Practical Design and the implications of the Blizzard of

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Practical Design and the implications of the
Blizzard of 96

• BSE 2294
• Animal Structures and Environment
• Dr. Susan Wood Gay
• S. Christian Mariger Ph.D.

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Practical sizing techniques for structural
components.

• We have looked at some of the engineering
  approaches for analyzing stresses in wood
  structural components.
• In practice span tables are used to determine the
  size and quality required for wood structural
  components.
• Span tables are produced by calculating the
  maximum span (L) for a given dimension and grade
  of lumber with a given distributed load (W).
• When designing the structure the builder will
  simply use the table to determine dimension and
  grade required instead of calculating the actual
  stress and deflection.

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Typical Span Table (Floor Joists)
Table 1 Southern Pine Floor Joists (Maximum spans given in feet and inches inside to inside of bearings) Table 1 Southern Pine Floor Joists (Maximum spans given in feet and inches inside to inside of bearings) Table 1 Southern Pine Floor Joists (Maximum spans given in feet and inches inside to inside of bearings) Table 1 Southern Pine Floor Joists (Maximum spans given in feet and inches inside to inside of bearings) Table 1 Southern Pine Floor Joists (Maximum spans given in feet and inches inside to inside of bearings) Table 1 Southern Pine Floor Joists (Maximum spans given in feet and inches inside to inside of bearings) Table 1 Southern Pine Floor Joists (Maximum spans given in feet and inches inside to inside of bearings) Table 1 Southern Pine Floor Joists (Maximum spans given in feet and inches inside to inside of bearings) Table 1 Southern Pine Floor Joists (Maximum spans given in feet and inches inside to inside of bearings) Table 1 Southern Pine Floor Joists (Maximum spans given in feet and inches inside to inside of bearings) Table 1 Southern Pine Floor Joists (Maximum spans given in feet and inches inside to inside of bearings) Table 1 Southern Pine Floor Joists (Maximum spans given in feet and inches inside to inside of bearings) Table 1 Southern Pine Floor Joists (Maximum spans given in feet and inches inside to inside of bearings) Table 1 Southern Pine Floor Joists (Maximum spans given in feet and inches inside to inside of bearings)
Design Criteria Deflection limited to span in inches divided by 360 (live load only) Strength based on 30, 40 or 50 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 360 (live load only) Strength based on 30, 40 or 50 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 360 (live load only) Strength based on 30, 40 or 50 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 360 (live load only) Strength based on 30, 40 or 50 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 360 (live load only) Strength based on 30, 40 or 50 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 360 (live load only) Strength based on 30, 40 or 50 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 360 (live load only) Strength based on 30, 40 or 50 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 360 (live load only) Strength based on 30, 40 or 50 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 360 (live load only) Strength based on 30, 40 or 50 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 360 (live load only) Strength based on 30, 40 or 50 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 360 (live load only) Strength based on 30, 40 or 50 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 360 (live load only) Strength based on 30, 40 or 50 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 360 (live load only) Strength based on 30, 40 or 50 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 360 (live load only) Strength based on 30, 40 or 50 psf live load plus 10 psf dead load.
Grade Live Load Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center)
Grade Live Load 2 x 6 2 x 6 2 x 6 2 x 8 2 x 8 2 x 8 2 x 10 2 x 10 2 x 10 2 x 12 2 x 12 2 x 12
Grade Live Load 12oc 16oc 24oc 12oc 16oc 24oc 12oc 16oc 24oc 12oc 16oc 24oc
No. 1 30 psf 12-0 10-11 9-7 15-10 14-5 12-7 20-3 18-5 16-1 24-8 22-5 19-6
No. 1 40 psf 10-11 9-11 8-8 14-5 13-1 11-5 18-5 16-9 14-7 22-5 20-4 17-5
No. 1 50 psf 10-2 9-3 8-1 13-5 12-2 10-8 17-1 15-6 13-4 20-9 18-10 15-11
No. 2 30 psf 11-10 10-9 9-4 15-7 14-2 12-4 19-10 18-0 14-8 24-2 21-1 17-2
No. 2 40 psf 10-9 9-9 8-6 14-2 12-10 11-0 18-0 16-1 13-2 21-9 18-10 15-4
No. 2 50 psf 9-11 9-1 7-9 13-1 11-11 10-0 16-9 14-8 12-0 19-10 17-2 14-0
No. 3 30 psf 10-5 9-1 7-5 13-3 11-6 9-5 15-8 13-7 11-1 18-8 16-2 13-2
No. 3 40 psf 9-4 8-1 6-7 11-11 10-3 8-5 14-0 12-2 9-11 16-8 14-5 11-10
No. 3 50 psf 8-6 7-5 6-0 10-10 9-5 7-8 12-10 11-1 9-1 15-3 13-2 10-9
Note only the better grades of lumber No. 1 No.
3 are included in the table!
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Floor Joist Example

