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Residential structure

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Residential structure

  1. 1. Presents Residential Structural Design, the Easy Way By Paul Malko, Foard Panel Inc.
  2. 2. © 2010 Paul Malko ●In-house engineer @ Foard Panel West Chesterfield, NH ●B.S. Mechanical Engineering ●Structural Insulated Panel Association Technical Committee Code Report Committee Education Committee ●Timber Frame Engineering Council ●Timber Frame Business Council Board of Directors
  3. 3. © 2010 Disclaimer I learn new things every day. This is the best of my knowledge with nothing held back. However, I reserve the right to change my mind when I learn something new.
  4. 4. © 2010 Structural Design The specification of the system resist the forces of nature and occupants. • Safety • Building Quality • Value Engineering • Code Compliance
  5. 5. © 2010 Structural Design Methods in Building Codes • 1 & 2 Family Residential •IRC Designed •IRC Prescriptive • 3+ Family Residential •IBC • Public Buildings •IBC
  6. 6. © 2010 1-2 Family Residential IRC Prescriptive Method • Based on tradition • Historical performance • No Math • Limits •“Typical” construction materials •“Typical” types of buildings •100 mph max wind speed
  7. 7. © 2010 1-2 Family Residential IRC Prescriptive Method • “Typical” construction materials
  8. 8. © 2010 1-2 Family Residential IRC Prescriptive Method • “Typical” types of buildings
  9. 9. © 2010 1-2 Family Residential IRC Prescriptive Method • “Typical” types of buildings 1950 1973 1995 2005 0 500 1000 1500 2000 2500 3000 House Size LivingSpace(SQFT)
  10. 10. © 2010 IRC Prescriptive Method • 100 mph max wind speed
  11. 11. © 2010 IRC Engineered • Applied loads from ASCE 7 • Resist loads with conventional engineering techniques •Foundations •Beams •Columns •Diaphragms
  12. 12. © 2010 ASCE 7 • Estimates from comparing: •Building damage (insurance investigations) •Weather/Conditions that caused damage •Strength of structure
  13. 13. © 2010 Design Loads • Dead Load •Attached Building Loads •Soil Loads & Hydrostatic Pressure • Live Load •Distributed •Flood •Wind •Snow •Seismic
  14. 14. © 2010 Design Loads • Dead Load •Attached Building Loads •Soil Loads & Hydrostatic Pressure • Live Load •Distributed •Flood •Wind •Snow •Seismic
  15. 15. © 2010 Dead Load Weight of Building Soil Pressure
  16. 16. © 2010 Dead Load - Soil Pressure • Pound per square foot of pressure per foot of depth Soil Type Up to 8' deep Over 8' deep Gravel & Sand/Gravel mix 35 psf/f 60 psf/f Clay Gravel mix 45 psf/f 60 psf/f Clay/Sand mix & Clay/Silt mix 85 psf/f 100 psf/f Inorganic Clay 100 psf/f Not Suitable
  17. 17. © 2010 Foundation Design • Keyed Footings • Horizontal & Vertical Rebar • Exterior Grading
  18. 18. © 2010 Design Loads • Dead Load •Attached Building Loads •Soil Loads & Hydrostatic Pressure • Live Load •Distributed •Flood •Wind •Snow •Seismic
  19. 19. © 2010 Live Load People & Furnishings
  20. 20. © 2010 Live Load People & Furnishings Space Uniform Load Uninhabitable Attic, no storage 10 psf Uninhabitable Attic, w/ storage 20 psf Habitable Attic & Sleeping Space 30 psf Stairs 40 psf All other areas 40 psf Balcony <= 100 sqft 60 psf Balcony > 100 sqft 100 psf
  21. 21. © 2010 Floor Stiffness L/? Organization Recommendation Ceramic Tile Institute of America L/360 w/ decoupling layer Marble Institute of America L/720 APA – The Engineered Wood Association L/480 Floors are usually deflection limited, not strength limited.
