Overview of ATC-63 Project “ Quantification of Building System and Response Parameters”

1. 2007 PEER Annual Meeting Overview of ATC-63 Project“Quantification of Building System and Response Parameters” Charles A. Kircher, Ph.D., P.E. Kircher & Associates Palo Alto, California January 19, 2007

2. ATC -63 Project Objectives • Primary – Create a methodology for determining Seismic Performance Factors (SPF’s) “that, when properly implemented in the design process, will result in the equivalent earthquake performance of buildings having different structural systems” (i.e., different lateral-force-resisting systems) • Secondary – Evaluate a sufficient number of different lateral-force-resisting systems to provide a basis for Seismic Code committees (e.g., BSSC PUC) to develop a simpler set of lateral-force-resisting systems and more rational SPF’s (and related design criteria) that would more reliably achieve the inherent earthquake safety performance objectives of building codes

3. FEMA Michael Mahoney Robert Hanson (Adv.) Project Organization TOP Management Chris Rojahn (PED) Jon Heintz (PTM) William Holmes (PQC) PRP Members Phipps (Chair) Elnashai - MAE Ghosh - SKGA Gilsanz- GMS Hamburger - SGH Hayes - NIST Holmes – R&C Klingner - UT Line - AFPA Manley - AISI Reinhorn - UB Rojahn - ATC Sabelli - DASSE PMC Members Charels Kircher (Chair) Greg Deierlein – Stanford M. Constantinou – Buffalo John Hooper - MKA James Harris – HA Allan Porush - URS Working Groups Stanford – NDA SUNY – NSA/NCA Filiatrault – Wood Krawinkler - AAC

4. Project Tasks and Schedule

5. Seismic-Force-Resisting Systems (Tasks 5 and 6) Concrete – Stanford Gregory Deierlein Curt Haselton Abbie Liel Brian Dean Jason Chou Ashpica Chhabra John Hooper (MKA) Brian Morgan (MKA) • Reinforced-Concrete Structures • 4-Story SMF, IMF and OMF • 12-Story IMF/OMF and Shear Wall (Core Wall) • Parametric Study of RC Frames • 1, 2, 4, 8, 12 and 20 stories • Space vs. perimeter configurations • Drift Limits (1% - 4%) • Weak story irregularities (Code limits: 80%, 65%)

6. Seismic-Force-Resisting Systems (Tasks 5 and 6) Wood - Buffalo Andre Filiatrault Ioannis Christovasilis Hiroshi Isoda Michael Constantino • Wood Structures (CUREE): • Townhouse – Superior, typical, poor quality • Apartment – Superior, typical and poor quality • Other (Japanese Home, Templeton Hospital) • Autoclaved Aerated Concrete (AAC) Test Structures • Steel Structures: • 4-Story (RBS) SMF (IMF, OMF) AAC - Stanford Helmut Krawinkler Farzin Zareian Kevin Haas Dimitiros Lignos Steel - Stanford Greg Deierlein Abbie Liel Helmut Krawinkler Dimitiros Lignos Curt Haselton

7. Elements of the Methodology

8. Guiding Principals • New Buildings – Methodology applies to the seismic-force-resisting system of new buildings and may not be appropriate for non-building structures and does not apply to nonstructural systems. • NEHRP Provisions – Methodology is based on design criteria, detailing requirements, etc. of the NEHRP Provisions (i.e., ASCE 7-05as adopted by the BSSC for future NEHRP Provisions development) and, by reference, applicable design standards • Life Safety – Methodology is based on life safety performance (only) and does not address damage protection and functionality issues (e.g., I = 1.0 will be assumed) • Structure Collapse – Life safety performance is achieved by providing uniform protection against local or global collapse of the seismic-force-resisting system for MCE ground motions • Ground Motions – MCE ground motions are based on the spectral response parameters of the NEHRP Provisions, including site class effects

