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Preliminary Results from the “Th

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Preliminary Results from the “Th Powered By Docstoc
					 Load Proximity Correlation of
Dynamic Strain Measurements in
      Concrete Pavement

2nd International Conference on Accelerated Pavement Testing
                     September 29, 2004


                   Tom Burnham, P.E.
              Minnesota Department of Transportation
                        Office of Materials
        Acknowledgements
• Mn/DOT Research staff
• MnROAD site staff
• Minnesota Local Road Research Board
  (LRRB)
             OUTLINE
• BACKGROUND

• STUDY OBJECTIVES

• MnROAD PROJECT TEST CELLS

• DATA COLLECTION AND ANALYSIS

• SELECTED RESULTS

• CONCLUSIONS & RECOMMENDATIONS
                 BACKGROUND
• Next generation of pavement design methods require
  calibration

• Need to match load response from finite element
  models with field measured responses

• Magnitude of response measured by sensor
  controlled by proximity of tire load

• Tire load wander can occur:
   – Naturally = Truck driven over test slabs
   – Programmed = Computer controlled APT devices
                BACKGROUND
• Minnesota Road Research Project (MnROAD) has
  conducted seasonal load response testing on PCC
  pavements since 1996

• Tire wander recorded, but only loads directly over
  sensor have been utilized in analysis

• Need for a representative model for defining the
  effects of tire wander on dynamic strain
  measurements in concrete pavement
           STUDY OBJECTIVES
• Utilize full-scale truck testing at MnROAD to
  develop correlation between dynamic strain and
  tire load wander

• Determine the effects of slab temperature
  gradients on the correlation curves
           MnROAD TEST CELL 52
• Became part of MnROAD low-volume road test loop
  in June 2000

• Duplicates one of the interstate designs on the
  “mainline” test road

• Allows for more frequent and controlled testing

• Refined sensor layout based on lessons learned at
  MnROAD
       CELL 52 DESIGN DETAILS
• 190 mm (7.5 inches) jointed plain concrete
   – 178 mm (5 inches) gravel base layer
   – silty-clay subgrade
• 4.6 m (15 feet) long slabs
• 4.0m (13 feet) and 4.3 m (14 feet) lane (tested)
  widths
• 25mm (1 inch) diameter dowels, non skewed
  joints
• Gravel shoulders
• Load response and environmental sensors
                CELL 52 SENSORS
• Dynamic Strain in PCC
   – Tokyo Sokki model PML-60 molded strain gages


• Static Strain in PCC
   – Geokon VCE 4200 vibrating wire strain gages
      • Includes thermistor


• Temperature in all layers
   – Type “T” thermocouples
        DATA COLLECTION

• Testing on morning of May 23, 2003
• MnROAD truck moved laterally across panels
   – 5 axle truck and trailer
   – 355 kN (80k) load configuration
• Test speed was 8 kph (5 mph)
   – quasi-static for future comparison with FEM models
• Tire offsets monitored using video camera
• Environmental data automatically collected every
  15 minutes
            AUTOMATIC TRIGGER AND
               CAMERA SYSTEM
• Data collection automatically triggered using traffic counter hoses
• Tire offset measurements collected using a video camera system
   MnROAD FACTOID:

There are still 366 Thermocouples in PCC
  tests cells, collecting data every 15
  minutes.
That’s 35,136 temperature readings every
 day
Or 12,824,640 readings every year!
           DATA ANALYSIS

• Dynamic strain data
  – CE sensors (strain in transverse direction)

   – Responses from steering axle (#1) and tandem
     drive axles (#2 and #3)

   – Data extrapolated to slab surfaces
      • sensor depths approximate
          DATA ANALYSIS

• Slab temperature gradients
   – Three time periods considered

   – Linear temperature gradients
     Ranges:      -0.21 to –0.16 oC/cm
                  -0.01 to 0.19
                   0.40 to 0.48
                                 SLAB TEMPERATURE PROFILES
                                         May 23, 2003
                            0
                            -2
Depth below surface (cm)




