6233625 aashto design method
DESCRIPTION
Diseño Pavimento FlexibleTRANSCRIPT
1
Design MethodsDesign Methods
• Highway PavementsAASHTOThe Asphalt InstitutePortland Cement Association
• Airfield PavementsFAAThe Asphalt InstitutePortland Cement AssociationU.S. Army Corps of Engineers
Objectives of Pavement DesignObjectives of Pavement Design
To provide a surface that is:
• StrongSurface strengthMoisture control
• Smooth
• SafeFrictionDrainage
• EconomicalInitial construction costRecurring maintenance cost
2
Pavements are Designedto Fail !!
Pavement Design MethodologiesPavement Design Methodologies
• Experience
• EmpiricalStatistical models from road tests
• Mechanistic-EmpiricalCalculation of pavement stresses/strains/deformationsEmpirical pavement performance models
• MechanisticCalculation of pavement stresses/strains/deformationsMechanics-based pavement performance models
3
Empirical Empirical vsvs. Mechanistic Design. Mechanistic Design
Wood Floor JoistWood Floor Joist
Empirical “Rule of 2”: d in inches= (L in feet / 2) + 2
Pd
L
Mechanistic: PL4Sbending allowableσ = ≤ σ
1993 Version
4
AASHTO Pavement Design GuideAASHTO Pavement Design Guide
• Empirical design methodology• Several versions:
1961 (Interim Guide)19721986
Refined material characterizationVersion included in Huang (1993)
1993More on rehabilitationMore consistency between flexible, rigid designsCurrent version
2002Under developmentWill be based on mechanistic-empirical approach
AASHO Road Test (late 1950’s)AASHO Road Test (late 1950’s)
(AASHO, 1961)
5
One Rainfall Zone...One Rainfall Zone...
(AASHO, 1961)
One Temperature Zone...One Temperature Zone...
(AASHO, 1961)
6
One Subgrade...One Subgrade...
A-6 / A-7-6 (Clay)Poor Drainage
(AASHO, 1961)
Limited Set of Materials...Limited Set of Materials...
• One asphalt concrete3/4” surface course1” binder course
• One Portland cement concrete (3500 psi @ 14 days)
• Four base materialsWell-graded crushed limestone (main experiment)Well-graded uncrushed gravel (special studies)Bituminous-treated base (special studies)Cement-treated base (special studies)
• One uniform sand/gravel subbase
7
1950’s1950’sConstructionConstructionMethods...Methods...
(AASHO, 1961)
1950’s1950’sVehicle Loads...Vehicle Loads...
(AASHO, 1961)
8
1.1M Axles1.1M Axles
2 Years2 Years
Time (Months)
Axl
e Lo
ads
(Tho
usan
ds)
Limited Traffic Volumes...Limited Traffic Volumes...
(AASHO, 1961)
1950’s1950’sData Analysis...Data Analysis...
(AASHO, 1961)
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Some Failures...Some Failures...
(Some pavements too!)
(AASHO, 1961)
AASHTO Design Basedon Serviceability Decrease
(AASHTO, 1993)
10
What is Serviceability?What is Serviceability?
• Based upon PresentServiceability Rating (PSR)
• Subjective rating byindividual/panel
Initial/post-constructionVarious times afterconstruction
• 0 < PSR < 5
• PSR < ~2.5: Unacceptable
(AASHO, 1961)
Present Serviceability Index (PSI)Present Serviceability Index (PSI)
• PSR correlated to physical pavement measures via PresentServiceability Index (PSI):
2 1/ 2
2
5.03 1.91log(1 ) 1.38 0.01( )
slope variance (measure of roughness)
average rut depth (inches) area of cracking and patching per 1000 ft
PSI SV RD C P
SV
RD
PSI P RP
SC
= − + − − +
=≈
=
=
+
Empirical!
