lrfd application in driven piles (recent development … application in driven... · (recent...
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1
LRFD Application in Driven Piles
(Recent Development in Pavement &
Geotech at LTRC)
2007 Louisiana Transportation Engineering Conference
February 12, 2007
Sungmin “Sean” Yoon, Ph. D., P.E.
and
Murad Abu-Farsakh , Ph. D., P.E.
2
Outline
Problem statement
Different design methods
Statistical concept
Methods used in LADOTD for driven piles
LRFD calibration
Conclusion
3
Problem Statement and Research Objectives
Working Stress Design (WSD), Allowable Stress Design (ASD) vs. LRFD
Bridge super structures vs. Foundation
Federal Highway Administration and ASSHTO set a transition date of October 1, 2007
Resistance Factor (Φ) reflecting Louisiana soil and DOTD design process
4
Calibration of the Design Code for Bridge
Substructure
Identify the load and resistance parameters for bridge
substructure
Formulate the limit state functions
Develop the reliability analysis procedure and calculate
reliability indices
Select the target reliability index
Determine the load and resistance factors for bridge
substructure (including earth pressure related loads)
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Stress Design Methodologies vs. LRFD
Working Stress Design (WSD) –also called Allowable Stress Design (ASD)
where, Q=design load; Qall=allowable design load; Rn=resistance of the structure, and Qult=ultimate resistance of the structure
n ultall
R QQ Q
FS FS
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Stress Design Methodologies vs. LRFD
Limit State Design (LSD)
Ultimate Limit Stress (ULS)
Service Limit Stress (SLS)
Factored resistance ≥ Factored load effects
Deformation ≥ Tolerable deformation to remain serviceable
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Stress Design Methodologies vs. LRFD
Load and Resistance Factor Design (LRFD)
where, Φ=resistance factor, Rn=ultimate resistance; rD=load factor for dead load; rL=load factor for live load; ri=corresponding load factor, and Qi=summation of load
n D D L L i iR r Q r Q rQ
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Working Stress Design (WSD) vs. LRFD
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Random Variation
Load and resistance parameters are random variables
Reliability index is a measure of structural
performance
Practical procedure for calculation of the reliability
indices
Target reliability index
Load and resistance factors that result in design that is
close to the target reliability index
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Statistical Concept
Mean (μ) and Mode
Variance (σ2) and Standard Deviation (σ)
Coefficient of Variation (COV)
Probability Density Function (PDF)
2
2( )
1
ix x
n
COV
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Limit State Function
Limit State Function can be defined as
g = R – Q
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Reliability Index,
2 2
R Q
g R Q
g
13
Reliability Based FS
FSLoad effect = Q
Capacity = R
design load design capacity
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Relationship between and Pf
Pf
10-1 1.28
10-2 2.33
10-3 3.09
10-4 3.71
10-5 4.26
10-6 4.75
10-7 5.19
10-8 5.62
10-9 5.99
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First Order Second Moment (FOSM)1
Load and Resistance Factor Design (LRFD)
where, Φ=resistance factor, Rn=ultimate resistance; rD=load
factor for dead load; rL=load factor for live load;
ri=corresponding load factor, and Qi=summation of load
n D D L L i iR r Q r Q rQ
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First Order Second Moment (FOSM) 2
n D D L L i iR r Q r Q rQ (1)
(2)
Combining eq (1) and (2) using Rn
AASHTO (1994)
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Methods used in LADOTD
(Ultimate Capacity for Driven Piles) Static method
α method - General adhesion for cohesive soil (Tomlison 1979)
Nordlund method
CPT method
Schmertmann, LCPC, de Ruiter and Beringen
Dynamic Analysis
GRL WEAP
Dynamic Measurement
CAPWAP
Measured Ultimate Pile Capacity
Davisson, Butler-Hoy
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Davisson (Interpretation of Pile Load Tests)
= QL/AE
x = 0.15 + D/120
(in)
Static Load Test Results
0.00
0.50
1.00
1.50
2.00
2.50
0 50 100
Load (Tons)
Se
ttle
me
nt (
in)
Qult
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Butler-Hoy (Interpretation of Pile Load Tests)
Static Load Test Results
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
2.00
0 50 100
Load (Tons)
Sett
lem
en
t (in) Slope =
0.05 in./ton
Qult
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Cone Penetration Test (CPT) Method
Tip
resistance, qc
Sleeve
friction, fs
Penetration Rate:
2 cm/sec
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Ultimate Pile Capacity from CPT
End-bearing Capacity, Qtip
= qt . At
Shaft friction Capacity,
Qshaft = fi . Asi
Qult = Qtip + Qshaft
f
qt
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Schmertmann method (CPT)
where,
qt: unit bearing capacity of pile
f: unit skin friction
c: reduction factor (0.2 ~ 1.25 for clayey soil)
fs: sleeve friction
e
D
a
b
b
Envelope of minimum qc values yD
?
