Wood Connections – Load Orientation and Capacity

Wood Connections and Load Orientation

This is a brief summary of the different directions that a force may be applied to a wood fastener and the appropriate capacity equations to use based on the NDS (produced by American Wood Council) .

If the load is applied at an angle between 0 and 90 the Hankinson formula may be used.

Note that if nails are used the 0 degree case and the 90 degree case are the same. The edge distances and spacing requirements are different. But if they are met then the cases are the same.

Hankinson Formula

Hankinson Formula

Also if the load is a combination of lateral and withdrawal the NDS equation

Combined Lateral and Withdrawal

Combined Lateral and Withdrawal

Withdrawal and Lateral Combination

 

Summary of loading conditions and capacities:

See Fastener Loading Diagram

Fastener Loading Diagram

Fastener Loading Diagram

Top/Bottom Loading
Fax => Capacity determined using lateral loading equations and theta=90 deg using NDS (perpendicular to grain loading condition)
Fay => Capacity determined using withdrawal equations in NDS.
Faz => Capacity determined using lateral loading equations and theta=0 deg using NDS (parallel to grain loading condition)

Side Loading
Fbz => Capacity determined with lateral loading equations and theta = 0 deg (parallel to grain loading condition)
Fby => Capacity determined with lateral loading equations and theta = 90 deg (perpendicular to grain loading condition)
Fbx => Capacity determined with withdrawal procedures in NDS.

End Loading
Fcx => Capacity determined with lateral loading equations and theta = 90 deg (perpendicular to grain loading condition) NDS end grain reduction of 0.67
Fcy => Capacity determined with lateral loading and theta = 90 deg (perpendicular to grain loading condition)NDS end grain reduction of 0.67
Fcz => Varies – Lag screws reduce 25%, withdrawal. Wood screws, nails not allowed (too variable),

 

Discussion:

http://www.eng-tips.com/viewthread.cfm?qid=330916

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