Centrifuge Models Design and Execution: Some Practical Considerations Student Researchers: Gabriel Candia & Roozbeh Geraili Advisor: Nicholas Sitar University of California, Berkeley Department of Civil and Environmental Engineering
Centrifuge Models Design and Execution: Some Practical Considerations Student Researchers: Gabriel Candia & Roozbeh Geraili Advisor: Nicholas Sitar University.
Dec 17, 2015
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Centrifuge Models Design and Execution: Some Practical Considerations
Student Researchers: Gabriel Candia & Roozbeh Geraili
Advisor: Nicholas Sitar
University of California, Berkeley
Department of Civil and Environmental Engineering
WHY CENTRIFUGE MODELING?
2
Advantages
•Correct scaling of stresses
•Repeatable and cost effective
•Ability to model large
structures with reasonable
boundary conditions
Limitations and challenges
•Non uniform gravity field•Need for high speed
instruments•Ability to reproduce recorded
ground motions•Boundary conditions
OVERVIEW EXPERIMENTS PERFORMED DESIGN AND EXECUTION
3
OVERVIEW EXPERIMENTS PERFORMED DESIGN AND EXECUTION
4
OVERVIEW EXPERIMENTS PERFORMED DESIGN AND EXECUTION
1.- INPUT GROUND MOTION
DESIGN AND EXECUTION ISSUES
5
OVERVIEW EXPERIMENTS PERFORMED DESIGN AND EXECUTION
10-1
100
0
0.4
0.8
1.2
1.6
2
Period (s)
Sa
(g
)
Original RecordLomaPrietaSC - 1
Loma Prieta SC - 5% Damping Response Spectrum
DESIGN AND EXECUTION ISSUES
2.- INSTRUMENTS LIMITATIONS
6
OVERVIEW EXPERIMENTS PERFORMED DESIGN AND EXECUTION
AccelerometersStrain Gages
Disp. Transducers Pressure sensors
0 100 200 300 400 500 600 700 800 900 1000
0 100 200 300 400 500 600 700 800 900 1000
Acceleration
Load Cells
7
OVERVIEW EXPERIMENTS PERFORMED DESIGN AND EXECUTION
PCB Piezotronics0.3-12000Hz
Interface Load Cell0-2000Hz
Frequency (Hz)
2.- INSTRUMENTS LIMITATIONS
0 100 200 300 400 500 600 700 800 900 1000
0 100 200 300 400 500 600 700 800 900 1000
Earth Pressure
Acceleration
8
OVERVIEW EXPERIMENTS PERFORMED DESIGN AND EXECUTION
Tactilus Free Form0-100Hz
Frequency (Hz)
PCB Piezotronics0.3-12000Hz
2.- INSTRUMENTS LIMITATIONS
9
Direct measurement Pressure Cells
max? max?
OVERVIEW EXPERIMENTS PERFORMED DESIGN AND EXECUTION
3. OUR CHALLENGE - EARTH PRESSURE IN RIGID BASEMENT
How to measure seismic earth pressure on rigid buried structures?
Indirect measurement Strain Gages
10
M+
M-M+
M-
OVERVIEW EXPERIMENTS PERFORMED DESIGN AND EXECUTION
3. OUR CHALLENGE - EARTH PRESSURE IN RIGID BASEMENT
11
Trend from Pressure Cells
Magnitude from Load Cells
OVERVIEW EXPERIMENTS PERFORMED DESIGN AND EXECUTION
Our approach Replace roof and floor with Load Cells
3. EARTH PRESSURE IN RIGID BASEMENT
OVERVIEW EXPERIMENTS PERFORMED DESIGN AND EXECUTION
12
0 5 10 15 20 25 30400
600
800
1000
1200
1400
Time (s)
Lo
ad
(lb
f/in
)
0 5 10 15 20 25 300
2
4
6
8
10
Time (s)
Pre
ssur
e (
psi
)
OVERVIEW EXPERIMENTS PERFORMED DESIGN AND EXECUTION
4.- BOUNDARY CONDITIONS – INFLUENCE OF MODEL GEOMETRY
13
Input acceleration
Flexible Shear Beam Container
OVERVIEW EXPERIMENTS PERFORMED DESIGN AND EXECUTION
14
0 0.5 1 1.5 20
1
2
3
4
Period
Sa(
g)
Soil
Ring
0 0.5 1 1.5 20
1
2
3
4
Period
Sa(
g)
Soil
Ring
2nd ring
5th ring
8 10 12 14 16 18-1
-0.5
0
0.5
1
Time (s)
Acc
(g)
Vertical Acc
Horizontal Acc
Vertical Input
EFFECTS OF MASS ASYMMETRY
LESSONS LEARNED
Equipment and Instrument Limitations•Instrument frequency response is an important consideration.
Earth Pressure in Rigid Structures•Currently available pressure sensors do give direct measurement, but are inconsistent•Use of redundant instrumentation is essential.
Boundary Conditions•Interaction with container can be an issue for large models•Check plain-strain assumptions
OVERVIEW EXPERIMENTS PERFORMED DESIGN AND EXECUTION
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