NEW GENERATION AIRCRAFT FLEXIBLE PAVEMENT DESIGN CHALLENGES. M. Thompson U of Urbana-Champaign

Transcription

1 NEW GENERATION AIRCRAFT FLEXIBLE PAVEMENT DESIGN CHALLENGES M. Thompson U of Urbana-Champaign

2 NEW GENERATION AIRCRAFT BOEING-777 (1995) -Gross Load 632,000 lbs A (2006) -Gross Load 1.23 million lbs

3 AIRCRAFT WHEEL LOAD (KIPS) PRESSURE (psi) A A-380 * B ER B B ER * B * DUAL-TRIDEM

4

5

6

7

8

9

10

11 787-8 Landing Gear Footprint FT FT 9 IN 9 IN (22.8 (22.8 M) M) FT FT 2 IN 2 IN (9.8 (9.8 m) m) TYP TYP FT FT 1 IN 1 IN (11.6 (11.6 M) M) Preliminary Data Data IN IN (1.3 (1.3 M) M) CHARACTERISTI CS MAX DESIGN NOSE TAXI GEAR WEIGHT TIRE NOSE SIZE GEAR TIRE PRESSURE MAIN GEAR TIRE SIZE MAIN GEAR TIRE PRESSURE MTOW: 482 kips UNITS POUNDS KILOGRAMS IN PSI KG/CM 2 IN PSI KG/CM IN IN (1.5 (1.5 M) M) , ,817 40x16.0R16/26PR MAIN GEAR TIRE LOAD: 55.5 kips MAIN GEAR TIRES: 221 psi 50X20.0R22/34PR

12 CBR-BASED DESIGN (COE / FAA AC No. 150/5320-6D) BASED ON ESWL Is ESWL Adequate for Dual Tandem & Dual-Tridem???

13 Mechanistic-Based Pavement Design Concepts for NEW GENEREATION AIRCRAFT

14 Mechanistic-Empirical Approach 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.

15 DESIRABLE M-E DESIGN FEATURES Technically Sound Understandable Minimum Inputs User Friendly M-E IMPLEMENTATION CONCERNS Airport Agency Resources Input Data Transfer Functions Calibration Data

16 Mechanistic-Empirical Approach START 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. OBTAIN CRITICAL RESPONSES Subgrade Deviator Stress (σ D ). Top Subgrade Vertical Strain (ε S ). Horizontal Strain (ε AC ) at the bottom of the AC layer. TRANSFER FUNCTIONS (F T ) DESIGN RELIABILITY And/Or Critical Response F T Pavement Distress (i.e. Damage) PAVEMENT PERFORMANCE Cumulative development of distress DESIGN ITERATIONS FINAL DESIGN

17 Mechanistic-Empirical Approach AC Layer ε AC Granular Base Layer Determine the Critical Responses Subgrade SSR = σ d / q u ε v ε AC : AC Fatigue SSR: Subgrade ε p ε v : Pavement ε p

18 STRUCTURAL RESPONSES * STRESSES * STRAINS * DEFLECTIONS

19 STRUCTURAL MODEL

20 STRUCTURAL MODEL SHOULD ACCOMMODATE MATERIAL PROPERTIES

21 Material Characterization Resilient Modulus Pavement Materials: + Asphalt Concrete: Temperature, frequency. + Unbound Granular: Stress hardening. Subgrade Soils: + Fine-grained soils: Stress softening + Granular: Stress hardening.

22 Material Characterization Asphalt Concrete Modulus * Temperature Dependent *Frequency Dependent * Must consider in M-E Design!!!

