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Performance Based Wind Design
Speaker: Russell Larsen, S.E.Senior Associate, MKA SeattleLeader of ASCE7-22 Wind Loads PBD Sub-Committee
In collaboration with:
Learning Objectives for Today
1) Understand the impetus for Performance Based Wind Design (PBWD)
2) Understand the current research supporting PBWD
3) Understand development of the ASCE PBWD guideline
Content Today
1) History – where has PBD wind been?
2) Why – what does PBD wind offer the profession?
3) Where are we going – how is PBD wind developing?
Wind Engineering History 1960s – Wind Tunnel Technique
Boundary layer flows first used in bluff body aerodynamics. Occupant comfort first investigated for the World Trade Center
Towers
Early 1980s – LRFD technique comes into being Concepts of reliability used as the basis to rationally find
resistance and load uncertainty Load factors found to achieve a level of reliability
1980s – 2000s Many advances in wind engineering, wind tunnel testing, and
model codes Root acceptance criteria are still based upon single element elastic
reliability.
History of PBWD 2000 - 2013: Initial PBWD work
Initial conceptual work by researchers (e.g. Tabbuso, Kareem) Isolated literature by practitioners (e.g. Griffis, Jain)
2013 - 2016: ASCE7 Ad Hoc PBWD group Formed from WLSC membership following the ASCE7-16
development cycle Membership assembled available work and identified gaps in
knowledge
2016 - 2019: PBWD & ASCE Prestandard Industry focused research initiated (NSF, MKA Foundation) Guideline development funded by Pankow Foundation PBWD made part of ASCE WLSC
Impetus of PBWD
Motivation: To express the full spectrum of relevant wind performance criteria Promote value and risk based design strategies Begin to explore limited inelasticity in strength design Replicate the design advanced PBD has allowed in seismic
engineering Allow improved building performance though targeted selection of
MWFRS elements based upon their demonstrated abilities Improve seismic performance where SLRS ductility is hampered
by contemporary wind demands Allow designers PBD tools for wind according to ASCE desire to
promote the use of PBD in the workplace. To answer the call from practitioners
Impetus of PBWD - Motivations
To express the full spectrum of relevant wind performance criteria
Impetus of PBWD - Motivations
Promote value and risk based design strategies t Modeling of the
structure and interrogation of the model reveals demands (strain, movement, stress) than can inform damage models (fragility)
Source: Aswegan, Charney and Jarrett
Impetus of PBWD - Motivations
Promote value and risk based design strategies
Source: ATC-58 PACT gypsum wall fragility
Impetus of PBWD - Motivations
Allow improved building performance though targeted selection of MWFRS elements based upon their demonstrated abilities At present we check on an element by element basis the reliability
of the structure. (ASCE7-16 Part 1.3.1 Wind MRI and load factors emerge from the reliability targets….
Impetus of PBWD - Motivations
Can we begin to explore limited inelasticity in strength design? Seismic engineering has advantageously applied ductility for many
years… Under what circumstances could wind engineering do the same?
Impetus of PBWD - Motivations
Improve seismic performance where SLRS ductility is hampered by contemporary wind demands
Ductile seismic elements may have to be strengthened for elastic wind loads…
If so, their ability to initiate yield is reduced (lower effective R)…
And force controlled (connections etc) see higher demands
Impetus of PBWD - Motivations
Allow designers PBD tools for wind according to industry and ASCE desire to promote the use of PBD in the workplace ASCE 2025 Vision:
Seismic Parallels- Motivations
Answer the call of practitioner and create a guideline to facilitate PBD Wind, and
Replicate the design advances PBD has allowed in seismic engineering PBD Seismic was assisted by key publications:
• ATC 33 / NEHRP 273/274 (1997) Guideline for the Seismic Rehabilitation of Buildings
• SEAOC Vision 2000 (1995) Definition of seismic performance states.• Los Angeles Tall Building Council Alternate procedure for seismic analysis
of tall buildings
ASCE and PBD Wind
Objectives Identified …
What next?
How do we do this?
2013 ASCE7 Wind Subcommittee began work
The ASCE Ad-Hoc Group 2013-2016
Four primary needs were identified to begin PBWD
Need #1 – Structural System Reliability for Strength Wind
Need #2 – Guidance for practitioners to launch PBWD
Need #3 – Protocols for AHJ and Peer Review
Need #4 – Further material research specific to wind performance
Need #1 - Reliability Reliability is the core of ASCE7
Reliability - Shakedown
Need #1 – Reliability -Summary
The work by Dr. Spence has shown that the reliability of a structural system can be efficiently determined for wind.
A building properly designed can achieve levels of safety equal to or better than required by ASCE while experiencing limited inelasticity.
