pavement thickness design methods
TRANSCRIPT
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Pavement Thickness Design Methods
Municipal Streets SeminarNovember 12, 2014
Ames, Iowa
Eric Ferrebee - ACPA
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U.S. JPCP Roadway Design Methods
AASHTOWarePavement ME (previously known as DARWin-ME and MEPDG)
AASHTO 93 (software as ACPA WinPAS)
ACPA StreetPave
325 & 330
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Design Method Basis
Mechanistic – Purely scientific and based on measured, defendable scientific rules and laws
Empirical – Based on observations or experimentation and requires a lot of tests to connect all the relationships
𝜖𝜖 = 𝜎𝜎/𝐸𝐸 ∆L = α ∗ ∆𝑇𝑇 ∗ 𝐿𝐿𝑜𝑜
𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪 = 𝒍𝒍𝒍𝒍𝑪𝑪𝒍𝒍𝒍𝒍 + 𝒆𝒆𝑪𝑪𝒆𝒆𝑪𝑪𝑪𝑪𝒍𝒍𝑪𝑪𝒆𝒆𝒆𝒆𝑪𝑪𝒆𝒆 + 𝒆𝒆𝑪𝑪𝒆𝒆𝒆𝒆𝑪𝑪𝑪𝑪𝑪𝑪𝒍𝒍
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AASHTO 93 / ACPA WinPAS
acpa.org/winpas
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AASHO Road Test (1958-1960)
Wholly empirical Included 368 concrete and 468 asphalt sections | focus was highway pavement
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Subgrade = Clay Soil
Necessary Thickness was Guessed!
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Max Single Axle
Max Tandem Axle
Sections Loaded for 2 Yrs | 1.1 Mil Reps
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Performance Estimated Subjectively
Present Serviceability Index (PSI)4.0 – 5.0 = Very Good3.0 – 4.0 = Good2.0 – 3.0 = Fair1.0 – 2.0 = Poor0.0 – 1.0 = Very Poor
“Failure” at the Road Test considered @ 1.5
Typical U.S. state agency terminal serviceability in practice = 2.5
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Note on Inference Space of ‘93
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• •• •• •
•
Data Limits(AASHO Road Test)
CurrentDesigns>100 million
1.1mil
AXLE LOAD REPETITIONS
PAVEM
ENT
THIC
KN
ESS
Current design traffic is far beyond AASHO road test limits
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Don’t Just Take My Word…“The current design guide and its predecessors were largely based on design equations empirically derived from the observations AASHTO’s predecessor made during road performance tests completed in 1959-60. Several transportation experts have criticized the empirical data thus derived as outdated and inadequate for today’s highway system. In addition, a March 1994 DOT Office of Inspector General report concluded that the design guide was outdated and that pavement design information it relied on could not be supported and validated with systematic comparisons to actual experience or research.”
…this is why Pavement ME exists!
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++
−∆
+−++=
46.8
7
)1(10*624.11
5.15.406.0)1(*35.7*)(
D
PSILogDLogsZESALLog oR
−
−−+
25.075.0
75.0'
)/(42.18**63.215
)132.1(***)*32.022.4(
kEDJ
DCSLogp
c
dct
Standard Normal Deviate
OverallStandard Deviation Thickness
Change in Serviceability
Terminal Serviceability
DrainageCoefficient
Load Transfer
Modulus ofRupture
Modulus of Elasticity
Modulus ofSubgrade Reaction
1986-93 JPCP AASHTO 93 Equation
Traffic
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MEPDG / DARWin-ME /AASHTOWare Pavement ME
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Pavement ME Design
Not “perfect” & not intended to be a “final” productComplex and relatively costlyFor highways and NOT street, road, parking lot, etc.
=+Mechanistic Calculation
of Responses
Empirical Tie to
Ground
Pavement Performance Prediction
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JPCP Calibration – BIG INF. SPACE!
LTPP GPS-3 & RPPR JPCP Sections LTPP SPS-2, MnROAD, & AASHO JPCP Sections
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AASHTO 93 vs. ME
AASHTO Pavement ME
AASHTO 93
50+ million load reps
1.1 million load reps
Wide range of structural and rehabilitation designs
Limited structural sections
1 climate/2 years
All climates over 20-50 years
1 set of materials
New and diverse materials
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Sounds Easy Enough, Right?
