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Building Design for Tornadoes

Building Design for Tornadoes. William L. Coulbourne, P.E. Applied Technology Council bcoulbourne@atcouncil.org. Agenda. EF damage scale 2011 history of tornado damage Design formulas for wind pressure Illustrations of design pressures Wind-borne missiles. Why Design for Tornadoes?.

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Building Design for Tornadoes

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  1. Building Design for Tornadoes William L. Coulbourne, P.E. Applied Technology Council bcoulbourne@atcouncil.org

  2. Agenda • EF damage scale • 2011 history of tornado damage • Design formulas for wind pressure • Illustrations of design pressures • Wind-borne missiles

  3. Why Design for Tornadoes? • Low probability but high consequence event • Property damage can be extreme • Loss of life is real threat • As professionals we should not assume there is nothing we can do • We can use existing technology

  4. Design Strategies for Tornadoes • Use ASCE 7 wind load provisions • Modify some of the factors • Use higher wind speeds than ASCE 7 • Understand the limitations of what we don’t know

  5. Tornado Damage Scale • EF scale is based on observed damage • Scale goes from Category EF0 – EF5 with corresponding wind speeds from 65 mph to 200 mph • Primary reference is from Texas Tech Univ. titled: A Recommendation for an ENHANCED FUJITA SCALE (EF-Scale) 2006

  6. Tornado Damage Scale • 28 Damage Indicators used – structure or use types (e.g.): • One or two family residences • Apartments, condos or townhouses • Large shopping mall • Junior or Senior high school • Warehouse building • Free standing towers

  7. Tornado Damage Scale • Each Damage Indicator has a range of wind speeds associated with degrees of damage for that structure type – for one and two family residences:

  8. Condos, apartments, townhouses

  9. Junior and Senior High Schools

  10. Elementary Schools

  11. Recent Events We’ve Learned From • OK/KS 1999 • Greensburg, KS 2007 • Enterprise, AL 2007 • Tuscaloosa, AL 2011 • Joplin, MO 2011

  12. Joplin Tornado Path - 5/22/11

  13. Joplin, MO Tornado – 5/22/11 Joplin, MO info Located in SW corner of Missouri Population of ~50,000 Established in 1873 Area of 31.5 sq. miles Previously had tornado impact town in 1971, killing one Evaluations for 5/22 tornado by NWS classify it as an EF-5 Fatality count ~ 160 Over 8000 buildings damaged (path crossed through major commercial and residential areas)

  14. Joplin Damage Assessment Map

  15. EF Damage Plotted

  16. Area % of EF Damage

  17. EF0 (65-85 mph)

  18. EF1 (86-109)

  19. EF2 (110-137)

  20. EF3 (138-167)

  21. EF3 (138-167)

  22. EF4 (168-199)

  23. EF5 (200-234)

  24. Multi-family Buildings (~2000)

  25. East Middle School (2009) Gymnasium

  26. Auditorium

  27. Joplin High School EF2

  28. Tuscaloosa Damage Path

  29. 29

  30. EF Damage Plotted

  31. 85+% Area % of EF Damage

  32. Housing Demographics

  33. EF0 (65-85 mph)

  34. EF1 (86-109)

  35. EF2 (110-137)

  36. EF3 (138-167)

  37. EF4 (168-199)

  38. Multi-family Building (Old) EF1

  39. Multi-family Buildings (New) EF4

  40. Greensburg, KS

  41. Well-built house, Birmingham, AL Jan 2012 tornado

  42. Steel moment frame, well-built house

  43. Roof stays together

  44. Devil is in the details

  45. Comparison – Hurricane to Tornado Wind Speeds

  46. What We Know How To Do • Maintain load path continuity • Maintain roof-to-wall connections • Maintain wall-to-floor and foundation connections • Keep walls standing

  47. Suggested Tornado Design Premise • Strengthen building like we do for hurricanes • Do not try and protect for wind-borne debris • Do design so interior walls stay in place • Keep exterior corners together • Maybe consider a way to ‘vent’ the upper portion of the building

  48. Ground Continuous Load Path Concept

  49. Research - Increase in Uplift Pressures • Reference: Tornado-Induced Wind Loads on a Low-Rise Building, Dr. Partha Sarkar, Dr. Fred Haan, Journal of Structural Engineering 2010 • Tornado simulator used to determine pressure coefficient differences with ASCE 7-05 standard • Results were: • Cx = 1.0 (no increase in lateral direction) • Cy = 1.5 (50% increase in wind parallel direction) • Cz = 1.5-3.2 (more than 3 times increase in vertical or uplift direction)

  50. ASCE 7-16 Commentary Proposed Changes • Modify standard wind pressure equation for differences in tornado wind structure • Discuss differences so practitioners have a basis for design • Use wind speed maps from ICC and FEMA • Provide rationale and references

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