Wood Screw- Shear Capacity

[Baffled Engineer]

Does the shear capacity of a wood to wood connection using wood screws get affected by which way the head of the screw is drilled from?

I'm reinforcing the ends of an existing wood joists with a new LVL ply, and I was wondering if it mattered which way the screw is drilled from. It would be easier for the contractor to drill from the new LVL side instead of the other, but the load I suppose needs to transfer from the existing joist to the new LVL.

My Canadian wood design handbook seems to be particular which is the side member and which is the main member, but I was thinking the magnitude of the shear load is the same on both ends of the screw whether it's the point-side or the head-side, so I'm thinking it would not matter which side the screw is driven from. Any thoughts on this?

Thank you.

 

[phamENG]

It does matter - which is why your Canadian wood design handbook is particular. Not sure how it's broken down in Canadian codes, but the NDS shear values for dowel type fasteners are based on yield limit equations. There are 6 of them and each applies to a different failure mode in various arrangements. Bending in the fastener, bearing failure of the fastener on the base material, etc.

 

[jayrod12]

Generally speaking it is thinner member to thicker. When doing what you are describing, i.e. sistering a joist, I can't imagine the thickness being drastically different and therefore I wouldn't expect that it matters significantly. I generally will specify some fasteners from each side however.