tornado resilience: latest developments at the national level · 2021. 5. 20. · icc/nssa standard...
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Tornado Resilience: Latest Developments at the National Level
Marc L. Levitan, Ph.D.Lead Research Engineer, National Windstorm Impact Reduction ProgramNational Institute of Standards and Technology
Why Don’t We Consider Tornadoes in Conventional Engineering Design?
Common Perceptions
• Too rare• Nothing we can do
about it• Inadequate knowledge• Buildings would all have
to be concrete bunkers • Too expensive
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Perceptions may shaped by the few violent tornadoes per year that make the headlines
Photo Credit: NOAA/ITAE
How Rare are Tornadoes?
Source: NWS
Over 1,200 reported tornadoes per year in the US
How Many Lives are Lost in Tornadoes?
Tornadoes kill more people per year in the U.S. than hurricanes and earthquakes combined, and tornado fatalities overwhelmingly occur inside buildings.
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High Tornado Death Toll5,600 killed (1950 – 2011)
Average deaths/year:Tornadoes: 91.6Hurricanes: 50.8Earthquakes: 7.5
Moore OK Tornado – 2013. Damage to the hallway and classrooms of the new main classroom building (complete loss of roof and many walls) where the 7 fatalities occurred (most of the debris has already been removed). This hallway area was a “designated area of safety.” NIST SP 1164 (2013)
Comparing Tornado and Hurricane Losses
Over the 20-year period, 1997 to 2016, events involving tornadoes, including other wind, hail and flood losses associated with tornadoes made up 39.9 percent of total catastrophe insured losses, adjusted for inflation.
Hurricanes and tropical storms were a close second largest cause of catastrophe losses, accounting for 38.2 percent of losses
https://www.iii.org/article/spotlight-on-catastrophes-insurance-issues#:~:text=Hurricanes%20and%20tropical%20storms%20were,winter%20storms%20(6.7%20percent)
• Touched down at 5:34 PM CDT, Sunday, May 22, 2011.1 Stayed on ground for about 22 miles (6 miles in City of Joplin) and 15 minutes
• Enhanced Fujita Scale EF-5 tornado1 (highest category)
• Estimated maximum wind speeds: 200+ mph1
• Damaged/destroyed ~ 8,000 buildings.2 Affected ~41% of City’s population (20,820 of 50,1753). Costliest tornado on record (~$1.8 billion insured loss2)
• 161 fatalities, >1,000 injuries. Deadliest single tornado on record. Exceeds U.S. average deaths/year for all tornados (91.6) 1, hurricanes(50.8) 1, & earthquakes (7.5) 4
• Official warning time of 17 minutes (national average is 14 minutes1)
Joplin Tornado
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© 2011 GeoEye. Used with permission. Enhancements by NISTSources: 1National Weather Service2City of Joplin3U.S. Census Bureau, 2010 Census4U.S. Geological Survey
Joplin Tornado
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Joplin Tornado
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National Construction Safety Team
Following a preliminary reconnaissance that began on May 24, 2011, the NIST Director established a Team under the NCST Act on June 29, 2011, to conduct a technical investigation of the Joplin Tornado.
