design for bearing?

[radiocontrolhead]

Hi all,

How do you handle the design of a thru rod with washer at the end of a wood beam? Assuming the beam is sized properly for all other loads is the design check at this connection primarily bearing? Providing a large enough washer to distribute the tension load?

Please see attached for diagram

 

[KootK]

1) Bearing is definitely important.

2) Make sure that the plate / washer is stiff enough to distribute the load relatively uniformly. Pretty easy in wood.

3) On the wood side, the situation is quite similar to the member checks at a bird's mouth connection and I'd give that some attention if you haven't already.

 

[jayrod12]

Yes, however did you take into account for the lost material for the thru rod in the design of the rafter?

 

[CivilSigma]

Bearing stress is a function of the washer area.
If the rod is "compressing" on the beam then you would have to check whether bearing there.

Other than that, I would also check in bending performance at the hole.

 

[radiocontrolhead]

Koot and Jayrod,

appreciate the responses

I have not yet checked the wood side of things and will do that just after I can get a good size on the washer needed.

However, on the wood side, is it just another bearing check of the wood itself for the effects of the "birds mouth" notch and the material lost for the thru rod?

Effectively two bearing checks?

 

[dhengr]

Radiocontrolhead:
Note that you are dealing with bearing (or compression) which is somewhere btwn. bearing perpendicular and bearing parallel to the grain. You are cutting a substantial amount of material out of the rafters, and you are adding an additional shear and moment component to the rafter design. And, the tension in the rod gets greater as you move the rod higher w.r.t. the rafter bearing elev. on the wall.

 

[KootK]

However, on the wood side, is it just another bearing check of the wood itself for the effects of the "birds mouth" notch and the material lost for the thru rod?

Sadly, I really don't know. I've not seen any bird's mouth checking other than my own and what I do disagrees with the presentation that I see often in the literature. The the diagram below from the Journal of Light Construction.