Ripping Down a Glu-Lam Post
Ripping Down a Glu-Lam Post
(OP)
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?
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?






RE: Ripping Down a Glu-Lam Post
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.
RE: Ripping Down a Glu-Lam Post
RE: Ripping Down a Glu-Lam Post
RE: Ripping Down a Glu-Lam Post
RE: Ripping Down a Glu-Lam Post
RE: Ripping Down a Glu-Lam Post
RE: Ripping Down a Glu-Lam Post
"Ripping" in both directions? or which direction?
RE: Ripping Down a Glu-Lam Post
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.
RE: Ripping Down a Glu-Lam Post
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.
RE: Ripping Down a Glu-Lam Post
RE: Ripping Down a Glu-Lam Post
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.
RE: Ripping Down a Glu-Lam Post
Are you spending all the money your contractor is saving? We can "bill" you if you want to back charge him.
RE: Ripping Down a Glu-Lam Post
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.
RE: Ripping Down a Glu-Lam Post
Brad805:
I’m not trying to pick a fight, but....
RE: Ripping Down a Glu-Lam Post
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.
RE: Ripping Down a Glu-Lam Post
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.