Improved Performance Evaluation of Road Pavements by Using …asphalt.csir.co.za/sim/sim...
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Improved Performance Evaluation of Road Pavements by
Using Measured Tyre LoadingJames Maina and Morris De Beer
CSIR Built Environment, South Africa
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•• Part 1:Part 1:•• General introduction;General introduction;•• Quality and importance of road infrastructure in SA;Quality and importance of road infrastructure in SA;•• Trucks on our road infrastructure;Trucks on our road infrastructure;•• Truck tyre loading and stresses;Truck tyre loading and stresses;•• StressStress--InIn--Motion (SIM) Technology;Motion (SIM) Technology;•• Typical StressTypical Stress--InIn--Motion (SIM) Data;Motion (SIM) Data;•• Part 2:Part 2:•• Equations for mechanistic road analysis;Equations for mechanistic road analysis;•• Analysis for multiple loading;Analysis for multiple loading;•• Strain Energy of Distortion (SED);Strain Energy of Distortion (SED);•• Worked Examples and Analytical Results;Worked Examples and Analytical Results;•• Summary of research findings;Summary of research findings;•• Recommendations.
Paper today: Paper today: ““Improved Performance Evaluation of Road Improved Performance Evaluation of Road Pavements by Using Measured Tyre LoadingPavements by Using Measured Tyre Loading””
Recommendations.
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SOUTH AFRICAN SOUTH AFRICAN MAJOR PAVED MAJOR PAVED ROAD NETWORK ROAD NETWORK ~ 20 000 km~ 20 000 km
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BackgroundBackground……
•• SA: 750 000 km of roads SA: 750 000 km of roads -- 20 % paved;20 % paved;•• Road Pavement Engineering critical for upgrade & Road Pavement Engineering critical for upgrade &
sustainability of road infrastructure;sustainability of road infrastructure;•• Locally developed StressLocally developed Stress--InIn--Motion (SIM) study part Motion (SIM) study part
of this process;of this process;•• Analytical: Strain Energies of Distortion (SEDs) at Analytical: Strain Energies of Distortion (SEDs) at
various sections within the road pavement various sections within the road pavement structure were determined structure were determined –– good promise !;good promise !;
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7 700 km National Roads in SA of
Freeway/Expressway standard
7 700 km National Roads in SA of
Freeway/Expressway standard
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•• The 4The 4thth annual State of Logistics Survey for SA annual State of Logistics Survey for SA indicated that total indicated that total land transportland transport accounted for accounted for 1,5 billion tonnes1,5 billion tonnes, with recent , with recent growth of highergrowth of higherthan 5 per centthan 5 per cent, mainly captured by the road , mainly captured by the road transport sector, as opposed to the transport sector, as opposed to the rail sectorrail sectorcarrying only 0.2 billion tonnes.carrying only 0.2 billion tonnes.
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Freight Transport in SAFreight Transport in SA…….(CSIR .(CSIR -- 44thth SA SA Logistics Report, 2007).Logistics Report, 2007).
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Freight Transport in SAFreight Transport in SA…….(CSIR .(CSIR -- 44thth SA SA Logistics Report, 2007).Logistics Report, 2007).
Figure 1. Historical freight transport data (CSIR, 2007).
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Traffic Volumes and Road DamageTraffic Volumes and Road Damage……..
•• Traffic volumes on our national highways are at all Traffic volumes on our national highways are at all time highs, for example, N3 has already carried time highs, for example, N3 has already carried the the equivalence of 20 yearsequivalence of 20 years of traffic over the of traffic over the last two years.last two years. (..2007..)(..2007..)
••Daily, newspapers carry articles on potholes and Daily, newspapers carry articles on potholes and other road shortcomings which cost motorists in other road shortcomings which cost motorists in excess of R200 billionexcess of R200 billion a year (News24, 2008).a year (News24, 2008).
It is therefore not surprising that there have been numerous calIt is therefore not surprising that there have been numerous calls ls for extensive revision of important parts of the SA road pavemenfor extensive revision of important parts of the SA road pavement t design method in order to cope with the new traffic realities, design method in order to cope with the new traffic realities, amongst other factors.amongst other factors.
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Heavy VehiclesHeavy Vehicles……..
