Glulam Beam Splice Moment Connection

[jerseyshore]

We are working on a splice detail to repair a 50 ft long glulam roof beam. The first 6 ft or so is completed damaged so the intention is to cut that part out and splice in a new matching member with a steel side plate on each side. The existing glulam is 6.5" wide x 32.5" deep.

We've run some calcs and came up with about (12) 3/4" (2 rows of 6) bolts with 4" dia. shear plates required at both the top and bottom of the beam to resist the tension/ compression forces.

If we don't use the shear plates, we would need roughly (14) or (16) bolts in each zone. Might even have to bump up to 1" dia bolts.

We normally try to avoid wood moment connections at all cost, but are stuck with it here. Client obviously wants to minimize the splice cost as best as possible.

My question is, do we stick with the shear plates, even with the added cost, to reduce slip in this connection? Or do they not add any additional advantage here and just go ahead with adding the extra bolts?

 

[XR250]

How much moment and shear at the joint?

 

[jerseyshore]

V=11.65 kips
M=81.6 k-ft

 

[JoshPlumSE]

This is a really good question you've posed. Honestly, there isn't much conceptually wrong with your approach. I just haven't really seen it done. And, like you, I've been taught not to even try moment connections for wood.

The closest I've ever come is sistering a new beam along the length of an old beam. Have you considered something like that. Like removing the damaged 6 ft and replacing it with a new 6.5x32.5" glu-lam. Then sistering a pair of 3x members along that are 10 or feet long or so.... Giving you a 5 ft sistering in both directions. You could still use nailing which means less slip in the members.

 

[EngDM]

Is there an option to add a plate to the underside of the beam too? With the shearplates on the side only I could see the bottom of the glulam still opening up a bit, just as it deflects.

 

[jerseyshore]

This is a really good question you've posed. Honestly, there isn't much conceptually wrong with your approach. I just haven't really seen it done. And, like you, I've been taught not to even try moment connections for wood.

The closest I've ever come is sistering a new beam along the length of an old beam. Have you considered something like that. Like removing the damaged 6 ft and replacing it with a new 6.5x32.5" glu-lam. Then sistering a pair of 3x members along that are 10 or feet long or so.... Giving you a 5 ft sistering in both directions. You could still use nailing which means less slip in the members.

The side plates are sized to be about 52" each side (104" in length) to satisfy the bolt spacing requirements.

We sister and reinforce big wood trusses all the time, but the forces are typically just tension so we do a similar splice to what you are describing.

 

[SWComposites]

4" dia. shear plates

can't envision what these are. do you have a sketch?

 

[jerseyshore]

Is there an option to add a plate to the underside of the beam too? With the shearplates on the side only I could see the bottom of the glulam still opening up a bit, just as it deflects.

I did consider something like that as well, but we have 12 bolts bottom, 12 bolts middle (for shear), and 12 bolts top of this beam. 36 bolts on each side doesn't really leave any room to fasten from below without hitting those bottom bolts.

 

[jerseyshore]

can't envision what these are. do you have a sketch?

 

[EngDM]

View attachment 8353

Neat. Do these get recessed into the glulam to provide more strength of each bolt in parallel bearing from the T/C couple?

 

[driftLimiter]

Thats a split ring connector right? I don't really see how that reduces the slip. The shear trasnfer mechanism of them is essentially the same as bolts, bearing on wood. The slip is that the bolts aren't a perfectly tight fit on the inside of the split ring.

 

[SWComposites]

video here shows the shear plates: https://www.shearplates.com/installation-video/

have seen similar inserts for wood joints, just not that term.

 

[dik]

Can you use plates and glulam rivets?

 

[ANE91]

You've got this covered, but I can't resist throwing out some crazy ideas:

1. Maybe you could embed specialty hardware to accommodate the splice (e.g., see below; not my project/photo). Owners tend to be more willing to pay when the solution is sexy.

2. In that same vein, you could knife the glulam with epoxy.
3. What about sticking with a good ol' shear connection but tacking on externally mounted post-tensioning and a reaction frame below the splice? Probably not cost effective...

Whatever you do, try to incorporate some vertically slotted holes into the top rows of bolts to accommodate shrinkage. Good luck!

 

[Eng16080]

I'm guessing you're already aware, but if not, the Timber Construction Manual has a Chapter concerning moment splices for glulams.

Another thing which might help: there are circumstances where using high strength bolts (like A325/A490) can result in a stronger double shear connection. You would need to be sure the correct bolts are actually used in the field, but it could be worth it in terms of limiting bolt quantity (and plate length).

 

[ANE91]

Also…the below is a fun read and validates your inclination toward shear plates.

 

[jerseyshore]

Neat. Do these get recessed into the glulam to provide more strength of each bolt in parallel bearing from the T/C couple?

Yes. The video SW shared is a good example of how they are installed.

Thats a split ring connector right? I don't really see how that reduces the slip. The shear trasnfer mechanism of them is essentially the same as bolts, bearing on wood. The slip is that the bolts aren't a perfectly tight fit on the inside of the split ring.

Those are shear plates. Split rings are just hollow rings.
And that is exactly our question. Does the shear plate give us meaningful help for this moment connection. Or are we better off spending money on a longer plate w/ more bolts.

Can you use plates and glulam rivets?

Never seen those designed or come across them before. Doubtful the contractor has either. What's the advantages/ disadvantages.

You've got this covered, but I can't resist throwing out some crazy ideas:

1. Maybe you could embed specialty hardware to accommodate the splice (e.g., see below; not my project/photo). Owners tend to be more willing to pay when the solution is sexy.
2. In that same vein, you could knife the glulam with epoxy.
3. What about sticking with a good ol' shear connection but tacking on externally mounted post-tensioning and a reaction frame below the splice? Probably not cost effective...

Whatever you do, try to incorporate some vertically slotted holes into the top rows of bolts to accommodate shrinkage. Good luck!

We did briefly talk about doing an internal knife plate connection because these glulams are exposed, but I don't think it's feasible here. And it's a gym space so we can't add anything below it.

How much shrinkage should we anticipate from a glulam? We almost never use them or spec them out so slotted connections weren't something we were adding. I was under the mindset that all the bolts are as tight as possible to reduce slip.

 

[jerseyshore]

I'm guessing you're already aware, but if not, the Timber Construction Manual has a Chapter concerning moment splices for glulams.

Another thing which might help: there are circumstances where using high strength bolts (like A325/A490) can result in a stronger double shear connection. You would need to be sure the correct bolts are actually used in the field, but it could be worth it in terms of limiting bolt quantity (and plate length).

We were just using the NDS and checking our work in WoodWorks, but we will look into that chapter for sure. Thanks!

Also…the below is a fun read and validates your inclination toward shear plates.

That is a great reference, thank you. And I'll be sure to use the word 'slop' every time I can now when talking about bolts.

 

[jerseyshore]

@ANE91
That tech bulletin doesn't like this detail because of shrinkage concerns. And of course this is exactly what we had started to sketch up.
They do like the 2nd detail, which I'm assuming shows plates top and bottom instead of on the sides. That feels impossible to actually build on an existing roof beam however.
So now we're stuck again. We pretty much have to do the side plates. But how can we limit shrinkage? Specify the new glulam to be extra dry?

 

[jerseyshore]

To answer myself, here is what Timber Construction Manual recommends and provides examples for: