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.

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 ( ).

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 Examples of basic nail types. Common Spike Box Finishing

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

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 – 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.

Nails are sized in pennyweight (d), which is related to their length. Penny SizeLength (in) 4d1 ½ 8d2 ½ 10d3 12d3 ¼ 16d3 ½ 20d4 60d6

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 locationSpacing (in) From edge, member in compression1½ From edge, member in tension2¼ Between nails, perpendicular to grain1 Between nails, parallel to grain2½

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 = 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 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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.