PEER Tall Building Seismic Design Guidelines

Transcription

1 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

2 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

3 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

4 Lead Investigators Academia Practice 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 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

5 The new breed of tall buildings Designed without dual moment-resisting frames Justified using nonlinear analyses and performance-based procedures adapted from ASCE 41

6 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

7 They started simple -

8 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

9 But became more complex

10 Cities developed ad hoc criteria

11 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

12 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

13 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

14 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

15 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

16 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 May not provide same protection as code

17 Maximum Considered Level 3-D nonlinear response history analysis Ground motion input at structure base SSI Permitted but not required Desired Typical Optional

18 Maximum Considered Level Cyclic Degradation 4 Methods Explicit incorporation of hysteretic effects Use of cyclic envelope curve Modified monotonic data Deterioration not considered

19 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

20 Deformation Controlled Elements No criteria other than deformation demand in any analysis can not exceed valid range of modeling or δ u.

21 Force-controlled elements φ = 1 for inconsequential failures φ = applicable resistance factor from material standards otherwise

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

23 Transient and residual drift Transient story drift Mean of 7 runs < 0.03 Maximum of any run < Residual story drift Mean of 7 runs < 0.01 Maximum of any run < 0.015

24 Model Building Studies 3 alternative design criteria Modified code approach Performance-based - LATBC criteria Performance + - PEER TBI criteria

25 Model Building Studies Steel Braced Frame Concrete Core Concrete Dual

26 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

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