1) The presentation discussed mechanistic-empirical (M-E) pavement design and the use of axle load spectra (ALS) to characterize heavy traffic loading. 2) Data from Sweden's national weigh-in-motion sites in 2007 was analyzed to develop ALS for different roads. 3) M-E design allows estimating pavement performance over time by relating accumulated damage from traffic and climate to distress development. 4) More comprehensive ALS data is needed in Sweden to fully implement M-E design approaches.

1. Transportforum
Linköping
8-9 Januari, 2009
Modellering av vägars beteende – dimensionering och nedbrytning
Sigurdur Erlingsson

2. Overview
» M-E design of pavements
» Pavements response and performance
» ESAL vs. ALS
» BWIM
» ALS
» General
» Examples
» M-E analysis and performance predictions
» ALS Comparison
» Conclusions

3. Mechanistic – Empirical Design
» Mechanistically calculate pavement response (i.e.,
stresses, strains, and deflections) due to:
» Traffic loading
» Environmental conditions
» Accumulate damage over time
» Empirically relate damage over time to pavement distresses,
e.g.:
» Cracking
» Rutting
» Faulting
» Roughness
» Calibrate (validation) predictions to observed field
performance

4. M-E design of pavements
Traffic
Climate
Materials
Structure
Damage
Time
Response Distress
Damage Accumulation

5. Design criteria - rutting
40
30
20
10

6. ESAL vs. ALS
» In the ESAL approach all axle loads (different
magnitudes and number) are converted to an
Equivalent number of Single Axle Loads
based on the EALF representing the relative
damage of each axle to the damage of a
standard axle.
» In the M-E Design approach truck traffic
loadings are given in terms of Axle Load
Spectra (ALS). This is a more direct and
rational approach for the analysis and design
of pavement structures to estimate the effects
of actual traffic on pavement response and
distress.

7. The Swedish BWIM system
F(t)

8. The National Sites
» 12 locations (always 2 lanes)
» 1 week sampling (2007)
» No distinction between lanes
» Accuracy, errors, gaps, . . .
» Limitations
» Lane distribution
» Tyre pressure
» Single wheel vs. Dual wheel
National sites » Lateral wander

9. The National BWIM measurements in 2007
Road Station Name No of Time period No of No of
lanes vehicles axles
E4 Torsboda 1+1 2007-08-01 - 2007-08-07 7163 22390
E4N Mjölby 2 2007-04-13 - 2007-04-19 10766 39594
E4S Mjölby 2 2007-04-13 - 2007-04-19 8896 33025
motorways
E6N Löddeköping 2 2007-05-09 - 2007-05-15 15448 49795
E6S Löddeköping 2 2007-05-09 - 2007-05-15 16868 53489
E10 Grundträskån 1+1 2007-08-23 - 2007-08-30 1179 4223
E14 Torvalla 1+1 2007-08-03 - 2007-08-09 2123 6483
E18 Rådmansö 1+1 2007-06-21 - 2007-06-27 3739 13165
E20 Marieberg 2 2007-04-12 - 2007-04-19 8661 32861
E65 Skurup 1+1 2007-05-23 - 2007-05-29 6061 19266
Rv40W Landvetter 2 2007-05-24 - 2007-05-30 6596 20937
County Arterial
Rv40E Landvetter 2 2007-05-24 - 2007-05-30 7649 24742
trunk
Rv50 Gärdshyttan 1+1 2007-10-09 - 2007-10-18 6705 25767
Rv73 Västerhaninge 2 2007-09-26 - 2007-10-02 3166 7723
Lv373 Storlångträsk 1+1 2006-08-25 - 2006-08-31 674 2593
road

10. Axle Load Spectra
Steering axles
Single axles
Tandem axles
Tridem axles

11. Axle Load Spectra
25
8
Steering
20
Heavy vehicles
Frequency [%]
6
Frequency [%]
15
10
10 Single 4
8
Frequency [%]
5
6 2
0
0 50 4
100 150 6 0
Axle Weights [kN] Tandem 0 2 4 6 8 10 12 14 16 18 20 22 24
2 Hour
Frequency [%]
4
0
0 50 100 150
Axle Weights [kN] 2
6
Tridem
E4N Mjölby 0
Frequency [%]
4
0 50 100 150 200 250
Axle Weights [kN]
Steering 10766 2
Single 12420
Tandem 12052 0
Tridem 4356 0 50 100 150 200 250 300
Σ 39594 Axle Weights [kN]