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INPUTS, INPUTS, INPUTS!!!!
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INPUTS, INPUTS, INPUTS!!!!
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OUTPUTS, OUTPUTS, OUTPUTS!!!
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Some Agencies Trying to Simplify
Note the inputs that have been deemed worth
varying…
…designers have a new
idea of “what
matters”!
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ACPA StreetPave
acpa.org/streetpave
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ACPA StreetPave
Roots date back to the 1960s PCA MethodTailored for streets and roadsFailure modes are cracking and faulting
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Total trucks in design lane over the design life… calculated from trucks/day (2-way), traffic growth rate (%/yr), design life (yrs), directional distribution (%) and design lane distribution (%)
Traffic Spectrum + CountsSingle Axles
Axle Load (kip) Axles/1,000 Trucks34 0.1932 0.5430 0.6328 1.7826 3.5224 4.1622 9.6920 41.8218 68.2716 57.07
Tandem AxlesAxle Load (kip) Axles/1,000 Trucks
60 0.5756 1.0752 1.7948 3.0344 3.5240 20.3136 78.1932 109.5428 95.7924 71.16
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Equivalent stress at the slab edge:
Me = equivalent moment, psi; different for single, tandem, and tridem axles, with and without edge support - func on radius of relative stiffness, which depends on concrete modulus, Poisson’s ratio, and thickness and the k-value
hc = pavement thickness, in.f1 = adjustment for the effect of axle loads and contact areaf2 = adjustment for a slab with no concrete shoulderf3 = adjustment to account for the effect of truck (wheel) placement at the slab edgef4 = adjustment to account for approximately 23.5% increase in concrete strength
with age after the 28th day and reduction of one coefficient of variation (COV) to account for materials variability
Traffic Loads Generate Stresses
𝜎𝜎𝑒𝑒𝑞𝑞 =6 ∗ 𝑀𝑀𝑒𝑒
ℎ𝑐𝑐2 ∗ 𝑓𝑓1 ∗ 𝑓𝑓2 ∗ 𝑓𝑓3 ∗ 𝑓𝑓4
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Stress Ratio (SR) = Stress / Concrete Strength
Limit Stress Ratio to Allow Design Reps
0.4
0.5
0.6
0.7
0.8
0.9
1
1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08 1.E+09 1.E+10
Stre
ss R
atio
Repetitions
Fatigue Data
StreetPave R=95%
Inference space normalized to SR
StreetPavemakes slab thicker to limit stress ratio low enough to achieve the design traffic repetitions
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A Conservative Approach!
StreetPave fatigue calculation should be conservative relative to ME Design because:
Size Effects – Slabs have a greater fatigue capacity than beamsSupport – The beam test has a k-value for support of 0 psi/in.!
L/3Span Length = L
d=L/3
…versus…
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Faulting Design in StreetPave
If dowels used, faulting mitigated & fails by cracksNo faulting data collected at the AASHO road test so model developed in 1980s using field performance data from WI, MN, ND, GA, and CASimilar to cracking models, the pavement is made thicker, as necessary, until faulting model predicts that the pavement will not fail by faulting during the design lifeStreetPave’sweak point
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StreetPave Accepted in MN
http://www.dot.state.mn.us/stateaid/admin/memos/12-sa-03.pdfhttp://www.dot.state.mn.us/research/documents/201210.pdf
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And Its Use is Growing!
Also “approved” in VA and many other state, city, and county engineers are using it in the U.S.StreetPave used in design tables in:
ACI 325 and 330 documentsDr. Norb Delatte’s textbook Concrete Pavement Design, Construction, and Performance
Internationally, used in Australia, Portugal, Mexico, Uruguay, Argentina, Chile, etc.
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StreetPave | Project Details
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StreetPave | Traffic Details
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StreetPave | Design Details | General
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StreetPave | Design Details | Concrete
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StreetPave | Design Results
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StreetPave | Design Report
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Comparison of Results and U.S. Trends
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100
125
150
175
200
225
250
275
300
325
350
4
5
6
7
8
9
10
11
12
13
14
- 10,000,000 20,000,000 30,000,000 40,000,000 50,000,000
Requ
ired
Thic
knes
s (m
m)
Requ
ired
Thic
knes
s (in
.)