• Determine the dimension and grade required for a
  floor joist spaced 24 on center, supporting a
  calculated live load of 47 lbs/ft2 and spanning
  14- 0 between bearings.

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Floor Joist Example

• Determine the minimum dimension and grade
  required for a floor joist spaced 24 on center,
  supporting a calculated live load of 47 lbs/ft2
  and spanning 14- 0 between bearings.
• Look at the span table for floor joists, 47 psf
  is greater than 40 psf so look at the rows for 50
  psf.

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Floor Joist Example

• Determine the minimum dimension and grade
  required for a floor joist spaced 24 on center,
  supporting a calculated live load of 47 lbs/ft2
  and spanning 14- 0 between bearings.
• Look at the span table for floor joists, 47 psf
  is greater than 40 psf so look at the rows for 50
  psf.
• Look at the columns for 24 on center. Work your
  way across the table from smallest to largest and
  up the table from lowest to highest grade.

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Floor Joist Example

• Determine the minimum dimension and grade
  required for a floor joist spaced 24 on center,
  supporting a calculated live load of 47 lbs/ft2
  and spanning 14- 0 between bearings.
• Look at the span table for floor joists, 47 psf
  is greater than 40 psf so look at the rows for 50
  psf.
• Look at the columns for 24 on center. Work your
  way across the table from smallest to largest and
  up the table from lowest to highest grade.
• What is the smallest/lowest grade joist that can
  be used?

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Answer

• A No. 2 Southern Pine 2 x 12 is the
  smallest lowest grade (most economical) joist
  that should be used to span 14 with a live load
  of 47 lbs/ft2.