9. Methodology Overview • Conceptual Framework– Methodology adopts the concepts and definitions of seismic performance factors (SPF’s) of the NEHRP Provisions (e.g., global pushover concept as described in the Commentary of FEMA 450 ) • Failure Modes – Methodology evaluates structural collapse defined by system-dependent local and global modes of failure • Collapse Probability – Methodology evaluates structural collapse probability considering response and capacity variability (and epistemic and aleatory uncertainty) • Archetypical Systems – Methodology defines “archetypical” structural systems that have configurations typical of a given type or class of lateral-force-resisting system • Analytical Models – Methodology incorporates models (of archetypical systems) that have sufficient complexity to realistically represent global performance of actual building systems considering nonlinear inelastic behavior of seismic-force-resisting components • Analytical Methods – Methodology utilizes nonlinear analysis methods (i.e., pushover and incremental dynamic analysis)

10. R = Response Modification Coefficient = VE/V Design Earthquake Ground Motions Cd = Deflection Amplification Factor = d/de Cd WO = System Over-strength Factor = VY/V = DY/de Base Shear VE Pushover Curve Rd R VY 0 V DY de d DE Roof Displacement Definition of Seismic Performance Factors (SPF’s)(from FEMA 450 Commentary)

11. SA-Based Collapse Fragility Collapse Level Ground Motions Median 10th Percentile T SC1 MCE Ground Motions Margin SM1 Spectral Acceleration (g) SD-Based Collapse Fragility 1.5R 1.5Cd Margin SY1 Median WO Cs 10th Percentile SDe SDM1 SDC1 Spectral Displacement SPF’s and MCE Collapse Margin

12. Building (Joe’s Bar) Incipient Collapse Scaled Ground Motion Record = + Example Collapse Fragility – One Data Point Evaluation of a single structure (one configuration/set of performance properties) to failure using one ground motion record scaled to effect incipient collapse

13. Comprehensive and representative collapse data Incipient Collapse Incipient Collapse Incipient Collapse Incipient Collapse Incipient Collapse Incipient Collapse Incipient Collapse Incipient Collapse Incipient Collapse Incipient Collapse Incipient Collapse Incipient Collapse Incipient Collapse Incipient Collapse Incipient Collapse Incipient Collapse Incipient Collapse Incipient Collapse Building (Joe’s Bar) Building (Joe’s Bar) Building (Joe’s Bar) Building (Joe’s Bar) Building (Joe’s Bar) Building (Joe’s Bar) Building (Joe’s Bar) Building (Joe’s Bar) Building (Joe’s Bar) Building (Joe’s Bar) Building (Joe’s Bar) Building (Joe’s Bar) Building (Joe’s Bar) Building (Joe’s Bar) Building (Joe’s Bar) Building (Joe’s Bar) Building (Joe’s Bar) Building (Joe’s Bar) Ground Motion Ground Motion Ground Motion Ground Motion Ground Motion Ground Motion Ground Motion Ground Motion Ground Motion Ground Motion Ground Motion Ground Motion Ground Motion Ground Motion Ground Motion Ground Motion Ground Motion Ground Motion = = = = = = = = = = = = = = = = = = + + + + + + + + + + + + + + + + + + Comprehensive models of building configuration/performance properties evaluated with representative earthquake records Example Collapse Fragility – Comprehensive and Representative Collapse Data

14. Margin 50% probability (median) of collapse at SC1 = 1.6 g Acceptably low probability of collapse (TBD) given MCE spectral demand 10% probability of collapse at SM1 = 0.9 g Notional Collapse Fragility Curve

15. Margin Collapse Fragility with Modeling Uncertainty

16. ATC-63 Ground Motion Record Sets - Objectives • Code (ASCE 7-05) Consistent – Pairs of horizontal components “selected and scaled from individual recorded events.” Section 16.1.3.1 of ASCE 7-05 • Very Strong Ground motions – Ground motions strong enough to collapse new buildings • Large Number of Records – Enough records in set to estimate median and RTR variability (collapse fragility) • Structure-Type Independent – Appropriate for NDA (IDA) of variety structures with different dynamic characteristics and performance properties • Site/Hazard Independent – Appropriate for evaluation of structures located at different sites/hazard levels