'x'
8D
Cone resistance qc
De
pth
qc1 + qc2
2
c
qc1
qc2
qt =
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LCPC method (CPT)
Pile
a=1.5 D
0.7qca
qca1.3qca
qc
De
pth
aa
qeq
D
qt = kb qeq (tip)
kb = 0.6 clay-silt
0.375 sand-gravel
max
s
eq
k
(side)/q ff
ks = 30 to 150
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de Ruiter and Beringen (CPT)
In clay
Su(tip) = qc(tip) / Nk Nk = 15 to 20
qt = Nc.Su(tip) Nc = 9
f = .Su(side) = 1 for NC clay
= 0.5 for OC clay
In sand
qt similar to Schmertmann method
TSF21
tension400side
ncompressio300side
iction)(sleeve fr
.
)( /)(q
)( /)(q
f
minfc
c
s
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Implementation into a Computer Program
Louisiana Pile
Design by Cone
Penetration Test
http://www.ltrc.lsu
.edu/
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Histograms
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
Rn / Rm
0
5
10
15
20
25
Pro
ba
bil
ity
(%
)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
Rn / Rm
0
5
10
15
20
25
Pro
ba
bil
ity
(%
)
0.0
0.5
1.0
1.5
2.0
2.5
Pro
ba
bil
ity
de
ns
ity
fu
nc
tio
n
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
Rn / Rm
LCPC methodDe Ruiter & Beringen method
Schmertmann method
0.0
0.5
1.0
1.5
2.0
2.5
Pro
ba
bil
ity
de
ns
ity
fu
nc
tio
n
- method
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
Rn / Rm
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Resistance Factors, (Davisson)
0 1 2 3 4 5 6 7 8 9 10
Ratio of dead load to live load (QD/Q L)
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
R
es
ista
nc
e f
ac
tor,
LCPC method
Schmertmann method
- ststic method
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Resistance Factors, (Butler-Hoy)
0 1 2 3 4 5 6 7 8 9 10
Ratio of dead load to live load (QD/Q L)
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
Re
sis
tan
ce
fa
cto
r,
LCPC method
Schmertmann method
- ststic method
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Resistance Factors, T=2.5
Load Test
Interpretation
Method
Pile Capacity
Prediction
Method
Span Length
30 ft 90 ft
Davisson
α-Method 0.57 0.53
LCPC 0.66 0.61
Schmertmann 0.50 0.47
De Ruiter 0.69 0.64
Butler-Hoy
α-Method 0.55 0.51
LCPC 0.65 0.6
Schmertmann 0.5 0.46
De Ruiter 0.68 0.63
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Conclusions
Tentative resistance factors ( ) for Louisiana soil were
evaluated for different driven pile design methods
(Research is on going).
Values of resistance factor depend on the pile load test
interpretation and design methods.
LRFD in deep foundation can improve its reliability due to
more balanced design.
There is a strong need for more statistical data to get
more rational resistance factor.
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LRFD Implementation in Louisiana
Dr. Ching Tsai
Wednesday 10:00 - 11:45 a.m.
Session 83: Geotechnical Services
Meeting Room 3
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Acknowledgement
The project is financially supported by the
Louisiana Transportation Research Center
and Louisiana Department of Transportation
and Development (LA DOTD).
LTRC Project No. 07-2GT.
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References
Paikowsky, S.G. 2007 TRB presentation.
Bea, Robert G. 2006 presentation
Nowak, Andrzej S. 2007 TRB presentation.
Mayne, Paul W.
<http://www.ce.gatech.edu/~geosys/Faculty/Mayne>
NCHRP report 507: Load and Resistance Factor Design (LRFD) for
Deep Foundation.
