Transcript Project 5: Feasibility Study for In-Home Storm Shelters in Florida Residential Homes Presented to the Florida Building Commission Building (Structural) Technical Advisory Committee State of Florida.

Project 5: Feasibility Study for In-Home
Storm Shelters in Florida Residential
Homes
Presented to the
Florida Building Commission
Building (Structural) Technical Advisory Committee
State of Florida Department of Business and Professional Regulation
June 24th, 2014
David O. Prevatt, Ph.D., P.E. (MA), Associate Professor
Austin Thompson, Keith Clabaugh, David B. Roueche Graduate Assistants
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Purpose of Study
Develop guidelines for strengthening a room or an area within
an existing home necessary to achieve an acceptable level of
protection from a severe windstorm.
Is the existing shelter criteria appropriate for Florida?
Should FL shelters be designed to resist tornado loads?
What are the cost/benefit implications of shelters in homes?
Outline a test program (if needed) for Florida shelters.
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
What minimum
requirements for structural strength and affordability
are needed to provide safety to life and property from wind (hurricane
and tornado) hazards for existing residential buildings?
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
FLORIDA’S STORM SURGE RISK
Storm surge heights ranges
6-9 ft : Zone 1
28-42 ft : Zone 5
Hurricanes per County
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Wind Damage Statistics, 1950-2013
• Hurricanes
– 31 of 91 US landfalling hurricanes hit Florida’s coasts (34%)
– Only two design level wind events (Andrew and Charley)
– $58 B in losses, 73 dead & 1,253 injured (1992 & 2004)
• Tornadoes
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3,183 tornadoes recorded in Florida (50 per year)
Only 39 EF-3 and larger tornadoes, 319 EF-2 tornadoes
1 in 5 Florida tornadoes are nocturnal (late evening to night)
45.8% of the killer tornados in Florida were nocturnal events
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ASCE 7 – Category II Design
Wind Speed Map
Tornado Distributions
Population Density
Extreme Wind Speed Distribution
Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
The Florida 2004 Hurricane Season
4 major hurricanes
47 dead, $45 B in damages, 40,000 homes damaged
2.8 million persons evacuated before Frances
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71.7 million sought temporary shelter
Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
The April 1966 Tampa Tornado Family
F4 -100 mile path,11 fatalities, 3,350 injuries
1 school, 280 homes & 150 trailers demolished
Widespread looting in 2 counties
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8 $50 million estimated damage
Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Tornado Damage Patterns vs Hurricane Damage
Damaged masonry house
Kissimmee, FL during 1998 F3
Wood-framed structure destroyed by
EF2 tornado Lake Placid 2012
Window broken  Roof removed  gable wall topples  exterior
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Aged Residential Buildings (pre-Andrew codes)
-9 million single-family housing units in Florida
-6.3 million homes are 20 years old & older
-Concentrated in North Central Florida and SE
i.e. 70% of our homes do not have wind resistant
details – vulnerable to hurricanes
Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
25-28 April 2011 Tornado Outbreaks
44% of the bodies recovered inside private homes
47% of the injuries were inside single-family homes
Exterior wall collapsed
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Roof structure fails, wall topple
Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Wind Related Mortality and Morbidity Rates
The degree of building failure is highly
correlated with risk of death or injury
Severe damage of buildings was most
significantly associated with PTSD, and
mental depression outcomes
Most major injured had not covered
themselves with blankets, or pillows
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Definitions
• Storm Shelter: a structure constructed in accordance with
NSSA/ICC-500, designated for use during a severe wind
storm event (hurricanes and tornadoes)
• Residential storm shelter: serving occupants of dwelling
units, occupant load up to 16 persons.
• Host Building: A building not designed or constructed as a
storm shelter that totally/partially encloses a storm shelter.
