3 Common Thickness Design Methods and How They Compare

Common Thickness Design Methods and How They Compare

Concrete Pavement Design Seminar

December 18, 2014

Robert Rodden, P.E.Senior Director of

Pavement Technology

Design Methods

Countries with Concrete Pavements

ArgentinaAustraliaAustriaBelgiumBoliviaBrazilCanadaChileChinaCosta RicaCzech RepublicDominican RepublicEcuadorEl SalvadorFranceGermanyGhana

GuatemalaHondurasIndiaIndonesiaIranItalyJapanKenyaKingdom of BahrainMexicoNetherlandsNew ZealandNicaraguaNorwayPakistanPeruPoland

PortugalPuerto RicoRussiaSouth AfricaSouth KoreaSpainSwedenSwitzerlandTaiwanThailandTurkeyUruguayUnited KingdomUSA ACPAs apps.acpa.org has been accessed in over 140 countries!

Certainly we have many design methods!!!

SOME of the Design Variety

AASHTOWare Pavement ME USA, Canada

AASHTO 93/WinPAS USA, Canada, most of South & Central America, etc. TCPavements OptiPave Chile, Guatemala, PerucncPave South Africa VENCON2.0 Belgium, NetherlandsCustom Catalog Germany, India, Poland

ACPA StreetPave (previously the PCA Method)

Australia, Portugal, USA (approved in MN and VA), Canada, Uruguay

IP-07/2004 BrazilCHAUSSEE2 CanadaFAARFIELD, AirPave, ACI 330, BCOA, CO 6x6x6, custom method, etc. USA

US Practices are Changing

Summary of State Agency practice in 2005:

At the end of 2013, 41 state agencies had performed ME Design calibration and implementation efforts, indicating a relatively quick shift from AASHTO 93.

Design Method Used

Percent of Responding Agencies State Agency

AASHTO 72/86/93 85%

AR, AZ, DE, FL, ID, IN, IA, KS, MD, MI, NV, NC, OH, OK, SC, SD, TN, UT, VA, WA, WV, WI, WY

AASHTO MEPDG 4% MOPCA Method 11% HI, IN, IA

State-Developed 7% IL, MT

U.S. Roadway Length (lane miles)

State Agency,

19%

County, 44%

Town, 32%

Other, 1% Federal, 3%

Source: HM-10, 2012 FHWA Highway Statistics

AASHTO tools are being developed for these owners

City, county, and other local engineers need

to decide what to use locally because

Pavement ME will not trickle down due to its

cost and complexity!

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

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

JRCP is not supported in the modern design methods!

AASHTO 93/WinPASacpa.org/winpas

AASHO Road Test (1958-1960)

Included 368 concrete and 468 asphalt sections | focus was highway pavementDesign first introduced in 62, revised several times thereafter until 93 version

Typical AASHO Loop Layout

Tangent = 6,800ft (2km)368 rigid sections 468 flexible sections

Subgrade = Clay Soil

AASHO Test Traffic

Max Single Axle

Max Tandem Axle

Performance Metric

Some AASHO Results Loop 2

1,114,000 load applications to end

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

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!

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46.8

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PSILogDLogsZESALLog oR

Standard Normal Deviate

OverallStandard Deviation Thickness

Change in Serviceability

Terminal Serviceability

DrainageCoefficient

Load Transfer

Modulus ofRupture

Modulus of Elasticity

Modulus ofSubgrade Reaction

1986-93 Concrete Pavement Equation

10 Inputs.Solve for 11th

Traffic

WinPAS Makes it Easy

MEPDG / DARWin-ME /AASHTOWare Pavement ME

AASHTOWare Pavement ME Design

15+ years in the makingDesign method and software not perfect; not intended to be a final productComplex and relatively costlyModels not for streets, roads, parking lots, etc.

=+Mechanistic Elements

Empirical Elements

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? MECHANISTIC -

EMPIRICAL

INPUTS, INPUTS, INPUTS!!!!

Notes on ME ESALs

Output in a .txt file and not included on reportTRB 2014:

Approaches to Relate Cumulative Traffic Loading to Performance for Pavements Designed Using MEPDGInvestigation of ESALs vs. Load Spectra for Rigid Pavement Design

ESALs/Truck TTC 1 1.69TTC 2 1.57TTC 3 1.82TTC 4 1.43TTC 5 1.90TTC 6 1.26TTC 7 1.63TTC 8 1.83TTC 9 1.16

TTC 10 1.46TTC 11 1.85TTC 12 1.05TTC 13 1.55TTC 14 0.83TTC 15 1.04TTC 16 1.33TTC 17 1.03

Whats the Concern in ME?

