Tall BuildingsPerformance-based guidelines and regulationsJoe MaffeiRutherford & ChekeneJack MoehleUC Berkeley

OutlineTodays tall buildingsApplicability of PBEE to tall buildingsPBEE practice needsPEER Tall Building Initiative

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

Types of Occupancy$

$STEEL GRAVITY FRAMING

Washington Mutual / Seattle Art Museum

Buckling-restrained braces

Whats different about these buildings?High-performance materialsFraming systems not satisfying code prescriptive limitsNon-prescriptive designs are accepted in the code by demonstrating at least equivalent seismic performance. UBC 1629.10.1, 1605.2, 104.2.8after 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 DesignDetermine the strengths at nonlinear locations using the building code requirements Code (DBE) level earthquake R factorMinimum base shearAll 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.

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

Protection against shear failure

Protection against sliding shear

RUTHERFORD & CHEKENEUCSD WallElastic ETABS ModelLinear and nonlinear modeling assumptions

Wall: Eeff = 0.2EcSlab: Eeff = 0.1EcRUTHERFORD & CHEKENE

PBEE Practice NeedsStructural Design (Joes top 15)Minimum base shearCapacity design factorsInherent slab-outrigger effectStory mechanism protectionWall shear strengthEffective damping in NLRH analysisOther NLRH assumptionsEffective elastic stiffnessPodium force transferRational drift limitsP-delta modelingConcrete slab to core wall connectionsSteel framing to core wall connectionsDeep mat slab behaviorDual system requirementsApplicable ground motions(e.g., T = 9 sec)Ground motion scalingInput motions for subterranean levelsPerformance objectives

Tall Buildings Initiative24 month initiative to advance design of tall buildingsMain participantsPEER, SCEC, USGS, SFDBI, LADBS, FEMAATC, LATBSDC, SEAOC, SEAONCProject Management Committee (T-PAC)J. Moehle, Y. BozorgniaN. Abrahamson, M. Lew, P. SomervilleR. Hamburger, H. Krawinkler, M. Moore, F. NaeimR. LuiKickoff meeting 11 August 2006

ScopeTall buildingsSeismic design of structural systemCoastal CaliforniaConcrete and steelResidential focus, but not excluding other occupancies

TasksEstablish and operate Project Advisory Committee (T-PAC)Research tasksConsensus performance objectivesAssessment of ground motion selection and scaling proceduresSynthetically generated ground motionsReview of synthetically generated ground motionsGuidelines on ground motion selection and modificationGuidelines on modeling and acceptance criteriaInput ground motions for tall buildings with subterranean levelsOther tasks to be defined.Guidelines for seismic design of tall buildingsWorkshops, presentations, etc.Final report to sponsoring organizations

Performance ObjectivesCore group: W. Holmes, C. Kircher, L. Kornfield, B. Petak, N. YousefApproach: Obtain input from stakeholders, formulate strawman performance objective, workshop,

Selection and scaling of ground motionCore group: J. Moehle, S. Mahin, J. Hooper, T. Yang, C. McQuiodApproach: 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 guidelinesCore 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 PSHAReview: F. Naeim, Y. Bozorgnia, N. Abrahamson, B. Chiou, CB Crouse, D. Dreger, Y. Moriwaki, Y. ZengGuidelines: Y. Bozorgnia, N. Luco, F. Naeim, J. Hooper, N. Abrahamson, J. Maffei

Guidelines for Modeling and Acceptance CriteriaCore group J. Malley, G. Deierlein, H. Krawinkler, J. Maffei, M. Pourzanjani and J. WallaceApproach: Workshop to identify key issues, assignments to experts to develop principles, procedures, and values.

Key issues:Basic principles, including capacity designGeneral modeling issues (e.g., effective damping)Podium force transferModeling of various systems and elements (core walls, frames, coupling beams, etc.)Foundation modeling (with Task 8)

Input ground motions for tall buildings with subterranean levelsCore Group: J. Stewart, C.B. Crouse, M. Lew, A. Mikami, F. Ostadan, E. TacirogluApproach: Report on the state of practice and art, and recommend future studies.Key issues:Quantifying ground motions in basements relative to free-fieldReductions of horizontal motionsIntroduction of rotationAre these effects significant at the EDP level (and beyond)?Importance of flexibility of embedded sub-structure

Final productGuidelines for performance-based seismic design of tall buildings

December 2008

PBEE practice needs(a) Building elevation(b) Summary of results

**