Glue nailing on existing beams or distribute on cc30 instead? Which gives the best result?

[Oldboy]

Visit the SBUF website and search from there for Svikt i träbjälklag, and you will find it.
The summary basically says that the best/easiest/cheapest way to reinforce existing wooden floor structures (rupture & deflection) is reduced spacing between joists and using better wood grades, as well as installing bridging to reduce deflection.

(Unfortunately, there is a lack of data for sensible comparisons, and furthermore, the calculation models do not seem to fully correspond with reality, or are sensitive to boundary conditions, etc. They are likely not designed for this type of calculations.)

 

[Martin_B]

And then you get the answer that the page does not exist or has been moved.... Maybe someone removed it after demand increased significantly following that report??

Extremely strange. It has worked for me all along and as recently as a few seconds ago, I checked just before I started writing this post.

How is it possible?

 

[Martin_B]

Go to the SBUF website and search from there for Deflection in timber floor joists and you'll find it.
The summary basically says that the best/simplest/cheapest way to reinforce existing timber floor joists (break & deflection) is to use smaller center-to-center distances and better wood grades, as well as cross-bracing to reduce deflection.

(Unfortunately, there's a lack of data for sensible comparisons, and moreover, the calculation models don't seem to fully match reality, or they are sensitive to boundary conditions, etc. Probably they aren't designed for this type of calculations.)

One of the few reports I have come across. Doesn't seem to be an abundance of such tests, do you think?

Kerto can be used instead of C24, C30, or C35. Kerto corresponds approximately to structural wood C50, but is probably a notch stronger in some respects.

Now that I looked more carefully, I see that I can probably fit about 180mm in height, so it's a bit disappointing not to be able to use the full height with C30 (which I think is the most economical considering deflection properties).
Because if I take 45x170 it won't be fully used, but if I take 45x195 it won't be C30 anymore if I split it. It might then fall to maybe C18 or worse, perhaps even C12 if you're unlucky.
But you can "cheat" the system a bit and split the edge you intend to have facing up, so it holds up reasonably well.

Ah well, doesn't matter, I'll use 45x170 C30 and cross everything. Even though cross-bracing is just a short-term solution. Once it settles in and the thing dries, it ends up just as loose and does almost more harm than good. Well, I'll zigzag with steel bands too, so maybe that will help a bit.

 

[pbengtsson]

If I understand correctly, it's bounce you want to get rid of without adding height. In that case, Kertu is unbeatable, laminated wood is just as good.
Buy Kertu beams that are slightly higher than the existing ones and place them between the compartments. If it's a middle floor and the ceiling is nailed to existing beams, you can align this by supporting from underneath and screw-gluing the Kertu to the existing beam, although there's a risk of squeaking.
If there's only a foundation underneath, perhaps a load-bearing beam can help a lot.

 

[Martin_B]

If I understand correctly, it's the flexibility you want to get rid of without adding height. In that case, Kertu is unbeatable, laminated wood is just as good.
Buy Kertu joists slightly taller than the existing ones and place them between the sections. If it's an intermediate floor and has a ceiling nailed to existing joists, you can also align this by supporting from below and screw-gluing Kertu with the existing joist, though there may be a risk of creaking.
If it's just a foundation underneath, maybe a supporting beam can help a lot.

Kerto is indeed really good for those properties, even better than regular laminated beams of the same dimension, but they are priced accordingly.
I don't have exact prices for Kerto beams, but they cost about 4 times as much as the equivalent C30.

And the difference isn't that big between C30 and Kerto, even though Kerto is sharper.

But I can promise that there will still be some flexibility in a 170mm tall Kerto over a span of about 3.6 meters.

If you want to get rid of all flexibility, then it's typically HEA or preferably HEB that are needed. But they also cost a bit, so

 

[pbengtsson]

When it comes to perceived deflection, there is a big difference between kertu and C30. Your problem is the building height, and in that case, there aren't many alternatives other than kertu, in my opinion. Steel beams also have deflection, so you have to decide: cheap (c24) with deflection or expensive and rigid
I can say that most people don't notice the difference in deflection between kertu or steel beams. Steel is also not pleasant to work with in a wooden construction.

