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SOIL-STRUCTURE-INTERACTIONSIMULATION MODELS
Juan M. Pestana
University of California, Berkeley
PEER 2001 Annual Meeting
Oakland, California. January 26, 2001
RESEARCH SUPPORTED BY THE PACIFIC EARTHQUAKE ENGINEERING RESEARCH CENTER IN COLLABORATIONWITH THE CALIFORNIA DEPARTMENT OF TRANSPORTATION AND THE NATIONAL SCIENCE FOUNDATION
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SEISMIC SSI- CONCLUSIONS� Key components are: (foundation) soil, foundation system &
structure.
� Key issue of Performance Based Design is the evaluation(estimation) of performance -> Requirement of robust, efficient &realistic numerical- analytical description of material response &system.
� Development & refinement of laboratory experiments which canaccurately represent the problem are essential to validate�individual� constructs (numerical/conceptual blocks). It thereforeprovides an invaluable resource for calibrating numerical Codes->Reduce inherent modeling uncertainty.
� Successful development of coupled site response and Soil-Pile-Superstructure Interaction analyses provides a Comprehensiveframework for Performance Based Design for increasingly highershaking levels
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Geotechnical Engineer�sView of the World
Geotechnical Geotechnical EngineerEngineer��ssView of the WorldView of the World
Structural Engineer�sView of the World
Structural EngineerStructural Engineer��ssView of the WorldView of the World
Courtesy of Dr. Lehman- University of Washington
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SOIL-STRUCTURE INTERACTION
� Types of structures (buildings, bridges, bunkers)
� Transfer Function: Empirically or analyticaldescription of the behavior of a structure givenresponse at ground level.
� Estimation of performance� Shallow foundations- A lot of work still needed (i.e.,
mat foundation). A lot of interest - effect of structureembedment.
� Deep Foundations- A lot of interest- Highway/retrofit of Bridges and other structures in soft soils-SSI is extremely important.
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SSI- DEEP FOUNDATIONSSoil-Pile-Superstructure Interaction
Coupled Model
Earthquake Motion
Overall Response
Modal Mass
input time history
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Large Scale Shaking Table Tests
Seismic Soil- Pile Group-Structure Interaction Test
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Far field element:radiation damping =f(soil nonlinearity innear and free field)
Soil Model
Interface element:gapping = f(plasticsoil deformation)
Near field element:partitioned dynamic nonlinearp-y/t-z spring = f(strain rate,#cycles, strain reversals)
Conceptual Soil - Pile Model
Interface Near field Far field Free field
Free field element:time domain site responseinputs motions at nodes
k1 k2 k3
c1 c2 c3
Modal Mass
input time history
Pilegap
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NONLINEAR SITE RESPONSEANALYSES- MODEL
• KEY ELEMENTS:
• ABILITY TO MODEL SMALLSTRAIN NON-LINEARITYAND DAMPINGCHARACTERISTICS
• FLEXIBILITY TOREALISTICALLY DESCRIBERESPONSE FROM SMALL TOLARGE STRAINS
• CORRESPONDENCE WITHMEASURED SOIL BEHAVIOR- ESTABLISHED PARAMETERDETERMINATION
• CHARACTERIZATION OFUNCERTAINTY
10-4
10-2
100
0
0.5
1Modulus Degradation for Clay ( Vucetic & Dobry)
G/G
max
10-4
10-2
100
0
10
20
30Damping for Clay (Vucetic & Dobry)
Shear Strain (%)
Dam
ping
Rat
io (
%)
model
model(Vucetic & Dobry)
(Vucetic & Dobry)
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TESTSERIES 1.1
CROSS-SECTION
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5%
Dam
ped S
pect
ral A
ccele
ratio
n (g)
Elev 0
Elev -8
Elev -18
Elev -30
Elev -48
0
2
0
2
0
2
0
2
0
2
NONLINEAR SITE
RESPONSE ANALYSIS
CALIBRATEDwith
VERTICALARRAY
INFORMATION
SPECTRAL ACCELERATION
5% D
ampe
d S
pect
ral A
ccel
erat
ion
(g
Period (sec)0.01 0.1 1 10
0
Modal Mass
input time history
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Formulationof nonlinear1-D element
