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Collaborative Research:Centrifuge M odeling forSoil-Pile-Bridge Interaction

University of California, Davis

Bruce Kutter, Professor

Mahadevan Ilankatharan, Graduate student

NEES 4 th Annual Meeting

June 21-23, 2006 Washington DC

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Main Points

Scope of projectScope of centrifuge test programCollaborative design column length issueComparison of centrifuge and shak ing table testsComponent tests vs system testsComparison of simulations and experimentsData archiving

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C o m p u t a t i o n a lModels

Pr o t o t y p e St r u c t u r e

UW , UCB, UCD OutreachSJSU

DataKansas

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Collaborat ion in Centrifuge Tests Design

UCD

UW

UNR UT

Ground motion,numerical simulations

Dimensions & details of structural models Soil properties

M any hours of

- Video conferences

- Conference phone calls

- Face to Face meetings- Email

NEESit

Data archiving

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NEES Geotechnical Centrifuge at Davis

41 1

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Centrifuge Model:

93.6

41.1

85.8

BENT 1

SINGLEPILE

PLAN VIEW

X X

ELEVATION AT X-X

3.9

27.8

6.4

BENT 2 BENT 3

BENT 4 BENT 5

2.6

FirstCentrifugeTest Series(MIL01)

Shakingdirection

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Features of centrifuge models:

Centrifuge g level : 52 g

Soil : dry Nevada Sand (Dr = 80 %)

Piles: strain gauged aluminum tube

Ground motion :Realistic ground motions selected by UW

Frequency sweeps

Scaled amplitude in successive events

20 different superstructuresTwo pile-bents,

Varied orientation relative to shaking

Varied mass of bentVaried clear height of pile

Single piles

Two span segment of bridge

Dates of testing: December 2004 January 2006

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6030

BENT B BENT C

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1/ 52 scalealuminum tube piles

- 1/ 4 scale reinforced concretecolumns

- fixed support on shake tables

UNR shake table test:

UCD Centrifuge test:

W hat should be the shaking table column height to achieve

similar natu ral frequencies, and m oment and shear distribution?

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H clear, pile = H col, shake table - L f

L f : Equivalent depthof fixity

(Chai, 2002)

Lf

Centrifuge Pile

H clear, pileH col, shake

table

Shake tablecolumn

Equivalent depth of fixity

We chose to modelthe column stiffness

so that naturalfrequencies would be

the same incentrifuge and shake

table.

Equivalent depth offixity would bedifferent if you wantto model the columncapacity .

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Instrumentation:

Bent cap

Free field soil

Strain gage instrumentation

C i f if & 1 h k bl l

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0 5 1 0 1 5 2 0 2 5

- 0 . 4

- 0 . 2

0 . 0

0 . 2

0 . 4

- 0 . 4

- 0 . 2

0 . 0

0 . 2

0 . 4

- 0 . 4

- 0 . 2

0 . 0

0 . 2

0 . 4

D e c k m o t i o n @ C e n t r i f u g e t e s tD e c k m o t i o n @ S h a k i n g t a b l e t e s t

( i ) S h o r t b e n t

( i i ) T a l l b e n t

( i i i ) M e d i u m b e n t

T i m e ( p r o t o t y p e s e c o n d s )

D e c

k a c c e

l e r a

t i o n

( g )

Deck accelerations

Medium amplitude shake: Peak base acc = 0 .25g (incentrifuge test)

Comparison of centrifuge & 1-g shake table test results :

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S T M

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0 1 2 3

Period (s)

0 1 2 3

A

R S ( g )

0

1

2

Free field motion @ 2.5 m depth @ Centrifuge test

Shaking table base motion

0 1 2 30

1

2

Deck motion @ Centrifuge test

Deck motion @ Shaking table test

(i) Short bent (ii) Tall bent

(vi) Medium bent(iv) Short bent (v) Tall bent

(iii) Medium bent

Shake table motions are a bit different for for each shake table (possiblespecimen-table interaction)

Comparison of Centrifuge and Shak e Table Results for 0.25 g shake

damping m ay be greater due to radiation damping in centrifugetw o modes (translation + torsion) are closer together in shake table testthan centrifuge test (distorted span length in centrifuge test).

