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Wood Fastener Capacity Calculator

Jonathan Ochshorn

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Directions: Enter values for type of fastener (bolt, lag screw, or nail); fastener dimensions; number of shear planes (single or double, with double only available for bolted connections); adjustments (duration of load, CD, and wet service factor, CM); material and section properties for main and side member(s); and fastener spacing, edge and end distances (not required for nails).

Press "update" button.

The unadjusted and adjusted capacity for a single fastener and for the entire connection are calculated, based on "yield limit" theory (per NDS 2005). Only the capacity based on the fasteners themselves is computed: neither the wood elements themselves, nor any steel side plates specified, are checked for strength or serviceability. Spacing, edge, and end distances for fasteners are checked for bolts and lag screws in wood members, with the capacity adjusted accordingly. Such spacing and edge/end distances are not checked for steel side plates.

More detailed explanations and examples can be found in the text.

type of fastener  
 
 
shear planes: Cd Cm  
 
   
 
  main member   side member  
material material  
modulus of elasticity, E (psi) modulus of elasticity, E (psi)  
spec gravity, G - wood only  
direction of load to grain direction of load to grain  
dimension parallel to fastener axis dimension par. to fastener axis  
dimension perp. to fastener axis dimension perp. to fastener axis  
 
no. rows  
 
 
  main member   side member  
edge dist, load parallel to grain (inches)
edge dist, load perp to grain, loaded edge (inches)
edge dist, load perp to grain, unloaded edge (inches)
end dist, load par. to grain, compression (inches)
end dist, load par. to grain, tension (inches)
end dist, load perpendicular to grain (inches)
 
1. Find the unadjusted capacity for a single fastener, Z (lb).  
2. For lag screws and nails, find penetration adjustment  
3a. Find duration of load adjustment, Cd  
3b. Find wet service adjustment, Cm  
3c. Find geometry factor adjustment, CΔ  
3d. Single fastener adjusted capacity (lb)  
4a. For multiple fasteners, find group action factor, Cg  
4b. Number of fasteners.  
4c. Total fastener adjusted capacity  
 
 
 
 
 
 
 
     
1. Group action factor, Cg:
 
2. Lateral design value, Z, based on yield limit equations:
 
3. Geometry factor adjustments, CΔ  
         
Minimum and full-value limits min distance min distance for full adjust.    
edge dist, load parallel to grain (inches)      
edge dist, load perp to grain, loaded edge (inches)      
edge dist, load perp to grain, unloaded edge (inches)      
end dist, load par. to grain, compression (inches)    
end dist, load par. to grain, tension, softwood (inches)    
end dist, load perpendicular to grain (inches)    
   
   
spacing, between rows, load par to gr (inches)      
spacing, between rows, load perp to gr (inches)      
         
Individual geometry factor candidates main member side member    
edge dist, load parallel to grain (inches)    
edge dist, load perp to grain, loaded edge (inches)    
edge dist, load perp to grain, unloaded edge (inches)    
end dist, load par. to grain, compression (inches)    
end dist, load par. to grain, tension (inches)    
end dist, load perpendicular to grain (inches)    
1    
1    
         
Overall geometry factor CΔ      
         
4. Reduction coefficient for penetration  
 
 
edge dist, load parallel to grain (main member) too small
edge dist, load perp to grain, loaded edge (main member) too small
edge dist, load perp to grain, unloaded edge (main member) too small
end dist, load par. to grain, compression (main member) too small
end dist, load par. to grain, tension (main member) too small
end dist, load perpendicular to grain (main member) too small
edge dist, load parallel to grain (side member) too small
edge dist, load perp to grain, loaded edge (side member) too small
edge dist, load perp to grain, unloaded edge (side member) too small
end dist, load par. to grain, compression (side member) too small
end dist, load par. to grain, tension (side member) too small
end dist, load perpendicular to grain (side member) too small
penetration inadequate