Just as rigid and flexible ESALs are different because of their different response

Single, tandem and tridem axle groups (and at differing loads) cause differing relative damages

Single-axles usually cause more fatigue damageTandem and tridem axles usually cause more erosion damage

so even within just rigid pavement design, ESAL count for same traffic spectrum and # of trucks in the design lane is really different for each distress type modeled!?!

OUTPUTS, OUTPUTS, OUTPUTS!!!

Simpler ME Option: MnDOT

Drainage in ME Design

The current state of the art is such that conclusive remarks regarding the effectiveness of pavement subsurface drainage or the need for subsurface drainage are not possible.

so we must rely on field studies: Subbase stiffness matters more than

drainage for JPCP performance Although excess moisture and poor

drainage was shown to be detrimental to pavement performance in the past, current designs are less susceptible to moisture damage (thicker sections, improved materials, widespread use of dowels, etc.)

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

Implementation in the US @ Jan 2014

Implementation work underway

Nearing Implementation

No Plans / No information

Using Pavement-ME

AlaskaHawaii

8 states have either fully or partially implemented

StreetPave/PCA Methodacpa.org/streetpave

StreetPaves Origins

PCA thickness design methodology for JPCPfirst published in 1966

used slab stress/fatigue asthe sole design criterionfor determining thickness

updated in 1984failure by erosion (pumping)edge support

ACPA Has Advanced the Design

StreetPaveTailored for streets and roadsImprovements included:

Enhanced concrete fatigue model w/reliability componentAbility to analyze tridem axles in the traffic spectrumSide-by-side design comparison to asphalt sections (MS-1)Inclusion of fibers in all concrete designsACI 330 traffic spectrumsOverlay designs..

Failure Modes Considered

FAULTINGCRACKING

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 Loads + # of RepetitionsSingle 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

2 1 2 3 4

Stress Ratio (SR) = Stress / Concrete Strength

Meet Design Reps by Limiting Stress Ratio

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 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 Asphalt Design

Per Asphalt Institutes MS-1Reliability considered as modifier of soil strength (see ACPAs R&T Update 9.01, StreetPaves Equivalent Design of Asphalt Proof of the Accuracy of StreetPaves Asphalt Module)Failure predefined according to Asphalt Institute at 20% cracking in the wheelpaths

Comparison of Software

Example with ME Design defaults

JPCP w/ 6 in. (150 mm) crushed stone on a A-7-6 subgrade with defaults except subbase thicknessAll traffic @ default valuesWeather @ Chicago (ORD)

@ Phoenix (PHX)

Passes with 1.5 (38 mm) dowels

Example with ME Design defaults

Conducted WinPAS/AASHTO 93 and StreetPave designs alongside for comparison

Used default values from ME Design as inputs where possibleIf ME Design variable not available, used typical defaultIn ME, also turned Sealant on and Erodibility Index to 2For k-value, used dynamic k-value to get static k-value

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

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iredTh

ickn

ess(mm)

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iredTh

ickn

ess(in.)

DesignLaneESALs

AASHTO93(ACPAWinPAS)

AASHTOWarePavementME@ORD

AASHTOWarePavementME@PHX

ACPAStreetPave

Example with defaults - DOWELED

remember AASHTO 93 limit?

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DesignLaneESALs




ACPAStreetPave

Example with defaults - UNDOWELED

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

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400 450 500 550 600 650 700 750 800

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ConcreteFlexuralStrength(psi)




ACPAStreetPave

Flexural Strength Sensitivity

(2.75 MPa) (5.5 MPa)

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

Requ

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m)

Requ

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ickne

ss(in.)

ModulusofElasticity(psi)




ACPAStreetPave

Modulus of Elasticity Sensitivity

in reality, need to change strength too!(20.7 GPa) (41.4 GPa)

0

25

50

75

100

0

0.5

1

1.5

2

2.5

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3.5

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

Thickn

essR

eductio

nw/EdgeSu

pport(m

m)

Thickn

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eductio

nw/EdgeSupp

ort(in.)

DesignLaneESALs




ACPAStreetPave

Thickness Reduction w/ Edge Support

Reliability is Very Different for Each

Damage

Dis

tres

s

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 DataStreetPave R=95%PCA

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Reliability




ACPAStreetPave

Reliability Sensitivity

Increasing k-value Doesnt Greatly Decrease the Required Thickness

Concrete pavement design thickness is relatively insensitive to support stiffness (modulus of subgrade reaction), so it is improper engineering to make a subgrade/subbase stronger or thicker in an attempt to decrease concrete pavement thickness

Analyses conducted in StreetPave

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Statickvalue(psi)




ACPAStreetPave

k-value Sensitivity

Very few designed for < 100

psi/in. (27

MPa/m)?

(136 MPa/m)

Get Your Software Loaded Up!

Documents

3 Common Thickness Design Methods and How They Compare