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Growth in Heavy Vehicle (HV) TrafficGrowth in Heavy Vehicle (HV) Traffic……
•• In terms of growth in HVs on the toll portion of the In terms of growth in HVs on the toll portion of the road, the rate was approximately 8 per cent road, the rate was approximately 8 per cent since 2002since 2002--2007, 2007, 20 per cent 200620 per cent 2006--20072007, and , and almost 40 per centalmost 40 per cent between February and between February and October 2007. October 2007.
•• The N3 is therefore the national road with the The N3 is therefore the national road with the highest growth and HV composition in SA (Le highest growth and HV composition in SA (Le Roux, 2007).Roux, 2007).
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More Specific issues in Paper todayMore Specific issues in Paper today……
•• South African Roads, Trucks @ Road Damage; South African Roads, Trucks @ Road Damage; •• Introduction into StressIntroduction into Stress--InIn--Motion (SIM) technology;Motion (SIM) technology;•• Tyre Studies with Heavy Vehicle Simulator (HVS);Tyre Studies with Heavy Vehicle Simulator (HVS);•• Full Scale SIM Testing @ N3Full Scale SIM Testing @ N3--Traffic Control Centre Traffic Control Centre
(TCC) (TCC) --Heidelberg, SA @ typical SIM Results;Heidelberg, SA @ typical SIM Results;•• Implications for Road Surface Design and Road Implications for Road Surface Design and Road
Preservation/Protection Preservation/Protection –– Analytical Evaluations..Analytical Evaluations..
•• Summary, Conclusions and RecommendationsSummary, Conclusions and Recommendations
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Vehicle-Tyre-Pavement Interaction:
STRESS-IN-MOTION (SIM)Technology
Vehicle-Tyre-Pavement Interaction:
STRESS-IN-MOTION (SIM)Technology
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Thin Asphalt Surfacings (30 mm to 50 mm) on crushed rock: Economical in dry regions.
Thin Asphalt Surfacings (30 mm to 50 mm) on crushed rock: Economical in dry regions.
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North of Buccleuch facing South2008/11/13; 17:05:40
From: http://www.i-traffic.co.za/index.php?q=cameras
At Buccleuch2008/11/13; 17:05:40
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Truck Tyre Inflation Pressure in South AfricaTruck Tyre Inflation Pressure in South Africa
FIGURE 1AVERAGE MEASURED TYRE INFLATION PRESSURE DISTRIBUTIONS
OF HEAVY VEHICLES (AXLE LOADS > 7 000 kg) ON ROADSIN THE PROVINCE OF GAUTENG, SOUTH AFRICA
100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 15000
5
10
15
20
25
TYRE INFLATION PRESSURE (kPa)
% O
F TY
RE
PRES
SUR
E PE
R 5
0 kP
a IN
TER
VAL
Van Vuuren (1974) De Beer (1995)
Average: 620 kPa Average: 733 kPa
c:/capsaf1.wmf
~ 20 % Increase
in 20
Years
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Road DamageRoad Damage……..
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EXAMPLES OF ROAD SURFACE FAILURES..
Surface Disintegration…
SURFACE DISINTEGRATION
RUTTING Fatigue Cracking and aging
POTHOLES : Water & Loads …
Water & Safety…
D elam in ation ..
Longitudinal Flow of AsphaltLongitudinal Flow of AsphaltLongitudinal Flow of Asphalt
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Tyres and Road Structures…..Tyres and Road StructuresTyres and Road Structures……....
……from SANRAL: from SANRAL: www.nra.co.zawww.nra.co.za
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Modern Tyre science…Modern Tyre scienceModern Tyre science…””SectometerSectometer””
S. Eckens, 1928S. Eckens, 1928
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Gautrans Heavy Vehicle Simulator (HVS) Mark IV+:Gautrans Heavy Vehicle Simulator (HVS) Mark IV+:Loading Device for Controlled loading tests on roads..Loading Device for Controlled loading tests on roads..
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LOADS & STRESSES FROM TYRES:LOADS & STRESSES FROM TYRES:
+Z
+X
Tyre Rotation
+Y
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425 /65 R22.5 HVS TYRE ON SIM SYSTEM425 /65 R22.5 HVS TYRE ON SIM SYSTEM
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StressStress--InIn--Motion testing with HVSMotion testing with HVSDual Load Configuration Dual Load Configuration –– Twin SIM padsTwin SIM pads
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STRESSSTRESS--ININ--MOTION TESTING USING THE HVSMOTION TESTING USING THE HVS
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TYRE DEFLECTION & TYRE PRINTSTYRE DEFLECTION & TYRE PRINTS……
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TYRE DEFLECTION & TYRE PRINTSTYRE DEFLECTION & TYRE PRINTS……
315/80 R22.5 HVS Tyre: 315/80 R22.5 HVS Tyre: OverloadedOverloaded
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Overloading on Tyres….and contact with road..Overloading on TyresOverloading on Tyres…….and contact with road...and contact with road..