Design Lane ESALs
AASHTO 93 (ACPA WinPAS)
AASHTOWare Pavement ME @ ORD
AASHTOWare Pavement ME @ PHX
ACPA StreetPave
Doweled JPCP Thickness Comparison
remember AASHTO 93 limit?
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Top 10 ME Design Most Sensitive
1. Concrete Flexural Strength at 28-Days2. Concrete Thickness3. Surface Shortwave Absorptivity (SSA)4. Joint Spacing5. Concrete Modulus of Elasticity at 28-Days6. Design Lane Width with a 14 ft (4.3 m) Widened Slab7. Edge Support via Widened Slab8. Concrete Thermal Conductivity9. Concrete Coefficient of Thermal Expansion (CTE)10. Concrete Unit Weight
Red = only ME Design input… the VALUE of the software!Blue + Bold = common for all
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100
125
150
175
200
225
250
275
300
325
350
4
5
6
7
8
9
10
11
12
13
14
400 450 500 550 600 650 700 750 800
Requ
ired
Thic
knes
s (m
m)
Requ
ired
Thic
knes
s (in
.)
Concrete Flexural Strength (psi)
AASHTO 93 (ACPA WinPAS)
AASHTOWare Pavement ME @ ORD
AASHTOWare Pavement ME @ PHX
ACPA StreetPave
Flexural Strength Sensitivity
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100
125
150
175
200
225
250
275
300
325
350
4
5
6
7
8
9
10
11
12
13
14
3,000,000 3,500,000 4,000,000 4,500,000 5,000,000 5,500,000 6,000,000
Requ
ired
Thick
ness
(mm
)
Requ
ired
Thick
ness
(in.
)
Modulus of Elasticity (psi)
AASHTO 93 (ACPA WinPAS)
AASHTOWare Pavement ME @ ORD
AASHTOWare Pavement ME @ PHX
ACPA StreetPave
Modulus of Elasticity Sensitivity
… in reality, need to change strength too…(20.7 GPa) (41.4 GPa)
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0
25
50
75
100
0
0.5
1
1.5
2
2.5
3
3.5
4
- 10,000,000 20,000,000 30,000,000 40,000,000 50,000,000
Thic
knes
s Red
uctio
n w
/Edg
e Su
ppor
t (m
m)
Thic
knes
s Red
uctio
n w
/Edg
e Su
ppor
t (in
.)
Design Lane ESALs
AASHTO 93 (ACPA WinPAS)
AASHTOWare Pavement ME @ ORD
AASHTOWare Pavement ME @ PHX
ACPA StreetPave
Thickness Reduction w/ Edge Support
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100
125
150
175
200
225
250
275
300
325
350
4
5
6
7
8
9
10
11
12
13
14
50% 60% 70% 80% 90% 100%
Requ
ired
Thic
knes
s (m
m)
Requ
ired
Thic
knes
s (in
.)
Reliability
AASHTO 93 (ACPA WinPAS)
AASHTOWare Pavement ME @ ORD
AASHTOWare Pavement ME @ PHX
ACPA StreetPave
Reliability Sensitivity
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100
125
150
175
200
225
250
275
300
325
350
4
5
6
7
8
9
10
11
12
13
14
0 100 200 300 400 500
Requ
ired
Thic
knes
s (m
m)
Requ
ired
Thic
knes
s (in
.)
Static k-value (psi)
AASHTO 93 (ACPA WinPAS)
AASHTOWare Pavement ME @ ORD
AASHTOWare Pavement ME @ PHX
ACPA StreetPave
k-value Sensitivity
Very few designed for < 100
psi/in. (27
MPa/m)?
(136 MPa/m)
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U.S. Agencies Quickly Changing
Summary of State Agency practice in 2005:
At the end of 2013, 41 state agencies had performed ME Design calibration and implementation efforts, indicating a relatively quick shift from AASHTO 93.
Design Method Used
Percent of Responding Agencies State Agency
AASHTO 72/86/93 85%
AR, AZ, DE, FL, ID, IN, IA, KS, MD, MI, NV, NC, OH, OK, SC, SD, TN, UT, VA, WA, WV, WI, WY
AASHTO MEPDG 4% MOPCA Method 11% HI, IN, IA
State-Developed 7% IL, MT
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U.S. Roadway Length (lane miles)
State Agency,
19%
County, 44%
Town, 32%
Other, 1% Federal, 3%
Source: HM-10, 2012 FHWA Highway Statistics
AASHTO tools are being developed for these owners…
City, county, and other local engineers need
to decide what to use locally because
Pavement ME will not trickle down due to its
cost and complexity!
