Charlie Kircher Kircher & Associates Project Director January 20, 2010 - PowerPoint PPT Presentation

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Charlie Kircher Kircher & Associates Project Director January 20, 2010

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  1. Building Seismic Safety Council Annual MeetingATC-84 ProjectImproved Structural Response Modification Factors for Seismic Design of New Buildings – Phase I Charlie Kircher Kircher & Associates Project Director January 20, 2010 ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  2. ATC-84 Project Organization Review Panel (PRP) Bob Bachman (REBC) Kelly Cobeen (WJE) Ron Hamburger (SGH) Greg Kingsley (KL&A) Richard Klingner (UT) Phil Line (URS Corp.) Jim Malley (Degenkolb) Bonnie Manley (AISI) Jack Moehle (UCBerkeley) Laurence Novak (PCA) Charles Roeder (UW) Kurt Stochlia (ICC-ES) NIST (NEHRP) John (Jack) Hayes (NIST) John (Jay) Harris (NIST) Technical Committee (PTC) Charles Kircher (K&A) Chair Finley Charney (VPI) Greg Deierlein (Stanford) James Harris (JRH&Co.) William Holmes (R&C) John Hooper (MKA) Laura Lowes (UW) Working Groups TBD ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  3. ATC-84 Project Objectives • Develop a framework for alternative formulations of seismic performance factors (e.g., R, Cd, WO) that consider inter-dependency of: • Period, Ductility, Overstrength • Site Classification • Seismic Design Category (and/or Occupancy) • Perform analyses to define SPFs in variable terms in order to achieve uniform risk • Identify research to improve alternative SPFs ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  4. Black Jack Numbering Scheme (?) • ATC-63 – Quantification of Building Seismic Performance Factors (FEMA P695, June 2009) • 63 Plus 21 = 84 • ATC – 84 – Improved Structural Response Modification Factors for Seismic Design of New Buildings – Phase I • 84 Minus 1 = 83 - Number of different SFRSs currently in Table 12.2-1 (ASCE 7-05) ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  5. 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 ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  6. Background and Overview Material Methodology Guidelines Supporting Material FEMA P695 Report • Introduction • Methodology • Required System Information • Archetype Development • Nonlinear Model Development • Nonlinear Analysis • Performance Evaluation • Documentation and Peer Review • Example Applications • Supporting Studies • Conclusions and Recommendations Appendices, References ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  7. Seismic Performance Factors (FEMA P695) • Methodology determines appropriate values for the following seismic performance factors: • Response modification factor (R factor) • Over-strength factor (WO factor) • Deflection amplification factor (Cd factor) • Methodology could be used to evaluate other performance-related design criteria: • Drift limits • Height limits • Other design requirements (e.g. weak-beam/strong-column requirements, seismic detailing, etc.) ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  8. Scope and Basis of the FEMA P695 Methodology • 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 (ASCE 7-05) – 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 an acceptably low probability of partial collapse and global instability of the seismic-force-resisting systemfor MCE ground motions • MCE Ground Motions – MCE ground motions are based on the spectral response parameters of the NEHRP Provisions (ASCE 7-05), including site class effects ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  9. Ground Motions Analysis Methods Design Information Requirements Test Data Requirements Peer Review Requirements Elements of the FEMA P695 Methodology Methodology ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  10. Notes Develop Test Data Develop Design Rules “Homework” phase Characterize System Behavior Define Archetypes Design archetypes (w/trial of R Factor) Develop Archetype Models Perform Pushover and NDA Analyze Archetype Models Evaluate CMR values (and overstrength) Evaluate System Performance P[Collapse] < Limit No Trial value of the R factor acceptable? Yes Peer Review applies to total process Review and Documentation Notional Flowchart of FEMA P695 Process ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  11. FEMA P695 RC SMF Example:Conclusions • Value of current SPFs (R=8) provide an acceptable level of collapse safety • The Methodology is reasonably well-calibrated to current design provisions • RC SMF systems didn’t fail miserably • RC SMF systems didn’t pass easily • This was true of all systems tested ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  12. FEMA P695 ExamplesObservations and Findings • Methodology was developed considering: • special concrete moment frames • ordinary concrete moment frames • special steel moment frames • wood shear walls • Some trends in our current design process have become apparent… ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  13. Ongoing Synergistic Activities UC San Diego Benson Shing Ioannis Koutromanos • NIST funded ATC-76-1, ATC-76-4 Projects • Beta testing the Methodology on the following systems: • Reinforced Masonry Shear Wall • Reinforced Concrete Shear Wall • Special Steel Concentric Braced Frame • Special Steel Moment Frame UCLA John Wallace Aysegul Gogus UC Berkeley Stephen Mahin Chui-Hsin Chen Stanford/UC Irvine Helmut Krawinkler Farzin