Reliability in Mechanistic-Empirical Pavement Design Guide Flexible Pavement Analysis Presented By: Manuel Ayres Jr., Ph.D. At: TRB Workshop 152 Date: Jan 21, 2007 S1SP ARA0127-1
Summary 1. MEPDG Performance Criteria 2. Components of Variability 3. Reliability Approaches 4. Input Variables 5. Calibration and Residuals 6. Modeling Variability 7. Advantages and Disadvantages of Current Approach 2
Reliability - Definition "The reliability of the pavement design-performance process is the probability that a pavement section designed using the process will perform satisfactorily over the traffic and environmental conditions for the design period." (AASHTO, 1993) 3
2006 Recalibration: : NCHRP 1-40D1 Recalibrated models for Bottom-Up, Top-Down and Transverse Cracking, Perm Deform and IRI. Improvement of database Added 4-5 years of data Additional climatic data Lower model error Sg backcalculated moduli Lower model errors Rational sensitivity to changes in inputs Improved reliability 4
MEPDG Performance Criteria Flexible Pavements Terminal IRI AC Surface Down Cracking AC Bottom Up Cracking AC Thermal Fracture AC Permanent Deformation Total Permanent Deformation 5
Components of Variability Design Factors Environment Traffic Materials Drainage characteristics Construction Materials Equipment Procedures Experience Performance Model errors Simplified assumptions Calibration data 6
Reliability Approaches Evaluated Monte Carlo Simulation Obtain probability distribution Number of simulation runs required is high Time to run is high Rosenblueth Procedure Number of iterations = 2 n (n is # of stochastic variables) First Order Second Moment (FOSM) Closed form solution Require partial derivatives Distribution of Residuals n f V[ f( x1, x2,... xn ) = V[ xi] x i= 1 i 2 7
Number of Input Stochastic Variables Level 3 Design Traffic 159+39*10*12+ 39*10*12+ 31*10*12+ 31*10*12+56 = 17015 Climate 19+5*24 = 139 Structure AC 14 Unbound 16 CTB 8 PCC - 13 Simple Pavement: AC + Base + Sg 17200 SV 8
Distribution of Residuals Predicted AC Rutting Actual AC Rutting 9
MEPDG Reliability Approach Estimated AC Rutting 1-R R AC Rutting Performance Criteria L R T1 1-R R 1-R Expected IRI R T0 R T 0 T 1 Time 10
Example MEPDG Output - Plot Permanent Deformation: Rutting 0.80 0.70 0.60 AC Rutting Design Value = 0.25 Total Rutting Design Limit = 0.75 SubTotalAC SubTotalBase SubTotalSG Total Rutting TotalRutReliability Total Rutting Design Limit 0.50 Rutting Depth (in) 0.40 0.30 0.20 0.10 0.00 0 12 24 36 48 60 72 84 96 108 120 132 Pavement Age (month) 11