Team MembersNIST Engineering Laboratory employees
• Dr. Marc Levitan Investigation Team Leader, Wind Engineer, Leader of NIST NWIRP R&D
• Dr. Erica Kuligowski Fire Protection Engineer and Sociologist
• Dr. Frank Lombardo Wind Engineer and Meteorologist
• Dr. Long Phan: P.E., Structural Engineer
National Oceanic and Atmospheric Administration (NOAA) employee• Dr. David Jorgensen Research Meteorologist and Chief,
National Severe Storms Lab (NSSL)/Warning R&D Div.9
Investigation Goals• To investigate the wind environment and technical
conditions associated with fatalities and injuries, the performance of emergency communications systems and the public response to such communications, and the performance of residential, commercial, and critical buildings, designated safe areas in buildings, and lifelines
• To develop findings and recommendations that can serve as the basis for:
• Potential improvements to requirements for design and construction of buildings
• designated safe areas, and lifeline facilities in tornado–prone regions
• Potential improvements to guidance for tornado warning systems and emergency response procedures
• Potential revisions to building, fire, and emergency communications codes, standards, and practices
• Potential improvements to public safety 10
Joplin Tornado Report
16 recommendations for improving:• Tornado hazard characterization
• Design and construction of buildings and shelters in tornado–prone regions
• Emergency communications that warn of threats from tornadoes
Final report published in March 2014
http://dx.doi.org/10.6028/NIST.NCSTAR.3
The first tornado study to include storm characteristics, building performance, emergency communication and human behavior together - with assessment of the impact of each on fatalities
List of Joplin Recommendations Ha
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R # RECOMMENDATION SUMMARY LEAD
1 Development and deployment of technology to measure tornado wind fields NOAA
2 Archival of tornado event data NWS
3 Development of tornado hazard maps NIST
4 Improvement of EF Scale; means for continued improvement; adoption by NWS NWS
5 Development of performance-based standards for tornado-resistant design ASCE
6 Development of risk-balanced tornado design methodologies NIST, FEMA
7 a) Development of tornado shelter standard for existing buildings; b) Installation of tornado shelters in more buildings in tornado-prone regions
ICC
8 Development of guidelines for public tornado sheltering strategies FEMA
9 Development of guidelines for selection of best available refuge areas FEMA
10 Prohibition of aggregate roof coverings and ballast in tornado-prone regions ICC
11 Development of requirements for enclosures of egress systems in critical facilities ICC, NFPA
12 a) Development of tornado vulnerability assessment guidelines for critical facilities;b) Performance of vulnerability assessments by critical facilities in tornado-prone areas
FEMA
13 Development of codes, standards, and guidance for emergency communications; Development of joint plan by emergency managers/media/NWS for consistent alerts
NFPA
14 Deployment of “push” technologies for transmission of emergency information FEMA
15 Research to identify factors to enhance public perception of personal risk NSF, NIST
16 Develop technology for real-time, spatially-resolved tornado threat information NOAA
NOTESummaries of the recommendations are provided here for context. The complete recommendations are available in the final report of the NIST Technical Investigation of the Joplin Tornado, at https://dx.doi.org/10.6028/NIST.NCSTAR.3
Progress on implementation of these recommendations is presented next
R4: Standardize the Enhanced Fujita scale and improve through addition of scientific and quantifiable damage indicators (DIs), including those to better distinguish between the most intense tornado events
Tornado Wind Speed Estimation
• NIST and the National Weather Service (NWS) proposed and co-chair the Committee
• Joint American Society of Civil Engineers and American Meteorological Society standard
• 100+ Committee members with expertise incl.• Meteorology• Wind engineering• Structural engineering• Architecture• Construction materials• Forest biology• Emergency management
• Draft for public comment anticipated in 2022
Scope• Measurements-based Methods
‒ Radar ‒ In situ
• Estimates Inferred from Damage‒ EF Scale‒ Forensic Engineering‒ Treefall Patterns‒ Remote Sensing Imagery
Data and Metadata collection and archival
New ASCE/AMS Standard on Wind Speed Estimation in Tornadoes and Other Windstorms under development
Tornado Wind Speed Estimation
• Explicit consideration of wind resistance for each DI (NIST proposed)o Typical resistanceo Stronger than typical resistanceo Weaker than typical resistance
