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Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

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Page 1: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

Wood Fasteners

BSE 2294

Animal Structures and Environment

Dr. Susan Wood Gay

Page 2: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

A primary objective in building wood structures is to design joints that are as strong as the members to be joined.

• Many wood building failures due to inadequate joints

– Design– Assembly

• Many farm buildings still stand without a single nail in them

– Mortise and tenon– Wooden pegs

Example of mortise and tenon joinery.

Page 3: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

Mechanical connectors for wood structures are a relatively new technology.

• Early 1800s – cut iron nails

• 1875 – steel wire nails

• 1930 – metal timber connectors

Cut nails from Shawnee Village – an early settlement in Ohio (1805-1808).

Page 4: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

Mechanical connectors allow the load to be transferred from one main member to another.

• Nails

• Screws

• Bolts

• Metal plate connectors

Wood screws.

Page 5: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

Common wire nails are used for framing where there will be considerable lateral load.

Common

Spike

Box

Finishing

Page 6: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

Nail holding capacity depends on numerous factors.

• Direction of nail loading

• Orientation of nail to grain

• Depth of nail penetration

• Diameter of nail

• Species of wood

• Nail Coating

• Nail type Examples of basic nail types.

Common

Spike

Box

Finishing

Page 7: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

Spikes parallel the length of a number of the sizes of common nails.

• Larger in diameter than common nails

• Greater holding power than common nails

• Must be used carefully to avoid splitting

Spike nail – 0.092” - 0.283” in diameter. (10d - 60d) or 3” – 6” in length

Page 8: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

Box nails are used for installing sheathing or roof decks.

• Smaller in diameter than common nails

• Lesser holding power than common nails

• Reduced danger of splitting

Box nail – 0.067” – 0.162” in diameter.(2d – 40d) or 1” – 5” in length

Page 9: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

Casing and finishing nails are used where a neat appearance is desired.

• Smaller in diameter than common nails

• Smaller head than common nails

• Can be countersunk and covered

Finishing nail – 0.058” – 0.135” in diameter.(2d -20d) or 1” – 4” in length.

Page 10: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

The shape of the point affects the tendency of the wood to split when a nail is used close to an end of edge.

• Diamond point is most widely used

• A sharper point increases:

– Holding power– Ease of driving nail– Tendency to split wood

Examples of common nail points.

Diamond

Blunt - diamond

Long diamond

Conical

Duckbill

Page 11: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

The type of nail shank affects the resistance of the nail to withdraw from the wood.

• Nail shanks types:

– Smooth– Spiral (helical) – Ringed (annular)

• Spiral and ringed nails have greater withdrawal resistances

Examples of smooth (top), spiral (middle), and ringed nails.

Page 12: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

Nail finish especially affects holding power and rusting.

• Electrogalvanized – average holding power; tends to rust

• Hot-dipped galvanized – zinc-coated to reduce corrosion

• Cement-coated – dipped in resin to increase holding power

• Blued nails – free of residues and improved appearance

Galvanized nails – 1 ¼ inches in diameter.

Page 13: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

Nails are sized in pennyweight (d), which is related to their length.

Penny Size Length (in)

4d 1 ½

8d 2 ½

10d 3

12d 3 ¼

16d 3 ½

20d 4

60d 6

Page 14: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

Slant driving or toe-nailing is superior in strength to straight driving.

Page 15: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

Clinching nails across the grain increases withdrawal strength by 170%.

Page 16: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

Withdrawal load from end grain is approximately zero.

Page 17: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

Proper nail spacing increases the strength of nailed joint.

Nail location Spacing (in)

From edge, member in compression 1½

From edge, member in tension 2¼

Between nails, perpendicular to grain 1

Between nails, parallel to grain 2½

Page 18: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

Nail Load Example

Determine the load that can be supported at the midspan of a

10-ft long, southern pine (species group 2) 2 x 6 if it is nailed at

both ends to 2 x 4’s with two, 10d nails. Also determine the

quality of the lumber to carry the load.