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Storm Shelters
• Small interior rooms can survive direct tornado hit
• Kiesling and Goolsby (1974) a reinforced small
room to resist tornado loads and provide life safety
• Feasible in concrete or wood material but must not
rely upon host building for support
• Shelter survives despite damage to the host building
• Door strength and locking details are critical
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Design Criteria for Storm Shelters
• NSSA/ICC-500 (Tornado)
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100 psf roof live load
200 mph design windspeed (FL)
15 lb 2x4 traveling at 100 mph
Resist collapsed host building load
Independent of host building
Provision of ventilation
3 sf space per person
• UF recommends no change
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Missile impact testing of storm shelter
at Texas Tech University
Hurricane Shelter Design Criteria
NSSA / ICC-500
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Design wind speed (see map)
Roof live load = 50 psf
Missile Test 9 lb 2x4 @ 0.4 times wind speed
Min. fl elev. 1 ft above flood
Occupant density = 7 sf
Venting = 4 in2 per occupant
Sanitation = no, water = no, Flashlights = yes
Doors and windows = 1.2 times design pressure
For Florida: Combination Shelter Recommended – use more stringent criteria
Wood-framed Shelter Wall Systems
TTU, 1998
9 lb 2x4 missile at 25mph
Dozens of wall configurations tested
and impact resistance established.
FPL, 2013
There is some potential to reduce
impact velocity of missile for Florida
but economic justification is not there.
Lin et al. (2007) paper suggests missiles
may travel faster than 100 mph
Structural framing shown generically –
must be designed for wind pressure
Clemson, 2000
15 lb 2x4 missile at 100 mph
Storm Shelters and Evacuation
Evacuation traffic from Pinellas County before
Hurricane Charley. (Source: Sun Times)
People have less risk of
injury in homes than in cars
Northbound volume on the
Turnpike was 14 times the
normal during Frances evac.
Reducing congestion traffic
will benefit persons most at
risk (leaving storm surge)
Recovery and repair occurs
faster when occupants
shelter-in-place
Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Shelters Protect People
180
Destroyed Homes
4000
160
Shelters
3500
140
Fatalities
3000
120
2500
100
2000
80
1500
60
1000
40
500
20
0
0
Tuscaloosa, AL
Joplin, MO
Moore, OK
EF 4
EF 5
EF 5
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Fatalities
Destroyed Homes / # Storm Shelters
4500
Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Wall Corner Failure
Joplin, MO
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Interior
Walls
Anchored
Interior
Walls
not
Anchored
Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Interior Wall Anchors – zero!
available capacity to support
walls without
roof, (Joplin, MO)
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Host Building Structural Failure
• 2014 research at UWO, Canada
studied stability of walls once
roof is lost
• Attached cables and load
spreaders to walls to examine
failure of exterior wall corner
and Tee-joint connections
Three Little Pigs Test Building
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Interior Partition to Exterior Wall Strength
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Failure Progression of Exterior Walls
• Interior-to-exterior wall connection strength
directly affects overall capacity of exterior wall.
JOINT
D10 IS FAILING
BOTH JOINTS
FAILED
BEFORE TEST
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Stedman (2014)
Corner Strength and Wall Stability
Angle
increases
Corner return provides hold-down anchor to
building. Preventing rotation increases wall stability
Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Recap: Why Florida Specific Shelters?
• No basements for protection in our Florida houses
• Storm surge threat - coastal population MUST evacuate
• Nocturnal tornados pose a higher risk of injury/death
• Hurricane protection must last for more than 2 hours
• Older homes features enable disproportionate collapse
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Protect the People – Inside the Shell (The Egg)
Safeguard the Structure from Damage (The Carton)
Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
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Egg and Carton Design Components
• Use structural fasteners and connections
– Ring shank nails, metal hurricane straps
– More anchor bolts into foundation
– Continuous structural sheathing on walls
• Reinforce exterior building corners to hold walls
• Utilize strength of interior partition wall buttresses
– Use same anchor and metal tie connections as exterior walls
– Brace exterior walls using strengthened interior walls
• Shelter Design (per NSSA / ICC-500, combination shelter)
– 200 mph for wind pressure calculations
– 100 mph for missile impact design speed
– Select interior room with no exterior walls
Corner
Retrofit
Tee-Joint
Retrofit
Storm Shelter
FEMA 320
Locations
Recommended
Shelter C (Laundry Room)
Shelter spaces may be too small for longterm (12-24 hour) sheltering.