• Additional EF Scale methodology improvementso Explicit consideration of uncertainty o Update existing DIso New DIs
• 1-2 family residences from FEM-based fragilities (NIST)*
• Concrete (Jersey) barriers (NIST)*• Passenger vehicles*• Center Pivot Irrigation Systems
Degree of Damage (DOD) 2
Wind Speed Estimation Standard: Status
• Complete drafts of chapters for all methods in the standard
• Chapters in Main Committee (MC) balloto Radaro EF Scaleo Forensic Eng.o Treefall Pattern
• Chapters in Subcommittee review prior to MC balloto In Situo Remote Sensing Condition
Assessment
EF-Scale Methodology Improvements
* based on validated modeling and/or wind tunnel testing (instead of the expert elicitation used in original EF Scale)
Tornado Shelter StandardR7a: Development of standard for tornado shelters in existing buildings and reference of this standard in model building codes
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• Significant updates includeo Expansion of scope from 2014 ed. to include shelters in existing
buildingso Treatment of design and construction issues specific to installation
of shelters in existing buildingso New 10,000-year MRI hurricane shelter design wind speed mapo Addition of provisions to address impact loads due to laydown
hazards and falling debris hazardso New load combinations provisions
• Development of next edition completedo Scheduled for publication by ICC in Dec. 2020 o Referenced by the 2021 IBC, IEBC, and IRC
ICC 500-2020: ICC/NSSA Standard on Design and Construction of Storm Shelters
2009 IBC/IRC and Later EditionsIF constructing a storm shelter, it must
comply with ICC 500-2008
Installation of More Tornado SheltersR7b: Tornado shelters be installed in new and existing multi–family residential buildings, mercantile buildings, schools and buildings with assembly occupancies located in tornado hazard areas
IBC/IEBC shelter requirements apply in the 250 mph tornado
wind speed zone
2015 IBC (s. 423) introduced requirements for installation of tornado shelters in new
o Schools, and Fire, rescue, ambulance, and police stationso 911 call centers and emergency operations centers
2018 IBC/IEBC expanded shelter requirements• Installation of tornado shelters in
o New buildings on existing school campuses (IBC) o Additions to buildings on existing school campuses (IEBC)
• Requires ICC 500 shelters large enough to protect the population of the school, provided the new construction is of sufficient size
• Applies to Group E occupancies and indoor assembly spaces associated with the Group E occupancy, e.g., theaters, auditoriums, gymnasiums w/bleachers
Direct Adoption of ICC 500 by States/Territories, requiring storm shelters in new K-12 schools
• Alabama (also requires tornado shelters in certain higher education buildings)• Illinois• Puerto Rico (requires ICC 500 hurricane shelters)
Sheltering Strategies
NFPA 1616-2017: Standard for Mass Evacuation, Sheltering, and Re-entry Programs
• Requirements for consideration of building safety in shelter selection criteria
• Requirements for sheltering facilities to be deemed appropriate for temporary occupancy of evacuees for the applicable hazards by the AHJ
• Guidance for shelter and best available refuge area selection (the latter also supports Recommendation 9)
• Checklists to aid in shelter assessment process
Hazards ConsideredTornadoesHurricanes
Winter StormsFloods
TsunamisEarthquakes
Annex Guidance• General‒Minimum Recommendations for Selection of Existing Buildings‒Minimum Recommendations for Construction of New Shelters‒Considerations for Shelter Exposure to the Hazard Event ‒Considerations for Post-event Shelters
• Risk and Condition Assessments‒Pre-event Risk Assessment supporting shelter/refuge selection‒During-event Risk Assessment‒During-event Condition Assessment‒Post-event Condition Assessment
NIST developed all building safety-related material in the standard and annexes, in collaboration with FEMA
R8: Guidelines enabling communities to create safe and effective public sheltering strategies
Prohibition of Loose Aggregate RoofingR10: Prohibition of aggregate used as surfacing for roof coverings and aggregate, gravel, or stone used as ballast on buildings in a tornado–prone region.
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• Developed proposal for 2018 IBC to ban loose aggregate, gravel, and stone surfacing and ballast on roofs of Risk Category III and IV buildings in the tornado-prone region• in coordination with ICC Building Code Action Committee (BCAC) and
FEMA
• Published study that showed negligible cost impact • Proposal defeated at Public Comment Hearings in Oct.
