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

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

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

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.

SSI- DEEP FOUNDATIONSSoil-Pile-Superstructure Interaction

Coupled Model

Earthquake Motion

Overall Response

Modal Mass

input time history

Large Scale Shaking Table Tests

Seismic Soil- Pile Group-Structure Interaction Test

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

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)

TESTSERIES 1.1

CROSS-SECTION

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

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

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

-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

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

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)

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

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

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

-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

MULTIDIRECTIONAL P-Y ELEMENTS

Numerical Tool

OpenSees

Platform

* Nonlinear Site

Response (2-D)

* Near Field, p-y

Near Field, t-z andQ-z Capabilities

New Elements

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