More feasible renovation to create space:
GIVE AN ORDINARY ROOM AN EXTRAORDINARY
PURPOSE (FLASH, 2010), SERRI Report# 89960-01
Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
PHASE II
• Enhanced robustness of residential (host) buildings is achievable by
providing inexpensive shear connectors at wall corners and at Teejoint connections between exterior and interior walls.
Conventional
Corner (IRC 2012)
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California Corner (APA
Advanced Framing
Guide)
Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Phase 2 Tests
Strength of wood-frame wall-to-wall connections
• Relevant Sections of Florida Building Code
– Section R602 Wood Wall Framing (ICC2009)
– Table 602.3(1) Fastener Schedules for Structural Members
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Item 7: Built-up corner studs: 10d at 24 in. o.c.
Item 16: Stud-to-sole plate:
Item 17: Top plate to stud:
Item 18: Top plate lap at corner & intersections
• Engineering Justification:
– Corner framing strength and details
– Interior-to-Exterior wall connection strengths
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Scope of Work
• Identify construction details for corner and Tee-joint construction
in existing homes (say pre-1994 homes)
• Construct and evaluate wind resistance per ASTM E330
– corner tests
– interior-to-exterior tests
• Construct, retrofit & evaluate wind resistance of retrofits
– retrofitted corner tests
– retrofitted interior-to-exterior tests
• Evaluate cost to implement in existing house (actual retrofit?)
• Produce structural design calculations example
• If indicated, develop code language for specifying wall-to-wall
connections in wood-frame Chap. R602.
Plan View of Test Setup
Test 1: Corner strength with roof in place
HAPLA
Test 2: Corner strength after roof failure
HAPLA
Test 3: Interior-exterior wall strength
HAPLA
Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Acknowledgements
• The authors gratefully acknowledge the National Science
Foundation for partial financial support for the tornado
climatology item of this study. That work was performed
under research grant 1150975. Any opinions, findings, and
conclusions or recommendations expressed in this
material are those of the authors and do not necessarily
reflect the views of the National Science Foundation.
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Leslie Chapman – Federal Alliance for Safe Homes
Dr. Ernst Kiesling – National Storm Shelter Association
Randy Shackelford – Simpson Strong-Tie
Dr. Gregg Kopp – University of Western Ontario
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Thank you!
Questions/Comments
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Thank you!
Questions/Comments
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Shelter-in-place Options
• Install/Construct a FEMA shelter
– Provide near-absolute protection
– Expect damage to house and long recovery time
• Retrofit/Strengthen the building envelope and structural framing
– Reduce property damage, yet it may be insufficient to ensure life safety.
• Retrofit/Strengthen the home to near-absolute protection.
– Risk may not warrant the costs for such renovation.
• Retrofit/Strengthen the vulnerable connections and build a hardened
interior room.
– Reduces damage to the house and protects the lives of the people
Egg and Carton Approach
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Impact Resistance Research
• TTU Carter MS 1998
– Tested 30 wood and 3 masonry composite wall systems
• Clemson 2000
– 36 wood-framed wall system
– Developed linear momentum model related to ultimate strength of a
FEMA/ICC Storm Shelter
• FPL 2013
– Examined the effectiveness of 30 wood panel wall designs for use in retrofitting
existing building with storm shelters.
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Missile impact testing at Forest Product Laboratories
Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
http://csc.noaa.gov/hurricane_county_strikes/index.html?county=pinellas&state=florida
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
Traffic volumes on major Florida roadways just prior to Hurricane Frances, 2004 (FDOT, 2009)
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
U.S. Catastrophe Losses, 1993-2012
Tornadoes: 36% or $141 Billion
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Source: ISO’s Property Claims Services Unit
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Source: ISO’s Property Claims Services
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
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Feasibility Study for In-Home Storm Shelters in Florida Residential Homes
IMPROVED BUILDING CODES =
FEWER WIND DAMAGED HOUSES
Year House Built
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Gurley and Masters (2011) “Post-2004 hurricane field survey of
residential building performance,” Nat. Haz. Review