2016• Will revise/resubmit after ASCE 7-22 tornado loads
adopted into IBC
Tornado Vulnerability AssessmentR12a: Development of tornado vulnerability assessment guidelines for critical facilities
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• Guidelines apply to critical facilities “both within and outside hurricane-prone regions and to critical facilities in tornado-prone regions”
• Methods to assess vulnerability of critical facilities to • wind pressure• wind-borne debris• wind-driven rain
• NIST provided input to FEMA on development of these guidelines
FEMA P-2062: Guidelines for Wind Vulnerability Assessments of Existing Critical Facilities
Emergency Communications Standards
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NFPA 1600 Standard on Continuity, Emergency, and Crisis Management• Annex K: Emergency Communications:
Public Alerts and Warnings in Disaster Response
NFPA 1616 Standard on Mass Evacuation, Sheltering, and Re-entry Programs• Annex K: Emergency Communication:
Public Alerts and Warnings• Annex L: Social Media Planning
Developed guidance for communities on the creation and provision of public alerts via outdoor siren (warning) systems and social media (incl. mobile alerts)• Stakeholder workshops on 1) siren policies and procedures and 2) short message alerting• Publications, including:
J. Sutton, E. Kuligowski, Alerts and warnings on short messaging channels: guidance from an expert panel process, Nat. Hazards Rev. 20 (2019). https://doi.org/10.1061/(ASCE)NH.1527-6996.0000324.
R13: Development of codes, standards, and guidance for emergency communications; and development of joint plan by emergency managers/media/NWS for consistent alerts
Impacts on Standards
E. Kuligowski, Field research to application: a study of human response to the 2011, Joplin tornado and its impact on alerts and warnings in the USA , Nat. Hazards (2020).
https://doi.org/10.1007/s11069-020-03945-6.
Tornado Hazard MapsR3: Develop tornado hazard maps for use in the engineering design of buildings and infrastructure be developed considering spatially based estimates of the tornado hazard instead of point–based estimates
1. Review of existing tornado maps revealed:• No consideration of tornado reporting limitations• No treatment of target size and tornado strike
position in terms of a reference wind speed (RWS)
• Use of judgment-based wind speeds • Narrow range of Return Periods • Uncertainties not systematically considered
2. The availability of EF scale-era tornado data (since 2007) provides a rich new source of information
ICC 500 and FEMA 361
ANSI/ANS 2.3 (2011)for Safety-Related Structures and
Components of Nuclear Power Plants
* 3-second gust at 33 ft
Rationale for Updated Tornado Hazard Maps
NUREG/CR-4461, Rev. 2
Tornado Hazard Maps
Tornado Data Tornado Windfield Wind Speeds
• Reporting Trends, Eras• Bias Analysis• Occurrence Rate• EF System• Random Encounter• Tornado Path Variables
Models /Analytics
Tornado Hazard Maps
Single Cell Vortex Probabilistic Parameters
• Intensity, RMW• Velocities, Profiles• Swirl
Engineering Model
• Tornado Strike• TORDAM (3D)• Prob. Load/Resistance• Progressive Failures• WBD• Internal Pressure• EF Scale, DIs, DODs• Building Stock Dist.
