PEER Ground Motion Research Projects: A Progress Report

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PEER Ground Motion Research ProjectsA Progress
Report

• Yousef Bozorgnia, Ph.D., P.E.
• PEER Associate Director

PEER Annual Meeting, January 20, 2007 San
Francisco
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PEER Ground Motions Projects

• NGA, and its associated projects
• Ground Motion Selection Modification
• Other GM projects
• Upcoming tasks/projects

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Latest Developments in Next
Generation Attenuation (NGA)
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Next Generation Attenuation (NGA) Is a Set of
Multidisciplinary Projects

• Bringing together seismologists, geologists,
  geotechnical engineers, structural engineers, and
  users of ground motion models

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Step1 Compiled Strong-Motion Database

• 173 worldwide earthquakes

• gt 10,000
• uniformly
• processed
• records

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NGA Database

• There are more than 100 variables describing the
  source/path/site conditions of a record

• 6 types of distance measures
• 4 site classification schemes
• Estimated VS30 for most of recording sites
• FW/HW classes

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NGA Model Developer Teams

• NGA empirical ground motion model developers
• Abrahamson Silva (updating their 1997 model)
• Boore Atkinson (updating Boore et al., 1997
  model)
• Campbell Bozorgnia (updating their 1997, 2003
  models)
• Chiou Youngs (updating Sadigh et al., 1997
  model)
• Idriss (updating his 1993 1996 models)
• All developers started with a common database

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NGA Attenuation Models

• Ground motion parameters
• Horizontal components
• PGA, PGV, PGD
• Pseudo spectral acceleration at 5 damping
• Period 0 - 10 sec

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NGA Models Were Constrained by Simulation

• To fill the gaps in data
• Simulations of 3-D basin and 1-D rock motions
• To model amplification due to sediment-depth
• To constrain attenuation models
• Nonlinear soil response analysis
• Amplification factors for different soil profiles
  subjected to a wide range of input motions

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Example of Predicted Acceleration
Spectra(Campbell-Bozorgnia) Strike Slip, RRUP
10 km, VS30 760 m/s
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Behavior at Long Periods CB06 Predicted
Spectral Displacement Strike Slip, RRUP 10 km,
VS30 760 m/s
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Standard Deviation vs. Magnitude
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Comparison with Previous Models
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Campbell Bozorgnia (CB) 06 vs. CB03 SS,
NEHRP B-C
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Chiou Youngs (CY) 06 vs. SAO97SS, NEHRP C
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Boore Atkinson 06 vs. BJF97NEHRP B-C
(Unspecified Mechanism)
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Comparison of Latest NGA Models
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PGA Strike-Slip, M 7.5, NEHRP B-C
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Sa(T1.0s) Strike-Slip, M 7.5, NEHRP B-C
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NGA US National Seismic Hazard Maps
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USGS is Adopting

• NGA relations with documentation
• Boore Atkinson
• Campbell Bozorgnia
• Chiou Youngs
• With equal weighting

Courtesy Art Frankel
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0.2 sec Spectral Acceleration 2 P.E. in 50 years
Percentage of Change Using 3 NGA
relations Versus 2002 Hazard Maps Abrahamson and
Silva (1997), Sadigh et al. (1997), Boore et al.
(1997), Campbell and Bozorgnia (2003), Spudich et
al. (1999) for extensional areas
Using same set of fault sources as 2002
maps Subduction zone and deep earthquakes are
not included
Rock site condition
Courtesy Art Frankel
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1.0 sec Spectral Acceleration 2 P.E. in 50 years
Percentage of Change Using 3 NGA
relations Versus 2002 Hazard Maps Abrahamson and
Silva (1997), Sadigh et al. (1997), Boore et al.
(1997), Campbell and Bozorgnia (2003), Spudich et
al. (1999) for extensional areas
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Reasons