23

24 MONTH MMAT(F) MMPT(F)/ E (ksi) JAN 15 18/* FEB MARCH APRIL /* 33/* 46/1,870 CALGARY Temperature Data 3 inch depth MAY 50 58/1,045 JUNE 57 66/710 JULY 62 72/530 AUG SEPT /615 59/1,000 For: f=10hz * > 3,000 ksi OCT 42 49/1,620 NOV 27 32/* DEC 17 21/*

25 ICM NCHRP 1-37A1 ENHANCED INTEGRATED CLIMATIC MODEL (Dempsey & Larson)

26 HIRSCH MODEL Hirsch Model for Estimating the Modulus of In-Place Asphalt Mixtures Christensen - Pellinen - Bonaquist AAPT Journal INPUTS VMA - VFA - Asphalt Modulus

27 PREDICTIVE EQUATIONS: Modified Hirsch Model 1 * 3 4,200, ) (1 10,000 * ,200,000 * = binder binder G VFA VMA VMA Pc VMA VFA G VMA Pc E * * = VMA G VFA VMA G VFA Pc binder binder IG*I binder VMA VFA vol. properties dynamic modulus

28 HIRSCH MODEL + G * INPUT (TEMP / FREQ) (ASPHALT MASTER CURVE) + G * COMPATIBLE WITH PG GRADE + VFA & VMA FROM MIX DESIGN

29 PG G* master curve G* (Pa) master curve C 21.1 C C 54.5 C E E E E E E E E E+04 Frequency (Hz)

30 GRANULAR MATERIALS

31 FROM RADA & WITCZAK

32 From Rada & Witczak

33 UZAN MODEL (1985) M R = K 1 Θ K2 (σ d ) K3 Θ =BULK STRESS Θ = σ 1 + σ 2 + σ 3

34 M R = K 1 Θ K2 (σ d ) K3 K1 & K2 MOST IMPORTANT!!

35 E Ri (ksi) = Q U (psi) + 0.9

36 MODULUS CLASSES FINE-GRAINED SOILS SOIL E Ri (ksi) Qu (psi) CBR STIFF MEDIUM SOFT VERY SOFT E Ri (ksi) = 0.42 Qu (psi) - 2

37 ESTIMATING E Ri E Ri (OMC) = (%C) (PI) E Ri Ri 95% T-99T C - %Clay

38

39 E CBR RELATIONS COE/FAA: E (psi) = 1,500 CBR TRL/UK : E (psi) = 2,555 CBR 0.64 (CBR: 2-12) (TRL Report # 1132) Deviator Stress =????

40 STRUCTURAL MODELS ELASTIC LAYER PROGRAMS FINITE ELEMENT PROGRAMS (2-D / 3-D)

41 ELASTIC LAYER PROGRAMS + LINEAR ELASTIC MATERIALS + MODULUS CONSTANT WITHIN THE LAYER + NO FAILURE CRITERION

42 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.

43 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.

44 ILLI-PAVE: 2D FEM Axis Of Revolution Surface Base Surface Base Subbase Subbase Subgrade Subgrade Results for Single Wheel Loads

45 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.

46 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.

47 MULTIPLE WHEEL SOLUTION Chou & Ledbetter (1973) MWHGL WES SUPERPOSITION WORKS for FLEXIBLE PAVEMENTS!!

48 SUPERPOSITION Studies USCOE Study 1973 (Examples ) Vertical deflection, 10-3 inches Section #1 Section # Offset, FT

49 SUPERPOSITION Studies USCOE Study 1973 (Examples ) Vertical Stress, lb/in Section #1 Section # Offset, FT

50 FAA NAPTF Study 2001 Uof IL FAA Airport Technology Transfer Conference Vertical Stress Vertical Stress Vertical Stress Actual Response, psi Rebound Response Actual Response, psi Rebound Response Actual Response, psi Rebound Response Superposed Response, psi Superposed Response, psi Superposed Response, psi Actual Response, psi Horizontal Stress (Radial or Tangential) Rebound Response Superposed Response, psi Actual Response, psi Horizontal Stress (Radial or Tangential) Rebound Response Equality Line Upper/Lower Bounds (2-psi or 10%) Superposed Response, psi Actual Response, psi Horizontal Stress (Radial or Tangential) Rebound Response Superposed Response, psi MFC Section HFS Section HFC Section

