STRESS-IN-MOTION (SIM) RESULTS IN PAVEMENT DESIGN AND - - PowerPoint PPT Presentation

TOWARDS THE APPLICATION OF STRESS-IN-MOTION (SIM) RESULTS IN PAVEMENT DESIGN AND INFRASTRUCTURE PROTECTION

Morris De Beer, Colin Fisher (CSIR, Transportek) and Louw Kannemeyer (SANRAL)

Layout of Presentation

• Introduction;
• Stress-In-Motion (SIM) system;
• Pavement Modeling using 3 loading

cases;

• Concept of Normalised Contact Stress

(NCP);

• Conclusions and recommendations.

Introduction

• Protection of road infrastructure – major

challenge to RA’s;

• Africa: Inter - regional traffic – as much as 70 %
• ver loading;
• World wide: Road user charges - complex;
• Current tensions: Road Authorities vs private

sector interests.

• CHALLENGE TO US “TECHNOCRATS”

FOR SOLUTIONS !

Stress-In-Motion (SIM) system

• Description;
• Calibration and data acquisition;
• Typical Data and outputs;

–Normalised Contact Pressure (NCP); –Effect of tyre speed; –Pavement response-top down cracking;

Figure 1: Single SIM pad configuration (used under Heavy Vehicle Simulator (HVS) with single test tyre)

Figure 4: SAE sign convention used during SIM measurements. X-Longitudinal, Y-Lateral and Z -Vertical loads/stresses

• Tyre Rotation

+Z +X +Y

Direction

• f

Traffic

Instrumented Pins

356 mm 755 mm

pattern1.wmf

TOP VIEW OF THE VRSPTA MK II TYRE PATCH TYRE PATCH TYRE PATCH

425 /65 R22.5 HVS TYRE ON SIM SYSTEM: EXAMPLE OF FOOTPRINT TO FOLLOW…..

5-Axial Load Cell: [+/- X; +/- Y; Z]

SIM Measuring Pins- 3-Axial

Laboratory Calibration Issues “Pin by Pin ” calibration- Jig A

Laboratory Calibration Issues “In-Situ” calibration - Jig B

Typical Pin Calibration data

• 800
• 700
• 600
• 500
• 400
• 300
• 200
• 100

100 200 300 400 500 600 700 800

• 4
• 3
• 2
• 1

1 2 3 4 ENTRAN LOADCELL (NEWTONS) LOADCELL (VOLTS) X Y Z

3D LOADCELL PIN 10

LOADING IN "X" DIRECTION

• 800
• 700
• 600
• 500
• 400
• 300
• 200
• 100

100 200 300 400 500 600 700 800

• 4
• 3
• 2
• 1

1 2 3 4 ENTRAN LOADCELL (NEWTONS) LOADCELL (VOLTS) X Y Z

3D LOADCELL PIN 10

LOADING IN "Y" DIRECTION

100 200 300 400 500 600 700 800

• 0.5

0.5 1.5 2.5 3.5 4.5 ENTRAN LOADCELL (NEWTONS) LOADCELL (VOLTS) X Y Z

3D LOADCELL PIN 10

LOADING IN "Z" DIRECTION

+/- X - LOAD (kN) +/- Y - LOAD (kN) Z - LOAD (kN) VOLTS VOLTS VOLTS

315/80 R22.5 HVS TYRE ON SIM MK II

HVS 04 SIM MEASUREMENTS OF 11R22.5 TYRE

INFLATION PRESSURE Z - LOAD

Figure 2: Twin (or dual) SIM pad configuration (used under Heavy Vehicle Simulator (HVS) with dual test tyres)

Figure 2: Quad (full) SIM pad configuration at a typical weighbridge site on National Road 3 (N3), near Heidelberg in Gauteng.

In operation: Quad (full) SIM pad configuration at a typical weighbridge site on National Road 3 (N3), near Heidelberg in Gauteng.