Nonlinear element
Gap element
Friction element
PileFar field
=
+
+
y/yc
p/pul
t
p-y element
gap element nonlinear element
friction element
y/yc
pgap
/pult
y/yc
p/pul
t
y/yc
pfric
tion
/pult
-1.0
1.0
1.0-1.0
-1.0
1.0
1.0-1.0
-1.0
1.0
1.0-1.0
-1.0
1.0
1.0-1.0
ygap
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NUMERICAL CAPABILITIES -NONLINEAR p-y, t-z springs with Gapping Capabilities
-1
-0.5
0
0.5
1
-8 -6 -4 -2 0 2 4 6 8
y/yc
p/p
u
p-y curve for clay
p-y w/ gap (loop 1)
p-y w/ gap (loop 2)
Pilegap
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-8
0
8
-8
0
8
-0.5 0 0.5Deflection Y (in)
-8
0
8
-0.5 0 0.5Deflection Y (in)
depth = 4d depth = 5d
depth = 6d depth = 7d
depth = 8d depth = 9d
Soi
l Res
ista
nce
P (l
b/in
)
Calculated
Test Data
NEAR FIELD RESPONSE
Modal Mass
input time history
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FOUNDATION RESPONSE- BENDING MOMENTS
D
6543210
Depth
(ft)
S3
0 0.5 1Bending Moment (k-in)
6543210
Depth
(ft)
S4
6543210
Depth
(ft)
S1
6543210
Depth
(ft)
S2
ft)
S3
Modal Mass
input time history
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PREDICTION OF STRUCTURAL RESPONSE
Modal Mass
input time history
PS
A (g
)
0
1
2
3
4
5
PS
A (g
)
S3
0.01 0.1 1 10Period (sec)
0
1
2
3
4
5
PS
A (g
)
S4
0
1
2
3
4
5
PSA
(g)
S1
0
1
2
3
4
5
PSA
(g)
S2
PSA
(g)
PSA
(g)
PSA (g)PSA (g)PSA (g)PSA (g)
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STRUCTURALRESPONSE
Compute
d Tp (sec
)
5
Compute
d Max. Sa
(g)
0 0.4 0.8 1.2 1.6 2Recorded amax (g)
0
0.4
0.8
1.2
1.6
2
Compute
d amax (g)
S1S2
S3
S4
(a)
0 0.1 0.2 0.3Recorded Tp (sec)
0
0.1
0.2
0.3
Comp
uted T
p (se
c)
S1
S3
0 1 2 3 4 5Recorded Max. Sa (g)
0
1
2
3
4
5
Comp
uted M
ax. S
a (g)
S1
S2
S3S4
(b)
(c)
S2
S4
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Performanceof Pile GroupsEquivalent Pier
Approach
0.0
1.0
2.0
3.0S
pect
ral A
ccel
erat
ion
(g) Recorded
e=1.0
e=0.8
e=0.6
e=0.4
e=0.2
0.01 0.1 1 1 0Period (sec.)
0.0
1.0
2.0
3.0
Spec
tral
Acc
eler
atio
n (g
) Recorded
e=1.0
e=0.8
e=0.6
e=0.4
e=0.2
Response of Structure
Response of Pile Cap
Damping=5%
Damping=5%
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
Input MHA
p-y
eff
icie
ncy
2x2 pile gr
3x3 pile gr
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Multidirectional Shaking2-D & 3-D Site Response Analyses
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
-0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08
Fault Parallel Sur
Fault Normal Surface Motion (m)
Pacoima Dam recorda
max = 0.05g
50 m Soil Profile
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-10.0
-5.0
0.0
5.0
10.0
-0.4 -0.2 0 0.2 0.4
5 %10 %
20 %50 %API
Normalized For
u.d.L)
Symbol A/d
Test B1D3L/D= 2
w (Hz) 3.0
Normalized Deflection, y/d
-10.0
-5.0
0.0
5.0
10.0
-0.4 -0.2 0 0.2 0.4
5 %10 %
20 %50 %API
Normalized Force , P/(s
u.d.L)
Symbol A/d
Test B3D4L/D= 8
w (Hz) 3.0
Normalized Deflection, y/d
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MULTIDIRECTIONAL P-Y ELEMENTS
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Numerical Tool
OpenSees
Platform
* Nonlinear Site
Response (2-D)
* Near Field, p-y
Near Field, t-z andQ-z Capabilities
New Elements
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CONCLUSIONS- DEJA VU� Key components are: (foundation) soil, foundation system &
structure.
� Key issue of Performance Based Design is the evaluation(estimation) of performance -> Requirement of robust, efficient &realistic numerical- analytical description of material response &system.
� Development & refinement of laboratory experiments which canaccurately represent the problem are essential to validate�individual� constructs (numerical/conceptual blocks). It thereforeprovides an invaluable resource for calibrating numerical Codes->Reduce inherent modeling uncertainty.
� Successful development of coupled site response and Soil-Pile-Superstructure Interaction analyses provides a Comprehensiveframework for Performance Based Design for increasingly highershaking levels