PEER Tall Building Seismic Design Guidelines

Ronald O. Hamburger Senior Principal Simpson Gumpertz & Heger Inc.

Jack P. Moehle University of California at Berkeley

PEER Annual Meeting October 15, 2009

The PEER Tall Buildings Initiative

  A focused program of research and development to:   Explore the seismic behavior of very tall

buildings   Identify appropriate performance goals   Identify methods of characterizing the

seismic hazard   Improve analytical procedures to predict

performance   Improve the codes, standards and guidelines

implemented in practice

The TBI Partners   Applied Technology Council   California Geologic Survey   California Office of Emergency Services   California Seismic Safety Commission   Federal Emergency Management Agency   Los Angeles Dept. of Buildings & Safety   Los Angeles Tall Buildings Council   National Science Foundation   Pankow Foundation   PEER   San Francisco Building Department   Southern California Earthquake Consortium   Structural Engineers Association of California   United States Geologic Survey

Lead Investigators   Academia

  Yousef Bozorgnia   William Petak   Greg Deierlein   Helmut Krawinkler   Stephen Mahin   Jack Moehle   Jonathan Stewart   John Wallace   Farzan Zaerian

  Government   Brad Aagard   Laurence Kornfield   Nico Luco   Raymond Lui

  Practice   Norm Abrahamson   C.B. Crouse   Anthony Ghodsi   Rob Graves   Ronald Hamburger   William Holmes   John Hooper   Charles Kircher   Ron Klemencic   Joe Maffei   James Malley   Mark Moore   Farzad Naeim   Paul Sommerville

The new breed of tall buildings

  Designed without dual moment-resisting frames

  Justified using nonlinear analyses and “performance-based” procedures adapted from ASCE 41

The motivation -   Design to achieve better performance   Design to be more certain that target

performance can be achieved   Enable use of new and innovative

systems   Reduce cost of seismic protection   Permit unobstructed floor to ceiling

window walls while maintaining short ceiling heights

They started simple -

Design approach was also simple

  Design per the building code with   a few exceptions

  Exceed height limits for structural systems   Use different R values   Neglect redundancy requirements

  Develop nonlinear analytical model   MCE (2%-50 year) shaking   Conservative values on acceptable

parameters

  Rigorous Peer Review

But became more complex

Cities developed ad hoc criteria

PEER Tall Buildings Initiative

  Purpose: Develop design criteria that will ensure safe and useable tall buildings following future earthquakes   Performance intent is similar to that

historically contained in SEAOC Blue Book, and presently contained in NEHRP Provisions Commentary

  Small risk of collapse (perhaps 10%) in MCE shaking

  Limited risk (50%) of loss of cladding in MCE shaking

  Negligible risk to life for design shaking   Negligible risk of occupancy loss for Service level

shaking

TBI Tasks

  Develop consensus on Performance Objectives   Baseline assessment of Tall Building Dynamic

Response   Synthetically generated ground motions   Selection and modification of ground motions   Modeling and acceptance (ATC-72)   Ground motion input to buildings with subgrade

levels   Quantification of Tall Building Perfomance

Scope -

  Design of tall buildings:   Fundamental periods >> 1

second   Slender aspect ratio

  Large portion of drift due to flexural behavior as opposed to shear behavior

  Significant mass participation and response in higher modes

Performance Objectives

  Limited discussions with stakeholders indicated many would prefer “better” performance for these important buildings

  Primary Objectives   MCE - Low probability of collapse   Service Level – Low probability of loss of use

  Other Objectives   Possible   Need to modify these criteria on project

-specific basis

Design Process

1.  Confirm approach acceptable   Building official   Development team

2.  Establish performance objectives 3.  Seismic input 4.  Conceptual design 5.  Design Criteria Document 6.  Service Level Design 7.  MCE Level Design 8.  Final Design 9.  Peer Review

Service Level Design

  50% - 30 years (43 year return)   Response Spectrum analysis – 2.5% damped

  Maximum DCRs 150% of expected strength   Nonlinear analysis permitted

  Story drift limited to 0.005   May not provide same protection as code

Maximum Considered Level

  3-D nonlinear response history analysis   Ground motion input at structure base   SSI Permitted – but not required

Desired Typical Optional

Maximum Considered Level

  Cyclic Degradation   4 Methods

  Explicit incorporation of hysteretic effects

  Use of cyclic envelope curve

  Modified monotonic data   Deterioration not

considered

Maximum Considered Level

  Acceptance Criteria   Deformation controlled – behavior modes

associated with slow deterioration   Force controlled

  Elements the failure of which could result in partial or total collapse

  Elements the failure of which have minor consequences

  Story strength loss   Peak transient drift   Residual drift

Deformation Controlled Elements

  No criteria other than deformation demand in any analysis can not exceed valid range of modeling or δu.

Force-controlled elements

  φ = 1 for inconsequential failures   φ = applicable resistance factor from

material standards otherwise

Story strength loss

  Deformation imposed on any story should not result in story shear strength loss of more than 20%

Transient and residual drift

  Transient story drift   Mean of 7 runs < 0.03   Maximum of any run < 0.045

  Residual story drift   Mean of 7 runs < 0.01   Maximum of any run < 0.015

Model Building Studies

  3 alternative design criteria   Modified code approach   Performance-based - LATBC criteria   Performance + - PEER TBI criteria

Model Building Studies

Steel Braced Frame

Concrete Core

Concrete Dual

Summary

  Successful multi-disciplinary effort   Geotechnical engineers & Seismologists   Structural engineers   Building Officials

  Project has had positive impact on the design of real structures

  Has also affected design practice internationally