Collaborative Research: Centrifuge Modeling for SoilPileBridge Interaction

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Collaborative Research Centrifuge Modeling for
Soil-Pile-Bridge Interaction
Bruce Kutter, Professor Mahadevan Ilankatharan,
Graduate student
University of California, Davis
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Main Points

• Scope of project
• Scope of centrifuge test program
• Collaborative design column length issue
• Comparison of centrifuge and shaking table tests
• Component tests vs system tests
• Comparison of simulations and experiments
• Data archiving

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UW, UCB, UCD
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Collaboration in Centrifuge Tests Design
UW

• Many hours of
• Video conferences
• - Conference phone calls
• Face to Face meetings
• Email

Ground motion, numerical simulations
Dimensions details of structural models
UCD
Soil properties
UT
UNR
Data archiving
NEESit
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NEES Geotechnical Centrifuge at Davis
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Centrifuge Model
Shaking direction
First Centrifuge Test Series (MIL01)
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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 superstructures
• Two pile-bents,
• Varied orientation relative to shaking
• Varied mass of bent
• Varied clear height of pile
• Single piles
• Two span segment of bridge
• Dates of testing December 2004 January 2006

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UCD Centrifuge test
1/52 scale aluminum tube piles

• 1/4 scale reinforced concrete columns
• fixed support on shake tables

UNR shake table test
What should be the shaking table column height to
achieve similar natural frequencies, and moment
and shear distribution?
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Equivalent depth of fixity
We chose to model the column stiffness so that
natural frequencies would be the same in
centrifuge and shake table. Equivalent depth
of fixity would be different if you want to model
the column capacity.
L f Equivalent depth of fixity (Chai, 2002)
H clear, pile H col, shake table - L f
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Comparison of centrifuge 1-g shake table test
results
Deck accelerations
Deck acceleration (g)
Medium amplitude shake Peak base acc 0.25g (in
centrifuge test)
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Comparison of Centrifuge and Shake Table Results
for 0.25 g shake
Shake table motions are a bit different for for
each shake table (possible specimen-table
interaction)
damping may be greater due to radiation damping
in centrifuge
two modes (translation torsion) are closer
together in shake table test than centrifuge test
(distorted span length in centrifuge test).
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Component vs System behavior
Single bent configuration
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Component vs System Behavior
Bridge bent configuration
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Component vs System Behavior
Short bent-cap motions
Spectral acceleration of bent cap motion is much
less when it is connected to the deck. But,
bending moments are only slightly smaller
Pile bending moments _at_ maximum bent-cap
displacement
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Component vs System Behavior
Medium bent-cap motions
Spectral acceleration of bent cap motion is
similar when it is connected to the deck. But
bending moments are much greater!
Pile bending moments _at_ maximum bent-cap
displacement
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Shin, Ilankatharan, Arduino, Kutter, and Kramer
(8 NCEE, 2006)
Excellent comparisons between OpenSEES and
centrifuge results! Some analyses done during
testing
P-y and shear beam analyses using OpenSEES are
verified for piles in dry sand.
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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
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Concluding Remarks

• Complementary experiments on multiple NEES sites
  requires collaboration amongst multiple experts.
  Cross-disciplinary training may lead to more
  holistic soil-structure system designs.
• Direct comparison of results from different types
  of facilities is valuable because it can clearly
  expose flaws that we might otherwise ignore,
  e.g.,
• importance of distorting bent spacing,
• specimen-actuator interaction
• Extension of element behavior to system behavior
  via numerical analysis cannot be taken for
  granted and must be tested. Major NEES facilities
  enable testing response of multiple component
  systems (e.g., multiple span bridge decks).

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Concluding Remarks

• Data from three series of highly instrumented
  centrifuge tests and approximately fifty shaking
  eventsis archived and available through
  NEEScentral
• Results from OpenSEES analyses were able to
  accurately predict the experimental results.

• A UW graduate student, Hyung-Suk Lee
• spent about a month helping Lanka perform each
  experiment.
• His assistance with the experiment helped him
  understand and confidently use the test data for
  his numerical simulations
• Pre-test analyses helped us design the specimens
• Analyses during the test helped us figure out how
  hard and how many times to shake the specimens
  and what to look for in the data.

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Acknowledgements

• Visiting Scholar Tetsuya Sasaki, PWRI, Japan
• Student at UNR Nathan Johnson
• Students at Austin Puneet Agarwal, and Asli
  Kurtulus
• Faculty Arduino, Kramer, Wilson, Jeremic, and
  Wood
• IT advice Roger Clermont and Shannon Whitmore
  (NEESit)
• Centrifuge Technicians Chad Justice, Tom Coker,
  and Tom Kohnke