                            -4
                            -6
                            -8
                           -10
                           -12
                           -14
                           -16
                           -18
                           -20
                                 5     10             15             20   25
                                              Slab Temperaure (C)

                                            5:55     8:10    10:26
             DATA ANALYSIS
• Tire Positions
   – Lateral offset measured relative to center of tire nearest
     shoulder or roadway centerline

• Axle positions
   – Position A near leave side of transverse joint
   – Position B middle of slab
   – Position C near approach side of transverse joint

• Position codes
     1-A-P1 = axle 1, position A, test panel 1
TRUCK TIRE LAYOUT
A   B   C   A   B   C
           DATA ANALYSIS

• Development of correlation curves
  – Plotted measured dynamic strain versus tire
    load offset
  – Found bivariate least squares lines using
    JMPTM statistical software
  – ANOVA and Students t-test to significance
    level of 0.05
  – Optimization of coefficients and elimination of
    variables not performed
                                                SAMPLE BEST-FIT CURVE
                                                                           AXLE 1
                          25


                          20

                                                                                            52CE01
                          15


                          10
Dynamic Strain (10 - 6)




                                     y = -0.001671x 3 + 0.611718x 2 - 73.2296x + 2862
                           5
                                     R2 = 0.97, RMSE = 2.21

                           0


                           -5


                          -10


                          -15


                          -20


                          -25
                                85         90      95      100     105     110     115   120       125   130   135   140

                                                           Offset from Roadway Centerline (inches)

                                                                 7:30 - 9:00 AM          Best-fit line
                                          SAMPLE BEST-FIT CURVE
                                                                             AXLE 2
                          25


                          20

                                                                                               52CE43
                          15


                          10
                                     y = -0.000573x3 + 0.079726x2 - 2.7937x + 8.51
Dynamic Strain (10 - 6)




                                      2
                                     R = 0.98, RMSE = 1.57
                           5


                           0


                           -5


                          -10


                          -15


                          -20


                          -25
                                20         25       30        35        40           45   50          55       60   65   70

                                                             Offset from Roadway Centerline (inches)