Model Components
Wind Speed DistributionsP(V|EF)
Windfield
Hazard/Risk Models
• Spatial Smoothing • Return Period
• PLIV• Path Width• RMW• Path Edge Wind Speeds• Spline Fit to PLIV
Swath Model
• Model/Parameter Uncertainties
• Derived Mean Frequencies
Databases:• SPC • Storm Data• DAT • Census, Hazus Data
LiteratureAugmented Database
Primary Data Sources
• Tornado Metrics• Physiographic Metrics• Develop Regions/
Subregions
Regional Climatology
• ARA TORRISK2• Single/Two Loop Simulations• Building/Facility Size Effects • Wind Speed Frequencies• Hazard Curves
Stochastic Model
Epistemic Uncertainties
• Tornado Risk Mapping Project Components
• Six year effort, working with Applied Research Associates, Inc. (ARA)
• The US Nuclear Regulatory Commission supplemented NIST funding to include the analysis of epistemic uncertainties
Map Development Overview
Tornado Hazard MapsTornado Risk Regionalization
Latitude, LongitudeElevationStd Dev ElevationLand Fraction
Animation of Sequential Cluster Formation - 1° Grid
Variables
Tornado Days/YrPath LengthOccurrence RatesPoint Strike Probability
• Broad regions of similar tornado climatology
• Ten climatology metrics evaluated
• Multivariate statistical analysis method used to discern areas of similar “climatology”
• Uniform climatology assumed within regions
• Grid based approach • Uncertainties in region
boundaries estimated and used in wind speed grid smoothing
Final Regions
Tornado Hazard MapsTornado Occurrence Rate Analysis
• Researchers have long studied tornado reporting efficiency (“population bias”) in order to estimate the under-reporting of tornadoes in rural areas
• Census Tract (CT) data coupled with Building Density (BD) data was used to estimate “unbiased” values of tornado occurrences
• High building density census tracts were found to have notably higher tornado densities
Reported tornado tracks overlaid on Census Tracts
with darker reds indicating higher Building Densities
Alabama
0.00.51.01.52.02.53.03.54.0
R1 R2 R3 R406 R407 R511 R512 R606 R609Repo
rtin
g Ef
f. (E
) "Bi
as Fa
ctor
"
Region/Subregion
Bias Factors (E) by Region/Subregion
E=1 (unbiased)
R1 R2 R3 R4a R4b R5a R5b R6a R6b
Tornado Hazard Maps
Tornado risk and tornado speeds are a function of building or facility size (plan area)
• Tornado strike probabilities increase with increasing plan area of the target building or structure (target size)
• For a given return period (i.e., mean recurrence interval), tornado speeds increase with increasing target size
Target Size Effects
Tornado Hazard MapsExample Maps
3,000 Year 100,000 Year
A. Target Sizes, ft2 (Square targets)1. Geometrical Point (no area) 2. 2,000 (45’ x 45’)3. 10,000 (100’ x 100’)4. 40,000 (200’ x 200’)5. 100,000 (316’ x 316’)6. 250,000 (500’ x 500’)7. 1,000,000 (1,000’ x 1,000’)8. 4,000,000 (2,000’ x 2,000’)
Maps Produced
B. Return Periods (Years)1. 3002. 700 3. 1,700 4. 3,000
5. 10,0006. 100,0007. 1,000,0008. 10,000,000Tornado speeds are 3-s peak gusts at 10 m height
113
99177
191
ResultsThe tornado hazard maps are based on the first-ever engineering-derived tornado wind speeds produced for the U.S.
Tornado Design Methods and Standards R5: Development of performance-based standards for tornado-resistant designR6: Development of risk-balanced tornado design methodologies
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• Built on ASCE 7-16 Wind Load Framework• Worked closely with mobile radar community to
analyze radar-measured tornado wind speeds and develop tornado velocity profile, consistent with assumptions used in development of tornado hazard maps
• Developed New and Modified Wind Load Factors for Tornadoeso Tornado Directionality Factor KdT, for MWFRS and C&Co Internal Pressure Coefficient GCpiT, including effects of
Atmospheric Pressure Changeo Tornado Pressure Coefficient Adjustment Factor for
Vertical Winds KvT, for MWFRS and C&C
Tornado Load Design Methodology
Planned Tornado Load Implementation in ASCE 7-22
WLSC Briefing for ASCE 7 MCMarch 4, 2020
NOAA Photo Library, NOAA Central Library; OAR/ERL/National Severe Storms Laboratory (NSSL).