12. 16
Axle Load Spectra 8
14 Steering
Heavy vehicles
12
Frequency [%]
6
Frequency [%]
10
8
16 4
6
14 Single
4
12 2
Frequency [%]
2
10
0
0
0 50 100 8 150
0 2 4 6 8 10 12 14 16 18 20 22 24
Axle Weights [kN] 6 8 Hour
4
Tandem
2 6
Frequency [%]
0
0 50 100 150
4
Axle Weights [kN]
25
2
Lv373 Storlångträsk 20 Tridem
Frequency [%]
0
15
Steering 674 0 50 100 150
Axle Weights [kN]
200 250
Single 466
10
Tandem 1431 5
Tridem 22 0
Σ 2593 0 50 100 150 200
Axle Weights [kN]
250 300

13. 25
ALS 2007 – All stations 16
E10 Grundträskån
E14 Torvalla Steering 14
E18 Rådmansö 16 12
20 E20 Marieberg
Frequency [%]
Single
10
E4 Torsboda
E4N Mjölby 10 8
E4S Mjölby
Frequenc y [% ]
15 E65 Skurup 12
E6N Löddeköping
6
Tandem
10 4
8
Frequency [%]
E6S Löddeköping
Tridem
Lv373 Storlångsträk 2
10 Rv40W Landvetter
8 0
Frequency [%]
Rv40E Landvetter 6 8 0 3 6 9 12 15 18 21 24
Rv50 Gärdshyttan
Rv73 Våsterhaninge Hour
5
Frequency [%]
4 4 6
0 2 4
0 20 0 40 60 80 100 120
0 20 40 60 80 100 120
Axle Weights [kN]
0 2
Axle Weights [kN]
0 50 100 150 200 250
0 Axle Weights [kN]
0 50 100 150 200 250 300
Axle Weights [kN]

14. ALS – Prediction
Station No of No of Ratio Singles/Steering Tandem/Steering Tridem/Steering
Road Name vehicles axles Axle/vehicle
E4 Torsboda 7163 22390 3.13 0.84 1.20 0.09
E4N Mjölby 10766 39594 3.68 1.15 1.12 0.40
E4S Mjölby 8896 33025 3.71 1.13 1.19 0.39
E6N Löddeköping 15448 49795 3.22 1.17 0.67 0.38
E6S Löddeköping 16868 53489 3.17 1.11 0.67 0.40
E10 Grundträskån 1179 4223 3.58 1.09 1.36 0.13
E14 Torvalla 2123 6483 3.05 1.02 0.98 0.05
E18 Rådmansö 3739 13165 3.52 1.23 0.87 0.42
E20 Marieberg 8661 32861 3.79 1.18 1.37 0.24
E65 Skurup 6061 19266 3.18 1.23 0.68 0.26
Rv40W Landvetter 6596 20937 3.17 0.94 0.89 0.35
Rv40E Landvetter 7649 24742 3.23 1.05 0.90 0.28
Rv50 Gärdshyttan 6705 25767 3.84 1.39 1.20 0.25
Rv73 Västerhaninge 3166 7723 2.44 1.01 0.39 0.04
Lv373 Storlångträsk 674 2593 3.85 0.69 2.12 0.03
Average 1.13 0.96 0.23

15. Performance Predictions and ALS
25 10 6 6
Steering Single Tandem Tridem
20 8
Frequency [%]
Frequency [%]
Frequency [%]
Frequency [%]
4 4
Each load 15
10
6
4
2 2
application 5
0
0 50 100 150
2
0
0 50 100 150
0
0 50 100 150 200 250
0
0 50 100 150 200 250 300
Axle Weights [kN] Axle Weights [kN] Axle Weights [kN] Axle Weights [kN]
Traffic
Rutting
AC
Modulus
Time
Granular Base
Modulus
Subgrade
Damage
Modulus
0 2 4 6 8
Time
Time, years

16. 25
ALS - Comparison
10 Steering
20
Single Motorway E4N
Frequency [%]
8 6
15 Mjölby
Frequency [%]
Tandem 6
6
10 Tridem Sweden
Frequency [%]
4
4
Frequency [%]
5 4
2
0 2
0 50 0100 150 2
Axle Weights [kN] 0 50 100 150
Axle Weights [kN] 0
0 50 100 0 150 200 250
Axle Weights0[kN] 50 100 150 200 250 300
Axle Weights [kN]
Highway 5
Redding, CA
USA

17. Conclusions
» The M-E Pavement design method represent a major
change in the way pavement design is performed.
» With the M-E design the performance of pavements can
be estimated.
» In M-E design of pavements Axle Load Spectra is used to
characterise the heavy traffic loading.
» A more comprehensive data sampling and analyses of
ALS is needed in Sweden if M-E pavement design will be
used in the future.
» ALS’s from USA(CA) are probably not representative for
Swedish conditions.