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.

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).

Mechanical connectors allow the load to be transferred from one main member to another.
• Nails
• Screws
• Bolts
• Metal plate connectors
Wood screws.

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

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.

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

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

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.

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
Diamond
Blunt - diamond
Long diamond
Conical
Duckbill
Examples of common nail points.

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.

Nail finish especially affects holding power and rusting.
• Electrogalvanized – average holding power; tends to rust
• Hot-dipped galvanized – zinccoated to reduce corrosion
• Cement-coated – dipped in resin to increase holding power
Galvanized nails
– 1 ¼ inches in diameter.
• Blued nails – free of residues and improved appearance

Nails are sized in pennyweight (d), which is related to their length.
Penny Size
4d
8d
10d
12d
16d
20d
60d
Length (in)
1 ½
2 ½
3
3 ¼
3 ½
4
6

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

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

Withdrawal load from end grain is approximately zero.

Proper nail spacing increases the strength of nailed joint.
Nail location
From edge, member in compression
From edge, member in tension
Between nails, perpendicular to grain
Between nails, parallel to grain
Spacing (in)
1½
2¼
1
2½

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.

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

1. Find the load per nail and the nail penetration (Table 7).
Load per nail = 94 lb/nail
Nail penetration = 1.5 in

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

3. Determine the total nail load for the whole board.
Total load = 188 lb x 2 = 376 lbs

4. Determine the bending moment of the board.
M = PL
4
M = 376 lb x 120 in = 11280 in-lb
4

5. Determine the bending stress of the board.
F b
= 6M bh 2
F b
= (6)(11280 in-lb) = 1492 psi
(1.5 in)(5.5 in) 2

6. Find quality of lumber from the
Southern Pine Use Guide.
Use No. 1, non-dense, Southern pine.

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.

Bolted joints may be used when loads on wood connections are particularly heavy.
• Greater lateral load capacities than nails
Machine
• No withdrawal load ratings
Carriage
Lag
• Predrill holes from 1/32 to 1/16 larger than bolt diameter
Stove
Examples of bolts used in wood connections.

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.

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.

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.

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.

Heavy- duty staples are often used in place of nails.
• Used to fasten:
– Plywood sheeting
– Subflooring materials
• Manufactured from 14- to 16gauge wire
Pneumatic staple gun.

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.

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.

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.

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.

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.

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.