Replacing roof rafters with glulam?

[Joukko]

In my garage, there are 2 studs with dimensions 175x50x5900mm holding up the roof. Since the roof has started to sag, I was thinking of replacing this with a glulam beam. It might be a bit difficult to say what size I should get, but that's what I'm wondering. I plan to buy this at Byggmax. I don't think there's terribly high pressure; the studs are almost 26 years old.

Jocke

 

[Joukko]

No one with an idea?

 

[pbengtsson]

What kind of ceiling is it?

 

[prototypen]

In itself, glulam is slightly stronger than solid wood, with a beam twice as high (2x175) the load-bearing capacity is 4 times. Now the beam becomes "slender" and then it wants to twist and lay itself on the plate but if it worked with a 50 mm, it will continue to work.

Protte

 

[magnu]

Hi,
I agree that glulam has higher fracture strength because fractures occur at imperfections and glulam has significantly fewer imperfections.

But here we have a problem with deflection. Is the deflection less for a glulam beam than for regular wood?
You know there are a lot of Greek letters, including sigma, in the study of strength of materials. But are these parameters significantly different for glulam compared to regular wood?

 

[prototypen]

Not essential but a little due to the absence of continuous knots.
If it's deflection, then the load-bearing capacity is the square of the height difference.

If you contact the glued laminated timber manufacturer, you'll surely get an answer, e.g., Martinssons.

Protte

 

[magnu]

In my garage, there are 2 rafters measuring 175x50x5900mm supporting the roof. Since the roof has started to sag, I thought about replacing them with a glued laminated beam. It might be a bit difficult to determine the size I should use, and that's what I'm wondering. I thought about buying it at Byggmax. I don't think there is a terribly high pressure, the rafters are almost 26 years old.

Jocke

An idea,
Since it's a garage, maybe it's not so important how nice it looks.

If you were to get two steel pipes 25mm square that are roughly the same length as the rafters.

Then attach the pipe in the middle of the roof rafter with a screw.

Now you can lift the pipe and rafter with a garage jack until the rafter has bent back. But lift carefully, you risk lifting off the roof rafter from its mount.

In any case, now you can screw the steel pipe with through-bolts. Screw with large screws about 3dm cc, I would have used 6x80 or bigger.

Remember that the steel pipe should be attached to the underside of the roof rafter.

 

[Joukko]

What do you think about gluing and screwing together 2 of these laminated beams: http://www.byggmax.com/se-sv/prod/pid-08842181.aspx

 

[prototypen]

Buy the RIGHT dimension from the start. If you insist, you can place 2 side by side, making it a little more than double compared to today, no gluing needed.

If you get a 42x250, it has the same load-bearing capacity as 2 of 42x180

Protte

 

[Joukko]

What size should I use then? Preferably, I don't want it to extend too much downward from the ceiling.

What can an iron beam cost?

 

[magnu]

What I suggested was reinforcing the existing beams with a 25mm x 25mm square steel tube.

Don't spend a lot of money on it, try with one of the roof beams first and see what happens.

You'll need to check with a steel company that has such items in stock to find out the cost. But the tube is probably not free.
I wonder if there's a way to determine what dimension is needed? It might be possible to make a wooden beam with approximately the same bending performance as the steel tube.

Additionally, I've been thinking a bit more about this.

The question is whether it's the bottom that has stretched out, or the top that has been compressed?
When you bend wood, you compress it, it can't withstand tension.
But it should have stretched at the bottom.

Unfortunately, I'm only coming up with more questions.