In operation – SIM N3-TCC

In operation: SIM N3-TCC

Table 1 Example of loading cases

Case Cold Inflation Pressure (kPa) Single tyre Loading (kN) % of rated loading @ 720 kPa[1] Comments

1 720 20

• 20

Under- loaded

2 720 35 + 45

Overloaded

3 720 50 + 107

Extremely

• verloaded

[1] For this test tyre the rated load at 720 kPa = 24 kN

(a) Case 1: 20 kN, 720 kPa (b) Case 2: 35 kN, 720 kPa, (c) Case 1: 50 kN, 720 kPa

Figure 6: Static Tyre Foot Prints

• 20 %

+ 45 % + 107 %

SIM DATA USED FOR ANALYSIS

SIM DATA : VERTICAL STRESSD (Z)

SIM DATA : LATERAL STRESS (Y)

SIM DATA: LONGITUDINAL STRESS (X)

Loading Case Max Vert Stress: Z (kPa) Max Lat Stress: Y (kPa) Max Long Stress: X(kPa) 1 (n- shape) 953 191 102 2 (m- shape) 1189 209 185 3 (m- shape) 1486 261 210

Table 2: Maximum Stresses

NORMALISED CONTACT PRESSURE (NCP) Maximum Contact Stress @ load P Inflation Pressure (rated tyre load) NCP = NCPz - Vertical Stress; NCPx - Long. Stress; NCPy - Lateral Stress; Performance Based Standard ?

Load Case NCPZ NCPY NCPX 1 (n- shape) 1.32 0.27 0.14 2 (m- shape) 1.65 0.29 0.26 3 (m- shape) 2.06 0.36 0.29 Table 3: NCPs

NCPs cont.

NORMALISED CONTACT PRESSURE (NCP)- FREE ROLLING TYRE NCPi 0.5 1 1.5 2 2.5 10 15 20 25 30 35 40 45 50 55 TYRE LOADING (kN)

NCPz-VERTICAL NCPy-LATERAL NCPx-LONGITUDINAL

LIMITING NCPz = 1.5

Interface shear stresses (x,y) Lateral (X)shear stresses

• Long. (Y) shear stresses

425 /65 R22.5 HVS TIRE ON SIM SYSTEM: EXAMPLE OF FOOTPRINT TO FOLLOW…..

SHEAR STRESS (X-Y) EXCURSION - Single Tyre: 20 kN, 720 kPa (Test T472A)

• 300
• 200
• 100

100 200 300

• 200
• 150
• 100
• 50

50 100 150 200

X-Longitudinal Stress (kPa) Y-Lateral Stress (kPa)

Pin 3 Pin 5 Pin 9 Pin 12 Pins: 3 5 9 12

Tyre Tread

LATERAL (X-Y) STRESS EXCURSIONS

SHEAR STRESS (X-Y) EXCURSION - Single Tyre: 35 kN, 720 kPa (Test T772A)

• 300
• 200
• 100

100 200 300

• 200
• 150
• 100
• 50

50 100 150 200 X-Longitudinal Stress (kPa) Y-Lateral Stress (kPa) Pin 3 Pin 5 Pin 9 Pin 12 Pins: 3 5 9 12

Tyre Tread

LATERAL (X-Y) STRESS EXCURSIONS

SHEAR STRESS (X-Y) EXCURSION - Single Tyre: 50 kN, 720 kPa (Test T1072A)

• 300
• 200
• 100

100 200 300

• 200
• 150
• 100
• 50

50 100 150 200 X-Longitudinal Stress (kPa) Y-Lateral Stress (kPa) Pin 3 Pin 5 Pin 9 Pin 12 Pins: 3 5 9 12

Tyre Tread

LATERAL (X-Y) STRESS EXCURSIONS

Effects of Tyre Speed on contact stress

• Not studied in detail with SIM;
• Preliminary work done in 1996 on car tyres;
• Changes in shape of stress regime expected;
• Axle lift may result in smaller contact patch

(6 % @ 100 km/h);

• Some pavement response parameters

decrease with increased speed.