Tyre Contact Patches:Tyre Contact Patches:(square not circular)(square not circular)……
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- Circular;- Variable Vertical load;- Variable pressure, but UNIFORM &No Shear Forcesincluded.
-- Circular;Circular;-- Variable Vertical load;Variable Vertical load;-- Variable pressure, Variable pressure, but UNIFORM &but UNIFORM &No Shear ForcesNo Shear Forcesincluded.included.
Tyre Loading, P (kN)Tyre Loading, P (kN)
Uniform Contact Stress, q (kPa)
Assumption of Tyre Loading Assumption of Tyre Loading -- Pavement Design Pavement Design Modeling:Modeling:
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Dual Tyre: 3D-Contact Stresses (Pressure)…Dual Tyre: 3DDual Tyre: 3D--Contact Stresses (Pressure)Contact Stresses (Pressure)……
Stress Ratio: 10:3:1
Stress Stress Ratio: Ratio: 10:3:1 10:3:1
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Typical SIM 3D Data Sets Typical SIM 3D Data Sets -- Variable loading:Variable loading:
3D 3D –– Z,X,Y Z,X,Y --Contact Stresses: Contact Stresses:
Variable loads: Variable loads: 315/80 R22.5 Tire315/80 R22.5 Tire
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TYRE “FINGER PRINTING”: (11R22.5 TYRE)…
TYRE INFLATION PRESSURE
TYRE
LOAD
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Truck Weighing Truck Weighing -- National Road 3 (N3), near Heidelberg National Road 3 (N3), near Heidelberg in Gautengin Gauteng……..
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QUAD SIM PAD TESTING AT WEIGHQUAD SIM PAD TESTING AT WEIGH--BRIDGE SITE:BRIDGE SITE:N3 NORTH N3 NORTH –– HEIDELBERG TRAFFIC CONTROL CENTREHEIDELBERG TRAFFIC CONTROL CENTRE
4 x SIM Scales4 x SIM Scales
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Quad (full) SIM pad configuration at a typical Quad (full) SIM pad configuration at a typical weighbridge site on National Road 3 (N3), near weighbridge site on National Road 3 (N3), near Heidelberg in GautengHeidelberg in Gauteng
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Examples of StressExamples of Stress--InIn--Motion (SIM) Testing on theMotion (SIM) Testing on theN3 N3 –– Freeway near HeidelbergFreeway near Heidelberg……..
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Quad (full) SIM pad configuration at a typical weighbridge site Quad (full) SIM pad configuration at a typical weighbridge site on on National Road 3 (N3), near Heidelberg in GautengNational Road 3 (N3), near Heidelberg in Gauteng
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Quad (full) SIM Scale on National Road 3 (N3), near Quad (full) SIM Scale on National Road 3 (N3), near Heidelberg in GautengHeidelberg in Gauteng ……..
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SIM Measurement: N3SIM Measurement: N3-- ““12321232”” TankerTanker……
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SIM In operation SIM In operation –– N3N3--TCC TCC …………..
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SIM Scales: Accuracy checking @ N3SIM Scales: Accuracy checking @ N3--TCCTCC……
SIM vs MULTI-DECK STATIC AND DAW 50 at N3-TCC (Heidelberg) (GVM/GCM)
05
10152025303540455055606570
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70
SIM (Tonne)
STA
TIC
& D
AW
50
Sca
les
(Ton
ne)
STATIC (1861) DAW50 (1501) Line of Equality Linear (STATIC (1861)) Linear (DAW50 (1501))
STATIC = 1.0025 x SIM(n = 1 245), R2 = 0.99;
Std. Y-Error: 1.37 Tonne;Std. Error (Coef) :
0.0001.
DAW 50 = 0.9931 x SIM (n = 1 245), R2 = 0.99;
Std Y-Error: 1.42 Tonne;Std. Error (Coef):
0.00011.
