reliabilityinthemepdgonestatesperspective(pierce)(1 2007)

8/3/2019 ReliabilityintheMEPDGonestatesperspective(Pierce)(1 2007)

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Reliability in the MEPDG

One States Perspective

Linda Pierce, PE

State Pavements EngineerWSDOT

Transportation Research Board86th Annual Meeting

January 21, 2207


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Introduction

What level of reliability to use?

NCHRP 1-40 results

Reliability and pavement thickness

Thoughts on the reliability concept inMEPDG


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What values to use? 1993 AASHTO Guide definition

The actual number of ESALs to a terminalserviceability level is less than the predictedESALs

MEPDG definition Each key distresses will be less than the critical

distress level over the design period

The more important the project (consequencesof failure) the higher the reliability


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MEPDG Flow Diagram

Image courtesy of Scott Wilson Pavement Engineering LTD, NCHRP 1-40A(03) Final Report


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MEPDG Reliability Process

1. Input design parameters (traffic,

climate, structure, material properties)

2. User defines target distress conditions

at the end of the design period3. User defines reliability level

4. MEPDG estimates distress at the end

of the design year and determinespass or fail condition


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MEPDG Recommended Values

50-7550-75Local

70-8075-85Collectors75-9080-95Principal Arterial

80-9585-97Interstate

RuralUrbanFunctional Class


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Distress Types

Fatigue cracking (chemically

stabilized layer)

Minimum and maximum

crack spacing

Rutting HMA onlyLoad transfer (cracks)

Rutting total pavementCrack width (CRCP)Thermal crackingPunchouts

Bottom up crackingFaulting

Top down crackingTransverse crackingTerminal IRITerminal IRI

Flexible PavementRigid Pavement


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WSDOT Recommendation Until local calibration/validation can be

completed New Construction

75%Minor Arterial and Collector

85%Principal Arterial

95%Interstate

ReliabilityFunctional Class

Rehabilitation

Reliability = 50 percent


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NCHRP 1-40 Results

Rehabilitation design may be conducedat a greater level

Traffic, material properties, subgrade

moisture conditions, pavement distress canbe measured in the lab and field


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Global Calibration Hypothesis

Image courtesy of ARA


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NCHRP 1-40 Results For some deterioration modes there is more

calibration data at low levels of distress Variability for higher distress levels is likely to

be less reliable (based on fewer data points)

Until more calibration data (at varying distresslevels) is available, it is difficult to asses theeffects of reduced input variability and

therefore, reliability of the output parameters


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NCHRP 1-40 Results

The same standard deviations are used

for all design levels (except for thermalcracking)

No improvement in reliability when moreaccurate input parameters are used

Investigate the use of

Monte Carlo simulation techniques Other alternative methods


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NCHRP 1-40 Results

Insufficient data in the LTPP database to

determine the effect of input level on thecalibration error

Except for thermal cracking properties

Need to have accurate measure of pasttraffic loadings

Local calibration needed to confirm thenational calibration models


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NCHRP 9-30 Results

Use of performance data from carefully

controlled experiments (WesTrack,MnRoad, NCAT, FHWA-ALF) are moreuseful for model validation/calibration

Recalibrate MEPDG


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Reliability and Thickness Design

HMA Example

Level 1 and 3 analysis

40 year design

Reliability levels: 50 and 90


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Reliability and Thickness Design

Fail19.770.340.25Permanent Deformation (AC Only) (in):903

Fail02112100AC Thermal Fracture (ft/mi):903

Pass99.99940.9100AC Bottom Up Cracking (%):903

Fail13.23226.5172Terminal IRI (in/mi)903

Fail19.770.340.25Permanent Deformation (AC Only) (in):503

Fail02112100AC Thermal Fracture (ft/mi):503

Pass99.99940.9100AC Bottom Up Cracking (%)503

Fail13.23226.5172Terminal IRI (in/mi)503Comment

Reliability

Predicted

Distress

Predicted

Distress

TargetPerformance CriteriaR

Input

Level


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Thoughts on the ReliabilityConcept

Process used in the MEPDG is a starting

point Local calibration is essential

reliabilityinthemepdgonestatesperspective(pierce)(1 2007)

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