7-22
Tornado Loads and ASCE 7
Tornado Loads: Placement in 7-22
• Chapter 1 • Add tornadoes to Risk Categorization Table 1.5-1
• Chapter 2 • Add Tornado Loads to load combinations
• Chapter 26• Add requirement that tornado loads be
determined per Ch. 32 for RC III and IV buildings and other structures
• New Chapter 32: Tornado Loads• Complete set of provisions to determine tornado
loads• Required for RC III and IV in tornado-prone region• Heavily reference methods from Ch. 26, 27, 29, 30,
31, with modifications• New Chapter 32 Appendix
• Tornado speed maps for longer return periods, in support of tornado PBD and other applications
Use or Occupancy of Buildings and Structures
Risk Category
Buildings and other structures that represent low risk to human life in the event of failure
I
All buildings and other structures except those listed in Risk Categories I, III, and IV
II
Buildings and other structures, the failure of which could pose a substantial risk to human life
III
Buildings and other structures designated as essential facilities
Buildings and other structures, the failure of which could pose a substantial hazard to the community
Buildings and other structures required to maintain the functionality of other Risk Category IV structures
IV
Table 1.5-1 Risk Category of Buildings and Other Structures for Flood, Wind, Tornado, Snow,
Earthquake, and Ice Loads
Chapter 32 Scope
Figure 32.1-1 Tornado-Prone Region
• User Note: The tornado loads specified in this chapter provide reasonable consistency with the reliability delivered by the existing criteria in Chapters 26 and 27 for MWFRS (see Return Period discussion in Section C32.5.1 for more information). These loads are based on tornado speeds using 1,700- and 3,000-year return periods for Risk Category III and IV, respectively. The tornado speed at any given geographic location will range from approximately Enhanced Fujita Scale EF0 – EF2 intensity, depending on Risk Category and Effective Plan Area of the building or other structure (see Section C32.5.1). Options for protection of life and property from more intense tornadoes include construction of a storm shelter and/or design for longer return period tornado speeds as provided in Appendix 32A, including performance-based design.
Chapter 32 - Limitations
Reliability/Return Periods
Key Finding: Using 1,700- and 3,000-year MRI Tornado Maps for Risk Category III and IV, respectively, the proposed tornadic wind load criteria provide reasonable consistency with the reliability delivered by the existing criteria in Chapters 26 and 27 for main wind force-resisting structures.
No significant tornado risk at 700-year MRI
ASCE 7 Ad-hoc Tornado Reliability/Return Period Working Group• Collaboration between NIST, ASCE 7 Load
Combinations Subcommittee and Wind Load Subcommittee
• Adapted reliability analysis used for ASCE 7-16 wind map return period analysis for use with tornado load provisions
• Conducted a series of risk-informed analyses that show the proposed tornadic wind load criteria provide reasonable consistency with the reliability delivered by the existing criteria in Chapters 26 and 27 for MWFRS
Risk Category
Wind Return Period
Tornado Return Period
I 300 n/a
II 700 n/a
III 1,700 1,700
IV 3,000 3,000
Case Study of New Tornado Load Provisions
Objectives• Compare MWFRS and C&C pressures between
ASCE 7-16 (non-tornado) and proposed tornado provisions in the Dallas / Fort Worth Area of Texas
• Consider cost impactFacilities• Risk Category III
• New Elementary School• New High School
• Risk Category IV• New Fire Station• New Hospital Campus
Key Variables
• Assume mean roof heights:• Elementary & high schools (two-story): 33 ft• Fire stations: 20 ft• Hospital campuses (mostly five-story buildings):
80 ft
• Exposure B & C considered
• Enclosure for tornado loads• Elementary & high schools: no impact-resistant
glazing = partially enclosed• Fire stations & hospitals require impact-resistant
glazing = enclosed• For basic ASCE 7-16 wind loads, all buildings in
this study are enclosed
Case study by Benchmark Harris and Blake Haney, with Huckabee, Inc. Information and graphics on this slide and the following 2 slides used with permission.