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Overlay Design – Bonded Concrete on Asphalt
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Bonded over Asphalt/Composite
AASHTO 93: not applicableAASHTO ME: limited to a joint spacing > 10 ft (3 m) and not applicable to thinner (2-6 in. [50-150 mm]) concrete overlays; refers people to ACPAACPA BCOA and StreetPave: account for bond to asphalt and short slab size, fibers, etc.
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Bonded over Asphalt/Composite
Not an extension of an existing design method; a completely custom-built design methodFor ACPA BCOA and StreetPave
based primarily on FHWA-ICT-08-016
Other methods include CDOT 6x6x6 and recently released FHWApooled fund TPF-5(165)
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FHWA pooled fund TPF-5(165)
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Pitt BCOA ME
FHWA Pooled Fund Study TPF 5-165
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BCOA ME failure modes5 to 7 ft
Long. & DiagCrack
Positive ΔT Negative ΔT
< 4.5 ftCorner Break
Positive ΔT
10 x 12 ft12 x 12 ft12 x 15 ft
Trans. Crack
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BCOA-ME
Inputs
Stress for corner cracks
Stress for long. & diag. cracks
Fatigue model hpcc
Jt. Spacing < 4.5 ft
Jt. Spacings5 to 6 ft
Pitt Model
PCA Model
ACPA Model
Stress for trans. cracks
CDOT Model
Jt. Spacings10 x 12 ft12 x 12 ft15 x 12 ft
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Wheel wander considered
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Variation in HMA stiffness
Seasonal variation
Daily variation
Stiff HMASoft HMA
Stiff HMASoft HMA
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Effective temp. gradient
Negative ΔT
Positive ΔT
0%2%4%6%8%
10%12%14%16%
-6.5
-5.5
-4.5
-3.5
-2.5
-1.5
-0.5 0.5
1.5
2.5
3.5
Rel
ativ
e Fr
eque
ncy
Equivalent linear temperature gradient, ºF/in
Design input required: Effective temp. gradient (ETG)
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Regional variation in temp. grad.
University of Pittsburgh Department of Civil & Environmental Engineering
0
0.02
0.04
0.06
0.08
0.1
-3 -2 -1 0 1 2 3
Rel
ativ
e Fr
eque
ncy
Pavement temperature gradient (F˚/in)Pittsburgh Phoenix Miami
Vandenbossche and Mu (2010)
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Calibration - Stress Adj. Factors
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0
Cal
cula
ted
stre
ss a
djus
tmen
t fa
ctor
Generated stress adjustment factor
Stress adjustment factor (Joint spacing > 4ft x 4ft)Linear (Series2)
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Pitt BCOA-ME Web App
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Pitt BCOA-ME Web App
ACPAk-valueweb app
Annual Mean Daily Average Temp
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Results of the BCOA-ME
• BCOA ME is <1/3 ACPA BCOA app, <1/3 CDOT procedure and the remainder was developed at Pitt
• Comparison to ACPA BCOA app:• JS ≤ 4.5 ft, the model is similar but thicknesses
possibly greater because BCOA ME was calibrated to field performance, accounting for loading directly in the wheel path
• JS > 4.5 ft, it will not compare because failure mode changes (e.g., no longer corner cracking); BCOA ME will almost always be thinner than ACPA BCOA for a 6’ x 6’ JS
• Comparison to CDOT design procedure:• Depends on failure mode
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Bonded over Asphalt/Composite
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Design considerations
Overlaythickness
Load carrying layer
HMA
PCC
Bond is essential
Bond enhances performance
PCC = 4 in or lessHMA
PCC = 5 in or more PCC
PCC = 4 in or less
PCC = 5 in or more
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Design considerations
10 in HMA
4 in PCC6 in HMA
6 in PCC4 in HMA
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Design considerations
10 in HMA
4 in PCC6 in HMA
6 in PCC4 in HMA
Critical Stress for 6ft x 6ft slab, psiPCC Thickness 3 in 4 in 6 in
HMA Thickness4 in 352 339 2746 in 246 234 2118 in 198 191 177
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Thank you.Questions? FEEDBACK!
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