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AASHTO Design Guide (1993)AASHTO Design Guide (1993)
Part I: Pavement Design and ManagementPart I: Pavement Design and ManagementPrinciplesPrinciples
• Introduction and Background
• Design Related to Project Level Pavement Management
• Economic Evaluation of Alternative Design Strategies
• Reliability
AASHTO Design Guide (1993)AASHTO Design Guide (1993)
Part II: Pavement Design Procedures for NewPart II: Pavement Design Procedures for NewConstruction or ReconstructionConstruction or Reconstruction
• Design Requirements
• Highway Pavement Structural Design
• Low-Volume Road Design
12
AASHTO Design Guide (1993)AASHTO Design Guide (1993)
Part III: Pavement Design Procedures forPart III: Pavement Design Procedures forRehabilitation of Existing PavementsRehabilitation of Existing Pavements
• Rehabilitation Concepts
• Guides for Field Data Collection
• Rehabilitation Methods Other Than Overlay
• Rehabilitation Methods With Overlays
Design ScenariosIncluded in
AASHTO Guide
(AASHTO, 1993)
13
AASHTO Design Basedon Serviceability Decrease
(AASHTO, 1993)
Flexible PavementsFlexible Pavements
14
Design EquationDesign Equation
W18 = design traffic (18-kip ESALs)ZR = standard normal deviateSo = combined standard error of traffic and performance prediction∆PSI = difference between initial and terminal serviceability indexMR = resilient modulus (psi)SN = structural number
( ) ( )
( )
( )
10 18 10
10
10
5.19
log 9.36log 1 0.20
log4.2 1.5 2.32log 8.0710940.40
1
R o
R
W Z S SN
PSI
M
SN
= + + −
∆ − + + −
++
Structural Number
(AASHTO, 1993)
15
Traffic Traffic vsvs. Analysis Period. Analysis Period
(AASHTO, 1993)
Analysis PeriodAnalysis Period
(Also basis for life-cycle cost analysis)
(AASHTO, 1993)
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Design Traffic (18KDesign Traffic (18K ESALs ESALs))
(AASHTO, 1993)
Design Traffic (18KDesign Traffic (18K ESALs ESALs))
• DD = 0.5 typically
• DL:
(AASHTO, 1993)
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Reliability
(AASHTO, 1993)
Recommended Values forRecommended Values forStandard Error SStandard Error Soo
• Rigid Pavements: 0.30 - 0.40
• Flexible Pavements: 0.40 - 0.50
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Standard Normal Deviate ZStandard Normal Deviate ZRR
(AASHTO, 1993)
Recommended Reliability LevelsRecommended Reliability Levels
(AASHTO, 1993)
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ServiceabilityServiceability
• PSI = Pavement Serviceability Index, 1 < PSI < 5
• po = Initial Serviceability IndexRigid pavements: 4.5Flexible pavements: 4.2
• pt = Terminal Serviceability Index
o tPSI p p∆ = −
(AASHTO, 1993)
Adjustment of Roadbed (Subgrade)
MR for SeasonalVariations
(AASHTO, 1993)
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Structural NumberStructural Number
SN = structural number = f (structural capacity)ai = ith layer coefficientDi = ith layer thickness (inches)mi = ith layer drainage coefficientn = number of layers (3, typically)
1 12
n
i i ii
SN a D a D m=
= +∑
No Unique Solution!