Page 19: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

Nail Lateral Loads

• Lateral Load (Pn) = KD3/2

– Pn = safe load in pounds per nail (assuming that the point penetrates ½ of it’s length

into the second member for hardwoods and 2/3 of it’s length into the second member for softwoods)

– K = a constant depending on the type of wood

– D = diameter of the nail in inches

Page 20: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

1. Find the load per nail and the nail penetration (Table 7).

Load per nail = 94 lb/nail

Nail penetration = 1.5 in

Page 21: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

2. Determine the load at the left end.

Load at left end = Load per nail x Number of nails

Load at left end = 94 lb/nail x 2 nails = 188 lb

Page 22: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

3. Determine the total nail load for the whole board.

Total load = 188 lb x 2 = 376 lbs

Page 23: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

4. Determine the bending moment of the board.

M = PL 4

M = 376 lb x 120 in = 11280 in-lb 4

Page 24: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

5. Determine the bending stress of the board.

Fb = 6M bh2

Fb = (6)(11280 in-lb) = 1492 psi (1.5 in)(5.5 in)2

Page 25: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

6. Find quality of lumber from the Southern Pine Use Guide.

Use No. 1, non-dense, Southern pine.

Page 26: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

Screws are unique in their particular resistance to withdrawal loads, compared to nails of equal diameter.

• Used where vibrations are common

– Floor sheathing to joists– Gypsum board to support

members

• Used to bring members into alignment

• Used for millwork and finishing rather than for structural framing

Example of double lead (top), single lead (middle), and tapping wood screws.

Page 27: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

Bolted joints may be used when loads on wood connections are particularly heavy.

• Greater lateral load capacities than nails

• No withdrawal load ratings

• Predrill holes from 1/32 to 1/16 larger than bolt diameter

Examples of bolts used in wood connections.

Machine

Carriage

Lag

Stove

Page 28: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

• Applications:

– Metal-to-metal– Wood-to-metal

• Washers between:

– Nut and wood surface– Nut and the bolt head

Machine bolts are precision made and generally applied where close tolerance is desirable.

Example of a square-headed machine bolt.

Page 29: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

• Applications:

– Wood-to-wood– Wood-to-metal

• Pre-bored holes

• Washers between:

– Nut and wood surface– Nut and the bolt head

Carriage bolts are not designed to be driven and are used where the bolt head is inaccessible.

Example of a round-headed carriage bolt with a square neck.

Page 30: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

• Applications:

– Wood-to-wood– Wood-to-metal

• Threaded along the length of the shank

• Washers between:

– Nut and wood surface– Nut and the bolt head

Stove bolts are less precisely made than machine bolts.

Example of a stove bolt with nut.

Page 31: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

• Applications:

– Wood-to-wood– Wood-to-metal

• Sharp points and coarse threads designed to penetrate and grip wood fiber

• Washers between:

– Head and wood surface

Lag bolts or screws are used where main member is too thick to be penetrated by machine bolts.

Example of a lag bolt or screw.

Page 32: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

• Used to fasten:

– Plywood sheeting– Subflooring materials

• Manufactured from 14- to 16-gauge wire

Heavy- duty staples are often used in place of nails.

Pneumatic staple gun.

Page 33: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

• Joists hangers

• Truss hangers

• Truss plates

Framing connectors are often used to connect wood members at critical locations.

Truss plates are an example of framing connectors.

Page 34: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

• Made from sheet metal:

– Light gauge– Galvanized

• Affixed to wood members with special nails

• Best method to:

– Affix joists to headers– Affix trusses to girders

Joists and truss hangers are manufactured to connect joists and trusses to supporting wood members.

Example of a single joist hanger.

Page 35: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

• Made from sheet metal

– Light gauge – Galvanized

• “Teeth” protrude from one side

• Connections

– Chord to chord– Chord to web

Truss plates are used to connect chords and webs to one another.

Truss plates connecting web members to chords.

Page 36: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

• Used for:

– Trusses– Beams– Posts

• Glue must be applied under controlled conditions

• Types

– Casein– Synthetic adhesives

Glued joints between wood members can be particularly strong and rigid

Example of wood glue.

Page 37: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

• Made with mold inhibitors

• Highly moisture resistant

• Fills well in imperfectly fitting joints

• Workable to 40 °F

• Best bond for naturally oily woods

Casein glue is made from the milk protein.

Source of casein.

Page 38: Wood Fasteners BSE 2294 Animal Structures and Environment Dr. Susan Wood Gay

• Resorcinol

– Water-proof– Used for high moisture

levels– Expensive– Short working time

• Urea-formaldehyde

– Moisture resistant– Light-colored glue line– Long working time

Synthetic adhesives include resorcinol and urea-formaldehyde.

Cans of resorcinol glue.