Case Study - Load Changes for MWFRS
School Steel Diaph. Foundation Wall TotalType Connection Anchorage Studs
ES 24,240.30$ -$ -$ -$ 24,240.30$ HS 139,777.61$ -$ 20,000.00$ -$ 159,777.61$
Case Study - Cost Impacts on Schools
This cost study only considered primary structural steel, foundation concrete and reinforcing, and exterior wall stud costs.
It did not include other costs, including but not limited to:• roofing assemblies• rooftop equipment (including anchorages)• miscellaneous steel• glazing
School Steel Diaph. Foundation Wall TotalType Connection Anchorage Studs
ES 24,240.30$ -$ -$ 24,120.00$ 48,360.30$ HS 139,777.61$ 7,500.50$ 20,000.00$ 90,000.00$ 257,278.11$
EXPOSURE B
EXPOSURE C
School BudgetType
ES $20M 48,360.30$ +0.24% 24,240.30$ +0.12%HS $200M 257,278.11$ +0.13% 159,777.61$ +0.08%
Cost IncreaseEXPOSURE B
Cost IncreaseEXPOSURE C
Consider this in the context of the overall building cost:
ADDITIONAL COSTS DUE TO TORNADO PROVISIONS:
Current Status: • All tornado ballots have passed the ASCE 7 Main Committee. • Currently working through resolution of comments
All ASCE 7 Committee meetings are public• meeting schedule:
https://www.asce.org/structural-engineering/asce-7-and-sei-standards/
Public Comment Draft of ASCE 7-22• June-July of 2021• 45-day comment period• All comments must be considered and responded to by the Main
Committee
Opportunities to Stay Informed/Participate
7-22
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Tornado Risk Assessment
The Hazus Program is collaborating with NIST for a long-term research project aimed at developing a Hazus Tornado model for use in risk assessments, mitigation planning, and disaster response.
https://www.hsdl.org/?view&did=830799
Upcoming Publications
NIST Technical Publications• Tornado Risk Maps for Building Design:
Research and Development of Tornado Hazard Risk Assessment Methodology
• Development of New K-factors and Internal Pressure Coefficients for Use in the Tornado Provisions of ASCE 7-22
• Tornado Load Criteria for ASCE Standard 7-22: A Probabilistic Approach
Upcoming Publications
Standards• ICC 500-2020 ICC/NSSA Standard for the Design and
Construction of Storm Shelters. • Available for free viewing on ICC web site Dec. 1 2020, and
for purchase shortly thereafter
• Separate version including commentary to follow
• ASCE 7-22 Minimum Design Loads and Associated Criteria for Buildings and other Structures
• Draft for Public Comment available in June 2021• Publication by the end of 2021
Credit: ICC
Tools:Tornado speed maps will be available through the ASCE 7 Hazards Tool, free of charge
Upcoming Publications
Guidelines• FEMA P-320. Taking shelter from the storm:
Building a safe room for your home , 5th ed• Available early in 2021
• FEMA P-361. Safe rooms for tornadoes and hurricanes: Guidance for community and residential safe rooms, 4th ed
• Available early in 2021
• Tornado Loads: Guide to the Tornado Load Provisions of ASCE 7-22
• Available from ASCE in 2022?
A few Key Challenges to Improving Tornado Resilience
Changing the common mindset that we can’t or shouldn’t be designing for tornadoes• Education and training on design for tornadoes• Continued state and local adoption of existing
model code requirements to construct ICC 500 compliant storm shelters in schools and other facilities in the 250 mph zone
• Incorporation of tornado loads in ASCE 7-22 into the model building codes (2024 IBC)
• Then, state and local adoption of the 2024 IBC
IBC/IEBC shelter requirements apply in the 250 mph tornado
wind speed zone
Tornado Resilience: Latest Developments at the National Level
Marc L. Levitan, Ph.D.Lead Research Engineer, National Windstorm Impact Reduction ProgramNational Institute of Standards and Technology
Questions?