How thick should the glulam beams be?

[Aniska]

We are renovating a long and narrow old house where there is 5.20 meters between the walls of the long sides. We have raised a floor and are going to furnish the old attic. The first step is to create a floor structure that spans the distance, and we're considering glulam beams. What thickness should they be in that case? Is the strength significantly affected if you screw into them?

Grateful for suggestions!

 

[hurk]

Moelven Töreboda has a good design program for glulam and kerto on their website. A quick calculation says 56 x270.. up to cc 900!

 

[Aniska]

What great links I found by googling moelven...!

Can you lay the glulam beam down (so it's only 56 high) with the same value?
We're trying to minimize the height of the floor structure - though it might end up being around 270 anyway, but a little knowledge never hurts.

 

[JanneSjo]

I can't calculate laminated beams - but there is generally a big difference in strength depending on whether you have the long side of the cross-section horizontally instead of vertically.

That is, you need to have 270mm upwards and 56mm as the width otherwise it will not hold.

A simple way to test the principle is to take a regular plank 22 mm thick and 120 mm wide, say 4 m long. 1) Support it at the ends as you would normally lay a plank - it will then sag in the middle under its own weight. 2) Try placing it on its edge - then you can probably walk on it without it flexing like in 1).

 

[jawen]

An alternative to reduce the construction height could be to use iron beams like I-beam or HEA/HEB, then maybe HEB 14 i.e. 14 cm thick beams would be sufficient, but check this with someone who can calculate the loads.

Used beams are often for sale; they are often found around industrial areas in piles, so knock on doors and ask what they want for them.

Best regards, Jawen