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  • Pavement Thickness Design Methods

    Municipal Streets SeminarNovember 12, 2014

    Ames, Iowa

    Eric Ferrebee - ACPA

  • U.S. JPCP Roadway Design Methods

    AASHTOWarePavement ME (previously known as DARWin-ME and MEPDG)

    AASHTO 93 (software as ACPA WinPAS)

    ACPA StreetPave

    325 & 330

  • Design Method Basis

    Mechanistic Purely scientific and based on measured, defendable scientific rules and laws

    Empirical Based on observations or experimentation and requires a lot of tests to connect all the relationships

    = / L =

    = + +

  • AASHTO 93 / ACPA WinPAS

    acpa.org/winpas

  • AASHO Road Test (1958-1960)

    Wholly empirical Included 368 concrete and 468 asphalt sections | focus was highway pavement

  • Subgrade = Clay Soil

    Necessary Thickness was Guessed!

  • Max Single Axle

    Max Tandem Axle

    Sections Loaded for 2 Yrs | 1.1 Mil Reps

  • Performance Estimated Subjectively

    Present Serviceability Index (PSI)4.0 5.0 = Very Good3.0 4.0 = Good2.0 3.0 = Fair1.0 2.0 = Poor0.0 1.0 = Very Poor

    Failure at the Road Test considered @ 1.5

    Typical U.S. state agency terminal serviceability in practice = 2.5

  • Note on Inference Space of 93

  • Data Limits(AASHO Road Test)

    CurrentDesigns>100 million

    1.1mil

    AXLE LOAD REPETITIONS

    PAVEM

    ENT

    THIC

    KN

    ESS

    Current design traffic is far beyond AASHO road test limits

  • Dont Just Take My WordThe current design guide and its predecessors were largely based on design equations empirically derived from the observations AASHTOs predecessor made during road performance tests completed in 1959-60. Several transportation experts have criticized the empirical data thus derived as outdated and inadequate for todays highway system. In addition, a March 1994 DOT Office of Inspector General report concluded that the design guide was outdated and that pavement design information it relied on could not be supported and validated with systematic comparisons to actual experience or research.

    this is why Pavement ME exists!

  • ++

    +++=

    46.8

    7

    )1(10*624.11

    5.15.406.0)1(*35.7*)(

    D

    PSILogDLogsZESALLog oR

    +

    25.075.0

    75.0'

    )/(42.18**63.215

    )132.1(***)*32.022.4(

    kEDJ

    DCSLogp

    c

    dct

    Standard Normal Deviate

    OverallStandard Deviation Thickness

    Change in Serviceability

    Terminal Serviceability

    DrainageCoefficient

    Load Transfer

    Modulus ofRupture

    Modulus of Elasticity

    Modulus ofSubgrade Reaction

    1986-93 JPCP AASHTO 93 Equation

    Traffic

  • MEPDG / DARWin-ME /AASHTOWare Pavement ME

  • Pavement ME Design

    Not perfect & not intended to be a final productComplex and relatively costlyFor highways and NOT street, road, parking lot, etc.

    =+Mechanistic Calculation

    of Responses

    Empirical Tie to

    Ground

    Pavement Performance Prediction

  • JPCP Calibration BIG INF. SPACE!

    LTPP GPS-3 & RPPR JPCP Sections LTPP SPS-2, MnROAD, & AASHO JPCP Sections

  • AASHTO 93 vs. ME

    AASHTO Pavement ME

    AASHTO 93

    50+ million load reps

    1.1 million load reps

    Wide range of structural and rehabilitation designs

    Limited structural sections

    1 climate/2 years

    All climates over 20-50 years

    1 set of materials

    New and diverse materials

  • Sounds Easy Enough, Right?

  • INPUTS, INPUTS, INPUTS!!!!

  • INPUTS, INPUTS, INPUTS!!!!

  • OUTPUTS, OUTPUTS, OUTPUTS!!!

  • Some Agencies Trying to Simplify

    Note the inputs that have been deemed worth

    varying

    designers have a new

    idea of what

    matters!

  • ACPA StreetPave

    acpa.org/streetpave

  • ACPA StreetPave

    Roots date back to the 1960s PCA MethodTailored for streets and roadsFailure modes are cracking and faulting

  • Total trucks in design lane over the design life calculated from trucks/day (2-way), traffic growth rate (%/yr), design life (yrs), directional distribution (%) and design lane distribution (%)

    Traffic Spectrum + CountsSingle Axles

    Axle Load (kip) Axles/1,000 Trucks34 0.1932 0.5430 0.6328 1.7826 3.5224 4.1622 9.6920 41.8218 68.2716 57.07

    Tandem AxlesAxle Load (kip) Axles/1,000 Trucks

    60 0.5756 1.0752 1.7948 3.0344 3.5240 20.3136 78.1932 109.5428 95.7924 71.16

  • Equivalent stress at the slab edge:

