Upload
lamthien
View
215
Download
2
Embed Size (px)
Citation preview
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 % over 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
of
Traffic
Instrumented
Pins
356 mm
755 mm
pattern1.wmf
TOP VIEW OF THE VRSPTA MK II
TYREPATCH
TYREPATCH
TYREPATCH
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 0 100 200 300 400 500 600 700 800
-4
-3
-2
-1
0
1
2
3
4
ENTRAN LOADCELL (NEWTONS)
LOAD
CELL
(VOL
TS)
X Y Z
3D LOADCELL PIN 10LOADING IN "X" DIRECTION
3D-CELLX/Y/Z.WK3
11/01/1999
-800 -700 -600 -500 -400 -300 -200 -100 0 100 200 300 400 500 600 700 800
-4
-3
-2
-1
0
1
2
3
4
ENTRAN LOADCELL (NEWTONS)
LOAD
CELL
(VOL
TS)
X Y Z
3D LOADCELL PIN 10LOADING IN "Y" DIRECTION
3D-CELLX/Y/Z.WK3
11/01/1999
0 100 200 300 400 500 600 700 800
-0.5
0.5
1.5
2.5
3.5
4.5
ENTRAN LOADCELL (NEWTONS)
LOAD
CELL
(VOL
TS)
X Y Z
3D LOADCELL PIN 10LOADING IN "Z" DIRECTION
3D-CELLX/Y/Z.WK3
11/01/1999
+/- X - LOAD (kN)
+/- Y - LOAD (kN)
Z - LOAD (kN)
VO
LT
SV
OL
TS
VO
LT
S
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
overloaded
[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
NC
Pi
0
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
0
100
200
300
-200 -150 -100 -50 0 50 100 150 200
X-Longitudinal Stress (kPa)
Y-L
ate
ral S
tress (
kP
a)
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
0
100
200
300
-200 -150 -100 -50 0 50 100 150 200
X-Longitudinal Stress (kPa)
Y-L
ate
ral S
tre
ss (
kP
a)
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
0
100
200
300
-200 -150 -100 -50 0 50 100 150 200
X-Longitudinal Stress (kPa)
Y-L
ate
ral S
tress (
kP
a)
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
0
200
400
600
800
1000
1200
1400
Case 1-std Case 1 Case 2-std Case 2 Case 3-std Case 3
Vert
ical S
tress (
kP
a)
Vertical Stress - Centre Vertical Stress - Edge
Case 1: 20 kN; 720 kPa Case 2: 35 kN; 720 kPaCase 3: 50 kN; 720 kPa
VERTICAL ELASTIC DEFLECTION ON SURFACE:
TYRE CENTRE AND EDGE
0
200
400
600
800
1000
1200
1400
Case 1-std Case 1 Case 2-std Case 2 Case 3-std Case 3
Ve
rtic
al D
efle
ctio
n (
um
)
Deflection - Centre Deflection - Edge
Case 1: 20 kN; 720 kPa Case 2: 35 kN; 720 kPaCase 3: 50 kN; 720 kPa
HORISONTAL STRAIN BOTTOM OF 20 mm ASPHALT
SURFACING: TYRE CENTRE AND EDGE
0
100
200
300
400
500
600
700
800
Case 1-std Case 1 Case 2-std Case 2 Case 3-std Case 3
Horisonta
l S
train
(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
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
Fa
cto
r o
f S
afe
ty (
Fo
S)
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
0
500
1000
1500
2000
2500
3000
3500
Case 1-std Case 1 Case 2-std Case 2 Case 3-std Case 3
Ve
rtic
al S
tra
in (
um
)
Vertical Strain - Centre Vertical Strain - Edge
Case 1: 20 kN; 720 kPa Case 2: 35 kN; 720 kPaCase 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
“La
ye
r L
ife
”
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