Performance-based guidelines and regulations Tall Buildings Performance-based guidelines and regulations Joe Maffei Rutherford & Chekene Jack Moehle UC Berkeley

Outline Today’s tall buildings Applicability of PBEE to tall buildings PBEE practice needs PEER Tall Building Initiative

Buildings over 240 ft (proposed, approved, or under construction) San Francisco – 38; Los Angeles – 53; Seattle …

Types of Occupancy CONDO HOTEL RETAIL $ PARKING $

STEEL GRAVITY FRAMING $

Washington Mutual / Seattle Art Museum

Buckling-restrained braces

What’s different about these buildings? High-performance materials Framing systems not satisfying code prescriptive limits Non-prescriptive designs are accepted in the code by demonstrating at least equivalent seismic performance. UBC 1629.10.1, 1605.2, 104.2.8 after MKA

What is “Equivalent” Performance? Consider both the intended performance of the code and the performance of a typical good prescriptive design. Equivalence to poorly-performing but code-prescriptive buildings should not be acceptable. Use Seismic Peer Review.

Two-Stage Design Determine the strengths at nonlinear locations using the building code requirements Code (DBE) level earthquake  R factor Minimum base shear All other actions are designed to remain elastic under MCE level ground motions: Wall shear, shear friction, wall flexure outside of intended yield locations, floor and roof diaphragms and collectors and connections, foundation perimeter walls, etc.

Example PBEE Practice Needs Acceptability of yielding outside base hinge zone.

Protection against shear failure

Protection against sliding shear

Linear and nonlinear modeling assumptions Elastic ETABS Model UCSD Wall RUTHERFORD & CHEKENE

Wall: Eeff = 0.2Ec Slab: Eeff = 0.1Ec RUTHERFORD & CHEKENE

PBEE Practice Needs Structural Design (Joe’s top 15) Minimum base shear Capacity design factors Inherent slab-outrigger effect Story mechanism protection Wall shear strength Effective damping in NLRH analysis Other NLRH assumptions Effective elastic stiffness Podium force transfer Rational drift limits P-delta modeling Concrete slab to core wall connections Steel framing to core wall connections Deep mat slab behavior Dual system requirements Applicable ground motions (e.g., T = 9 sec) Ground motion scaling Input motions for subterranean levels Performance objectives

Tall Buildings Initiative 24 month initiative to advance design of tall buildings Main participants PEER, SCEC, USGS, SFDBI, LADBS, FEMA ATC, LATBSDC, SEAOC, SEAONC Project Management Committee (T-PAC) J. Moehle, Y. Bozorgnia N. Abrahamson, M. Lew, P. Somerville R. Hamburger, H. Krawinkler, M. Moore, F. Naeim R. Lui Kickoff meeting – 11 August 2006

Scope Tall buildings Seismic design of structural system Coastal California Concrete and steel Residential focus, but not excluding other occupancies

Tasks Establish and operate Project Advisory Committee (T-PAC) Research tasks Consensus performance objectives Assessment of ground motion selection and scaling procedures Synthetically generated ground motions Review of synthetically generated ground motions Guidelines on ground motion selection and modification Guidelines on modeling and acceptance criteria Input ground motions for tall buildings with subterranean levels Other tasks to be defined…. Guidelines for seismic design of tall buildings Workshops, presentations, etc. Final report to sponsoring organizations

Performance Objectives Core group: W. Holmes, C. Kircher, L. Kornfield, B. Petak, N. Yousef Approach: Obtain input from stakeholders, formulate strawman performance objective, workshop, … What do you think of this performance scenario? Rare earthquake scenario damage, (one in ten chance of occurring during the 50-yr life of condominium towers)

Selection and scaling of ground motion Core group: J. Moehle, S. Mahin, J. Hooper, T. Yang, C. McQuiod Approach: Select ground motion bins, analyze building models to develop response statistics, and test various ground motion selection and scaling methods against the “true” result. Story Moment Story level

Ground motion simulation, review, and selection and scaling guidelines Core group: P. Somerville, B. Aagaard, N. Collins, R. Graves Approach: Develop waveforms for large-magnitudes, small distances in SF and LA, constrained by PSHA Review: F. Naeim, Y. Bozorgnia, N. Abrahamson, B. Chiou, CB Crouse, D. Dreger, Y. Moriwaki, Y. Zeng Guidelines: Y. Bozorgnia, N. Luco, F. Naeim, J. Hooper, N. Abrahamson, J. Maffei Core group: P. Somerville, B. Aagaard, N. Collins, R. Graves Approach: Develop waveforms for large-magnitudes, small distances in SF and LA, constrained by PSHA

Guidelines for Modeling and Acceptance Criteria Core group – J. Malley, G. Deierlein, H. Krawinkler, J. Maffei, M. Pourzanjani and J. Wallace Approach: Workshop to identify key issues, assignments to experts to develop principles, procedures, and values. Key issues: Basic principles, including capacity design General modeling issues (e.g., effective damping) Podium force transfer Modeling of various systems and elements (core walls, frames, coupling beams, etc.) Foundation modeling (with Task 8)

Input ground motions for tall buildings with subterranean levels Core Group: J. Stewart, C.B. Crouse, M. Lew, A. Mikami, F. Ostadan, E. Taciroglu Approach: Report on the state of practice and “art,” and recommend future studies. Key issues: Quantifying ground motions in basements relative to free-field Reductions of horizontal motions Introduction of rotation Are these effects significant at the EDP level (and beyond)? Importance of flexibility of embedded sub-structure uf ug qf

Guidelines for performance-based seismic design of Final product Guidelines for performance-based seismic design of tall buildings December 2008

Wall moment at 13th floor, 1000 x k-ft PBEE practice needs BASE 13th ROOF Roof drift, ft Wall base shear, k Wall moment at 13th floor, 1000 x k-ft Minimum Maximum Mean (m) m + s c.o.v. Nonlinear static 2.1 6.7 4.2 5.4 0.23 7600 29700 15500 22200 0.43 5500 513 1080 900 1090 0.21 760 (a) Building elevation (b) Summary of results