Buildings over 240 ft

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Buildings over 240 ft (proposed, approved, or
under construction, at last count) San Francisco
38 Los Angeles 53 Seattle
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Whats different about these buildings?

• High-performance materials
• Framing systems not satisfying code prescriptive
  limits
• Non-prescriptive designs are accepted in the code
  by demonstrating at least equivalent seismic
  performance.UBC 1629.10.1, 1605.2, 104.2.8

after MKA
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Tall Buildings Initiative

• 24 month initiative to advance design of tall
  buildings
• Main participants
• PEER, SCEC, USGS, FEMA, SFDBI, LADBS, OES, CSMIP,
  CSSC, Pankow Foundation
• ATC, LATBSDC, SEAOC, SEAONC
• Project Management Committee (T-PAC)
• J. Moehle, Y. Bozorgnia
• N. Abrahamson, M. Lew, P. Somerville
• R. Hamburger, H. Krawinkler, M. Moore, F. Naeim
• R. Lui
• Kickoff meeting 11 August 2006

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Scope

• Tall buildings
• Seismic design of structural system
• Coastal California
• Concrete and steel
• Residential focus, but not excluding other
  occupancies

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Task 2 - Performance Objectives

• Core group W. Holmes, C. Kircher, L. Kornfield,
  B. Petak, N. Yousef
• Approach Define credible scenarios, stakeholders
  input, workshop,

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Preliminary Results

• Stakeholders were surprised by, and not
  necessarily accepting of, current code
  performance expectations for normal buildings.
• The great need is to be able to clearly
  articulate performance levels and risks
• Stakeholders strongly advocate disclosure of
  risks and anticipated performance, including
  serviceability and fire risks. This disclosure
  is necessary as a part of the risk management
  of development, where risk is transferred from
  the developers to the owners/occupants/insurers/Ci
  ty. It must be made clear what risk is being
  transferred.
• Many believed that a higher standard should be
  required for tall buildings.
• approval of tall buildings requires resolution of
  many issues having greater impacts on occupants,
  neighbors and the City than other/low-rise
  buildings
• tall buildings have a great impact on the City
  and City services
• high occupant loads on small land area
• few exits and the other special conditions of
  high-rises

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Task 3 Building Pilot Studies

• Core group J. Moehle, S. Mahin, J. Hooper, T.
  Yang, C. McQuoid
• Approach
• Representative building models
• Variations in model parameters
• 100s of ground motions in various M, r , etc.
  bins
• Ground motion selection and scaling tests

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Preliminary results- M7, 10 km -
Floor Number
Interstory Drift,
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Accidental outrigger force
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48-story core wall model
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Preliminary results
Base Shear, N
Base Shear, N
Sa, T1, g
Sa, T2, g
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Ground motion selection and scaling
Abrahamson, 2006
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Ground motion selection and scaling
Baker, 2006
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Ground motion simulation, review, and selection
and scaling guidelines

• Core group P. Somerville, B. Aagaard, N.
  Collins, R. Graves
• Review F. Naeim, Y. Bozorgnia, N. Abrahamson, B.
  Chiou, CB Crouse, D. Dreger, Y. Moriwaki, Y. Zeng
• Guidelines Y. Bozorgnia, N. Luco, F. Naeim, J.
  Hooper, N. Abrahamson, J. Maffei
• Approach Develop waveforms for large-magnitudes,
  small distances in SF and LA, constrained by
  PSHA extensive review

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Ground motion simulation, review, and selection
and scaling guidelines
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Ground motion simulations
SCEC
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Guidelines for Modeling and Acceptance Criteria

• Core group J. Malley, G. Deierlein, H.
  Krawinkler, J. Maffei, M. Pourzanjani and J.
  Wallace
• Approach Workshop identified key issues,
  assignments to experts to develop principles,
  procedures, and values.

• Key issues
• Good practices in nonlinear dynamic analysis
  (H.
  Krawinkler, G. Deierlein, J. Heintz)
• Podium and basement modeling and performance
  characterization (J. Maffei, J.
  Malley)
• Wall modeling and performance characterization
  (J.
  Wallace, M. Pourzanjani)

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Preliminary results wall modeling
48 in.

• PERFORM-3D model
• Each element (compound)
• Wall fiber inelastic section
• Elastic shear material (G 1800 ksi)

12 in.
12 in.
12 in.
12 in.
12 in.
12 in.
J. Wallace
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Comparisons TW2
Lateral Loads (kips)
Top Drift Ratios
Tests
PERFORM-3D Analyses
J. Wallace
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Input ground motions for tall buildings with
subterranean levels

• Core Group J. Stewart, C.B. Crouse, M. Lew, A.
  Mikami, F. Ostadan, E. Taciroglu
• Approach Report on the state of practice and
  art, and recommend future studies.

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Final product
Guidelines for performance-based seismic design
of tall buildings
December 2008