHI = 45° & C = 0

F = DEV. STRESS / 4.8 * SIG 3

DECREASED “F”: MORE RUTTING

HMA FATIGUE(TRADITIONAL)

HMA FATIGUE CRACKING

LEDFAA – HMA FATIGUE

LOG C = 2.68 – (5*LOG ε) - (2.665*LOG EHMA)

C – COVERAGES TO FAILURE

ε - HMA STRAIN @ BOTTOM OF P401 HMA SURFACE

EHMA – HMA MODULUS (200 ksi)

Heukelom & Klomp – AAPT (1964)

AASHTO TP 8-94

Standard Test Method for Determination of

the Fatigue Life of Compacted HMA

Subjected to Repeated Flexural Bending

FATIGUE DESIGN• Tensile Strain at Bottom of Asphalt• Tensile Strain in Flexural Beam Test

Other Configurations

FATIGUE TESTING

• Tensile Strain in Flexural Beam Test– Other Configurations

– 10 Hz Haversine Load, 20o C, Controlled Strain

STIFFNESS CURVE

2000

3000

4000

5000

6000

7000

8000

0.0E+00 5.0E+06 1.0E+07 1.5E+07 2.0E+07 2.5E+07 3.0E+07 3.5E+07 4.0E+07

Number of Load Cycles

Stiff

ness

, mPa

Failure

FAILURE: 50% Reduction

LABORATORY ALGORITHM

0.00001

0.0001

0.001

0.01

1.0E+02 1.0E+04 1.0E+06 1.0E+08 1.0E+10

Load Repetitions

Tens

ile S

trai

n

K1 = InterceptK2 = Slope

FATIGUE ALGORITHMS

Nf = K1(1/ε)K2

Nf = K1 (1/ε)K2 (1/E*)K3

AC FATIGUE

LOG N

LOG

εA

CN = K1(1/εAC)K2

K2’>K2

K2’

K2K2

K1

HMA FATIGUE @ UIUCCarpenter - Ghuzlan - Shen

IDOT HMA FATIGUE DATA SUMMARY

84 MIXES

N = K1 (1/ ε)K2

Minimum K2: 3.5

90% K2: 4.0

Average K2: 4.5

OTHER STUDIES

0

1

2

3

4

5

6

7

-16 -14 -12 -10 -8 -6 -4 -2 0

Lo g (K1)

K2

U of IllinoisMaupin Resu ltsMyr eF HWAF innLinear (U of Illinois)Linear (Maupin Resu lts)Linear (Myr e)Linear (F H WA)

K – n RELATIONS

Myre / Norway NTH (1992)LOG K1 = (1.332 – K2) / 0.306

U of IL / IDOT HMAsCarpenter – et al

LOG K1 = (1.178 – K2) / 0.329

0.710.490.330.23250

7.13.82.01.1150

160.660.022.48.4**

75

K24.5

k24.0

K23.5

K23.0

HMA STRAIN

*

N = K1(1/HMA STRAIN)K2

* Micro-strain **Mreps

NO “UNIQUE”

THERE IS

HMA FATIGUE ALGORITHM !!!!

HMA ENDURANCE LIMIT

Monismith & McLean

“Technology of Thick Lift Construction: Structural Design Considerations”

1972 AAPT Proceedings

70 Micro-Strain Endurance Limit!!

Michael Nunn“Long-Life Flexible Pavements”

8th ISAP ConferenceSeattle, WA - 1997

M32

M32CORE

TRL

Longitudinal

crack in

M1

TRL

LOW STRAIN TESTING

10

100

1000

10000

1.E+00 1.E+05 1.E+10 1.E+15 1.E+20 1.E+25 1.E+30 1.E+35 1.E+40

Load Repetitions, E50

Flex

ural

Stra

in, m

icro

stra

in

70 Micro Strain Limit

21 Mixes Tested for Endurance Limit

HMA FATIGUE

N (LOG)

ε AC

(LO

G)

N = K1 (1 / εAC)K2

70 µε

ENDURANCE LIMIT

PERPETUAL PAVEMENT

FATIGUE ENDURANCE LIMIT

0.00001

0.0001

0.001

0.01

1.0E+02 1.0E+04 1.0E+06 1.0E+08 1.0E+10

Load Repetitions

Tens

ile S

train

K1 = InterceptK2 = Slope

FATIGUE ENDURANCE LIMIT

• Damage and Healing Concepts and Test Data Support a Strain Limit Below Which Fatigue Damage Does Not Accumulate

• Strain Limit Is Not The Same for All HMAs.

FATIGUE ENDURANCE LIMITIDOT DATA

NEVER < 70 micro-strain!!!

GENERALLY: 70 –100 micro-strain

MAY BE > 100 micro-strain

EFFECT OF REST PERIODS

SMALL REST PERIODS BETWEEN STRAIN REPETITIONS SIGNIFICANTLY

INCREASES HMA FATIGUE LIFE

IDOT HMA5 SECONDS: 10 X

OVERLOADING

• HMA CAN SUSTAIN “SPORADIC OVERLOADS” AND RETURN TO “ENDURANCE LIMIT” PERFORMANCE

• SUBSEQUENT HMA STRAIN REPETITIONS < ENDURANCE LIMIT:

“DO NOT COUNT”

NAPTF – PAVEMENT RUTTING

NAPTF TEST SECTIONS

75 FEET LONG60 FEET WIDE

“As-Built” NAPTF Test Sections

AC Surface (P-401)

Granular Base(P-209)

LOW StrengthSubgrade

Granular Subbase(P-154)

5 in.