D:\ICAP-2006\[MODIFIED-2SEPT-17OCT-ICAP-2006.xls]Total Load-GVM-GCM-
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N3 TCC - SELECTED HEAVY VEHICLE (HV) TRUCK TYRE PRESSURE DATA (26 Feb 2003 - 06 March 2003)
0
0.2
0.4
0.6
0.8
1
1.2
0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500
TYRE INFLATION PRESSURE (kPa)
Nor
mal
ised
Fre
quen
cy
LEFT-FRONT-(225 tyres) RIGHT-FRONT-(225 tyres) REST-LEFT-(845) REST-RIGHT-(845)
H:\CAPSA04\[Tyre Inflation Pressure Information-MORTON-MDB-
Tyre Inflation Pressure Distributions Tyre Inflation Pressure Distributions –– N3N3-- 20032003
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GVM/GCM-SIM N3 TCC - 2003RESULT RATINGS 1 AND 2 (n = 2 297)
[2 Sept - 17 Oct 2003]
0
25
50
75
100
125
150
175
200
225
250
1.000
4.000
7.000
10.00
013
.000
16.00
019
.000
22.00
025
.000
28.00
031
.000
34.00
037
.000
40.00
043
.000
46.00
049
.000
52.00
055
.000
58.00
061
.000
64.00
067
.000
70.00
073
.000
76.00
079
.000
82.00
0
Bin: Vehicle Mass: GVM/GCM [Tonne]
Num
ber o
f Tru
cks
15 Tonne
29 Tonne
51 Tonne
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Gross Vehicle Mass (GVMs)Gross Vehicle Mass (GVMs)…………..
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ALL TYRES MEASURED: n = 45 227 (This Study) - N3 -TCC-2003
0
200
400
600
800
1000
1200
1400
1600
0.050
0.300
0.550
0.800
1.050
1.300
1.550
1.800
2.050
2.300
2.550
2.800
3.050
3.300
3.550
3.800
4.050
4.300
4.550
4.800
Bin: Tyre Mass Weight [Tonne]
Num
ber o
f Tyr
es
0
20
40
60
80
100
120
All Other Tyres Axle 1 Left Axle 1 Right
Steering Tyres:
2.95 Tonne
All other Tyers:
1.9 Tonne
H:\ICAP-2006 Summary N3 TCC-FINAL-4-B-ICAP-2006.xls TYRES-1-2 -Histogram-Paper (2)
Axle Mass Distributions Axle Mass Distributions –– N3N3-- 20032003
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Vertical Stress Cumulative Frequency Vertical Stress Cumulative Frequency –– N3N3-- 20032003
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Measured Tyre Foot PrintsMeasured Tyre Foot Prints :Two Axle Truck Two Axle Truck –– Vertical Vertical Contact Stress Contact Stress ––……....
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4 Axle Truck4 Axle Truck……..
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5 Axle Truck5 Axle Truck……..
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6 Axle Truck6 Axle Truck……..
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Eight (8) Axle Truck Eight (8) Axle Truck –– Vertical Contact Vertical Contact Stress Stress -- Foot PrintsFoot Prints……..
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10 20 30 40 50 60 70 80
50
100
150
200
250
300
350
400
450
Across the SIM pads
Cou
nts
TEST 009: KTD 904 GP 13/10/2003: AXLE 1
266 mm; 3.739 Ton 185 mm; 1.938 Ton
STEERING AXLE STEERING AXLE –– UNEQUAL LOADINGUNEQUAL LOADING…………..
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10 20 30 40 50 60 70 80
50
100
150
200
250
300
350
400
450
500
550
Across the SIM pads
Cou
ntsTEST 768-09/10/2003: DDT235N AXLE 2
189 mm;0.037 Ton
297 mm;4.312 Ton
202 mm;1.874 Ton
194 mm;1.223 Ton
TYRE BARELY IN CONTACT WITH SURFACETYRE BARELY IN CONTACT WITH SURFACE
UNEQUAL LOADING ON TRUCK TYRESUNEQUAL LOADING ON TRUCK TYRES……..
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10 20 30 40 50 60 70 80
50
100
150
200
250
300
350
Across the SIM pads
Cou
nts
TEST 765: NKR 9519 - 09/10/2003 AXLE 2244 mm;1.782 Ton
196 mm;1.032 Ton
195 mm;0.661 Ton
AXLE 2: MISSING TYRE !! AXLE 2: MISSING TYRE !!
