Glulam Beam - Checking Problem

[LouNY]

A timber screw with a fully threaded shank as you show can only provide a clamping force to the area directly under the head - and that force is limited becase it cannot exceed the the compressive stress of the fibers it bears on. The force is farther reduced by the angle of head.
Think about it: a fully threaded shank CANNOT pull two pieces of wood together, and the head angle only hurts that effort.
That type of screw is a poor choice for the purpose.
I am afraid that you need to find some competent engineering help.
rScotty

I would be concerned that their is no cinching power in that type of screw. Is the top of the beam accessible?
Adding epoxy and pairs of though bolts with backing plates to spread the clamping force would seem to be preferable to me.
But I'm certainly not a glulam engineer and I tend to believe that stout and stouter is better.

 

[rScotty]

I would be concerned that their is no cinching power in that type of screw. Is the top of the beam accessible?
Adding epoxy and pairs of though bolts with backing plates to spread the clamping force would seem to be preferable to me.
But I'm certainly not a glulam engineer and I tend to believe that stout and stouter is better.

That's what I would do as well. It concerns me that they would recommend a fastening that cannot provide any clinching or clamping forces. Why put the screws in there anyway? What are they supposed to be doing? The threads actually resist the clamping forces....

I am not a glulam engneer either, but that "fix" is odd enough to make me wonder if their engineering department has an degreed engineer - or if so, if their engineer has looked at this type of repair.

But just because the splits result in a beam is not as stong as it should be does not mean it is going to fail. Not at all. There is a lot of extra strength in the way houses are designed these days - AND in the materials. It is just that I join with several others on this forum in being a belt and suspenders kind of guy.

If it were mine, I would look ask another engineer - a local structural engineer - to estimate the importance of that beam. It very well might be small enough or overbuilt enough that I would just accept it and continue. Probably is. Or I might decide it is critical and use through bolts, backing plates, and yes... it wouldn't hurt to fill the cracks with some thickened epoxy as well. But having done one or the other, I wouldn't find something else to worry about.

BTW, it is good practice to use an end grain sealer on wet wood or dry climates or the reverse. There are special ones, but even a coat of paint helps. It allows wood to adjust to different humidity more slowly.

rScotty

 

[ponytug]

General gluing strategy is to get the glue in, then keep the wood under compression while it sets.

You can get epoxy tube/applicator tools that do a combined mix and injection that makes getting perfectly mixed glue into crevices easy.

I use those Simpson strong ties a lot, and like them, but look at the threads. They will only compress from the head to the top of the threads, which isn't much. My concern on the toe nailing is the lack of compression, given the depth of your beam. I would glue, then compress the beam, then toenail. But I'm neither a structural engineer nor a glue expert.

My primary use is of the Simpson strong ties is fastening a single 2by to something else, e.g. a 2x6 fence board on post. They can support the use of a washer, but the screws have a relatively small diameter, which is great for not splitting wood, but it means that they aren't lag bolts, and can shear if over torqued.

Glad to see the progress.

All the best,

Peter

 

[Pettrix]

That's what I would do as well. It concerns me that they would recommend a fastening that cannot provide any clinching or clamping forces. Why put the screws in there anyway? What are they supposed to be doing? The threads actually resist the clamping forces....

I am not a glulam engneer either, but that "fix" is odd enough to make me wonder if their engineering department has an degreed engineer - or if so, if their engineer has looked at this type of repair.

But just because the splits result in a beam is not as stong as it should be does not mean it is going to fail. Not at all. There is a lot of extra strength in the way houses are designed these days - AND in the materials. It is just that I join with several others on this forum in being a belt and suspenders kind of guy.

If it were mine, I would look ask another engineer - a local structural engineer - to estimate the importance of that beam. It very well might be small enough or overbuilt enough that I would just accept it and continue. Probably is. Or I might decide it is critical and use through bolts, backing plates, and yes... it wouldn't hurt to fill the cracks with some thickened epoxy as well. But having done one or the other, I wouldn't find something else to worry about.

