atlantic city, nj / april 25, 2012 federal aviation administration airport pavement working group...
TRANSCRIPT
Atlantic City, NJ / April 25,
2012
Federal Aviation AdministrationAirport Pavement Working Group Meeting
Mechanistic-Empirical PCN Procedure
Gabriel Bazi, PhD, PE
DCI History of Dynatest ME PCN Procedure
ELPCN ≈1987 – 1998 DOS Version
WinPCN 1998 – 2003 Windows Version
ELMOD PCN 2003 – Present ELMOD sub-module
2
DCI Revised ME PCN Procedure
Existing and revised procedures are similar except
for the last step in PCN calculation
Existing Procedure
Permissible response
ESWL
» PCN
Revised procedure
Permissible response
Permissible gross weight
» PCN3
Presented today
DCI ME PCN Procedure Advantages
ME PCN procedure has same advantages as ME analysis
Flexible and rigid pavements
Rehabilitation or new design
Layer moduli (stiffnesses)
No need for layer equivalency factors/equivalent
pavement…
Considers the failure modes of all layers:
Fatigue cracking for AC and PCC layers
Permanent deformation for unbound layers (base, subbase,
subgrade)…
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DCI ME PCN Procedure Advantages
Considers various seasons
AC moduli change due to temperature
Unbound layer moduli change due to moisture (& freezing
and thawing)
Different aircrafts (weights, repetitions….)
Aircraft lateral wander
Normal distribution
P/C
…
5
DCI ME PCN Procedure
100% compatible with ME design
If Remaining life (RL) = Design Life (DL) PCN = ACN
If RL < DL PCN < ACN
If RL > DL PCN > ACN
6
DCI Layer Moduli
New Design
WES modulus procedure for unbound layer moduli [UFC
TM 5-822-13/AFJMAN 32-1018]
Currently used in FAARFIELD
Lab/Assumed
Existing structures (Rehabilitation)
HWD testing and backcalculation
LWD for unbound layers
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DCI
8
Flexible Pavement Structural Evaluation
Calculate critical stresses and strains under load
Fatigue cracking: Horizontal tensile strain at bottom of AC
Permanent deformation in unbound layers: Vertical
compressive stress or strain on top of layer
Horizontal tensile strain at the bottom of the AC layer
Vertical compressive stress or strain on top of the base layer
Vertical compressive stress or strain on top of the subgrade
AC
AB
SG
DCI
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Rigid Pavement Design
Calculate critical stresses under load
Fatigue cracking: Horizontal tensile stress at bottom of
PCC
Horizontal tensile stress at the bottom of the PCC layer
PCC
Support
DCI ME Structural Evaluation
For each failure criterion, calculate the total damage (dt)
using empirical models
If dt 1.0 Structure is adequate
If dt > 1.0 Structure is not adequate
Remaining life
Limit remaining life to 40 years
10
td
PeriodDesign Life Remaining
Structural Evaluation
is Complete
DCI Permissible Gross Weight (wp)
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Total damage (dt) calculated for all
aircrafts combined
Each aircraft from mix is evaluated separately (or just evaluate aircraft
with largest ACN):
If dt < 1 Increase dt to 1:wp > gross weight PCN > ACN
If dt > 1 Decrease dt to 1:wp < gross weight PCN < ACN
DCI Permissible Gross Weight (wp) 1) 2)
The permissible gross weight is the weight that would cause a total
damage of 1.0 with the traffic mix converted to each aircraft.
where w: gross weight of aircraft,
wp: permissible gross weight, and
dt: total damage
B: parameter from empirical model
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Btp dww
1) Assuming one model is used per criterion2) Refer to Appendix A for alternative calculation procedure
B
w
Life Remaining
PeriodDesign
Permissible Weight Multiplier
Btd
DCI Various Forms of Empirical Models
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ClogBconstantσor εlog
Cconstantσor ε
σor ε
constantC
σor εlogB
1constantClog
B
B
1
Use B in previous equation to determine wp
DCI PCN Calculation
Using the permissible gross weight, calculate the ACN for
each aircraft and assign it as its PCN
COMFAA
Power curve fit using ACNs for min. and max. weights
Polynomial curve fit using ACNs for min., max., ½ min.