• Some of the decrease of 1 sec Sa from the 2002
  maps is caused by
• Difference in the Vs30 assigned for rock sites
  in the 2002 maps and the average Vs30 for rock
  sites reported in NGA (shouldnt be a factor in
  the Campbell-Bozorgnia and Boore-Atkinson NGA
  relations)
• Most of the decrease is from having additional
  data from moderate and large earthquakes and
  improved functional forms to fit the data

Courtesy Art Frankel
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NGA Models Give Prediction on Geometric Mean of
Two Horizontal Components

• You have to convert these, if you need prediction
  on
• Random horizontal component
• Maximum of two horizontal components
• FN, FP components

Standard deviation can be slightly larger than
that for Geo-Mean
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Summary of NGA Significant Accomplishments

• Quantity and quality of data
• Amount of time the developers spent on models
• Interactions among model developers
• Number of independent variables
• Availability of supporting ground motion
  simulations
• Public participation via workshops and
  conferences
• Formal peer review commissioned by USGS

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And, it would have been much more difficult
without a national earthquake engineering center

• For NGA, we have had contracts with
• USGS (different researchers)
• California Geological Survey
• SCEC (various contracts)
• Various universities
• Several practitioners

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PEER Ground Motion Selection Modification
(GMSM) Working Group
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Current state-of-the-practice in GMSM

• Is confusing
• Structural engineers rely on geotechnical
  engineers
• Geotechs/seismologists have little understanding
  on how the selected THs will be used by
  structural engineers
• GMSM methods have different objectives
• Methods can give VERY different results, even if
  they have the same objective

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The only possible improvement is

• To assemble a multi-disciplinary team of
• Seismologists
• Geotechs
• Structural engineers
• They interact in frequent meetings workshops
• They interact with other groups
• Come up with an evaluation platform

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PEER GMSM Working Group
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GMSM Working Group Objectives

• Examine existing GMSM methods,
• Examine emerging GMSM methods,
• Cast a platform for objective evaluation and
  comparison of GMSM methods

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GMSM Methods to be Tested for Nonlinear Analysis
of

• Buildings
• Bridges
• Earth structures
• Non-structural

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What GMSM Working Group Has Done

• Compiled and classified as many as GMSM methods
  as possible

• Compiled existing building models of
• Different building sizes
• Different structural systems
• OpenSees, DRAIN and PERFORM models of various
  buildings

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Structural Models Are Subjected to

• Hundreds of input GMs
• Suppose you have unlimited resources
• Compute statistics of various structural
  responses (EDPs)
• Run the models with the scaled/modified GMs
• Compare the results

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GMSM Working Group Link to Other
RD Projects

• PEER NSF (core) research projects
• Several of researchers have funding from PEER NSF
  program
• Tall Buildings Initiative

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Upcoming Tasks in GMSM

• Upcoming tasks
• Other building structural models
• Bridge structures
• Earth structures

• We are not done

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Other PEER GM Projects
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Other On-Going GM Projects

• Investigation of various IMs
• Attenuation of inelastic spectra
• Input motion for tall buildings with large
  embedded structure
• Collaboration with PGE/DOE on Extreme Ground
  Motion at Yucca Mountain nuclear waste
  repository
• More

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Future GM Tasks and Projects
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Maintaining and Updating GM Database

• Processing records from recent EQs
• Adding metadata for the EQs and sites
• Adding engineer-friendly features to the
  database
• Adding utility software for engineering
  applications
• e.g., a module for selection and scaling

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Upcoming GM Tasks

• Attenuation models
• Incorporation of directivity into NGA
• Attenuation of vertical ground motion
• Completion of inelastic spectra

• GM Selection and Modification
• Various structural models
• Guidelines for tall buildings

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An Important Issue to be Considered
Near-fault Effects

• Example in CA, there are 8,386 bridges within 10
  km of faults
• Technical aspects of the issue
• Seismological
• Engineering implications, especially for
  nonlinear response

• Possibly we have to initiate a working group with
  focus on Near-Fault GM Characterization and
  Effects

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Thank You !