                                                                   10:00 - 11:00 AM            Best-fit line
  LOAD PROXIMITY CORRELATION
• Best-fit correlation curves and equations
  – Categorized by axle position
  – Compiled into tables and graphs
  – Polynomial least squares lines
     y = ax4 +bx3 + cx2 +dx + e
  – Second and third order polynomial equations
    dominant
  – High R2 values, and RMSE values of 1 to 3
    microstrain
LOAD PROXIMITY CORRELATION
• Offset range
  – Valid tire offset range for given equation
  – Approximately ± 1.5 feet (46 cm) in
    wheelpaths and ± 2 feet (61 cm) near shoulder
  – Correlation equations not valid outside given
    range
                  SAMPLE CORRELATION TABLE
                                           SLAB POSITION A
                                 Offset                                                  (b)
Position                                             Correlation equation coefficients
           Sensor                Range
     (a)                                                                                                      2
Code         ID   Test Period     (in)      a            b             c           d              e          R      RMSE
1-A-P1      CE43    5:20-6:20    24-68                -1.735E-03    0.251532    -11.0725         139.849   0.9783    1.29
                    7:30-9:00    24-63                -1.783E-03    0.256954    -11.3493         143.171   0.9332    2.00
                  10:00-11:00    26-66                -1.596E-03    0.238130    -10.8200         139.015   0.9665    1.65
1-A-P1      CE45    5:20-6:20   98-137                -2.073E-03    0.747836    -88.3510        3417.079   0.9893    1.32
                    7:30-9:00   94-134                -1.401E-03    0.513906    -61.6212        2408.813   0.9884    1.19
                  10:00-11:00   102-137                                           0.8756        -111.223   0.9733    1.71
1-A-P3      CE12    5:20-6:20   98-137                2.475E-03    -0.903642    108.1096       -4235.093   0.9823    1.88
                    7:30-9:00   94-134                1.457E-03    -0.542139     65.8054       -2599.710   0.9618    2.52
                  10:00-11:00   102-137                                          -0.9853         123.659   0.9173    3.50
2-A-P1     CE43     5:20-6:20    26-67                -1.128E-03    0.154787   -5.9955    56.187           0.9926   1.07
                    7:30-9:00    26-67                -6.340E-04    0.092499   -3.5437    22.305           0.9822   1.60
                  10:00-11:00    26-67                -5.730E-04    0.079726   -2.7937     8.508           0.9811   1.57
2-A-P1     CE45     5:20-6:20   94-133                              0.057680 -12.5364    661.703           0.9895   1.09
                    7:30-9:00   97-138                              0.045319 -10.0667    535.371           0.9621   2.28
                  10:00-11:00   94-138                -1.095E-03    0.427262 -54.1725   2219.474           0.9429   2.63
2-A-P3     CE12     5:20-6:20   94-133    8.80E-05    -3.856E-02    6.265224 -446.6249 11799.023           0.9664   1.30
                    7:30-9:00   97-138                 2.227E-03   -0.816159   98.5905 -3905.305           0.9675   1.54
                  10:00-11:00   94-138                 1.552E-03   -0.571975   69.3982 -2751.533           0.9487   1.69
3-A-P1     CE43     5:20-6:20    26-67                -1.238E-03    0.164655   -6.0201    46.675           0.9952   1.02
                    7:30-9:00    26-67                -8.000E-04    0.115158   -4.4322    29.690           0.9894   1.38
                  10:00-11:00    26-67                -1.102E-03    0.151961   -5.8041    44.170           0.9933   1.10
3-A-P1     CE45     5:20-6:20   94-133                              0.053089 -11.4758    602.414           0.9819   1.40
                    7:30-9:00   97-138                              0.041143   -9.0615   475.465           0.9707   1.96
                  10:00-11:00   94-138                -8.720E-04    0.345006 -44.1611   1817.352           0.9361   2.61
3-A-P3     CE12     5:20-6:20   94-133                             -0.066142   14.4217  -764.557           0.9738   1.93
                    7:30-9:00   97-138                             -0.056040   12.5632  -679.724           0.9457   3.12
                  10:00-11:00   94-138                -4.240E-04    0.103052   -7.0723   117.388           0.9835   1.45
                                    SAMPLE CORRELATION CURVES
                                               AXLE 2, POSITION A, PANEL 1
                         20

                                                          52CE43                     52CE45
                         15


                         10


                          5
Dynamic Strain (10 -6)




                          0


                          -5


                         -10


                         -15


                         -20


                         -25


                         -30
                               20    30   40    50       60     70     80     90     100      110   120    130   140

                                                     Offset from Roadway Centerline (inches)

                                                52CE43 5:20-6:20 AM                52CE45 5:20-6:20 AM
                                                52CE43 7:30-9:00 AM                52CE45 7:30-9:00 AM
                                                52CE43 10:00-11:00 AM              52CE45 10:00-11:00 AM
    CORRELATION AT POSITION A
• Approximately 6 inches (15 cm) from leave side
  of transverse joint
   – Example: Axle 2, Sensors CE43 and 45
   – Compressive response (top of slab)
   – Response more compressive as slab
     temperature gradient and time of day increase
   – Maximum response does not occur when
     reference point at location of sensor
       • Dual tire and slab shape effects
                          POSITION A CORRELATION CURVES
                                                        AXLE 2, PANEL 1
                         20

                                                        52CE43                     52CE45
                         15


                         10


                          5
Dynamic Strain (10 -6)




                          0


                          -5


                         -10


                         -15


                         -20


                         -25


                         -30
                               20   30   40   50       60     70     80     90     100      110   120    130   140

                                                   Offset from Roadway Centerline (inches)

                                              52CE43 5:20-6:20 AM                52CE45 5:20-6:20 AM
                                              52CE43 7:30-9:00 AM                52CE45 7:30-9:00 AM
                                              52CE43 10:00-11:00 AM              52CE45 10:00-11:00 AM
    CORRELATION AT POSITION B
• Midway between transverse joints
  – Example:
    Axle 3, sensors CE38 (bottom) and 39 (top)
  – Responses, tensile or compressive, increase
    with increase in slab temperature gradient and
    time of day
  – Maximum response does not occur when
    reference point at location of sensor
                                     POSITION B CORRELATION CURVES
                                                              AXLE 3, PANEL 1