51 SOLUTION FOR MULTIPLE WHEELS ILLI-PAVE + Superposition σ σ xx yy = = ( 2 ) ( 2 σ cos α + σ sin α ) rr ( 2 ) ( 2 σ sin α + σ cos α ) rr tt tt ILLI-PAVE + Superposition σ τ τ τ zz xy yz xz = σ = = τ = τ ( σ σ ) rz rz zz rr tt sinα cosα sinα cosα Y r σ rr, σ tt, σ zz, τ rz α X

52 Mechanistic-Empirical Approach AC Layer ε AC Granular Base Layer Determine the Critical Responses Subgrade SSR = σ d / q u ε v ε AC : AC Fatigue SSR: Subgrade ε p ε v : Pavement ε p

53 CONCEPTS FOR DEVELOPING A M-E BASED ACN PROCEDURE FOR NEW GENERATION AIRCRAFT 2006 ISAP Quebec City, Canada Thompson & Gomez-Ramirez (U of IL) Gervais & Roginski (Boeing)

54 AIRCRAFT WHEEL LOAD (KIPS) PRESSURE (psi) A A-380 * B ER B B ER * B (REF) * DUAL-TRIDEM

55 ICAO Subgrade "Representative" CBR Q U (psi) E Ri (ksi) A B C D ICAO SUBGRADES C = Q U /2 PHI = 0

56 GRANULAR LAYERS T GRAN = BASE + SUBBASE M R (psi) = 5,000 (THETA) 0.5 C = 0 PHI = 45

57 ICAO SUBGRADE D (CBR-3) D (CBR-3) C (CBR-6) C (CBR-6) B (CBR-10) B (CBR-10 A (CBR-15) A (CBR-15) AC (INCHES) & GRANULAR (INCHES) PAVEMENT PARAMETERS

58 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)

59 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)

60 ILLIPAVE Analysis Results AC Surface Thickness: 10-in -- Modulus: 500-ksi GB Thickness: 40-in -- SG Eri: 5-ksi Deflection, mils A340M A340B A380M A380W B ER Aircraft Type B B B MLG--Surface DMax

61 ILLIPAVE Analysis Results AC Surface Thickness: 10-in -- Modulus: 500-ksi GB Thickness: 40-in -- SG Eri: 5-ksi Deflection, mils A340M A340B A380M A380W B ER Aircraft Type B B B MLG--Surface DMax

62 ILLIPAVE Analysis Results AC Surface Thickness: 10-in -- Modulus: 500-ksi GB Thickness: 40-in -- SG Eri: 5-ksi Microstrain A340M A340B A380M A380W B ER Aircraft Type B B B MLG--Max AC Surface Strain

63 ILLIPAVE Analysis Results AC Surface Thickness: 10-in -- Modulus: 500-ksi GB Thickness: 40-in -- SG Eri: 5-ksi Stress, psi A340M A340B A380M A380W B ER Aircraft Type B B B MLG--Deviator Top of Subgrade Layer

64 ILLIPAVE Analysis Results AC Surface Thickness: 10-in -- Modulus: 500-ksi GB Thickness: 40-in -- SG Eri: 5-ksi SSR A340M A340B A380M A380W B ER Aircraft Type B B B MLG--Subgrade Stress Ratio (SSR)

65 ILLIPAVE Analysis Results AC Surface Thickness: 10-in -- Modulus: 500-ksi GB Thickness: 40-in -- SG Eri: 5-ksi Microstrain A340M A340B A380M A380W B ER Aircraft Type B B B MLG--Vertical Top of Subgrade Layer

66 ILLIPAVE Analysis Results AC Surface Thickness: 10-in -- Modulus: 500-ksi GB Thickness: 40-in -- SG Eri: 5-ksi Ratio WRT B A340M A340B A380M A380W B ER B ER B ER B Aircraft Type MLG--Surface DMax MLG--Max AC Surface Strain

