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 …
CONDO HOTEL $ RETAIL PARKING Types of Occupancy $
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.
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 • Applicable ground motions • (e.g., T = 9 sec) • Ground motion scaling • Input motions for subterranean levels • Performance objectives 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
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
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) Performance Objectives • Core group: W. Holmes, C. Kircher, L. Kornfield, B. Petak, N. Yousef • Approach: Obtain input from stakeholders, formulate strawman performance objective, workshop, …
Story level Story Moment 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.
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 • 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
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)
qf ug uf 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
Final product Guidelines for performance-based seismic design of tall buildings December 2008
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 13th BASE PBEE practice needs (a) Building elevation (b) Summary of results