                          25
                                                                        52CE38
                          20
                                                                                      52CE39

                          15
Dynamic Strain (10 - 6)




                          10


                           5


                           0


                           -5


                          -10


                          -15
                                95    100   105   110   115     120     125   130     135    140   145      150   155

                                                    Offset from Roadway Centerline (inches)

                                                  52CE38 5:20-6:20 AM               52CE39 5:20-6:20 AM
                                                  52CE38 7:30-9:00 AM               52CE39 7:30-9:00 AM
                                                  52CE38 10:00-11:00 AM             52CE39 10:00-11:00 AM
    CORRELATION AT POSITION C
• Approximately 6 inches (15 cm) from approach
  side of transverse joint
   – Example: Axle 1, Sensors CE01 (top) and
     02 (bottom)
   – Tire offset locations between centerline and
     sensors show little change in response with
     changing slab temperature gradient
   – Tire offset locations between sensors and
     shoulder are very dependent on changes in slab
     temperature gradient
                                 POSITION C CORRELATION CURVES
                                                         AXLE 1, PANEL 3

                          30

                                                                                  52CE01 / 52CE02

                          20
Dynamic Strain (10 - 6)




                          10



                           0



                          -10



                          -20



                          -30
                                90   95   100      105     110        115   120       125     130      135   140

                                                  Offset from Roadway Centerline (inches)

                                                52CE01 5:20-6:20 AM            52CE02 5:20-6:20 AM
                                                52CE01 7:30-9:00 AM            52CE02 7:30-9:00 AM
                                                52CE01 10:00-11:00 AM          52CE02 10:00-11:00 AM
  MEASUREMENT REPEATABILITY
• Correlation equations and curves only valid if
  data is repeatable
   – Between sensors at similar locations:
      CE39, panel 1 and CE07 panel 3
   – Between axles:
      CE03, axles 2 - 5
   – Both cases show good repeatability
   – More sensitive to magnitude of loading than
     proximity of neighboring tandem axle
                         CORRELATION CURVE REPEATABILITY
                                        AXLE 3, POSITION B, PANELS 1 & 3
                         25

                                                          52CE07 / 52CE39
                         20


                         15
Dynamic Strain (10 -6)




                         10


                          5


                          0


                          -5


                         -10


                         -15


                         -20
                            115   120      125      130          135        140      145          150   155

                                             Offset from Roadway Centerline (inches)

                                           52CE07 5:20-6:20 AM              52CE39 5:20-6:20 AM
                                           52CE07 7:30-9:00 AM              52CE39 7:30-9:00 AM
                                           52CE07 10:00-11:00 AM            52CE39 10:00-11:00 AM
                          CORRELATION CURVE REPEATABILITY
                                           AXLES 2-5, POSITION B, PANEL 3
                          15

                                                      52CE03
                          10


                           5
Dynamic Strain (10 - 6)




                           0


                           -5


                          -10


                          -15


                          -20


                          -25


                          -30
                                90   95   100   105      110   115    120    125     130    135     140   145

                                                Offset from Roadway Centerline (inches)

                                                Axle 2 7:30-9:00 AM           Axle 3 7:30-9:00 AM

                                                Axle 4 7:30-9:00 AM           Axle 5 7:30-9:00 AM
              CONCLUSIONS
• Best-fit equations and curves developed for
  correlating dynamic strain to tire load proximity
• Polynomial trendlines very good fit with data in all
  cases
• Dynamic strain responses increase as slab
  temperature gradients increase
• Maximum dynamic strain response does not occur
  when reference point at location of sensor
   – Could be used to better locate sensors in future
• Strong repeatability in measured dynamic strain
  response
      RECOMMENDATIONS
• Analyze more data
  – Additional panel locations
  – More slab temperature gradient conditions

• Perform similar study using FEM models
  Thank you




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