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P/σ
Surfacing: h1, E1, v1
SelectedLayer:
h4, E4, v4
BaseLayer:
h2, E2, v2
Subgrade/Foundation:
h5, E5, v5
SubbaseLayer:
h3, E3, v3
APPLIED LOAD/STRESSESP/σ
Pavement Response:
Stresses &
Strains
StressRotation
Vertical,Longitudinal &
Lateral 3D ContactStresses
Side view of tyre
End viewof tyre
ANALYTICAL ROAD PAVEMENT MODELANALYTICAL ROAD PAVEMENT MODEL……..
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General Features & AssumptionGeneral Features & AssumptionGeneral Features & Assumption
Pavement: Multilayer elastic system with a possibility of interface slip.
Surface load: Single/Multiple circular loads.
Analysis: Single/Multiple points of interest.
Response: Stresses, strains, and displacements
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Uniformly distributed circular loadUniformly distributed circular load
vertical + horizontal loadsVertical
loadHorizontal load
surfaceBase
Subgrade
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θr
x
y
z
Load
τrzτrz
σθσr
σz
τzθτzθ
τrθτrθ
Stresses within a Road Pavement Structure- rθz Axes -Stresses within a Road Pavement StructureStresses within a Road Pavement Structure-- rrθθzz Axes Axes --
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Stresses within a Road Pavement Structure..Stresses within a Road Pavement Structure..Stresses within a Road Pavement Structure..
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y
x
θ r
τrz=τzr
z
z
σz
τzθ=τθz
τrθ=τθrσθ
σrArrows give directions for positive sign
Local Cartesian and cylindrical coordinates
Global Cartesian coordinate system
θ
Stress acting on an element
Y
X
Z
αload
r
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Multilayer Structural Model:Multilayer Structural Model:Multilayer Structural Model:
2a
measurement point
X
Y
(0, 0, 0)
(X0+r Cos(θ +α), Y0+r Sin(θ +α), 0)
y
xrθ
α
h1
h2
hi-1
hi
E1
E2
Ei-1
Ei
En
ν1
ν2
νi-1
νn
νi
Layer Modulus Poisson’s ratio
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- Circular;- Variable Vertical load;- Variable pressure, but UNIFORM &No Shear Forcesincluded.
-- Circular;Circular;-- Variable Vertical load;Variable Vertical load;-- Variable pressure, Variable pressure, but UNIFORM &but UNIFORM &No Shear ForcesNo Shear Forcesincluded.included.
Tyre Loading, P (kN)Tyre Loading, P (kN)
Uniform Contact Stress, q (kPa)
Assumption of Tyre Loading Assumption of Tyre Loading -- Pavement Design Pavement Design Modeling:Modeling:
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SIM systems..SIM systems..
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RuttingRutting-- Controlled testing with Heavy Vehicle Controlled testing with Heavy Vehicle Simulator (HVS)Simulator (HVS)……
Controlled Field Tests with HVS…on R80 route.
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Wide Base Single TyreWide Base Single Tyre-- Input Data: Vertical Input Data: Vertical Stress Patterns: Stress Patterns: ““nn”” and and ““mm”” –– ShapesShapes……
“n – Shape” “m – Shape”
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Wide Base Single TyreWide Base Single Tyre-- Input Data: Vertical Input Data: Vertical Stress Patterns: Stress Patterns: ““nn”” and and ““mm”” –– ShapesShapes……
“n – Shape” “m – Shape”
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RuttingRutting-- Controlled testing with Heavy Vehicle Controlled testing with Heavy Vehicle Simulator (HVS)Simulator (HVS)……
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Vertical Tyre Stress: Vertical Tyre Stress: ““nn--ShapeShape”” tyre stress tyre stress results in results in ““nn--ShapeShape”” rutting in asphalt overlay..rutting in asphalt overlay..
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Vertical Tyre Stress: Vertical Tyre Stress: ““mm--ShapeShape”” stress result in stress result in ““mm--ShapeShape”” rutting in asphalt overlay..rutting in asphalt overlay..
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Vertical Tyre Stress: Vertical Tyre Stress: ““nn--ShapeShape”” tyre stress tyre stress distributiondistribution
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Strain Energy of Distortion (SED) on road Strain Energy of Distortion (SED) on road surface: From surface: From ““nn”” –– Shape single tyre stressShape single tyre stress……
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Vertical Tyre Stress: Vertical Tyre Stress: ““nn--ShapeShape”” tyre stress tyre stress distribution.distribution.
