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

2

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.

4

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

6

© 2011 GeoEye. Used with permission. Enhancements by NISTSources: 1National Weather Service2City of Joplin3U.S. Census Bureau, 2010 Census4U.S. Geological Survey

Joplin Tornado

7

Joplin Tornado

8

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

zard

Ch

arac

teris

tics

Build

ings

, She

lters

, Des

igna

ted

Safe

Are

as, a

nd L

ifelin

esEm

erge

ncy

Com

mun

icat

ion

12

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

15

• 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.

18

• 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

19

• 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

20

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

27

• 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

36

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?