 

[Martin_B]

I can always buy a sheet of plyfa (as thick as possible), cut it, and glue it with some additional layers.

Kerto is basically plyfa, but with higher specifications of course. A couple of layers of 15mm construction plywood should do quite a bit. Or why not 3 layers, then I have my 45.

 

[Martin_B]

Can say that most people can't tell the difference in deflection between kertu or steel beam. Steel is also not pleasant to work with in a wooden construction.

I forgot to respond to this.
Of course, it depends on the dimensions. The deflection in kerton is likely to be significantly higher than the corresponding HEA or especially HEB, provided the equivalent is measured in beam height.

So in, for example, 100mm kerto, there is likely more deflection than in 100 mm HEA, or again especially HEB. If we take 180mm, it's the same thing.

It's only when we talk about weight-performance ratio that kerto wins. Kerto wins in relation to its weight, then. A kerto is thus much more resistant to deflection if you compare it with a steel beam of the same height and the same weight.

My guess is that even IPE beams are more deflection-resistant than kerto, provided you use the same beam height. But again, in this comparison, the steel beam also weighs more than the kerto beam, so the comparison becomes unfair when considering the weight.

 

[Martin_B]

Squeezed in 75x180 kerto between the beams as a complement to the old beams, which were glued and nailed 45x170 C30.

The construction seems extremely stable. However, it remains to be seen how the entire floor behaves when I get the floorboards (28x120 tongue and groove) in place.

So now it's just over cc30 and also kerto in between. I guess it now corresponds to at least 45x220 cc60 based on the flex in the construction.

I wonder what 75x180 kerto corresponds to in K24 lumber? Just instinctively, considering how the flex feels, I guess well over (45x) 220mm in height.

However, this kerto is a special one that was custom ordered for a project a couple of years ago, where high strength was required, so the comparison might not be entirely fair. It was originally 195 in height if I remember correctly, so I split it down to 180.

 

[sblixten]

Fitted 75x180 kerto between the beams as a complement to the old beams, glued and nailed 45x170 C30.

The construction seems extremely stable. However, it remains to be seen how the entire floor behaves once I've installed the floorboards (28x120 tongue and groove).

So now it's slightly more than cc30 and also kerto in between. I guess it now corresponds to at least 45x220 cc60 based on the deflection of the construction.

I wonder what 75x180 kerto corresponds to in K24 timber? Spontaneously thinking about how the deflection feels, I guess well over (45x) 220mm in height.

However, this kerto is a special one that was custom-ordered for a project a couple of years ago, where high strength was required, so the comparison may not be entirely fair. It was originally 195 in height if I remember correctly, so I cut it down to 180.

Sounds like a very good construction, but wasn't it expensive?

 

[huggan]

Sounds like a very good construction, but wasn't it expensive?

"However, this kerto is a special one that was custom-ordered for a project a couple of years ago."

Either he already had it because it was his project, or he got them cheaply, I assume.

 

[Martin_B]

Sounds like a very good construction, but wasn't it expensive?

"However, this kerto is a special one that was specially ordered for a project a couple of years ago"

Either he already had it because it was his project, or he got them cheaply, I guess.

45x170 C30 weren't cheap, so I had to pay full price for them. The kerto has been lying around for a couple of years, or probably more (time flies), and was leftover material, so it only cost a bit of gas for transport. If you'd ordered new kerto, it would probably have cost 500-600 SEK per beam, they're expensive those babies, but you get what you pay for. They're extremely stiff relative to their weight. They're also very rigid and don't warp like K-virke. If it's split straight once, it stays straight.

If you only had your own glue press, you could manufacture your own, just slice up the K-virke on edge and glue it together. Reinforcing with plyfa isn't as highly recommended as kerto since plyfa is cross-ply, while kerto is straight-ply for maximum stiffness against flex in floor constructions. And then it's almost better to buy the most cost-effective and widest kerto and slice it into several narrow beams to reinforce with. Just a tip