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