NDS "Fastener Head Perimeter" for fastener head pull-through in wood 1

[DTS419]

NDS Equation C12.2.5-2 for fastener head pull-through uses "Fastener Head Perimeter", P-sub-H. What is "fastener head perimeter" and how is this obtained for common hex head bolt sizes? And, how does using a washer come into play when used with fasteners with other than round heads such as hex bolts?

 

[Eng16080]

What is "fastener head perimeter"

Since that equation is "for round-head fasteners and washers," this value is simply the perimeter of a circle (pi times diameter).

and how is this obtained for common hex head bolt sizes?

The equation doesn't cover a hexagonal shape, but to me it seems reasonable to assume an inscribed circle for the analysis. That would seem conservative unless perhaps the edges are sharp, which could have a detrimental effect.

And, how does using a washer come into play when used with fasteners with other than round heads such as hex bolts?

In this case, I would base the calculation on the washer since that is what's in contact with the wood.

For what it's worth, I don't normally check Pull-Through for Fasteners (like bolts) that don't have round heads. At least that's based on my interpretation of the language in Table 11.3.1. Normally I would check perpendicular to grain bearing instead for a bolted connection. I've assumed (without any further investigation) that this limit state is only really applicable to nails/screws, basically smaller fasteners.