Zarein ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  14. FEMA P695 Sections (90% Draft Report) • Introduction • Methodology • Required System Information • Archetype Development • Nonlinear Model Development • Nonlinear Analysis • Performance Evaluation • Documentation and Peer Review • Example Applications • Supporting Studies • Conclusions and Recommendation Appendices, References Chapter 11. Conclusions and Recommendations 11.2 Observations and Conclusions 11.2.1 Generic Findings ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  15. Systems Approach • Collapse Performance and associated seismic performance factors must be evaluated in terms of the behavior of the overall seismic-force-resisting system: • Collapse failure modes are highly dependent on configuration and interaction of elements within a seismic-force-resisting system • Seismic performance factors apply to an entire system, not elements comprising it. ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  16. Precision of Seismic Performance Factors • In general, there is no practical difference in the collapse performance of systems designed with fractional differences in the response modification factor, R, for example: • Essentially the same performance, R = 6 and 6.5 • Modest difference in performance, R= 6 and 8 • Significant difference in performance, R = 3 and 6 • Current values of R (Table 12.2.1 of ASCE/SEI 7-05) reflect a degree of precision not supported by results of example collapse evaluations ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  17. Spectral Content of Ground Motions • Consideration of spectral content (spectral shape) of ground motions can be very important to the evaluation of collapse performance of ductile seismic-force-resisting systems • Epsilon-neutral earthquake records scaled to represent very rare ground motions significantly overestimate demand on ductile systems • Methodology incorporates a spectral shape factor (SSF) to adjusts calculated response (margin) to account for spectral content of rare ground motions and avoid overestimation of nonlinear response ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  18. Short-Period Buildings • In general, results of example evaluations found smaller values of collapse margin ratios for short-period buildings • True for all types of seismic-force-resisting systems • Consistent with findings of previous research (Newmark & Hall, 1973, Nassar and Krawinkler, 1991, Miranda and Bertero, 1994, etc.) • Findings suggest possible need for short-period buildings: • Period-dependent R-factors? • More liberal collapse performance objectives? ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  19. Comparison of Strength Reduction Factors (Rm) (Figure 8. Strength Reduction Factors for Earthquake-Resistant Design, Miranda & Bertero, Earthquake Spectra, Vol. 10, No. 2, 1994) ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  20. Effective R Factor(Based on C1Factor of ASCE 41-06) ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  21. Governing Seismic Design Category • In general, results of example evaluations found smaller values of collapse margin ratios for seismic-force-resisting systems designed and evaluated for seismic criteria of Seismic Design Category (SDC) D than for the same system designed and evaluated for SDC C, all else equal • Trend attributed to increasing role of gravity loads in the strength of systems as the level of seismic load decreases (i.e., increased overstrength) • Findings suggest possible need for load-dependent (SDC dependent) seismic performance factors ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  22. Overstrength • In general, example evaluations found values of collapse margin ratio strongly related to calculated values of overstrength. For larger values of overstrength, large values of collapse margin ratio were observed • True for all types of seismic-force-resisting systems • Consistent with findings of previous research • Calculated values of overstrength of different archetypes vary widely, depending on configuration and seismic design criteria • Current values of WO (Table 12.2-1 of ASCE/SEI 7-05) are not representative of actual seismic-force-resisting system overstrength ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  23. Distribution of Inelastic Response • In general, example evaluations found values of collapse margin ratio strongly related to the distribution of inelastic response over the height of structure archetype • True for all types of seismic-force-resisting systems • Consistent with findings of previous research • Values of collapse margin ratio are significantly larger for systems with more evenly distributed inelastic response over height ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  24. Effect of Minimum Design Base Shear Strength OUTCOME: Minimum base shear requirement from ASCE 7-02 (V/W = 0.04) reinstituted in ASCE 7-05 ASCE 7-05 Perimeter ASCE 7-02 Space ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  25. FEMA P695 - Conclusion • Methodology provides a powerful tool for investigating importance of design requirements (not just the R factor) to collapse performance of seismic-force-resisting systems ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings

  26. But, if all else fails ....... • Rely on traditional methods R 3/8RW RW 0.7R W0 Cd I ATC-84 Improved Seismic Performance Factors for Seismic Design of New Buildings