Example MEPDG Output - Tabular Predicted Rutting: Project HMA-new Pavement Maximum R age Location Location Location Location mo yr Month AC1 (in) AC2 (in) AC3 (in) GB4 (in) SG5 1 0.08 October 0.0001 6 0.0032 0 0.0009 0 0.0193 0 0.0209 2 0.17 November 0.0001 6 0.0033 0 0.0009 0 0.0197 0 0.0216 3 0.25 December 0.0001 6 0.0033 0 0.0009 0 0.0197 0 0.0216 4 0.33 January 0.0001 0 0.0033 0 0.0009 0 0.0197 0 0.0216 5 0.42 February 0.0002 0 0.0034 0 0.0009 0 0.0197 0 0.0216 6 0.5 March 0.0003 0 0.0035 0 0.0009 0 0.0205 0 0.0229 7 0.58 April 0.0003 0 0.0043 0 0.0013 0 0.0282 0 0.0393 8 0.67 May 0.0003 0 0.0067 0 0.0019 0 0.0316 0 0.043 9 0.75 June 0.0008 6 0.0188 0 0.0039 0 0.0363 0 0.0474 10 0.83 July 0.0012 6 0.0256 0 0.0051 0 0.0377 0 0.0488 11 0.92 August 0.0013 6 0.0284 0 0.0056 0 0.0383 0 0.0493 Maximum Rutting (inch) Location Location SubTotalA SubTotalB SubTotalS Location TotalRutR SG5 (in) SG6 (in) C ase G Total (in) eliability 0.0209 0 0.0768 0 0.0042 0.0193 0.0977 0.1212 0 0.1754 0.0216 0 0.0844 0 0.0042 0.0197 0.106 0.13 0 0.1862 0.0216 0 0.0851 0 0.0043 0.0197 0.1067 0.1307 0 0.1871 0.0216 0 0.0851 0 0.0044 0.0197 0.1067 0.1308 0 0.1872 0.0216 0 0.0851 0 0.0045 0.0197 0.1067 0.1309 0 0.1873 0.0229 0 0.0852 0 0.0047 0.0205 0.1081 0.1333 0 0.1901 0.0393 0 0.1284 0 0.0059 0.0282 0.1676 0.2017 0 0.2714 0.043 0 0.139 0 0.0089 0.0316 0.182 0.2225 0 0.2951 0.0474 0 0.1452 0 0.0235 0.0363 0.1926 0.2524 0 0.3281 0.0488 0 0.1481 0 0.0318 0.0377 0.197 0.2665 0 0.3441 0.0493 0 0.1498 0 0.0353 0.0383 0.1991 0.2726 0 0.351 12
Bottom Up Fatigue Cracking 13
Bottom Up Cracking Distribution of Residuals Residuals 2500 Error (Predicted - Measured Cracking) 2000 1500 1000 500 0-4 -3-2 -1 0-500 1 2 3-1000 -1500-2000 -2500 Adjusted Damage 14
Bottom-Up Cracking Groups and Ranges 2003 Calibration 15
Top Down Cracking Se Model 16
GB Permanent Deformation Se = 0.1477 GBRut 0.67 17
AC Permanent Deformation SeRDAC = 0.24 ACrut 0.8026 18
Sg Permanent Deformation SeRDSG = 0.1235 SGrut 0.5012 19
Total Permanent Deformation 20
Top Down Cracking 21
IRI Models Flexible New or Rehab Flexible New or Rehab over PCC IRI = f(iri 0, Rutting, Fat. Crack, Transv. Crack, Site Factor) Site Factor = f(subgrade, Climate, Age) Subgrade: % fine sand, silt, clay & PI Climate: Freezing index, precipitation Age (cycles hot/cold, wet/dry, freeze/thaw) First-Order, Second-Moment (FOSM) method n f V[ f( x1, x2,... xn ) = V[ xi] x i= 1 i 2 22
HMA - Residuals for IRI 23
HMA over PCC - Residuals for IRI 24
Thermal Fracture Std.Dev (Thermal) = -0.0899 * Thermal + 636.97 25
Advantages & Disadvantages Advantages Improvement relative AASHTO 1993 Practical and more realistic Based on residuals from calibration May allow more economical design for local calibration Disadvantages Does not allow to evaluate change in performance due to differences in variability of individual factors Currently variability and reliability analysis does not depend upon level of design 26
MEPDG Reliability Approach Level 3 AC Rutting 1-R Rut f AC Rutting Performance Criterion 1-R Expected Rutting Rut T1 R T 1 Time 27
MEPDG Reliability Approach Level 1 Level 3 Calibration AC Rutting 1-R Rut AC Rutting Performance Criterion 1-R f Expected Rutting Rut T1 R T 1 Time 28
MEPDG Reliability Approach Level 1 Level 1 Calibration AC Rutting 1-R Rut f AC Rutting Performance Criterion Expected Rutting Rut T1 R T 1 Time 29
Thank You! 30