and 2max. weights
Select the largest PCN from the mix as the PCN for the
structure
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DCI Subgrade Category for ACN/PCN
If subgrade category (CBR or k-value) changes
along a feature (e.g. FWD test points along a runway, or
various CBR tests on a taxiway…)
determine average conditions for PCN calculation
over various seasons
determine weighted average conditions for PCN calculation
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DCI Flexible Pavement Example
2 Seasons:
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E1 = 500 ksi
E3 = 6 ksiCBR = 4Code D
AC:
SG:
Season 1 (3 months)
E2 = 37.5 ksi AB:
h = 6 in
h = ∞
h = 36 in
Season 2 (9 months)
E3 = 24 ksiCBR = 16Code A
E2 = 50 ksi
E1 = 250 ksi
= 0.35 for all layers
DCI
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Aircraft Mix used in the Analyses
Aircraft MTOW(lb)
% Grosson OneMainGear
GearType
WheelSpacing
(in)
AxleSpacing
(in)
TirePressu
re (psi)
Annual Coverage
s n
Adv. B727-200C Basic
185,200 47.5 Dual 34 -- 148 1,000
A330-200 std 509,047 47.5 Dual
Tandem 55 78 206 1,000
A330-200B727-200
Notes: Coverages assumed to be same for AC fatigue and AB/SG PD failure criteria. Load uniformly distributed throughout the year
DCI AC Fatigue Cracking Failure Model
AC Fatigue Cracking Failure Model (USACE/FAA)
log(C) = 2.68 – 5log() – 2.665log(E)
where: C = number of coverages to failure
E = AC modulus (psi)
= horizontal strain at the bottom of the surface
asphalt layer
For this model: 18
0.2B5B
1
DCI AB/SG Permanent Deformation Model
Unbound Material Permanent Deformation (Kirk)
where: 1,p = vertical stress on top of unbound layer, ksi
N = number of coverages in millions
E = modulus of material, ksi
E0 = 23.2 ksi
C = 1.16 for E<E0
C = 1 for E E0
For this model: 19
Cp E
EN )(0174.0
0
307.0,1
0.307B
DCI Flexible Pavement Example
Analysis period = 20 years
1) Analysis performed using ELMOD (w/ LET) 2) Calculated using a maximum remaining life of 40 years
Lowest dtB = 0.826 PCN analysis is controlled by the AC
layer fatigue cracking20
Layer
CriterionTotal
Damage dt
Remaining Life
(Years) 1)
BPermissible
Weight Multiplier (dtB)
1 AC Fatigue Cracking 2.604 7.7 – 0.2 0.826
2AB Permanent Deformation
1.683 11.9–
0.3070.852
3SG Permanent Deformation
0.103 > 40–
0.3071.237 2)
Lowest Permissible Weight Multiplier (dtB) 0.826
DCI PCN
Weighted subgrade modulus
CBR = 13 Subgrade code A
PCN Calculation:
1) ACN for permissible gross weight calculated using COMFAA
PCN: 45/F/A/X/T
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AircraftGross
Weight w(lb)
Permissible Weight
Multiplier (dtB)
Permissible Gross
Weight (wp)
ACN = PCN 1)
Adv. B727-200C Basic 185,200 0.826 152,975 36.0
A330-200 std 509,047 0.826 420,473 45.4
Select largest ACN as PCN for the structure 45.4
ksi 19.512
42963
DCI ACN-PCN Comparison
Largest ACN:
PCN: 45/F/A/X/T
Remaining life (7.7 years) < Design life (20 years) PCN <
ACN
Analysis controlled by AC fatigue cracking
About 3-inch of AC are needed to restore the structural
capacity
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Aircraft ACN
A330-200 std 57/F/A
DCI Subgrade Category Selection
ACN-PCN Ratios calculated for various subgrade categories
ACN-PCN ratios are almost the same for all subgrade
categories
Subgrade code selection is not critical (at this level)
Subgrade properties are important in ME analysis
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Subgrade Code ACN PCN ACN-PCN Ratio
A 57.0/F/A 45.4/F/A/X/T 1.26
1.3B 61.9/F/B 48.3/F/B/X/T 1.28
C 71.6/F/C 54.8/F/C/X/T 1.31
D 96.8/F/D 73.1/F/D/X/T 1.32
DCI If Only SG Criterion was Considered!!