67 ILLIPAVE Analysis Results AC Surface Thickness: 10-in -- Modulus: 500-ksi GB Thickness: 40-in -- SG Eri: 5-ksi Ratio WRT B A340M A340B A380M A380W B ER B ER B ER B Aircraft Type MLG--Deviator Top of Subgrade Layer MLG--Vertical Top of Subgrade Layer

68 TRANSFER FUNCTIONS (RESPONSES DISTRESS) CRITICAL FACTORS!!!

69 FLEXIBLE PAVEMENT DISTRESSES HMA FATIGUE RUTTING: + HMA (MATL. SELECTION / MIX DESIGN) + GRANULAR BASE/SUBBASE + SUBGRADE

70 SUBGRADE TRANSFER FUNCTIONS SUBGRADE VERTICAL STRAIN SUBGRADE STRESS RATIO (SSR) (SSR= DEV STRESS / Q U)

71 VERTICAL STRAIN CRITERIA ε AGENCY AI SHELL 50% 85% 95% TRL/1132 (85%) ε = L (1/N) m L m 1.05* * * * * RD (INS)

72 WES / TOWNSEND & CHISOLM / 1976 Vicksburg BUCKSHOT CLAY (CH)

73 1.5 Transfer Functions: Subgrade Rutting- Vertical Strain Design Criteria VERTICAL COMPRESSIVE STRAIN AT TOP OF SUBGRADE, ε v E S = 30,000 PSI 0.6 1,000 2,000 5,000 10,000 20,000 15,000 9,000 3,000 ANNUAL STRAIN REPETITIONS (20 YEAR LIFE) COE / FAA LEDFAA

74 FAA FAA SUBGRADE STRAIN CRITERIA (Revised) C = (0.004 / ε v ) 8.1 Coverages < 12,100 C = ( / ε v ) Coverages > 12,100 C - Coverages ε v - Subgrade Vertical Compressive Strain

75 Transfer Functions: Subgrade Rutting-SSR Permanent Strain Influence of SSR on Permanent Deformation 1.00 SSR Bejarano & Thompson (2001) UNSTABLE!!! Load Applications DuPont Clay q u = 28 psi γ d = 98 pcf w = 26 % STABLE Behavior

76 Transfer Functions: Subgrade Rutting-SSR p after N= Permanent Deformation vs. SSR 20.0% CSSC 23.0% 24.5% 23.0% DPC 26.0% 28.5% 30.5% Bejarano & Thompson (2001) Subgrade Stress Ratio

77 SUBGRADE RUTTING ALGORITHM LOG ε P = A + b (LOG N) ε P = AN b

78 Development of a Simplified M-E Design Procedure for Low-Volume Flexible Roads Zhao & Dennis University of Arkansas TRR # 1989 Vol. 1

79 Subgrade Stress Ratio (SSR) / A

80 Subgrade Stress Ratio (SSR) / b

81 Transfer Functions: Subgrade Rutting-SSR SSR General Guidelines Damage Potential Low/Acceptable Limited High SSR 0.5 / to 0.75 > 0.75

82 GRANULAR LAYER RUTTING * COE NOT A CRITERION * FAA / LEDFAA - NOT A CRITERION INDIRECT ACCOMODATION: MINIMUM HMA SURFACE THICKNESS STABILIZED BASE - > 100 KIPS

83 GRANULAR BASE Minimum HMA Surface Thickness FAA 4-5 ins. / Critical 3-4 ins. / Noncritical (Base CBR - 80) S. African F

84 South African Mechanistic Approach Stress Based Safety Factor F Material Shear Strength / Shear Stress F = [σ 3 φ term + c term ] / [σ 1 - σ 3 ] where: φ term = [tan 2 (45 + φ/2) - 1] c term = 2 * C * tan(45 + φ/2) φ - friction angle, degrees C - cohesion, psi

