Charles A. Kircher, Ph.D., P.E. 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

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

Project Organization FEMA Michael Mahoney Robert Hanson (Adv.) 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

Project Tasks and Schedule

Seismic-Force-Resisting Systems (Tasks 5 and 6) 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%) Concrete – Stanford Gregory Deierlein Curt Haselton Abbie Liel Brian Dean Jason Chou Ashpica Chhabra John Hooper (MKA) Brian Morgan (MKA)

Seismic-Force-Resisting Systems (Tasks 5 and 6) 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) Wood - Buffalo Andre Filiatrault Ioannis Christovasilis Hiroshi Isoda Michael Constantino AAC - Stanford Helmut Krawinkler Farzin Zareian Kevin Haas Dimitiros Lignos Steel - Stanford Greg Deierlein Abbie Liel Helmut Krawinkler Dimitiros Lignos Curt Haselton

Elements of the Methodology

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 7-05 as 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

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)

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

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

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

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

Notional Collapse Fragility Curve 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

Collapse Fragility with Modeling Uncertainty Margin

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

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) 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)

Response Spectra - Far-Field Record Set

Spectral Shape – Far-Field Record Set

Comparison of Median Response Spectra at Collapse – 4-Story R/C SMF Model Building 60% increase 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 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)

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)

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)

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

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 High gravity (space frame) configuration 1, 2, 4, 8, 12 and 20-story archetypes 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)

Index Archetype Configuration (4-Story)

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

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

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

Initial Results – RC SMF (ASCE 7-05)

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.

Revised Results – RC SMF (ASCE 7-02)