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SLIDE ‹#› Project 5: Feasibility Study for In-Home Storm Shelters in Florida Residential Homes Presented to the Florida Building Commission Building (Structural)

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Presentation on theme: "SLIDE ‹#› Project 5: Feasibility Study for In-Home Storm Shelters in Florida Residential Homes Presented to the Florida Building Commission Building (Structural)"— Presentation transcript:

1 SLIDE ‹#› 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 24 th, 2014 David O. Prevatt, Ph.D., P.E. (MA), Associate Professor Austin Thompson, Keith Clabaugh, David B. Roueche Graduate Assistants

2 SLIDE 2 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.

3 SLIDE 3 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?

4 SLIDE 4 Feasibility Study for In-Home Storm Shelters in Florida Residential Homes Hurricanes per County FLORIDA’S STORM SURGE RISK Storm surge heights ranges 6-9 ft : Zone ft: Zone 5

5 SLIDE 5 Feasibility Study for In-Home Storm Shelters in Florida Residential Homes Wind Damage Statistics, 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 –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

6 Extreme Wind Speed Distribution Tornado Distributions Population Density ASCE 7 – Category II Design Wind Speed Map

7 SLIDE 7 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 1.7 million sought temporary shelter

8 SLIDE 8 Feasibility Study for In-Home Storm Shelters in Florida Residential Homes The April 1966 Tampa Tornado Family F mile path,11 fatalities, 3,350 injuries 1 school, 280 homes & 150 trailers demolished Widespread looting in 2 counties $50 million estimated damage

9 SLIDE 9 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 (side wall) falls  interior partitions collapse  occupants injured  fatalities occur

10 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

11 SLIDE 11 Feasibility Study for In-Home Storm Shelters in Florida Residential Homes April 2011 Tornado Outbreaks 44% of the bodies recovered inside private homes 47% of the injuries were inside single-family homes Exterior wall collapsedRoof structure fails, wall topple

12 SLIDE 12 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

13 SLIDE 13 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.

14 SLIDE 14 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

15 SLIDE 15 Feasibility Study for In-Home Storm Shelters in Florida Residential Homes Design Criteria for Storm Shelters NSSA/ICC-500 (Tornado) – 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 Missile impact testing of storm shelter at Texas Tech University

16 Hurricane Shelter Design Criteria NSSA / ICC-500 Design wind speed (see map) Roof live load = 50 psf Missile Test 9 lb 0.4 times wind speed Min. fl elev. 1 ft above flood Occupant density = 7 sf Venting = 4 in 2 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

17 Wood-framed Shelter Wall Systems 9 lb 2x4 missile at 25mph 15 lb 2x4 missile at 100 mph Dozens of wall configurations tested and impact resistance established. 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 TTU, 1998 FPL, 2013 Clemson, 2000

18 Storm Shelters and Evacuation 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 Evacuation traffic from Pinellas County before Hurricane Charley. (Source: Sun Times)

19 SLIDE 19 Feasibility Study for In-Home Storm Shelters in Florida Residential Homes Shelters Protect People EF 5 EF 4

20 SLIDE 20 Feasibility Study for In-Home Storm Shelters in Florida Residential Homes Wall Corner Failure Joplin, MO

21 Interior Walls Anchored Interior Walls not Anchored

22 SLIDE 22 Feasibility Study for In-Home Storm Shelters in Florida Residential Homes Interior Wall Anchors – zero! available capacity to support walls without roof, (Joplin, MO)

23 SLIDE 23 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

24 SLIDE 24 Feasibility Study for In-Home Storm Shelters in Florida Residential Homes Interior Partition to Exterior Wall Strength

25 SLIDE 25 Feasibility Study for In-Home Storm Shelters in Florida Residential Homes Failure Progression of Exterior Walls Stedman (2014) Interior-to-exterior wall connection strength directly affects overall capacity of exterior wall. BEFORE TEST JOINT D10 IS FAILING BOTH JOINTS FAILED

26 Corner return provides hold-down anchor to building. Preventing rotation increases wall stability Angle increases Corner Strength and Wall Stability

27 SLIDE 27 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

28 SLIDE 28 Feasibility Study for In-Home Storm Shelters in Florida Residential Homes Protect the People – Inside the Shell (The Egg) Safeguard the Structure from Damage (The Carton)

29 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

30

31 Corner Retrofit Tee-Joint Retrofit FEMA 320 Recommended Storm Shelter Locations

32 Shelter C (Laundry Room) Shelter spaces may be too small for long- term (12-24 hour) sheltering. More feasible renovation to create space: GIVE AN ORDINARY ROOM AN EXTRAORDINARY PURPOSE (FLASH, 2010), SERRI Report#

33 SLIDE 33 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 Tee- joint connections between exterior and interior walls. California Corner (APA Advanced Framing Guide) Conventional Corner (IRC 2012)

34 SLIDE 34 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 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

35 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.

36 Plan View of Test Setup

37 Test 1: Corner strength with roof in place HAPLA

38 Test 2: Corner strength after roof failure

39 HAPLA Test 3: Interior-exterior wall strength

40 SLIDE 40 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 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. 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

41 SLIDE 41 Feasibility Study for In-Home Storm Shelters in Florida Residential Homes Thank you! Questions/Comments

42 SLIDE 42 Feasibility Study for In-Home Storm Shelters in Florida Residential Homes Thank you! Questions/Comments

43 SLIDE 43 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

44 SLIDE 44 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. Missile impact testing at Forest Product Laboratories

45 SLIDE 45 Feasibility Study for In-Home Storm Shelters in Florida Residential Homes

46 SLIDE 46 Feasibility Study for In-Home Storm Shelters in Florida Residential Homes

47 SLIDE 47 Feasibility Study for In-Home Storm Shelters in Florida Residential Homes

48 SLIDE 48 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)

49 SLIDE 49 Feasibility Study for In-Home Storm Shelters in Florida Residential Homes U.S. Catastrophe Losses, Tornadoes: 36% or $141 Billion Source: ISO’s Property Claims Services Unit 49 Source: ISO’s Property Claims Services

50 Annual Probability of Wind Speed Exceedance due to Tornadoes (Note: ASCE 7 Windspeed POE is based on geographic location (i.e. contour lines) and the tornado POE are for the entire state Twisdale and Dunn (1983) and Banik et al. (2007) Methodology for prediction of tornado wind probabilities

51 SLIDE 51 Feasibility Study for In-Home Storm Shelters in Florida Residential Homes

52 SLIDE 52 Feasibility Study for In-Home Storm Shelters in Florida Residential Homes Gurley and Masters (2011) “Post-2004 hurricane field survey of residential building performance,” Nat. Haz. Review IMPROVED BUILDING CODES = FEWER WIND DAMAGED HOUSES Year House Built


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