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Southern Pine Rafter Table
Table 11 Rafters No Finished Ceiling Snow Load (CD 1.15)1 (Maximum spans given in feet and inches inside to inside of bearings) Table 11 Rafters No Finished Ceiling Snow Load (CD 1.15)1 (Maximum spans given in feet and inches inside to inside of bearings) Table 11 Rafters No Finished Ceiling Snow Load (CD 1.15)1 (Maximum spans given in feet and inches inside to inside of bearings) Table 11 Rafters No Finished Ceiling Snow Load (CD 1.15)1 (Maximum spans given in feet and inches inside to inside of bearings) Table 11 Rafters No Finished Ceiling Snow Load (CD 1.15)1 (Maximum spans given in feet and inches inside to inside of bearings) Table 11 Rafters No Finished Ceiling Snow Load (CD 1.15)1 (Maximum spans given in feet and inches inside to inside of bearings) Table 11 Rafters No Finished Ceiling Snow Load (CD 1.15)1 (Maximum spans given in feet and inches inside to inside of bearings) Table 11 Rafters No Finished Ceiling Snow Load (CD 1.15)1 (Maximum spans given in feet and inches inside to inside of bearings) Table 11 Rafters No Finished Ceiling Snow Load (CD 1.15)1 (Maximum spans given in feet and inches inside to inside of bearings) Table 11 Rafters No Finished Ceiling Snow Load (CD 1.15)1 (Maximum spans given in feet and inches inside to inside of bearings) Table 11 Rafters No Finished Ceiling Snow Load (CD 1.15)1 (Maximum spans given in feet and inches inside to inside of bearings) Table 11 Rafters No Finished Ceiling Snow Load (CD 1.15)1 (Maximum spans given in feet and inches inside to inside of bearings) Table 11 Rafters No Finished Ceiling Snow Load (CD 1.15)1 (Maximum spans given in feet and inches inside to inside of bearings) Table 11 Rafters No Finished Ceiling Snow Load (CD 1.15)1 (Maximum spans given in feet and inches inside to inside of bearings)
Design Criteria Deflection limited to span in inches divided by 180 (live load only) Strength based on 30 or 40 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 180 (live load only) Strength based on 30 or 40 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 180 (live load only) Strength based on 30 or 40 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 180 (live load only) Strength based on 30 or 40 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 180 (live load only) Strength based on 30 or 40 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 180 (live load only) Strength based on 30 or 40 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 180 (live load only) Strength based on 30 or 40 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 180 (live load only) Strength based on 30 or 40 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 180 (live load only) Strength based on 30 or 40 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 180 (live load only) Strength based on 30 or 40 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 180 (live load only) Strength based on 30 or 40 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 180 (live load only) Strength based on 30 or 40 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 180 (live load only) Strength based on 30 or 40 psf live load plus 10 psf dead load. Design Criteria Deflection limited to span in inches divided by 180 (live load only) Strength based on 30 or 40 psf live load plus 10 psf dead load.
Grade Live Load Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center) Size (inches) and Spacing (inches on center)
Grade Live Load 2 x 4 2 x 4 2 x 4 2 x 6 2 x 6 2 x 6 2 x 8 2 x 8 2 x 8 2 x 10 2 x 10 2 x 10
Grade Live Load 12oc 16oc 24oc 12oc 16oc 24oc 12oc 16oc 24oc 12oc 16oc 24oc
No. 1 30 psf 9-8 8-9 7-8 15-2 13-9 11-9 20-0 18-0 14-9 24-9 21-5 17-6
No. 1 40 psf 8-9 8-0 7-0 13-9 12-6 10-6 18-2 16-2 13-2 22-2 19-2 15-8
No. 2 30 psf 9-6 8-7 7-1 14-5 12-6 10-2 18-8 16-2 13-2 22-3 19-3 15-9
No. 2 40 psf 8-7 7-9 6-4 12-11 11-2 9-1 16-8 14-5 11-10 19-11 17-3 14-1
No. 3 30 psf 7-7 6-7 5-4 11-2 9-8 7-11 14-3 12-4 10-1 16-10 14-7 11-11
No. 3 40 psf 6-9 5-10 4-9 10-0 8-8 7-1 12-9 11-0 9-0 15-1 13-0 10-8
(1) CD duration of load factor see table A-3
for additional information on adjustment factors.
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Rafter Example

• Given a closed 4/12 pitch gable roof heated high
  risk 20 wide x 30 long x 16 wall height
  building in a windy unsheltered area near
  Richmond. The dead load for the roofing material
  is 9lbs 8oz/ft2. Determine the minimum size and
  grade lumber for common rafters spaced 24 on
  center for the building.

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Rafter Example (Live/Environmental Loads)

• Ps R (1.0) x Ce (0.8) x Is (1.0) x Cs (0.95) x
  Ct (1.0) x Pg (15) 11.4 psf
• Mid Roof Elevation Eave height (16) ½ Gable
  Height (3.33) 17-8
• (q) 0.00256 x Kz (1.08) x V2 (80)2 x Iw (1.00)
  17.7 psf
• Pw q (17.7) x G (0.85) x Cp (0.7) 10.53 psf
• Total Live/Environmental Load 21.9 psf

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Rafter Example (Finding the Rise)

• To find the rise for the mid roof elevation the
  rafter span find the run (1/2 x width of
  building) so ½ x 20 a run of 10
• Then plug in the run as the denominator in a
  fraction and cross multiply with the pitch to
  find the unknown rise.

