GROUND MOTION INTENSITY MEASURES

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GROUND MOTION INTENSITY MEASURES THAT CORRELATE
TO ENGINEERING DEMAND PARAMETERS Jonathan Bray
and Thaleia Travasarou University of California,
Berkeley PEER IM Working Group Abrahamson,
Bray, Conte, Cornell, Deierlein, Kramer,
Krawinkler, Porter, Silva, Somerville, Stewart,
Stojadinovic Pacific Earthquake Engineering
Research Center
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SHAKING-INDUCED DAMAGE to Bridges and Buildings
Moehle
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Seismic Displacement
LIQUEFACTION-INDUCED DAMAGE
EERC Slide Collection
EERC Slide Collection
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• PRIMARY PEER EARTHQUAKE ENGINEERING ISSUES
• Building or Short Bridge, including site
  response and SSI
• Long-Span Bridge, including site response and
  SSI
• Networks with Multiple Structures
• Liquefaction and Lateral Spreading
• Seismic Slope Instability and Permanent Ground
  Deformations

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BUILDING OR SHORT BRIDGE, INCLUDING SITE RESPONSE
AND SSI Engineering Damage Parameters
(EDP) Story Drift, Base Shear, Input Energy,
and Floor Acceleration Drift, Max. Curvature,
Column Curvature or Displacement
Ductility Intensity Measures (IM) Sa(T1),
PGV, PGD, SPGA, Sa(T1)Sa(2T1)/Sa(T1)0.5
Other combinations by Cornell involving Sa(T1)
and Sa(T2) Vectors by Conte or
Krawinkler Tpulse, D 5-95, Ia
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LONG-SPAN BRIDGE, INCLUDING SITE RESPONSE AND SSI
Engineering Damage Parameters (EDP) Drift,
Max. Curvature, Column Curvature or Displacement
Ductility Intensity Measures (IM) Sa(T1),
PGV, PGD Vector by Hutchinson et al. D 5-95,
CAV, Ia
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NETWORKS WITH MULTIPLE STRUCTURES Engineering
Damage Parameters (EDP) The IM (e.g.
PGA) Intensity Measures (IM) PGA Sa(T1) PGV Ia
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LIQUEFACTION AND LATERAL SPREADING Engineering
Damage Parameters (EDP) Factor of Safety Against
Liquefaction (FSl) Pore Pressure Ratio
(ru) Intensity Measures (IM) Cyclic Stress
Ratio (CSR) or PGA CAV5 Ia Equivalent Number of
Uniform Stress Cycles or D 5-95 Combination or
Vector
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SEISMIC SLOPE INSTABILITY AND PERMANENT GROUND
DEFORMATIONS Engineering Damage Parameters
(EDP) Permanent Ground Displacement
(U) Intensity Measures (IM) Ia Sa(T1) PGV or
EPGV Response Spectrum Intensity
(SI) Characteristic Intensity (Ic) Combination or
Vector
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Notes on the Intensity Measure Breakout Session -
PEER Annual Meeting - Jan. 17, 2002      Testbeds
will not provide definitive answers as to the
best single IM for all future use.      The
preferred way to compare IMs is to use stripes.
(i.e., for each IM, scale records to the same IM
level, do nonlinear runs, and compare their
dispersions, with secondary recognition of
possible difficulties with respect to
sufficiency). The most efficient solution is
to use the same runs on records scaled to the
same first-mode Sa to test all IMs. However, it
is not yet clear that such runs can be
effectively used to study other
IMs.      Another solution is to provide the
same records in their original unscaled
condition, and then apply the cloud method
(i.e., a regression of response on IM) to
estimate the dispersion. This is equally
applicable to all IMs, but it will take one
additional set of runs for all records.
     For each record, it should contain the
list of IM values and the list of EPD outputs.
Standard IM values (e.g., Sa, Ia) can probably be
provided by an individual other more exotic IM
values should be provided by the
proponent.      The lists of preferred IMs and
EDPs to be studied for each testbed need to be
compiled.      A standardized procedure for
evaluating efficiency and sufficiency of IMs
needs to be agreed to and documented for others
to use.
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• PEER IM-EDP Meeting of April 26, 2002
• Overall Objective
• Identify ground motion Intensity Measures
  that best correlate to meaningful Engineering
  Demand Parameters
•  
• develop a refined list of promising IMs
• standardize the manner in which IMs will be
  evaluated
• resolve some of the difficult issues identified
  at January's meeting.
•  

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PRIMARY PEER EARTHQUAKE ENGINEERING ISSUES

• Original
• Building or Short Bridge, including site
  response and SSI
• Long-Span Bridge, including site response/SSI
• Networks with Multiple Structures
• Liquefaction and Lateral Spreading
• Seismic Slope Instability and Permanent Ground
  Deformations

• Revised
• Short-period systems, Ia
• Long-period systems, SI
• Specific Systems, Sa(T1) or more sophisticated IMs

