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Overview of Damage Assessments

Overview of Damage Assessments. Ron W. Przybylinski Science and Operations Officer NWS St. Louis. Outline. Damage Patterns (Tornadic and Downburst (Microbursts) Brief review of the Enhanced Fujita (EF) Scale Example – “You Make the Call”

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Overview of Damage Assessments

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  1. Overview of Damage Assessments Ron W. PrzybylinskiScience and Operations OfficerNWS St. Louis

  2. Outline • Damage Patterns (Tornadic and Downburst (Microbursts) • Brief review of the Enhanced Fujita (EF) Scale • Example – “You Make the Call” • What can I do for you. What can you do for me.

  3. Why do damage assessments? • Determine tornado intensity • Estimate wind speeds • Storm track, width • Determine warning response

  4. Heard this Before? • It sounded like a freight train • The trees (or whatever) are twisted • Only a tornado could do this much damage • I felt my ears “pop”

  5. Tornadic Damage From Dr. Ted Fujita – Univ. of Chicago Convergence pattern – arrows pointing to the center axis of the tornadic damage path (Red).

  6. June 10 2003 – tornadic damage two miles NNW of Nashville IL – weak tornado. BAMEX Project 2003

  7. House trailer damage from a violent tornado –2:00 am CST November 6 2007 Evansville IN. Eastbrook Mobile Home Park – southeast of Evansville Indiana

  8. View from a plane viewing SE - Eastbrook Mobile Home Park

  9. Multiple Vortex Tornado Multiple Vortex pattern – the strongest winds often occur with this type of ground pattern (suction vortices) .

  10. Remains of a corn field from a violent tornado Are you able to observe part of a convergent pattern ?

  11. Downburst clusters associated with bow echoes

  12. Classic example of a microburst – starburst pattern

  13. Small part of a downburst cluster over southern Clinton County Illinois – July 21 2006

  14. Damage characteristics we look for:

  15. Introduction to the Enhanced Fujita (EF) scale • Dr. Ted Fujita (1971) developed the Fujita scale to provide a method to rate the intensity of tornadoes. • However after 33 years of using the Fujita scale, users have found many limitations to this scale (e.g. lack of damage indicators). • In many cases NWS personnel would over estimate the wind speeds with tornadoes.

  16. Enhanced Fujita (EF) scale • Steering committee (23 members) developed the following: • Identify “Damage Indicators.” • Correlate appearance of damage to wind speed • Preserved the historical data base • Seek additional input from users

  17. EF Scale vs. Traditional Fujita Scale Wind Speed Ranges

  18. 28 Damage Indicators

  19. EF Scale Development • Each DI has several Degrees of Damage (DOD) • Range from no damage to total destruction • Arranged in order of increasing damage

  20. One-and Two-Family Residences (FR12) • Typical Construction: • Asphalt shingles, tile, slate or metal roof covering • Flat, gable, hip, mansard or mono-sloped roof or combination thereof • Plywood/OSB or wood plank roof deck • Prefabricated wood trusses or wood joists and rafter construction • Brick veneer, wood panels, stucco, EIFS, vinyl or metal siding • Wood or metal stud walls, concrete blocks or insulating concrete panels • Attached single or double garage

  21. One-and Two-Family Residences (FR12)

  22. One-and Two-Family Residences Degree of Damage (DODs)

  23. One-and Two-Family Residences FR12: DOD4: Uplift of roof deck and loss of roof covering (>20%); garage door collapses outward (LB 81 mph; UB 116 mph; Exp 97 mph)

  24. One-and Two-Family Residences FR12: DOD7: Top floor (First floor in this case) exterior walls collapsed. (LB 113 mph; UB 150 mph; Exp 132 mph).

  25. One-and Two-Family Residences FR12: DOD10: Total destruction of entire building(LB 165 mph; UB 220 mph; Exp 200 mph).

  26. Recommended steps for assessing tornado damage • Conduct a survey (aerial if possible) • Select several damage indicators (trees, buildings, power poles, etc…) that tend to indicate the highest wind in the damage path • Assign an EF-scale to individual DIs – document • Rate the tornado intensity by applying the highest rated DI, provided there is supporting evidence of similar damage nearby. • Document the basis for assigning the EF-Scale, and record other pertinent data related to the event

  27. Structures’ Response to Wind • Type • Design • Orientation of structure to the winds • The upstream terrain • Duration and gustiness of the wind • Missiles

  28. Pressure on the building’s interior increases, resulting in additional outward forces. That is why opening windows is not a good idea.

  29. Failure Points Rafter/top plate Roof joist/top plate Wall stud/bottom plate Wall/foundation

  30. Look For Reinforcements

  31. You make the call Large Industrial building

  32. Another Image

  33. Remains of a corn field

  34. What can I do to help you out? What can you do to help me out?

  35. Questions??

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