4/12 n/10 (n (rise) 3.33 or 3-4)
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Rafter Example (Rafter Span)
a run of the rafter b rise of the rafter
c
b
a
The length of the hypotenuse is the span a2 b2
c2 c rafter span
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Rafter Example (Span of the Rafter)

• Plug the rise and run into the Pythagorean
  formula for the hypotenuse to find the span.
• (10)2 (3.33)2 111.09
• Solve for the square root of 111.09 10.54 or
  10 - 6 -1/8

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Rafter Example

• Refer to the rafter table for no-finished ceiling
  
• Check the rows for 30 psf live load
• Check the columns for 24 on center spacing
• Work across the table from smallest to largest
  size
• Work up the table from lowest to highest grade

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Rafter Example (Answers)

• No. 3 2 x 10
• No. 2 2 x 8
• No. 1 2 x 6
• How to choose (what is most important to you?)
• Price
• Ease of handling (weight)

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Fastener Facts Figures
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Common Nail Lateral Loads

• Lateral Load (Pn) KD3/2
• Pn safe load in pounds per nail (assuming that
  the point penetrates ½ of its length into
  the second member for hardwoods and 2/3 of its
  length into the second member for softwoods)
• K a constant depending on the type of wood
• D diameter of the nail in inches

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Common Nail Lateral Loads
Number/Weight Calculated (Pn) lbs/nail Table Value (Pn) lbs/nail
6d 52.25 63
8d 65.18 78
10d 78.38 94
12d 78.38 94
16d 89.65 107
20d 115.64 139
30d 129.53 154
40d 146.85 176
60d 185.49 223
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Common Nail Lateral Load Example

• Given a nailed joint between an S4S Southern Pine
  2 x 8 and a 6 x 6 post the joint
  contains 8 evenly spaced 20d common nails.
• Does this joint meet the assumptions for Pn?
• What is the maximum lateral load for the joint?

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Common Nail Lateral Load Example

• Given a nailed joint between an S4S Southern Pine
  2 x 8 and a 6 x 6 post the joint
  contains 8 evenly spaced 20d common nails.
• Does this joint meet the assumptions for Pn?
• A 20d common nail is 4 in length so it will
  penetrate the 1-1/2 2 x 8 and about 2/3 of
  its length will be in the second member the 6 x
  6
• What is the maximum lateral load for the joint?
• The max lateral load will be between 925 lbs and
  1,112 lbs depending on the value you choose.

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Common Nail Withdrawal Loads

• Withdrawal Load (P) 1150 G5/2 D
• P load-pounds per inch of penetration (into
  the second member!)
• G specific gravity of the wood
• D diameter of the nail

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Common Nail Withdrawal Loads
Number Diameter (in) Length (in) P lbs/in of penetration
6d 0.113 2 34.70
8d 0.131 2-1/2 40.22
10d 0.148 3 45.44
12d 0.148 3-1/4 45.44
16d 0.162 3-1/2 49.72
20d 0.192 4 58.95
30d 0.207 4-1/2 63.56
40d 0.225 5 69.09
50d 0.244 5-1/2 74.92
60d 0.263 6 80.75
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The Blizzard of 1996 affected much of the eastern
US.

• January 6 8, 1996
• January 6 Explosion of moisture on satellite
  photos
• January 7 Storm reached the Blue Ridge
  Mountains
• January 8 Storm tapered off in NYC area in
  early morning

Snowfall map of the Blizzard of January 6 8,
1996.
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The Blizzard of 96 snowfall totals for the
Mid-Atlantic States.
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Numerous agricultural structures collapsed due to
the use of reduced or inadequate structural
design loads.

• Barns
• Machinery sheds
• Poultry houses

Snowfall map of the Blizzard of January 6 8,
1996.
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