Effect of Tyre Speed: 27.6 km/h

Effect of Tyre Speed: 58.1 km/h

Top Down Cracking in (“thick”) AC layers

• MAJOR REASON:Non-

Traffic associated- shrinkage, temperature, construction, etc.;

• Traffic associated- tyres

and stresses – but not solely responsible for this type of cracking;

• Working conjointly - most

probable scenario;

Circular load - Tyre Model (Blab, 2001)

AC G3 Subgrade

VERTICAL STRESS: TYRE CENTRE AND EDGE

200 400 600 800 1000 1200 1400

Case 1-std Case 1 Case 2-std Case 2 Case 3-std Case 3 Vertical Stress (kPa)

Vertical Stress - Centre Vertical Stress - Edge

Case 1: 20 kN; 720 kPa Case 2: 35 kN; 720 kPa Case 3: 50 kN; 720 kPa

VERTICAL ELASTIC DEFLECTION ON SURFACE: TYRE CENTRE AND EDGE

200 400 600 800 1000 1200 1400

Case 1-std Case 1 Case 2-std Case 2 Case 3-std Case 3 Vertical Deflection (um)

Deflection - Centre Deflection - Edge Case 1: 20 kN; 720 kPa Case 2: 35 kN; 720 kPa Case 3: 50 kN; 720 kPa

HORISONTAL STRAIN BOTTOM OF 20 mm ASPHALT SURFACING: TYRE CENTRE AND EDGE

100 200 300 400 500 600 700 800 Case 1-std Case 1 Case 2-std Case 2 Case 3-std Case 3

Horisontal Strain (um)

Tensile Strain - Centre Tensile Strain - Edge Case 1: 20 kN; 720 kPa Case 2: 35 kN; 720 kPa Case 3: 50 kN; 720 kPa

FACTOR OF SAFETY (FoS) - GRANULAR BASE TYRE CENTRE AND EDGE

0.1 0.2 0.3 0.4 0.5 0.6 Case 1-std Case 1 Case 2-std Case 2 Case 3-std Case 3

Case

Factor of Safety (FoS) FoS-Centre FoS-Edge

Case 1: 20 kN; 720 kPa Case 2: 35 kN; 720 kPa Case 3: 50 kN; 720 kPa

VERTICAL STRAIN ON TOP OF SUBGRADE: TYRE CENTRE AND EDGE

500 1000 1500 2000 2500 3000 3500

Case 1-std Case 1 Case 2-std Case 2 Case 3-std Case 3

Vertical Strain (um) Vertical Strain - Centre Vertical Strain - Edge

Case 1: 20 kN; 720 kPa Case 2: 35 kN; 720 kPa Case 3: 50 kN; 720 kPa

PAVEMENT LIFE : MECHANISTIC – EMPIRICAL: CRITICAL LAYER APPROACH (me-PADS)

0.00E+00 2.00E+04 4.00E+04 6.00E+04 8.00E+04 1.00E+05 1.20E+05 Case 1-std Case 1 Case 2-std Case 2 Case 3-std Case 3

“Layer Life”

Surfacing-Centre G3-Base-Centre Subgrade-Centre Layer Life > 1.00+06 1<NCPc<1.5 NCPe > 1.5 NCPc = NCPe ~ 1.0

PERFORMANCE BASED STANDARD (PBS)

NCPz (for Vertical Stress) < 1.5 ….for rated tyre loading on thinly surfaced pavements.. ?

IN SUMMARY…….

• Use of SIM technology demonstrated;
• Tyre contact stress shapes: Vertical: typically

“n-shapes and “m”-shapes;

• X-Y Shear excursion plots- useful concept ?;
• Three-circle modeling in MLLE analyses;
• NCP useful concept recommended for PBS;

RECOMMENDATIONS…..

• Continued R & D with SIM:

– Higher speeds; – Braking and acceleration (down hill);

• Analysis of a wider range of pavement

types;

• Improved modeling (tyre contact patch non-

uniform & non-circular);

• NCPz, NCPx, NCPy to be further

investigated for PBS applications.

Thank you