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Wood Fasteners

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Carriage bolts are not designed to be driven and are used where the bolt head ... * Many wood building failures due to inadequate joints Design Assembly Many ... – PowerPoint PPT presentation

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Title: Wood Fasteners


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

2
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.
3
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).
4
Mechanical connectors allow the load to be
transferred from one main member to another.
  • Nails
  • Screws
  • Bolts
  • Metal plate connectors

Wood screws.
5
Common wire nails are used for framing where
there will be considerable lateral load.
Common
Spike
Box
Finishing
6
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

Common
Spike
Box
Finishing
Examples of basic nail types.
7
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
8
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
9
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.
10
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.
11
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.
12
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.
13
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
14
Slant driving or toe-nailing is superior in
strength to straight driving.
15
Clinching nails across the grain increases
withdrawal strength by 170.
16
Withdrawal load from end grain is approximately
zero.
17
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
18
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 4s with two, 10d nails. Also determine the
quality of the lumber to carry the load.
19
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

20
1. Find the load per nail and the nail
penetration (Table 7).
Load per nail 94 lb/nail
Nail penetration 1.5 in
21
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
22
3. Determine the total nail load for the whole
board.
Total load 188 lb x 2 376 lbs
23
4. Determine the bending moment of the board.
M PL
4 M 376 lb x 120 in 11280 in-lb
4
24
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
25
6. Find quality of lumber from the Southern Pine
Use Guide.
Use No. 1, non-dense, Southern pine.
26
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.
27
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

Machine
Carriage
Lag
Stove
Examples of bolts used in wood connections.
28
Machine bolts are precision made and generally
applied where close tolerance is desirable.
  • Applications
  • Metal-to-metal
  • Wood-to-metal
  • Washers between
  • Nut and wood surface
  • Nut and the bolt head

Example of a square-headed machine bolt.
29
Carriage bolts are not designed to be driven and
are used where the bolt head is inaccessible.
  • Applications
  • Wood-to-wood
  • Wood-to-metal
  • Pre-bored holes
  • Washers between
  • Nut and wood surface
  • Nut and the bolt head

Example of a round-headed carriage bolt with a
square neck.
30
Stove bolts are less precisely made than machine
bolts.
  • 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

Example of a stove bolt with nut.
31
Lag bolts or screws are used where main member is
too thick to be penetrated by machine bolts.
  • 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

Example of a lag bolt or screw.
32
Heavy- duty staples are often used in place of
nails.
  • Used to fasten
  • Plywood sheeting
  • Subflooring materials
  • Manufactured from 14- to 16-gauge wire

Pneumatic staple gun.
33
Framing connectors are often used to connect wood
members at critical locations.
  • Joists hangers
  • Truss hangers
  • Truss plates

Truss plates are an example of framing
connectors.
34
Joists and truss hangers are manufactured to
connect joists and trusses to supporting wood
members.
  • 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

Example of a single joist hanger.
35
Truss plates are used to connect chords and webs
to one another.
  • Made from sheet metal
  • Light gauge
  • Galvanized
  • Teeth protrude from one side
  • Connections
  • Chord to chord
  • Chord to web

Truss plates connecting web members to chords.
36
Glued joints between wood members can be
particularly strong and rigid
  • Used for
  • Trusses
  • Beams
  • Posts
  • Glue must be applied under controlled conditions
  • Types
  • Casein
  • Synthetic adhesives

Example of wood glue.
37
Casein glue is made from the milk protein.
  • Made with mold inhibitors
  • Highly moisture resistant
  • Fills well in imperfectly fitting joints
  • Workable to 40 F
  • Best bond for naturally oily woods

Source of casein.
38
Synthetic adhesives include resorcinol and
urea-formaldehyde.
  • Resorcinol
  • Water-proof
  • Used for high moisture levels
  • Expensive
  • Short working time
  • Urea-formaldehyde
  • Moisture resistant
  • Light-colored glue line
  • Long working time

Cans of resorcinol glue.
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