Ripping Down a Glu-Lam Post

[dcarr82775]

One a project the framer has run out of 5.5"x6" glu-lam posts, and wants to substitute (2)3.125"x7" glu-lam posts instead. The posts are western species Grade 3. The (2) pieces can be bolted together per NDS. My concern is with ripping them down to fit.

I believe glu-lam posts have consistent grade of wood throughout their full thickness so ripping it down wouldn't substantially change the strength of the wood itself. Is this right?

 

[KootK]

1) Column laminations are generally balanced but I'm not so sure that they're necessarily uniform throughout.

2) With posts as small as these, I would expect the laminations to be uniform throughout.

3) Technically, if you modify the dimensions of the individual laminations, you also mess with the grading of those laminations.

4) This is one of those situations where I'd just up my FOS a little and run with it in the interest of trying to be reasonable.



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.

 

[BUGGAR]

How did the framer run out of posts?

 

[dcarr82775]

He screwed up a few along the way and doesn't want to spend the $ and time to get a new one if he doesn't have to.

 

[Brad805]

What is the grade of the glulams? If they are a 16c, the grading problems Koot mentioned are not too onerous. If 20fE, you will have some B laminations on the exterior and C or D's at the middle. If your utilization factor is low I would not be overly concerned if he ripped an equal amount from each side.

 

[dcarr82775]

Western Species #3. NDS says laminations are class L2D material which is good stuff, and I would think consistent throughout. I can't see how it could not be the same throughout, but stranger things have happened

 

[Brad805]

The Canadian rules allow them to change the middle laminations. The company that supplies our projects MSR all of their material, so they do alternate where they can to optimize their material usage. I am not familiar with the NDS rules. It seems you have it covered.

 

[Triangled]

is the grade you state for the originally specified post or the proposed "beams" as the proposed size sounds more like a beam size and therefore a different spec than a post size.
"Ripping" in both directions? or which direction?

 

[dhengr]

Brad805:
I’m not trying to pick a fight, but.... I can see them allowing the change in plys for bending members, but not as likely for compression members, which would have all the plys loaded/stressed the same. Are you sure what you read doesn’t pertain primarily to bending members? I’m not sure, and don’t have the rules in front of me. The OP’er. might ask the manuf’er. of those posts, if he really wants the correct answer, right from the horses mouth. I would glue the two pieces together, then screw them together from both sides.

 

[KootK]

See column applications here: Link.

but not as likely for compression members, which would have all the plys loaded/stressed the same. Are you sure what you read doesn’t pertain primarily to bending members? I’m not sure, and don’t have the rules in front of me.

Any column that would fail via flexural buckling is, to some degree, a flexural member when it comes to planning the laminations. This is because buckling depends of flexural stiffness which is optimized when the quality lams are on the outside.


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.

 

[dhengr]

Except in one orientation the best plys won’t be on the outside. There will be lesser quality plys at a max. stress surface. My thinking on the matter doesn’t preclude the post acting as a bending member, which it might. But, the fact remains, that in many instances all the plys will be loaded/stressed about the same. So where to put the weaker plys; not the same problem as a true bending member which is laid up to act as a solid beam. The OP’er. might ask the manuf’er. of those posts, if he really wants the correct answer, right from the horses mouth.

 

[Brad805]

dcarr, I do not read that as picking a fight.

The 16c is a compression member, and they do not change the plies in those cases from my recollection. We have used higher grades (20fEX, 24fEX) to keep our column size down in cases where we have eccentric loads and in those cases they use a higher grade on both sides. For this small of columns they might not change any of them, so you might be correct. It was a lot of years ago when we were reinforcing a lot of of glulam beams due to missed drift loads. I recall the diagram from the CSA manual, but I will admit my memory is not perfect on the subject and that was several computer systems ago, so I did not see it when I looked. I checked the Boise website, and they have a layup diagram, but it is not clear for the columns.

 

[BUGGAR]

Are there any fire ratings required? If you "re-grade" the material, do you re-mark it too so we don't have another one of those "what is this?" questions on this forum a year from now?
Are you spending all the money your contractor is saving? We can "bill" you if you want to back charge him.

 

[dcarr82775]

I didn't say anyone was picking a fight, and I don't think any comments above come close to doing so.

I finally found an APA document that says the laminations on post/column members are uniform throughout as there is no cost benefit to mixing lamination grades as there is with beams.

Cheers all.

 

[Brad805]

My error, it was dhengr that made the comment. Glad it is sorted out.

Brad805:
I’m not trying to pick a fight, but....

 

[dhengr]

Dcarr & Brad:
Brad seemed pretty confident/certain in his comments about laminated columns and varying lams, and the Canada codes. And, I was more or less asking him to reread what he thought he read to make sure that what he said applied to column sections. Obviously, someone might buy a beam section and use it as a column; but usually a real column section would not allow this (varying plys) given the way it is loaded and stressed. Now, it seems that both of you have found some info. which helps clear this up and generally confirms what I was trying to say. I think you do have to watch out that you are not mixing column and beam sections because of this potential problem. I suspect it would not be a failure mechanism in either case, under normal conditions. You do run the risk of changing the stress grade of dimensional lumber pieces when you start cuttin on them, so you have to pay attention to that too. They are generally graded for their intended use and approx. as-sawn sizes. We all understand the reasons and logic in the varying lamination layup for beam sections. But then, I’ve seen beam sections installed up-side-down or bass-acwards when they are laid up as unbalanced sections. So, you have to detail them or mark them for erection so they can’t be (are less likely to be) mis-installed.

No fighting, please.

 

[Brad805]

I have very thick skin dhengr. I know what my contractor buddies say about me behind my back.

We do use a lot of 20fEX or 24fEX columns for our large overhead doors. An 18'-0" OH door with a 60'-0" truss over it is not uncommon for us, and nobody ever wants to fur out their walls to save a marginal amount on a few sticks of glulam. Most glulams are still built using huge clamp assemblies, and the material cost is not always the biggest part of the equation. It was a good discussion.