85 GRANULAR BASE RATIO FOR PHI = 45 & C = 0 F = DEV. STRESS / 4.8 * SIG 3 DECREASED F : MORE RUTTING

86 HMA FATIGUE (TRADITIONAL)

87 HMA FATIGUE CRACKING

88 LEDFAA HMA FATIGUE LOG C = 2.68 (5*LOG ε) - (2.665*LOG E HMA ) C COVERAGES TO FAILURE ε - HMA BOTTOM OF P401 HMA SURFACE E HMA HMA MODULUS (200 ksi) Heukelom & Klomp AAPT (1964)

89 AASHTO TP 8-94 Standard Test Method for Determination of the Fatigue Life of Compacted HMA Subjected to Repeated Flexural Bending

90 FATIGUE DESIGN Tensile Strain at Bottom of Asphalt Tensile Strain in Flexural Beam Test Other Configurations

91

92 FATIGUE TESTING Tensile Strain in Flexural Beam Test Other Configurations 10 Hz Haversine Load, 20 o C, Controlled Strain

93 STIFFNESS CURVE Stiffness, mpa Failure 3000 FAILURE: 50% Reduction E E E E E E E E E+07 Number of Load Cycles

94 LABORATORY ALGORITHM 0.01 K1 = Intercept K2 = Slope Tensile Strain E E E E E+10 Load Repetitions

95 FATIGUE ALGORITHMS N f = K1(1/ε) K2 N f = K1 (1/ε) K2 (1/E*) K3

96 AC FATIGUE N = K1(1/ε AC ) K2 K2 >K2 LOG ε AC K1 K2 LOG N K2 K2

97 HMA UIUC Carpenter - Ghuzlan - Shen

98 IDOT HMA FATIGUE DATA SUMMARY 84 MIXES N = K1 (1/ ε) K2 Minimum K2: % K2: 4.0 Average K2: 4.5

99 OTHER STUDIES U of Illinois Maupin Results Myre FHWA Finn Linear (U of Illinois) Linear (Maupin Results) Linear (Myre) Linear (FHWA) 4 K Log(K1)

100 K n RELATIONS Myre / Norway NTH (1992) LOG K1 = (1.332 K2) / U of IL / IDOT HMAs Carpenter et al LOG K1 = (1.178 K2) / 0.329

101 N = K1(1/HMA STRAIN) K2 HMA K2 K2 k2 K2 STRAIN * ** * Micro-strain **Mreps

102 THERE IS NO UNIQUE HMA FATIGUE ALGORITHM!!!!

103 HMA ENDURANCE LIMIT

104 Monismith & McLean Technology of Thick Lift Construction: Structural Design Considerations 1972 AAPT Proceedings 70 Micro-Strain Endurance Limit!!

105 Michael Nunn Long-Life Flexible Pavements 8 th ISAP Conference Seattle, WA

106 TRL M32 CORE M32

107 Longitudinal crack in M1 TRL

108 LOW STRAIN TESTING Mixes Tested for Endurance Limit Flexural Strain, micro strain Micro Strain Limit 10 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, E 50

109 HMA FATIGUE N = K1 (1 / ε AC ) K2 ε AC (LOG) 70 µε ENDURANCE LIMIT PERPETUAL PAVEMENT N (LOG)

110 FATIGUE ENDURANCE LIMIT 0.01 K1 = Intercept K2 = Slope Tensile Strain E E E E E+10 Load Repetitions

111 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.

112 FATIGUE ENDURANCE LIMIT IDOT DATA NEVER < 70 micro-strain!!! GENERALLY: micro-strain MAY BE > 100 micro-strain

113 EFFECT OF REST PERIODS SMALL REST PERIODS BETWEEN STRAIN REPETITIONS SIGNIFICANTLY INCREASES HMA FATIGUE LIFE IDOT HMA 5 SECONDS: 10 X

114 OVERLOADING HMA CAN SUSTAIN SPORADIC OVERLOADS AND RETURN TO ENDURANCE LIMIT PERFORMANCE SUBSEQUENT HMA STRAIN REPETITIONS < ENDURANCE LIMIT: DO NOT COUNT

