Ground Motions and Liquefaction The Loading Part of the Equation

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Ground Motions and Liquefaction The Loading
Part of the Equation Steve Kramer Roy
Mayfield Bob Mitchell University of
Washington Seattle, Washington USA
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Evaluation of Liquefaction Potential

• Intensity Measure (IM)
• PGA M (simplified method)
• Ih (Arias intensity method)

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Performance-Based Earthquake Engineering
Covers range of hazard (ground motion)
levels Includes effects of ground
motions Accounts for uncertainty in parameters,
relationships
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Performance-Based Earthquake Engineering
Covers range of hazard (ground motion)
levels Includes effects of ground
motions Accounts for uncertainty in parameters,
relationships
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Performance-Based Earthquake Engineering
Covers range of hazard (ground motion)
levels Includes effects of ground
motions Accounts for uncertainty in parameters,
relationships
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Intensity Measures
Desirable characteristics of an IM
Efficient should be closely correlated to EDP
of interest
Sufficient should not require additional
information to predict EDP
Predictable should be accurately predictable
9 profiles 22 earthquakes gt450 motions 300
candidate IMs
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Intensity Measures
Efficiency
EDP depth-averaged excess pore pressure ratio,
(ru)ave
(ru)ave
PGA (cm/sec2)
Arias intensity (m/sec)
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Intensity Measures
Sufficiency
EDP depth-averaged excess pore pressure ratio,
(ru)avg
PGA
PGA
Ia
Ia
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A New Intensity Measure for Liquefaction
CAV5 Cumulative absolute velocity 5 cm/sec2
threshold
Accelerogram
a(t)
a(t) after threshold
Integral
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A New Intensity Measure for Liquefaction
CAV5 Predictability attenuation relationship
developed from database of CA earthquakes
Standard error
sln PGA 0.620
sln Ia 1.070
sln CAV5 0.708
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Implications for Performance-Based Liquefaction
Hazard Evaluation
Discrete form
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Implications for Performance-Based Liquefaction
Hazard Evaluation
Influence of predictability
log lm
ln Y
M M
log R
M
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Implications for Performance-Based Liquefaction
Hazard Evaluation
Influence of predictability
How does uncertainty in attenuation relationship
affect lIM?
log lm
ln Y
M M
log R
M
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Implications for Performance-Based Liquefaction
Hazard Evaluation
Influence of predictability
log lm
Reducing uncertainty in attenuation relationship
reduces PY gt Y M,R, which reduces lIM.
ln Y
ln Y
M M
R R
log R
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Implications for Performance-Based Liquefaction
Hazard Evaluation
PEDPgtEDP IM
1.0
lru proportional to sum of thick red lines
0.0
IM
lIM
IM
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Implications for Performance-Based Liquefaction
Hazard Evaluation
PEDPgtEDP IM
Fragility curve with less uncertainty (in
prediction of EDPIM)
1.0
lru proportional to sum of thick red lines
0.0
IM
lIM
IM
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Implications for Performance-Based Liquefaction
Hazard Evaluation
PEDPgtEDP IM
1.0
lru proportional to sum of thick red lines
0.0
IM
lIM
IM
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Implications for Performance-Based Liquefaction
Hazard Evaluation
PEDPgtEDP IM
Increasing efficiency of IM leads to reduction in
lEDP
1.0
lru proportional to sum of thick red lines
0.0
IM
lIM
IM
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A New Intensity Measure for Liquefaction
CAV5 Frequency domain characteristics
Relationship between IM and spectral
acceleration Depends on period at which spectral
acceleration is computed
20 Chi-Chi motions 0.1g lt PGA lt 0.3g 11 km lt R lt
26 km
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A New Intensity Measure for Liquefaction
CAV5 efficiency w/r/t Chi-Chi motions
Same 20 motions
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A New Intensity Measure for Liquefaction
CAV5 efficiency w/r/t Chi-Chi motions
Same 20 motions Soil profile consistent with
Berth 4 at Port of Taichung
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A New Intensity Measure for Liquefaction
CAV5 efficiency w/r/t Chi-Chi motions

• Same 20 motions
• Soil profile consistent with Berth 4 at Port of
  Taichung
• Scaled three times
• to produce surface PGA 0.1g (5 probability of
  liquefaction) in equivalent linear analysis
• to produce surface Ia 0.265 m/sec
• to produce surface CAV5 5.39 m/sec

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A New Intensity Measure for Liquefaction
CAV5 efficiency w/r/t Chi-Chi motions

• Same 20 motions
• Soil profile consistent with Berth 4 at Port of
  Taichung
• Scaled three times
• to produce surface PGA 0.1g (5 probability of
  liquefaction) in equivalent linear analysis
• to produce surface Ia 0.265 m/sec
• to produce surface CAV5 5.39 m/sec
• Applied as input motions to three sets of
  nonlinear, effective stress analyses

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A New Intensity Measure for Liquefaction
CAV5 efficiency w/r/t Chi-Chi motions

• Same 20 motions
• Soil profile consistent with Berth 4 at Port of
  Taichung
• Scaled set of 20 motions three times
• to produce surface PGA 0.1g (5 probability of
  liquefaction) in equivalent linear analysis
• to produce surface Ia 0.265 m/sec
• to produce surface CAV5 5.39 m/sec
• Applied each set of scaled motions as input
  motions to three sets of nonlinear, effective
  stress analyses
• Three sets of pore pressure ratio profiles
  computed

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A New Intensity Measure for Liquefaction

• Same 20 motions
• Soil profile consistent with Berth 4 at Port of
  Taichung
• Scaled three times
• to produce surface PGA 0.1g (5 probability of
  liquefaction) in equivalent linear analysis
• to produce surface Ia 0.265 m/sec
• to produce surface CAV5 5.39 m/sec
• Applied as input motions to nonlinear, effective
  stress analyses
• Pore pressure ratio profiles computed

PGA
CAV5
Arias intensity
Upper 20 m (N1)60 15 FC 15
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A New Intensity Measure for Liquefaction
Dispersion in ru lowest for CAV5, highest for PGA
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A New Intensity Measure for Liquefaction
Attenuation relationship M7.6, reverse
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Summary
Tremendous advances have been made in
liquefaction hazard evaluation over the past 40
yrs
Performance-based earthquake engineering will
place additional demand on liquefaction hazard
evaluators
Most research efforts have focused on
liquefaction resistance, but progress can also be
made on loading side of equation
Optimum characterization of loading requires
parameter that is efficient, sufficient, and
predictable
CAV5 appears to have combination of efficiency,
sufficiency, and predictability that is better
than that of parameters more commonly used for
liquefaction hazard evaluation. CAV5-based
liquefaction hazard evaluation procedures should
be investigated.