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Road Surface: Strain Energy of Distortion (SED) Road Surface: Strain Energy of Distortion (SED) –– from from ““n n –– ShapeShape”” single tyre stresssingle tyre stress……
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Road Surface: Strain Energy of Distortion (SED) Road Surface: Strain Energy of Distortion (SED) –– from from ““n n –– ShapeShape”” single tyre stresssingle tyre stress……
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Strain Energy of Distortion (SED)Strain Energy of Distortion (SED)-- ““nn”” and and ””m m ––ShapeShape”” -- dual tyres..dual tyres..……..
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Strain Energy of Distortion (SED) Strain Energy of Distortion (SED) –– Dissipation Dissipation with road pavement depthwith road pavement depth……
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50 mm AC layer50 mm AC layer
1 x Truck 1 x Truck -- 30 Tyres: 1 mm x 1 mm resolution 30 Tyres: 1 mm x 1 mm resolution –– 500k points 500k points ––SED under Steering Axle SED under Steering Axle …………
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50 mm AC layer50 mm AC layer
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……SED under Steering AxleSED under Steering Axle
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Summary, Conclusions (1):Summary, Conclusions (1):Summary, Conclusions (1):
•• South African Roads, Trucks @ Road Damage South African Roads, Trucks @ Road Damage –– real real cause of concern; cause of concern;
•• Tyre Studies with Heavy Vehicle Simulator (HVS); Tyre Studies with Heavy Vehicle Simulator (HVS); •• Successful Demonstration Successful Demonstration -- StressStress--InIn--Motion (SIM) Motion (SIM)
technology;technology;•• Analytic approach Analytic approach -- SED shows good promise for SED shows good promise for
further implementation;further implementation;•• Implications for Road Surface Design and Road Implications for Road Surface Design and Road
Preservation/Protection Preservation/Protection –– Important to be Important to be implemented;implemented;
•• SIM future of existing WeighSIM future of existing Weigh--InIn--Motion (WIM) ??.Motion (WIM) ??.
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Summary, Conclusions (2):Summary, Conclusions (2):Summary, Conclusions (2):
•• The concept of SED as a response parameter that The concept of SED as a response parameter that quantifies road pavementquantifies road pavement’’s s ““potential for failurepotential for failure””: : seems to resonate well with the applied tyre stresses seems to resonate well with the applied tyre stresses and its different shapes. and its different shapes.
•• Single wide base tyres induce more than double the Single wide base tyres induce more than double the potential for failure compared with the dual tyre potential for failure compared with the dual tyre configuration on the same road pavement. configuration on the same road pavement.
•• UnderUnder--inflatedinflated--heavilyheavily--loaded tyres may cause more loaded tyres may cause more damage on the surface of the road compared to damage on the surface of the road compared to correctly inflated tyres. correctly inflated tyres.
•• The combination of SIM technology and SED from The combination of SIM technology and SED from numerical modelling may be used to identify areas of numerical modelling may be used to identify areas of high potential for failure on the road pavement high potential for failure on the road pavement system.system.
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Conclusions- based on SED Evaluation:…ConclusionsConclusions-- based on SED based on SED Evaluation:Evaluation:……
•• Depending on the shape of the vertical contact stress Depending on the shape of the vertical contact stress distribution, the damaging effect in terms of SED of distribution, the damaging effect in terms of SED of the single tyre appears to be 2.0 to 4.3 times higher the single tyre appears to be 2.0 to 4.3 times higher than dual tyres under the same total loading.than dual tyres under the same total loading.
•• For both tyres, the damaging effect appears to be For both tyres, the damaging effect appears to be between 1.7 and 3.5 higher for the mbetween 1.7 and 3.5 higher for the m--shape contact shape contact stress distribution.stress distribution.
•• The top 5 mm to 10 mm of road pavements is The top 5 mm to 10 mm of road pavements is potentially more prone to failure (toppotentially more prone to failure (top--down cracking down cracking or rutting) than was perhaps realised in the past.or rutting) than was perhaps realised in the past.
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Recommendations:Recommendations:Recommendations:
•• Further research work is needed to establish Further research work is needed to establish if this trend of tyre type is similar for all road if this trend of tyre type is similar for all road pavement structures in South Africa before it pavement structures in South Africa before it is safe to argue against the use of is safe to argue against the use of single tyres single tyres vs dual tyresvs dual tyres or make recommendation on or make recommendation on tyre inflation pressure for HVs.tyre inflation pressure for HVs.
•• Implementing concept of SED in road design; Implementing concept of SED in road design;
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