17. Ground Motion Record Sets (PEER NGA database) • Far-field Record Set (Basic Set): • 22 records (2 components each) • 14 Events • Mechanisms: 9 strike-slip, 5 thrust • Near-field Record Set: • 28 records (2 components each) • 14 Events • Half of records with a pulse, half without a pulse • Scale records (consistent with ASCE 7-05): • Normalize individual records by PGV • Anchor record set median spectral demand to MCE demand (at period of structure)

18. Response Spectra - Far-Field Record Set

19. Spectral Shape – Far-Field Record Set

20. 60% increase in margin due to increase in mean epsilon (0.36 to 1.1) Comparison of Median Response Spectra at Collapse – 4-Story R/C SMF Model Building

21. 60% increase in margin due to increase in mean epsilon (0.36 to 1.1) 10-fold decrease in margin due to increase in mean epsilon (0.36 to 1.1) Comparison of Collapse Fragility Curves – 4-Story R/C SMF Model Building

22. Spectral Shape Factor • The Need - Incorporation of spectral shape effect is essential to accurate estimation of collapse margin required to achieve acceptably low probability of collapse • The Problem - Currently available maps of epsilon (from hazard de-aggregation) are not directly applicable and development of applicable maps/methods is not feasible near term • The Solution - Alternatively, generically applicable site-independent spectral shape factors (SSF’s) can be used to approximate “typical” epsilon effect on spectral shape (i.e., factors used to bias margin calculated using “epsilon-neutral” records) • Trial Values (SSF) - Generic spectral shape factor would be a function of system ductile capacity: • High ductility Systems SSF = 1.6 (e.g., R = 8) • Moderate ductility Systems SSF = 1.2 (e.g., R = 4) • Low Systems SSF = 1.0 (e.g., R = 2)

23. Reinforced-Concrete (RC) Special Moment Frame (SMF) System Example • Purpose • Illustrate methodology for an existing seismic-force-resisting (RC SMF) system (as if it were a new system being proposed for the Code) • Demonstrate validity of the methodology (show R = 8 is reasonable for RC SMF) • Approach • Develop comprehensive set of archetypical systems (e.g., 18 designs) based on ASCE 7-05 (and ACI 318) • Determine over-strength factors (WO) from push over • Determine margins from IDA’s • Adjust margins for spectrum shape factor (epsilon) • Evaluate margin acceptability (considering total uncertainty (RTR + modeling + design + testing)

24. Notional Flowchart of Process Develop System Characterize Behavior Establish Design Provisions Develop Archetype Models Evaluate Collapse Performance No P[C] < Limit Yes Peer Review

25. Archetype Design Configurations (18) • Basic Set - High Seismic (SDC D) designs (6) • Low gravity (perimeter frame) configuration • 1, 2, 4, 8, 12 and 20-story heights • 20-foot bay size • Basic Set - High Seismic (SDC D) designs (6) • High gravity (space frame) configuration • 1, 2, 4, 8, 12 and 20-story archetypes • 20-foot bay size • Check Low Seismic - Low Seismic (B/C) designs (4) • 8, 12, and 20-story heights – Low gravity (perimeter) • 20-story height – high gravity (space frame) • Check Bay Size - 30-foot bay designs (2) • High Seismic (SDC D) designs • 4-story – low gravity (perimeter frame) • 4-story – high gravity (space frame)

26. Index Archetype Configuration (4-Story)

27. Summary of Archetype Design Properties Initial Design ASCE 7-05)

28. 2.5 Margin (2.77/1.11) Median Collapse Sa = 2.77g MCE Sa = 1.11g Example IDA Results and Margin(4-story, SDC D, space frame with 30-foot bays)

29. Acceptable Collapse Margin (based on composite uncertainty and collapse goal)

30. Initial Results – RC SMF (ASCE 7-05)

31. Re-design to Improve Collapse Margin of Tall Buildings (12 and 20-story heights) • Restore minimum base shear provision removed from ASCE 7-02 (Eq. 9.5.5.2.1-3): Cs 0.044 SDS I (I = 1.0) 1. Effective value of R due to limits on the seismic coefficient, Cs.

32. Revised Results – RC SMF (ASCE 7-02)