(AASHTO, 1993)
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Layer Coefficient Layer Coefficient aa11: Asphalt Concrete: Asphalt Concrete
(AASHTO, 1993)
Layer Coefficient Layer Coefficient aa22: Granular Base: Granular Base
( )2 100.249 log 0.977
in psi
base
base
a E
E
≅ −
(AASHTO, 1993)
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Layer Coefficient Layer Coefficient aa22: Cement Treated Base: Cement Treated Base
(AASHTO, 1993)
Layer Coefficient Layer Coefficient aa22::Bituminous Treated BaseBituminous Treated Base
(AASHTO, 1993)
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Layer Coefficient Layer Coefficient aa33: Granular Subbase: Granular Subbase
3 100.227(log ) 0.839
in psi
subbase
subbase
a E
E
= −
(AASHTO, 1993)
Quality of DrainageQuality of Drainage
(AASHTO, 1993)
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Drainage Coefficient Drainage Coefficient mmii
mi increases/decreases the effective value for ai
(AASHTO, 1993)
Next Slide
(AASHTO, 1993)
25
Traffic Traffic vsvs. Analysis Period. Analysis Period
(AASHTO, 1993)
(AASHTO, 1993)
26
Effect of Froston Performance
PSI = Pavement Servicability Index
1 < PSI < 5
“Failure”: PSI < 2+
(AASHTO, 1993)
(AASHTO, 1993)
Frost Heave Rate φ
φ = f (-0.02mm)
27
(AASHTO, 1993)
MaximumServiceability
Loss
∆PSImax = f (frost depth, drainage)
Effect ofSwelling on
Performance
PSI = Pavement Servicability Index
1 < PSI < 5
“Failure”: PSI < 2+
(AASHTO, 1993)
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(AASHTO, 1993)
Swell Rate Constant θ
θ = f (moisture supply,soil fabric)
(AASHTO, 1993)VR = f (PI, compaction, thickness)
Maximum PotentialHeave VR
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Rigid PavementsRigid Pavements
Design EquationDesign Equation
W18 = design traffic (18-kip ESALs)ZR = standard normal deviateSo = combined standard error of traffic and
performance predictionD = thickness (inches) of pavement slab∆PSI = difference between initial and terminal
serviceability indicespt = terminal serviceability value
Sc’ = modulus of rupture (psi) for Portland cementconcrete
J = load transfer coefficient
Cd = drainage coefficient
Ec = modulus of elasticity (psi) for Portlandcement concrete
k = modulus of subgrade reaction (pci)
( ) ( )
( )
( ) ( )
( )
10 18 10
' 0.7510
1070.75
8.46 0.25
log 7.35log 1 0.06
log 1.1324.5 1.5 4.22 0.32 log1.64x10 18.421 215.631 /
R o
c dt
c
W Z S D
PSIS C D
p
J DD E k
= + + −
∆
− − + + − + − +
PCC Thickness
30
(AASHTO, 1993)
(AASHTO, 1993)
31
Design InputsDesign Inputs
W18 = design traffic (18-kip ESALs)
ZR = standard normal deviate
So = combined standard error of traffic and performance prediction
∆PSI = difference between initial and terminal serviceability indices
pt = terminal serviceability index (implicit in flexible design)
All consistent with flexible pavements!
Additional Design InputsAdditional Design Inputs
• S′c = modulus of rupture for concrete
• J = joint load transfer coefficient
• Cd = drainage coefficient (similar in concept to flexiblepavement terms)
• Ec = modulus of elasticity for concrete
• k = modulus of subgrade reaction
Additional inputs reflect differences inAdditional inputs reflect differences inmaterials and structural behavior.materials and structural behavior.
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Modulus of RuptureSc’
(AASHTO, 1993)
Joint Load Transfer Coefficient Joint Load Transfer Coefficient JJ
Pavement Type(no tied shoulders)
J
JCP/JRCPw/ load transfer devices
3.2
JCP/JRCPw/out load transfer devices
3.8-4.4
CRCP 2.9
33
Joint Load Transfer Coefficient Joint Load Transfer Coefficient JJ
Additional benefits of tied shoulders:
(AASHTO, 1993)
Drainage Coefficient Drainage Coefficient CCdd
• Two effects:Subbase and subgrade strength/stiffnessJoint load transfer effectiveness
(AASHTO, 1993)
34
PCC Modulus of Elasticity PCC Modulus of Elasticity EEcc
• Measure directly per ASTM C469
• Correlation w/ compressive strength:
Ec = 57,000 (fc’)0.5
Ec = elastic modulus (psi)fc’ = compressive strength (psi) per AASHTO T22, T140, or ASTM
C39
Effective Subgrade Modulus Effective Subgrade Modulus kk
• Depends on:Roadbed (subgrade) resilient modulus, MR
Subbase resilient modulus, ESB
• Both vary by season
35
Determining Effective Determining Effective k k (See Table 3.2)(See Table 3.2)
• Identify:Subbase typesSubbase thicknessesLoss of support, LS (erosion potential of subbase)Depth to rigid foundation (feet)
• Assign roadbed soil resilient modulus (MR) for each season
• Assign subbase resilient modulus (ESB) for each season15,000 psi (spring thaw) < ESB < 50,000 psi (winter freeze)ESB < 4(MR)
(AASHTO, 1993)
36
Determining Effective Determining Effective k k ((cont’dcont’d))
• Determine composite k for each seasonFor DSB = 0: k = MR/19.4For DSB > 0: Use Figure 3.3
• If depth to rigid foundation < 10 feet, correct k for effect ofrigid foundation near the surface (Figure 3.4)
• Estimate required thickness of slab (Figure 3.5) anddetermine relative damage ur for each season
• Use average ur to determine effective k (Figure 3.5)
• Correct k for potential loss of support LS (Figure 3.6)
k = f (MR , ESB , DSB )
Composite Modulusof Subgrade Reaction
(AASHTO, 1993)
37
Rigid FoundationCorrection
(AASHTO, 1993)
Relative Damage
ur = f ( k, D)
(AASHTO, 1993)
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(AASHTO, 1993)
Loss of Support, Loss of Support, LSLS
Subbase/subgradeerosion at joints causes
Loss of Support,impairs load transfer.
