Timber fastener edge distance at end grain

[Enhineyero]

Trying to find guidance for screws fixed to end grain of a member. Do standard bolt/screw spacing apply for fasteners installed at the cross-section of timber/beam joist? loads perpendicular to grain require an edge distance of 5 x bolt diameter, which cannot be achieved if the fastener is installed at the cross-section of a member.

Say a 90mm deep x 45mm wide joist with 6mm dia screws at the end grain, this will require an edge distance of 30mm, if the screw is placed central to the cross-section, the edge distance of the screw will only be 22.5mm. This is quite a common detail/practice but cannot find any guidance relating to it. Is it just assumed that edge distances do not apply for those installed at the end grain? and limit the fastener layout to a single row?

 

[SWComposites]

Can you show a picture? Do you means screws in the side of the member at the ends, loaded in shear? Or screws installed into the end of the member?

 

[Enhineyero]

Here is a sketch:

 

[jayrod12]

How much load are you trying to put through the connection? Because screws/nails into end grain don't have much capacity.

That being said, it is my opinion that end grain fasteners are more like parallel to grain failures than perpendicular to grain. Because they can slide between the adjacent fibres instead of shearing through the wood fibres. I believe the CSA O86 has capacities for end grain fasteners.

Edited for a brain fart. I agree with the perp to grain values.

 

[jerseyshore]

NDS has reduction factors for end grain fastening as well, but I don't think I've ever specified a connection like this, even if the average framer has no problem with it. This is why we have joist hangers now.

 

[Eng16080]

If you were using the NDS code (U.S.), there are (surprisingly) no requirements for wood screw spacings and end/edge distances, although the code commentary does provide recommended distances.

This connection would be allowed per NDS. However, there is a reduction factor of 0.67 required for fasteners inserted into the end grain. This type of connection should probably only be used for light loads.

I'm guessing you're in Canada, though, and there are different requirements there. Another thing to keep in mind is that you might also be limited by center to center fastener spacing, assuming that your code has requirements for that. Considering a member depth of only 90mm, I wonder if you can actually fit 3 screws.

 

[Enhineyero]

If you were using the NDS code (U.S.), there are (surprisingly) no requirements for wood screw spacings and end/edge distances, although the code commentary does provide recommended distances.

I am actually surprised by this. Thought they would "require" one considering how ACI/AISC has lots of minimum requirements to improve serviceability (i.e. reduction of cracks).

End grain capacity reduction factor in Australia is 0.6. Loads I'm looking at arent huge (<5kN) and wasn't too concerned about it, but was curious if there is any rule of thumb on screws/nail edge distance if installed at end grain.

 

[Harbringer]

If you were using the NDS code (U.S.), there are (surprisingly) no requirements for wood screw spacings and end/edge distances, although the code commentary does provide recommended distances.

Not sure what you mean, of course the NDS has screw spacing and edge distance requirements for screws, it's in section 12.5. All the edge distance and spacing requirement for this end grain connection are the same as in the face of a stud for example just adjusted for the grain orientation. As Eng16080 noted there is an edge grain reduction factor of 0.67 on top of the edge distance requirements.

The bigger picture is the OP's detail is likely unnecessary and there is a better connection to be made or an alternative load path that makes more sense. I think the edge distance is 4D not 5D to the loaded edge. This looks like a nailed fascia where you would only have vertical load on the fasteners. How do you have shear in the weak axis of this board? Try posting more detail. If you really need to transfer shear in the weak axis you could use a Simpson HGA10KT.

 

[dvd]

Two points, neither of them addressing the question -

1. I think that whether the holes are pre-drilled for end grain fastening has consequences to edge spacing.
2. These half-moon fasteners are used in many types of furniture kits. A 6mm fastener is not much of a structural fastener. Maybe some variation on this theme could provide good results.

 

[Eng16080]

Not sure what you mean, of course the NDS has screw spacing and edge distance requirements for screws, it's in section 12.5.

Those requirements are only for fasteners with a diameter of 1/4" or greater (see Section 12.5.1.1). Therefore, they don't apply to most wood screws and nails.

NDS Commentary Section C12.1.5.7 for wood screws states: "For diameters less that 1/4", specific requirements are not provided." There are recommended spacing and edge distances provided in Tables C12.1.5.7 and C12.1.6.6.

The lack of spacing and edge distance requirements is a little surprising, considering the overwhelming requirements for everything else concerning wood connections.

 

[Enhineyero]

The bigger picture is the OP's detail is likely unnecessary and there is a better connection to be made or an alternative load path that makes more sense. I think the edge distance is 4D not 5D to the loaded edge. This looks like a nailed fascia where you would only have vertical load on the fasteners. How do you have shear in the weak axis of this board? Try posting more detail. If you really need to transfer shear in the weak axis you could use a Simpson HGA10KT.

Loads are of course in the strong axis.

Below are relevant pages of Australian standards for bolts and screw. Wouldnt the 5xD apply as the side edge distance for end grain connections?

 

[Eng16080]

Wouldnt the 5xD apply as the side edge distance for end grain connections?

In my opinion, yes. I would apply that distance to all 4 sides for the end grain condition.