ᐅ Glued laminated timber beam (GLT) / orientation of the laminations

Hello,

Our roof has 3 glulam purlins, two of which have a square cross-section. Naturally, with this square shape, there is a 50/50 chance of installing them correctly, and in one case it was not done properly. It is installed with the laminated veneers oriented vertically.

Our structural engineer and site manager say (after thorough research) that the load-bearing capacity is somewhat reduced but still sufficient.

My questions are: by what percentage does the load-bearing capacity actually decrease, and are there any other factors we should consider?

I would really appreciate a reliable answer.

alive&kicking

Hello,
Solution or answer found.
I have read that the load-bearing capacity of vertically oriented slats is only slightly lower.
The explanation was that the glue joint itself is more stable/stronger than the wood. So, in this case, our construction manager was actually right.

alive&kicking schrieb:

I read that the load-bearing capacity of vertically oriented slats is only slightly lower. The reason given was that the adhesive bond itself is stronger/more stable than the wood itself.

Between these two statements, I find it hard to decide which one makes me smile more.

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https://www.instagram.com/11antgmxde/
https://www.linkedin.com/company/bauen-jetzt/

@11ant
Then go ahead and share what made you smile.

Of course, I don’t want to post anything nonsensical here.

alive&kicking schrieb:

Of course, I don’t want to post anything nonsense here.

Apart from assuming the site managers are correct, you haven’t posted any nonsense here yet. How many houses do you actually have? – here it sounds like one is currently being built, while in your other threads you always refer to a project that has been completed for several years.

alive&kicking schrieb:

@11ant
then share with me your smirk.

You mention an overall square cross-section, which for glued laminated timber (glulam) logically results in a very clearly vertical or horizontal cross-section of the individual laminated layers/stacks. The tensile and compressive forces act perpendicularly on the narrow edge of the individual boards, while the glue joints have to resist twisting between the boards. When oriented horizontally, this effectively creates a wooden leaf spring. This is a difference like apples and pears, so the claim that there is only a marginal difference is not understandable. Someone sold you a sloth as a bear.

Either the applications/load cases differ, meaning two similarly oriented purlins serve the same function (like the pair of foot purlins) and the third is the ridge purlin, then this can be correct. Or the three are oriented randomly without rhyme or reason, in that case the specialists/field experts should really be held accountable for order’s sake.

With some “thorough research” on the difference between parallel and series circuits, you will find an example of something, loosely speaking, “the same in electricity.”

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https://www.linkedin.com/company/bauen-jetzt/

@11ant

We have been living in our house for nearly four years. Several things have gone wrong, and some construction defects are already part of an independent evidence-gathering procedure. Gradually, it’s becoming clear that these are not the only defects. Our attempts with building experts to identify additional issues have not been successful, as we encountered disappointing levels of expertise.
We will definitely need further expert opinions, that’s clear, but for now we will complete the current procedure to see where we stand.
We are increasingly realizing that our own site manager, to put it mildly, was not always close to the truth, and now the question of possible negligence arises, and if so, how serious it might be.

In the next few days, I will tackle some potentially significant issues and post here (exposed reinforcement, insufficient concrete cover, tanked basement and waterproofing).

Back to the topic of purlins, which are, by the way, intermediate purlins.
You have already helped others in this forum a lot, but if I may ask, where do you get your assessment regarding the square purlins from?
Okay, I am an amateur, far from able to judge this properly. One theory was that glued wood rarely fails at the glue joints but rather in the wood itself. This would mean the glue joint is “stronger” than the wood.
At first, your explanation of the horizontal “leaf spring” makes perfect sense to me. But isn’t it the case that the glued joint, being stronger, effectively creates a “new horizontal” layer, which is of course interrupted by the (stronger) glue joints?

I hope I have expressed this clearly.

Thank you for your effort
a&k