(AASHTO, 1993)
39
Loss of Support
(AASHTO, 1993)
(AASHTO, 1993)
40
Consistent with flexible pavement approach!
Next Slide
(AASHTO, 1993)
Traffic Traffic vsvs. Analysis Period. Analysis Period
(AASHTO, 1993)(AASHTO, 1993)
41
Joint DesignJoint Design
• Joint TypesContractionExpansionConstructionLongitudinal
• Joint GeometrySpacingLayout (e.g., regular, skewed, randomized)Dimensions
• Joint Sealant Dimensions
Types of JointsTypes of Joints
• ContractionTransverseFor relief of tensile stresses
• ExpansionTransverseFor relief of compressive stressesUsed primarily between pavement and structures (e.g., bridge)
• Construction
• LongitudinalFor relief of curling and warping stresses
42
Typical Contraction Joint DetailsTypical Contraction Joint Details
(Huang, 1993)
Typical Expansion Joint DetailTypical Expansion Joint Detail
(Huang, 1993)
43
Typical Construction Joint DetailTypical Construction Joint Detail
(Huang, 1993)
Typical Longitudinal Joint DetailTypical Longitudinal Joint Detail
(Huang, 1993)
Full Width Construction
44
Typical Longitudinal Joint DetailTypical Longitudinal Joint Detail
(Huang, 1993)
Lane-at-a-Time Construction
Joint SpacingJoint Spacing
• Local experience is best guide
• Rules of thumb:JCP joint spacing (feet) < 2D (inches)W/L < 1.25
45
Joint DimensionsJoint Dimensions
• Width controlled by joint sealant extension
• Depths:Contraction joints: D/4Longitudinal joints: D/3
• Joints may be formed by:SawingInsertsForming
Joint SealantDimension
Governed by expected joint
movement,sealant resilience
(AASHTO, 1993)
46
Design InputsDesign Inputs
Z αc
(AASHTO, 1993)
Reinforcement Design (JRCP)Reinforcement Design (JRCP)
• Purpose of reinforcement is not to prevent cracking, but to hold tightlyclosed any cracks that may form
• Physical mechanisms:Thermal/moisture contractionFriction resistance from underlying material
• Design based on friction stress analysis(Huang, 1993)
47
Dowel Bars: Transverse Joint Load TransferDowel Bars: Transverse Joint Load Transfer
• “…size and spacing should be determined by the localagency’s procedures and/or experience.”
• Guidelines:Dowel bar diameter = D/8 (inches)Dowel spacing: 12 inchesDowel length: 18 inches
Friction StressesFriction Stresses
(Huang, 1993)
Induces tensile stresses in concreteCauses opening of transverse joints
48
Applies to both longitudinaland transverse steel reinforcement
(Generally, Ps=0 for L< ~15 feet)
(AASHTO, 1993)
Friction FactorFriction Factor
(AASHTO, 1993)
49
Steel Working StressSteel Working Stress
Based on preventing fracture and limiting permanent deformation.
(AASHTO, 1993)
TransverseTie Bars
(AASHTO, 1993)
50
TransverseTie Bars
(AASHTO, 1993)