Slotted Hole Connection to Timber

[Robert_L]

Hi,

I’m dealing with the following scenario and am wondering if anyone here has encountered something similar and can offer a bit of guidance.

I’m designing a cross-laminated timber balustrade that’s braced with steel angles.
The angles are bolted to WT brackets which have lag screws to the CLT.
Where the lag screws connect to the balustrade, the brace supplier has shown vertical slotted holes in the WT bracket.
I've attached the cutsheet detail for reference.

Strictly in terms of structural performance, it would be ok if the connection could slide a small amount; however, I want to limit deflection in the balustrade to protect finishes and prevent any uneasiness if someone pushes on it.

I’m wary of trying to restrict sliding by relying on a tight connection and friction between the lag and the bracket. Can I achieve enough resistance screwing into the CLT, or is there another approach I can consider? I've looked for references dealing with slotted hole connections to timber and am coming up short; does anyone know of a reference that could apply to this scenario?

Thanks.

 

[JAE]

I'm not sure I understand the need for slotted holes with lag screws.
Just set the assembly where you want it and pre-drill and screw in the lags.
No need for slots.

Might be that the fabricator "thinks" they need slots in case the "bolts" that they "think" are going to connect the assembly are fixed in place.

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[molibden]

As JAE said.
Why lag screws? We always use self-tapping screws for wood. But I work in Europe.

 

[Robert_L]

The slots are there so the contractor can temporarily secure the balustrade after it's lifted into place by a crane.
Some adjustment likely will be required later to get everything plumb.

 

[molibden]

Then do 1 or 2 slotted holes and 2 holes with tight fit to screw after adjustment is made.

 

[DETstru]

If they want slotted holes they need to be in addition to the ones you specified. I would not rely on friction.

 

[KootK]

You might fab the brace as two lapped angles connected with slip critical bolts in slotted holes. Or pretensioned bolts if you're able to weld the finished product. Both of those paths embody cost of course. I suppose you could also field drill final set screws into the angles.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.