115 NAPTF PAVEMENT RUTTING NAPTF TEST SECTIONS 75 FEET LONG 60 FEET WIDE

116 As-Built NAPTF Test Sections LFC MFC LFS MFS AC Surface (P-401) 5 in. AC Surface (P-401) 5.1 in. AC Surface (P-401) 5 in. AC Surface (P-401) 5 in. Granular Base (P-209) 7.75 in. Granular Base (P-209) 7.9 in. Asphalt Stab. Base (P-401) 4.9 in. Asphalt Stab. Base (P-401) 4.9 in. Granular Subbase (P-154) 36.4 in. Granular Subbase (P-154) 12.1 in. Granular Subbase (P-209) 29.6 in. Granular Subbase (P-209) 8.5 in. LOW Strength Subgrade MEDIUM Strength Subgrade LOW Strength Subgrade MEDIUM Strength Subgrade Subgrade=94.7 in. Subgrade=94.8 in. Subgrade=104.5 in. Subgrade=101.6 in.

117 NAPTF Traffic Test Program N -30 ft ft. B777 0 ft. Wheel Load: 45,000 lbs Tire Pressure: 188 psi Traffic Speed: 5 mph C/L 12.8 ft. B ft.

118 NAPTF Traffic Wander Track # -4 Track # -3 Track # -2 Track #-1 Track #0 Track #1 Track #2 Track #3 Track #4 Track # -4 Track # -3 Track # -2 Track #-1 Track #0 Track #1 Track #2 Track #3 Track #4 B777 B Passes (33 East, 33 West) σ = 30.5 in. C/L N 9.8 in. -19 ft ft. -7 ft. 7 ft ft. 19 ft. B777 WANDER AREA B747 WANDER AREA 0

119 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

120

121 High Severity Rutting

122 Number of Passes to Failure NAPTF Test Section 45,000-lb Wheel Load 65,000-lb Wheel Load Total MFC 12,952 * - 12,952 MFS 19,869 * - 19,869 LFC 19,950 24,145 44,095 * LFS 19,939 24,749 44,688 * * - "Failure" achieved

123 Max Rut Depths at Failure NAPTF Test Section RD under 45,000-lb Wheel Load (in.) RD Under 65,000-lb Wheel Load (in.) Total RD (in.) B777 B747 B777 B747 B777 B747 MFC MFS LFC LFS

124 RD Vs N MFC1 Rut Depth (mils) 5,000 4,000 3,000 2,000 B777-SE B747-SE B777-TSP B747-TSP 1, Number of Load Repetitions (N)

125 Rut Depth (mils) 5,000 4,000 3,000 2,000 RD Vs N LFC1 B777-SE B747-SE B777-TSP B747-TSP 1, ,000 20,000 30,000 40,000 50,000 60,000 Number of Load Repetitions (N)

126 Rut Depth (mils) 5,000 4,000 3,000 2,000 1,000 B777-SE B747-SE B777-TSP B747-TSP RD Vs N LFS ,000 20,000 30,000 40,000 50,000 60,000 Number of Load Repetitions (N)

127 N to Reach Specific RD Low Strength Sections Rut Depth (mils) LFC1 LFC2 LFS1 LFS2 B777 B747 B777 B747 B777 B747 B777 B ,743 12, ,008 8,083 7,791 8,723 20,068 20,642 15, ,612 21,414 21,084 22,759 22,888 26,153 21,488 21,488 Medium Strength Sections Rut Depth (mils) MFC1 MFC2 MFS1 MFS2 B777 B747 B777 B747 B777 B747 B777 B , ,529 5,373 7, ,343 1,193 1,193 1,448-19,869 12,440 15,108

128 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

129 M-E DESIGN TOOLS ARE: AVAILABLE AND TECHNOLOGICALLY ADEQUATE

130 IT IS TIME TO: MOVE ON