C t S t b h i Single bent configuration

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Component vs System behavior: Single bent configuration

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S T M

C t S t B h i Bridge bent configuration

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Component vs System Behavior: Bridge bent configuration

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S T M

Component vs System Behavior:

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0.0

0.5

1.0

1.5Single bentBridge bent

(i) Short Bent (Hc/D=2.2)

-2000 -1000 0 1000

D e p

t h f r o m g r o u n

d s u r f a c e ( m

)

-8

-4

0

4

8

12

(i) Short Bent (Hc/D=2.2)

Single bent

Bridge bent

Period (s)0.0 0.5 1.0 1.5 2.0 2.5 3.0

.


Pile bending moments @ maximumbent-cap displacement

Short bent-cap motions

Spectral acceleration of bent capmotion is much less when it isconnected to the deck. But,bending moments are onlyslightly smaller


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-2000 -1000 0 1000

(iii) Medium Bent (Hc/D=3.3)

Single bentBridge bent

Period (s)0.0 0.5 1.0 1.5 2.0 2.5 3.0

0.0

0.5

1.0

1.5Single bentBridge bent

(iii) Medium Bent (Hc/D=3.3)

.


Pile bending moments @ maxim umbent-cap displacement

Medium bent-cap motions

Spectral acceleration of bent capmotion is similar when it isconnected to the deck. But

bending moments are muchgreater!

Shin Ilankatharan Arduino Kutter and Kramer

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Excellentcomparisonsbetween

OpenSEESand centrifugeresults! Some

analyses doneduring testing

Shin, Ilankatharan, Arduino, Kutter, and Kramer(8 NCEE, 2006)

P-y and shearbeamanalysesusingOpenSEES areverified for

piles in drysand.

Data archives:

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Data archives:

-MIL data is the most completely documented experiment in NEEScentral

-Have already heard about this data in NEESit report later-Recent interactions with NEESit have been productive! Project

Experiments

Trials

Data

DAQs

-Unprocessed data-Converted data-Corrected data-Derived data

Concluding Remarks:

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Complementary experiments on multiple NEES sites

requires collaboration amongst multiple experts. Cross-disciplinary training may lead to more holistic soil-structuresystem designs.

Direct comparison of results from different types offacilities is valuable because it can clearly expose flawsthat we might otherwise ignore, e.g.,

importance of distorting bent spacing,specimen-actuator interaction

Extension of element behavior to system behavior vianumerical analysis cannot be taken for granted and must betested. Major NEES facilities enable testing response of

multiple component systems (e.g., multiple span bridgedecks).

Concluding Remarks:

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Concluding Remarks:

A UW graduate student, Hyung-Suk Lee

spent about a month helping Lanka perform each experiment.His assistance with the experiment helped him understand andconfidently use the test data for his numerical simulationsPre-test analyses helped us design the specimens

Analyses during the test helped us figure out how hard and how manytimes to shake the specimens and what to look for in the data.

Data from three series of highlyinstrumented centrifuge tests andapproximately fifty shaking eventsisarchived and available throughNEEScentral

Results from OpenSEES analyseswere able to accurately predict the

experimental results.

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Acknowledgements:

Visiting Scholar: Tetsuya Sasaki , PW RI, Japan

Student at UNR : Nathan Johnson

Students at Austin: Puneet Agarwal, and Asli Kurtulus

Faculty: Arduino, Kramer, W ilson, Jeremic, and W ood

IT advice Roger Clermont and Shannon W hitm ore (NEESit)

Centrifuge Technicians: Chad Justice, Tom Coker, and TomKohnke

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