Permissible Weight Multiplier (dtB) = 1.237 > 1.0
PCN >ACN
Knowing that the pavement is failing (RL = 7.7 years)
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CONSIDER ALL FAILURE CRITERIA FOR PCN
CALCULATION
DCI Notes
For PCN calculation, limit calculated remaining life to 40
years
PCN values are associated with the traffic used in the
evaluation
An increase in traffic during the evaluation period will
reduce the PCN
PCN is highly dependent on aircraft mix
Existing structures: PCN to be calculated for existing
conditions and after rehabilitation, if needed
When PCN is evaluated for several points on a feature, report
84th percentile (Average – standard deviation)25
DCI Notes
Possibly complement the PCN number with the additional
number of allowable coverages of aircraft having ACN = PCN
Instead of having unlimited operations when
ACN/PCN ≤ 1.0
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DCI
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Discussion & Questions
DCI
28
Thank You
DCI Appendix A: Permissible Gross Weight (wp)
1. For every aircraft, calculate the equivalent number of load
repetitions that would cause the same total damage (dt) as the
aircraft mix = Allowable number of load reps. (N) Total damage
(dt)
2. Calculate the allowable stress or strain using the empirical model
for the equivalent number of load repetitions calculated in step 1
3. Calculate the permissible gross weight (wp) as the MTOW
multiplied by the ratio of allowable stress or strain (from step 2)
and the actual stress or strain of that aircraft (use of response
ratio is valid if contact area is constant)
Note: If various seasons are available, the use of any
season would provide same permissible gross weight29
DCI Appendix B: Rigid Pavement Example
2 Seasons:
30
E1 = 4,000 ksi, = 0.15
E3 = 7.5 ksi, = 0.35k = 82.4 pci 1)
Code D
PCC:
SG:
Season 1 (6 months)
h = 14 in
h = ∞
Season 2 (6 months)
E3 = 15 ksi, = 0.35
k = 141.4 pci 1)
Code C
E1 = 4,000 ksi, = 0.15
1) Equation used to convert E (psi) to k (pci):ESG = 26k1.284 FAA AC 150/5320-6E page 34
Note: Interface assumed to be bonded
DCI
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Aircraft Mix used in the Analyses
Aircraft MTOW(lb)
% Grosson OneMainGear
GearLoad
(lb)
GearType
WheelSpacin
g(in)
TirePressur
e (psi)
Annual Coverage
s n
B737-800 174,700 46.78 81,725 Dual 34 205 1,200
A320-100 150,796 47 70,874 Dual 36.5 200 1,500
A320-100
B737-800
Note: Load uniformly distributed throughout the year
DCI PCC Fatigue Cracking Failure Model
PCC Fatigue Cracking Failure Model (PCA)
where: PCC = Tensile stress at bottom of PCC (ksi)
N = No. of coverages to failure in millions
E = Modulus of PCC (ksi)
For this model32
5000408.0 0575.0 E
NPCC
0.0575B
DCI Rigid Pavement Example
Analysis period = 20 years
1) Responses calculated using MnLayer at center of slab
dtB = 1 PCN = ACN
Remaining life = Analysis period (20 years)
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Layer
CriterionTotal
Damage dt
Remaining Life
(Years) 1)
BPermissible
Weight Multiplier (dtB)
1 PCC Fatigue Cracking 1.0 20.0–
0.0571.0
DCI PCN
Weighted k-value
Subgrade Code C
PCN Calculation:
1) ACN for permissible gross weight calculated using COMFAA
PCN: 54/R/C/W/T
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AircraftGross
Weight w(lb)
Permissible Weight
Multiplier (dtB)
Permissible Gross
Weight (wp)
ACN = PCN 1)
B737-800 174,700 1.0 174,700 54.1
A320-100 150,796 1.0 150,796 44.3
Select largest ACN as PCN for the structure 54.1
pci 111.912
141.4682.46