7.75 in.

36.4 in.

LFCLFC

Subgrade=94.7 in.

AC Surface (P-401)




5 in.

7.75 in.

36.4 in.

LFCLFC

Subgrade=94.7 in.

AC Surface (P-401)


MEDIUM StrengthSubgrade


5.1 in.

7.9 in.

12.1 in.

MFCMFC

Subgrade=94.8 in.

AC Surface (P-401)




5.1 in.

7.9 in.

12.1 in.

MFCMFC

Subgrade=94.8 in.

AC Surface (P-401)

Asphalt Stab. Base(P-401)



5 in.

4.9 in.

29.6 in.

LFSLFS

Subgrade=104.5 in.

AC Surface (P-401)




5 in.

4.9 in.

29.6 in.

LFSLFS

Subgrade=104.5 in.

AC Surface (P-401)



5 in.

4.9 in.

8.5 in.


Subgrade=101.6 in.

MFSMFS

AC Surface (P-401)



5 in.

4.9 in.

8.5 in.


Subgrade=101.6 in.

MFSMFS

NAPTF Traffic Test ProgramN

30 ft.

12.8 ft.

0 ft.

-12.8 ft.

-30 ft.

B747

C/L

Wheel Load: 45,000 lbs

Tire Pressure: 188 psi

Traffic Speed: 5 mph

B777

NAPTF Traffic Wander

0

-7 ft.-12.8 ft.-19 ft. 7 ft. 12.8 ft. 19 ft.

Trac

k #-

1

Trac

k #1

Trac

k #2

Trac

k #3

Trac

k #4

Trac

k #

-2

Trac

k #

-3

Trac

k #

-4

Trac

k #-

1

Trac

k #0

Trac

k #1

Trac

k #2

Trac

k #3

Trac

k #4

Trac

k #

-2

Trac

k #

-3

Trac

k #

-4

9.8 in.

B777 WANDER AREA B747 WANDER AREA

B77

7Tr

ack

#0

B74

7

66 Passes(33 East, 33 West)

σ = 30.5 in.

C/L

N

NAPTF “Failure” Criteria

• “At least 1 inch surface upheaval adjacent to the traffic lane” (USCOE MWHGL tests)

• This is considered to reflect structural or shearing failure in the subgrade

• 1 inch surface upheaval may be accompanied by a 0.5-inch rut depth or rut depths in excess of 3 inches

High Severity Rutting

Number of Passes to “Failure”

MFC 12,952* - 12,952

MFS 19,869* - 19,869

LFC 19,950 24,145 44,095*

LFS 19,939 24,749 44,688*

NAPTF Test

Section

* - "Failure" achieved

45,000-lb Wheel Load

65,000-lb Wheel Load Total

Max Rut Depths at “Failure”

B777 B747 B777 B747 B777 B747

MFC 3.4 3.1 - - 3.4 3.1

MFS 3.5 1.0 - - 3.5 1.0

LFC 0.7 0.9 2.5 2.2 3.2 3.1

LFS 0.5 0.4 1.6 1.7 2.1 2.1

Total RD (in.)NAPTF Test

Section

RD under 45,000-lb Wheel Load (in.)

RD Under 65,000-lb Wheel Load (in.)

0

1,000

2,000

3,000

4,000

5,000

0 2000 4000 6000 8000 10000 12000 14000Number of Load Repetitions (N)

Rut

Dep

th (m

ils)

B777-SEB747-SEB777-TSPB747-TSP

RD Vs N – MFC1

0

1,000

2,000

3,000

4,000

5,000

0 10,000 20,000 30,000 40,000 50,000 60,000Number of Load Repetitions (N)

Rut

Dep

th (m

ils)


RD Vs N – LFC1

RD Vs N – LFS1

0

1,000

2,000

3,000

4,000

5,000

0 10,000 20,000 30,000 40,000 50,000 60,000Number of Load Repetitions (N)

Rut

Dep

th (m

ils)


N to Reach Specific RDLow Strength Sections

Medium Strength Sections

B777 B747 B777 B747 B777 B747 B777 B747

250 28 516 28 531 10,743 12,442 28 28

500 5,008 8,083 7,791 8,723 20,068 20,642 15,111 515

1000 21,612 21,414 21,084 22,759 22,888 26,153 21,488 21,488

LFS2Rut Depth (mils)

LFC1 LFC2 LFS1

B777 B747 B777 B747 B777 B747 B777 B747

250 28 28 28 28 - 28 28 5,295

500 299 133 133 133 - 10,529 5,373 7,513

1000 3,343 1,193 1,193 1,448 - 19,869 12,440 15,108

Rut Depth (mils)

MFC1 MFC2 MFS1 MFS2

Conclusions

• Max RD at “failure” higher for conventional sections compared to stabilized sections

• More passes at higher wheel loads was required by L sections to reach “failure” compared to M sections

• N required by B777 and B747 gears to reach 1-inch RD were similar

• B777 RDs and B747 RDs do not differ significantly

M-E DESIGN TOOLS ARE:

“AVAILABLE” AND

“TECHNOLOGICALLY ADEQUATE”

IT IS TIME TO:

“MOVE ON”

new generation aircraft flexible pavement design challenges

Documents