Need #2 – Guidance to Practitioners
The Concern: No systematic approaches to PBD Wind were available. Answer: The Charles Pankow Foundation and ASCE SEI teamed
to create a Prestandard for PBWD of Tall Buildings
Additional Support American Institute of Steel
Construction (AISC) American Concrete Institute
(ACI)
Need #2 – Guidance to Practitioners
Who is writing and reviewing* the Prestandard?Answer: Members of the ASCE7 Wind Loads Subcommittee
Design Industry Wind Research Governmental / Jurisdictional /
ApprovalDon Scott, PCS (Chair) Scott Bondi, SGH Roy Denoon, CPP Terri McAlister, NIST
Russell Larsen, MKA Tom Smith, TLSmith John Kilpatrick, RWDI Bruce Ellingwood (*)
Melissa Burton, ARUP Larry Griffis, WP Moore (*)
Seymour Spence, U. Michigan
Tim Reinhold, IBHS (*)
Anurag Jain, Walker Viral Patel, WP Moore (*) Findley Charney, Virginia Tech
Cheryl Burwell, City of Seattle (*)
Ron Hamburger, SGH Brad Young, SOM (*) Peter Irwin, FIU / RWDI (*)
John Hooper, MKA Philip Dregger, TRS (*) Xinzhong Chen, Texas Tech (*)
Jennifer Goupil, ASCE Tali Mejicovsky, ARUP (*)
Need #2 – Guidance to Practitioners
How is the Prestandard being written? Chapter 1 – Introduction, Terms, Glossary, etc Chapter 2 – Design Process Overview Chapter 3 – Determination of Risk Chapter 4 – Performance Objectives Chapter 5 – Wind Demand Characterization Chapter 6 – Modeling and Analysis Chapter 7 – Acceptance Criteria for MWFRS Chapter 8 – Building Envelope Criteria Chapter 9 – Project Peer Review
Need #2 – Guidance to Practitioners
What will the structure design process look like? The Prestandard is written to give practitioners an actionable guide
to use PBWD for non-prescriptive wind design. Methods will include:
Path 1: A quasi-prescriptive time history method with acceptance criteria.
Path 2: A first-order reliability technique similar to FEMA P-695
Path 3: System reliability evaluation technique
Path 1 will be the most commonly traveled and the Prestandard has the most guidance for this path.
Structure Design Process
Case Study
60 Story Office 900 ft above grade Concrete Core BRB Outriggers to perimeter
column
Seismic demands “turned off”
NO SEISMIC DETAILING
Seattle wind climate104 h 1700
Case Study
Case Study 25% Reduction in BRB size at outrigger system
Case Study Plastic beam response can be interrogated
Example Moment Rotation Time History Response
Prestandard – Summary & Fine Print
The Pankow / ASCE Prestandard to PBWD of Tall Buildings Offers paths to use Non Prescriptive Design (PBWD) Limited ductile response can be entertained Specific sources of loss are identified and the design team makes
decisions to appropriately avoid unacceptable loss Specific loss avoidance enhancements are described for the
envelope system
How will practitioners use it? By documenting and demonstrating building performance in a Peer
Reviewed design process in collaboration with the AHJ
Prestandard – Guidance to Practitioners
What are the limitations? Limited to bespoke engineered major buildings and envelopes. (This version) does not address non-building structures such as antennae,
equipment support, or solar equipment. All PBD is an alternate to the prescriptive methods of ASCE. The designer must have collaboration and agreement of the AHJ. The design process is certainly more rigorous than contemporary design. A Peer Review is required for non-prescriptive design.
Is it economical? More sophisticated design will require additional effort, time, and cost by
the design and peer review teams. Targeted selection of structure and envelope for system loss reduction
and greater system utilization can give overall project savings. Likely PBWD will only be used for major projects at first.
Need #3 – Guidance for AHJ The Concern: Alternate non-prescriptive (PBD) methods
are allowed by ASCE7, but how will an AHJ have confidence that suitable performance or standard of care is being met? Answers: #1 The Pankow / ASCE Prestandard includes Peer Review and
acceptance criteria for non-prescriptive design. #2 The Prestandard is modeled after the PEER TBI Initiative
widely used for non-prescriptive design. #3 The Prestandard has been Peer Reviewed by a panel of highly
regarded industry, wind engineering, and reliability experts.
Need #4- Further Material Research
Select MWFRS response to strength wind demand is sparse Answer: Industry Groups are beginning investigation to enhance
PBWD the understanding of structural element response to wind effects.
The present Prestandard is based upon known response established in 40+ years of seismic research – for “special detailed” and “non special detailed” structural elements.
Further PBWD material research will enable further growth Example: UCLA is testing concrete coupling beam performance to
simulated low cycle fatigue wind demands.• The test campaign is roughly half way complete. Results thus far
suggest very good performance of contemporary beam design for low cycle wind demands.
Looking Forward ASCE PBWD Prestandard
Scheduled for electronic publication July 1, 2019 from ASCEDocument will be free (in pdf form)
ASCE PBWD SubcommitteeCreating further case studies for PBWD
Advocating support for PBWD within ASCE7-22
Support for PBWD from the Material Standard Institutes Interest is expressed by ACI & AISC to advance material codes More to come!
Wrap Up“We are advancing our profession’s quest for better ways to design and build, and performance-based (wind) design is key to this advancement.”
-- R. Klemencic
“The Pre-Standard currently being developed will allow the designer more flexibility and creativity in the design of the lateral force resisting system for the building and advance the requirements for the design of the components and cladding systems that protect the building interior.”
-- D. Scott
Structure Magazine March 2019