BTW, it is good practice to use an end grain sealer on wet wood or dry climates or the reverse. There are special ones, but even a coat of paint helps. It allows wood to adjust to different humidity more slowly.

rScotty

When we cut the beams to size, I immediately put a wood glue at the ends to prevent drying out. I used Titebond III on the ends to seal the exposed wood. It is a waterproof glue. Beams were installed in about 1 week after delivery and never got wet and the SIPS roof was installed the same day the beams were installed.

Even the 4x6 wood top plates split in some spots. They were also supposedly Kiln Dried but ended up checking and I had to replace one as it warped so badly it lifted 2"+. This is how wood reacts to this dry climate. Hence why I built with concrete walls but had to use wood on the roof areas.

 

[Pettrix]

Here are the engineering calcs:
21 Simpson screws spaced at 12" OC

 

[ponytug]

We also have a dry climate and wood just splits, no matter what one does. I do keep my stocks of wood that I am planning to use strapped at all times. It doesn't stop the checking, but it does slow the warping. With items like fences, I come back a year or later, and add fasteners where needed. Some boards warp too badly to keep because they were sawn poorly and warp as they hit final dryness. It is what it is.

It seems like you have a detailed engineering calculation there. That would be reassuring to me.

All the best,

Peter

 

[ning]

It strikes me that the portion of the wood under the check/split is still in tension unless it completely separates at the ends from the other parts of the beam. I assume given their computations that the manufacturer is assuming that that portion is no longer useful in case of complete separation. Personally I'd go with injecting a glue in the split and compressing from below just so that there's no visually obvious sign of the checking, but it looks like the calcs say it's fine otherwise. I don't think the screws are necessarily a good idea as others have mentioned in that they will compromise some of the wood fibers for dubious gain.

We have a 28' beam in our house; originally our house was built basically as a 2-story only with the top floor finished and a cavernous crawl space; when we bought the place, we realized that it would be a great daylight basement (actually there are small windows on the uphill side as well so we don't need lighting except at night).

In the big room where the beam is, it replaced a bunch of columns in the previous crawlspace; originally they said something like a 24" glue-lam (idk this was 1996) and I was like "um that's going to intrude quite a bit into our living space - like 16" or so - how about a steel I-beam? and they're like "???!!!" so instead we've got a 5" intrusion in that ceiling that's wrapped in sheetrock (required for fire actually).

 

[Pettrix]

Engineer also mentioned that the glue in the glulam does NOT transfer shear, per their calculations. The wood fibers transfer shear while glue adheres wood together but for calculation purposes, they do not use the glue to transfer shear. The beam never de-laminated but experienced checking in the wood fibers.

 

[Pettrix]

It strikes me that the portion of the wood under the check/split is still in tension unless it completely separates at the ends from the other parts of the beam. I assume given their computations that the manufacturer is assuming that that portion is no longer useful in case of complete separation. Personally I'd go with injecting a glue in the split and compressing from below just so that there's no visually obvious sign of the checking, but it looks like the calcs say it's fine otherwise. I don't think the screws are necessarily a good idea as others have mentioned in that they will compromise some of the wood fibers for dubious gain.

The engineer said that most glues are "expansive" and when injected, can actually cause further splits/checking to form elsewhere as the glue expands and pushes on other glulam members. He said the screws will provide the proper specs to bring the beam back into its original strength.

 

[ponytug]

Some glues are certainly expansive in that the wood swells a little, as it absorbs glue, but that's one of the reasons to compress after glueing to maintain dimensional specifications, as well as to improve the glue to wood fiber bond. I have glued wood both ways, both work. I think one of the challenges for modeling a glue repair of checking is the very nature of the irregular surface, and how that irregular section would alter the transmitted forces. Screws are much easier to model and predict.

To me the great thing about the check is that it is along the fibers, in a beam that you want fiber strength. So at a first approximation you have lost very little of what you / your engineer want/need for functional strength.

Again, it sounds like your engineer is looking after you well.

All the best,

Peter