  22. 22. © 2010 Beam Deflection, D W = (distributed + dead load) * span * joist spacing L = Span E = Stiffness I = 1/12 * width * depth3 (rectangular beams only) D= 5×W ×L 3 384×E×I
  23. 23. © 2010 Beam Deflection
  24. 24. © 2010 Design Loads • Dead Load •Attached Building Loads •Soil Loads & Hydrostatic Pressure • Live Load •Distributed •Flood •Wind •Snow •Seismic
  25. 25. © 2010 Live Load Flood Load Nature Always Wins!
  26. 26. © 2010 Design Loads • Dead Load •Attached Building Loads •Soil Loads & Hydrostatic Pressure • Live Load •Distributed •Flood •Wind •Snow •Seismic
  27. 27. © 2010 Live Load Wind
  28. 28. © 2010 Wind Load ● Wind force depends on: ● Building Importance ● Wall & Roof Size ● Average Roof Height ● Roof Pitch ● Exposure ● Topographic Factor (hill, escarpment, etc.) ● Wind Speed
  29. 29. © 2010 Wind Load ● Wind Force on Structure = Wind Pressure X Area ● Wind Pressure from table ● Wind speed ● Roof pitch ● Multiplied by adjustments ● Height & Exposure ● Topographic ● Importance
  30. 30. © 2010 Wind Load
  31. 31. © 2010 Wind Pressure ps = Pressure (psf) λ = Height & Exposure Adjustment Kzt = Topographic Adjustment I = Importance Factor ps30 = Base pressure from table ps=×K zt×I× ps30
  32. 32. © 2010 ps30 , Basic Wind Pressure ● Roof pitch matters ● + = pressure toward the wall/roof ● - = lift away from wall/roof Wind Speed Roof Pitch Wall Horiz. Roof Vertical Roof Edge Field Edge Field Windward Leeward Eave Over- hang Gable Over- hangEdge Field Edge Field mph psf psf psf psf psf psf psf psf psf psf 90 Flat 13 9 -7 -4 -15 -11 -9 -7 -22 -17 90 3:12 16 11 -5 -3 -15 -11 -10 -8 -22 -17 90 6:12 16 12 3 3 -7 -5 -10 -8 -13 -11 90 8:12- 12:12 14 12 10 8 6 5 -9 -8 -5 -6
  33. 33. © 2010 ps30 , Basic Wind Pressure Wind Speed Matters Wind Speed Roof Pitch Wall Horiz. Roof Vertical Roof Edge Field Edge Field Windward Leeward Eave Over- hang Gable Over- hangEdge Field Edge Field mph psf psf psf psf psf psf psf psf psf psf 90 10:12 14 12 10 8 6 5 -9 -8 -5 -6 100 10:12 18 14 12 10 7 6 -12 -9 -6 -7 110 10:12 12 17 15 12 8 7 -13 -11 -8 -9 120 10:12 26 20 18 14 10 9 -16 -13 -9 -10 130 10:12 30 24 21 17 12 10 -18 -16 -11 -12
  34. 34. © 2010 Wind Exposure ● B = Wooded or suburban ● C = Exposed ● D = Exposed on water
  35. 35. © 2010 λ, Height & Exposure Adjustment Average Roof Height Exposure B Exposure C Exposure D 15 1.0 1.21 1.47 20 1.0 1.29 1.55 25 1.0 1.35 1.61 30 1.0 1.40 1.66 35 1.05 1.45 1.70 40 1.09 1.49 1.74 45 1.12 1.53 1.78 50 1.16 1.56 1.81
  36. 36. © 2010 I, Importance Factor ● How important is the building? ● If building fails, what is the human loss? ● Will people gather there during storms?
  37. 37. © 2010 I, Importance Factor ● I = Minor storage & Agricultural ● II = Everything else ● III = > 300 people, >150 children, public works ● IV = Hospitals, emergency response Category Wind <= 100 mph Wind > 100 mph I 0.87 0.77 II 1.00 1.00 III 1.15 1.15 IV 1.15 1.15
  38. 38. © 2010 Kzt , Topographic Factor
  39. 39. © 2010 Wind Pressure Example ● House ● 10:12 Roof, 25' tall ● Located in middle of a field ● No extreme terrain ps= ps30××K zt×I corner of wall=14×1.35×1.0×1.0=19 psf edgeof roof =−9×1.35×1.0×1.0=−12 psf
  40. 40. © 2010 Wind Resistant Structure ● Diaphragms ● Shear Connections ● Overturning Resistance
  41. 41. © 2010 Wind Resistant Structure ● Exterior walls w/ modest RO sizes ● Interior shear walls ● Plan lateral system during design
  42. 42. © 2010 Wind Resistant Structure
  43. 43. © 2010 Wind Resistant Structure ● Diaphragms ● Shear Connections ● Overturning Resistance
  44. 44. © 2010 Design Loads • Dead Load •Attached Building Loads •Soil Loads & Hydrostatic Pressure • Live Load •Distributed •Flood •Wind •Snow •Seismic
  45. 45. © 2010 Live Load Snow
  46. 46. © 2010 Live Load Snow
  47. 47. © 2010 Live Load Snow
  48. 48. © 2010 Live Load Snow
  49. 49. © 2010 Snow Load ● Snow weight depends on: ● Roof Size ● Building Importance ● Exposure ● Thermal Factor (Heat Loss) ● Ground Snow Load ● Roof Shape ● Roof Pitch ● Roofing Friction
  50. 50. © 2010 ps, Sloped Roof Snow Load ps = Sloped roof snow load (psf) Ce = Exposure Factor Ct = Thermal Factor Cs = Sloped Roof Factor I = Importance Factor pg = Ground snow load (psf) ps=0.7×Ce×Ct×Cs×I× pg
  51. 51. © 2010 pg , Ground Snow Load ● Grey = Case Study, Too variable ● Elevation limits
  52. 52. © 2010 Ce, Roof Exposure Factor Site Exposure Fully Exposed Partially Exposed Sheltered B 0.9 1.0 1.2 C 0.9 1.0 1.1 D 0.8 0.9 1.0 Above Tree Line 0.7 0.8 N.A.
  53. 53. © 2010 Ct, Thermal Factor Category Ct Heated w/ whole surface R < 2 0.85 Default 1.00 Heated w/ whole surface R 16-29 1.10 Unheated or Heated w/ whole surface R > 30 1.20
  54. 54. © 2010 Cs, Sloped Roof Factor ● Adjusts for Ct ● Adjusts for roof ventilation Roof Pitch Med.- High Grip Low Grip 3:12 1.0 0.9 6:12 1.0 0.7 8:12 1.0 0.6 10:12 0.8 0.4 12:12 0.6 0.3 ● Assume Ct = 1.0
  55. 55. © 2010 I, Importance Factor ● I = Minor storage & Agricultural ● II = Everything else ● III = > 300 people, >150 children, public works ● IV = Hospitals, emergency response Category I I 0.8 II 1.0 III 1.1 IV 1.2
  56. 56. © 2010 Roof Plan ● Size and shape matters greatly ● Complex roofs must be calculated as individual simple roofs ● Consider several conditions ● Balanced snow ● Unbalanced snow ● Drifts (aerodynamic shade) ● Sliding snow ● Ponding
  57. 57. © 2010 Drifting and Sliding Snow pg = 65 psf 112 psf 0 psf ps = 53 psf 65 psf
  58. 58. © 2010 Ponding ● Usually only applies to very shallow pitch roofs ● High risk for complete failure
  59. 59. © 2010 Design Loads • Dead Load •Attached Building Loads •Soil Loads & Hydrostatic Pressure • Live Load •Distributed •Flood •Wind •Snow •Seismic
  60. 60. © 2010 Seismic Nature always wins!
  61. 61. © 2010 A Punching Engineer May Help Yes, engineers can be annoying... but our job is to be professional worriers and keep people safe.
  62. 62. © 2010 Paul Malko Paul Malko, Chief Engineer Foard Panel Inc. paul@foardpanel.com 800-644-8885

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