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PERIOD-INDEPENDENT INTENSITY MEASURES
Peak Ground Acceleration PGA Peak Ground
Displacement PGD Arias Intensity (Arias,
1970) Cumulative Absolute Velocity (Kramer
2002 5 cm/sec2 threshold) Response Spectrum
Intensity (Housner, 1959) Peak Ground
Velocity PGV Pulse Period Tv
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PERIOD-DEPENDENT INTENSITY MEASURES Spectral
Acceleration at Fundamental Period Spectral
Combination (Cordova et al. 2000) Spectral
Vector (Conte, 2002) Spectral Combination
IM1I2E (Luco and Cornell, 2001)
Sa(T1)
Sa(T1)
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Summary of Discussion of April 26, 2002
Meeting Participants discussed specific
findings from their studies on the ability of
various IMs to estimate important EDPs for their
particular problems, which included from bridge
response, nonlinear building response,
liquefaction and seismically induced permanent
slope displacements. Allin Cornell discussed
procedures for studying alternative candidate
IMs, and his current recommendations are located
at www.peertestbeds.net/Crosscutting.htm Here,
efficiency and sufficiency are discussed. Both
the stripes method and the direct regression
cloud method were found to be acceptable ways
of moving forward. Efficiency was determined to
be more tractable and more important than
sufficiency. An IM with twice the dispersion
requires 4x as many runs to obtain an equivalent
sense of the true median response. Joel Contes
work was especially helpful for understanding how
a vector of IMs may be developed (see
www.peertestbeds.net/Crosscutting.htm) Most
found that the spectral acceleration at the
fundamental period of the system being analyzed
worked well and is the default IM for most
problems. Some promising combinations of
spectral acceleration and some vectors containing
spectral acceleration for normal cases and PGV
for near-fault cases were also identified.
Several researchers noted the advantage of
using a non-system specific IM for studies that
involved many systems of various characteristics
(several sites that might liquefy or experience
permanent displacement and network studies of
many systems). For problems involving the
response of short period systems, Arias Intensity
was found to be promising, and a new attenuation
relationship for this ground motion parameter was
distributed at the meeting.  
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EFFICIENCY Seismic Displacement Ts 0.3 s, ky
0.05
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EFFICIENCY Seismic Displacement Ts 1.0 s, ky
0.05
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SUFFICIENCY
ln(D) a b ln(Ia) c ln(Ia)2 d Me ln(R)
Ts 0.3s ky 0.05
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Longitudinal drift ratio
Longitudinal drift ratio
(Mackie and Stojadinovic, 2002)
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Standard deviation of the random error for
different intensity measures for a M7.5
strike-slip earthquake at R 10 km on soil.
   
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Rel. PGA Sa Ia D5-95 U Atten 0.50
0.58 0.90 0.49 2.3 DM/IM 1.09 0.96 0.84 2.23
-
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• Cornell (2002) Guidance for Evaluating
  Alternative IMs
• Stripes Analysis each record within a hazard
  bin must be scaled to the same IM value for that
  hazard level, say Sa(T1s) and PGAmed
• compare the dispersion of the EDP vs. each IM
  within a hazard bin (median should be similar)
  a dispersion reduction of 30 implies that half
  the number of nonlinear dynamic analyses are
  required.
• Need a new set of runs for each candidate IM
• Regression (Direct/Cloud) Method use unscaled
  records perform regression of EDP vs. candidate
  IM, and estimate standard deviation of the
  residuals of the fitted model compare standard
  deviations of each candidate IM but it is a
  measure of both the variability of the EDP vs. IM
  and the regression model used.
• Need only one set of runs
• Modified Stripes Analysis use stripes method to
  evaluate primary IM, say Sa(T1s) and then
  evaluate scatter of other IMs given that records
  have been scaled to Sa(T1s) implies dependency
  Cornell et al. are currently investigating this
  approach.
• Need only one set of runs

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A Vector of Ground Motion Intensity Measures
(Conte et al. 2002)
84-percentile Sa level
Primary Intensity Measure Sa(T0, x)

• Ground Motions scaled to three levels of Sa
  Median Sa, 16-percentile and 84-percentile.
• Distortion of earthquake records minimized by
  restricting the scale factors to reasonable
  values, namely

Sa g
Median Sa level
16-percentile Sa level
Secondary Intensity Measures
T0 sec

• Proposed Intensity Measures
• Maximum Value of 1
• Measures of damage effectiveness of a given
  ground motion record
• Obtained using Bilinear Inelastic SDOF system
  with a 0

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Testbed Ground Motions Somerville and Collins
(2002) Uniform Hazard Spectra developed for
outcropping soft rock for 50 in 50 yrs, 10 in
50 yrs, and 2 in 50 yrs level. Using available
recorded ground motion records that represent the
controlling events M and R at each hazard level,
10 to 20 ground motions were selected. For
Humbolt Bay Bridge, M 7 to 8 and R 5 to 20 km
for Sa(T1.23s) All motions provided unscaled and
scaled so that each record has Sa at T1.23s
equal to that of uniform hazard spectra at each
hazard level. For I-880 Bridge, M 6.6 to 7 and
R 7 km for Sa(T1s) All motions provided only
unscaled until representative period is selected.
User must transform FN and FP components into
logitudinal and transverse components. Motion
sets inherently contain some forward-directivity
and fling motions.
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ENGINEERING DEMAND PARAMETERS BRIDGES Drift
Ratio, Peak Column Curvature, Displacement
Ductility, Curvature Ductility Mackie and
Stojadinovic (2002) PEER Report 1.) global
response - drift ratio 2.) intermediate response
- maximum column moment 3.) local response -
material stress BUILDINGS Ductility Demand,
Residual Ductility Demand Peak Story Drift, Peak
Story Drift Angle Normalized Hysteretic Energy
Dissipated LIQUEFACTION Pore Pressure
Ratio Factor of Safety Against Liquefaction
SEISMIC SLOPE STABILITY Seismically-Induced
Permanent Displacements
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SUMMARY OF PRIMARY INTENSITY MEASURES

• PGA
• PGD
• PGV Pulse Period
• Ia
• CAV5
• SI
• Sa(T1)
• Spectral Combination
• Spectral Vector

Bold IMs have attenuation relations available