    Me = equivalent moment, psi; different for single, tandem, and tridem axles, with and without edge support - func on radius of relative stiffness, which depends on concrete modulus, Poissons ratio, and thickness and the k-value

    hc = pavement thickness, in.f1 = adjustment for the effect of axle loads and contact areaf2 = adjustment for a slab with no concrete shoulderf3 = adjustment to account for the effect of truck (wheel) placement at the slab edgef4 = adjustment to account for approximately 23.5% increase in concrete strength

    with age after the 28th day and reduction of one coefficient of variation (COV) to account for materials variability

    Traffic Loads Generate Stresses

    =6

    2 1 2 3 4

  • Stress Ratio (SR) = Stress / Concrete Strength

    Limit Stress Ratio to Allow Design Reps

    0.4

    0.5

    0.6

    0.7

    0.8

    0.9

    1

    1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 1.E+09 1.E+10

    Stre

    ss R

    atio

    Repetitions

    Fatigue Data

    StreetPave R=95%

    Inference space normalized to SR

    StreetPavemakes slab thicker to limit stress ratio low enough to achieve the design traffic repetitions

  • A Conservative Approach!

    StreetPave fatigue calculation should be conservative relative to ME Design because:

    Size Effects Slabs have a greater fatigue capacity than beamsSupport The beam test has a k-value for support of 0 psi/in.!

    L/3Span Length = L

    d=L/3

    versus

  • Faulting Design in StreetPave

    If dowels used, faulting mitigated & fails by cracksNo faulting data collected at the AASHO road test so model developed in 1980s using field performance data from WI, MN, ND, GA, and CASimilar to cracking models, the pavement is made thicker, as necessary, until faulting model predicts that the pavement will not fail by faulting during the design lifeStreetPavesweak point

  • StreetPave Accepted in MN

    http://www.dot.state.mn.us/stateaid/admin/memos/12-sa-03.pdfhttp://www.dot.state.mn.us/research/documents/201210.pdf

  • And Its Use is Growing!

    Also approved in VA and many other state, city, and county engineers are using it in the U.S.StreetPave used in design tables in:

    ACI 325 and 330 documentsDr. Norb Delattes textbook Concrete Pavement Design, Construction, and Performance

    Internationally, used in Australia, Portugal, Mexico, Uruguay, Argentina, Chile, etc.

  • StreetPave | Project Details

  • StreetPave | Traffic Details

  • StreetPave | Design Details | General

  • StreetPave | Design Details | Concrete

  • StreetPave | Design Results

  • StreetPave | Design Report

  • Comparison of Results and U.S. Trends

  • 100

    125

    150

    175

    200

    225

    250

    275

    300

    325

    350

    4

    5

    6

    7

    8

    9

    10

    11

    12

    13

    14

    - 10,000,000 20,000,000 30,000,000 40,000,000 50,000,000

    Requ

    ired

    Thic

    knes

    s (m

    m)

    Requ

    ired

    Thic

    knes

    s (in

    .)

    Design Lane ESALs

    AASHTO 93 (ACPA WinPAS)

    AASHTOWare Pavement ME @ ORD

    AASHTOWare Pavement ME @ PHX

    ACPA StreetPave

    Doweled JPCP Thickness Comparison

    remember AASHTO 93 limit?

  • Top 10 ME Design Most Sensitive

    1. Concrete Flexural Strength at 28-Days2. Concrete Thickness3. Surface Shortwave Absorptivity (SSA)4. Joint Spacing5. Concrete Modulus of Elasticity at 28-Days6. Design Lane Width with a 14 ft (4.3 m) Widened Slab7. Edge Support via Widened Slab8. Concrete Thermal Conductivity9. Concrete Coefficient of Thermal Expansion (CTE)10. Concrete Unit Weight

    Red = only ME Design input the VALUE of the software!Blue + Bold = common for all

  • 100

    125

    150

    175

    200

    225

    250

    275

    300

    325

    350

    4

    5

    6

    7

    8

    9

    10

    11

    12

    13

    14

    400 450 500 550 600 650 700 750 800

    Requ

    ired

    Thic

    knes

    s (m

    m)

    Requ

    ired

    Thic

    knes

    s (in

    .)

    Concrete Flexural Strength (psi)

    AASHTO 93 (ACPA WinPAS)

    AASHTOWare Pavement ME @ ORD

    AASHTOWare Pavement ME @ PHX

    ACPA StreetPave

    Flexural Strength Sensitivity

  • 100

    125

    150

    175

    200

    225

    250

    275

    300

    325

    350

    4

    5

    6

    7

    8

    9

    10

    11

    12

    13

    14

    3,000,000 3,500,000 4,000,000 4,500,000 5,000,000 5,500,000 6,000,000

    Requ

    ired

    Thick

    ness

    (mm

    )

    Requ

    ired

    Thick

    ness

    (in.

    )

    Modulus of Elasticity (psi)

    AASHTO 93 (ACPA WinPAS)

    AASHTOWare Pavement ME @ ORD

    AASHTOWare Pavement ME @ PHX

    ACPA StreetPave

    Modulus of Elasticity Sensitivity

    in reality, need

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