Which glulam calculation to trust? Different results on different pages.

[Magnus_Nordmark]

I am going to build a garage with a shed roof, span 4m, and 5-degree slope, cc 1200, snow zone 2. The rafters will be made of glulam, and I'm confused about the sizing. A thickness of 45mm would be convenient considering insulation, although 56 works too.

Through byggbeskrivningar.se, I get the following results:

We see that the deflection for e.g., 56x225 is 18 mm, and does not meet the requirement of L/200.

Then I looked at Moelven's calculation page and found that their 56x225 only deflects 12mm, definitely meets the maximum deflection of L/300.



Definitely, different manufacturers can have different stiffness in the material, but a 50% difference in deflection is significant. Or does byggbeskrivningar.se add an additional safety margin?

It seems like it will be glulam from Holmen, if that would help with the calculations.

Anyone with good input?

 

[klaskarlsson]

I am going to build a garage with a shed roof, span of 4m and a slope of 5 degrees, cc 1200, snow zone 2. The roof beams will be made of glulam and I am confused about the sizing. A thickness of 45mm would be convenient for insulation purposes, although 56 works too.

Through byggbeskrivningar.se I get the following result:
[image]
Here we see that deflection for something like 56x225 is 18 mm and does not meet the requirement of L/200.

Then I looked at Moelven's calculation page and find that their 56x225 only deflects 12mm and meets the maximum deflection of L/300.

[image]

Certainly, different manufacturers may have different rigidity in their material, but a 50% difference in deflection is a lot. Or is byggbeskrivningar.se adding an additional safety margin?

It is leaning towards glulam from Holmen, if that would help in calculating.

Anyone with good input?

Which snow zone are you considering?

Assuming that everything else is equal, they seem to be based on different loads: Even though I'm not quite sure if you can directly compare column load and support reaction (I don't know the difference, if there is any)?

 

[plåtrickard]

The top one has the rating gl28cs
What does moelven have?

 

[Magnus_Nordmark]

The top one is rated GL28cs
What does Moelven have?

GL28cs (because I assume 56 is a split beam from 115).

 

[Magnus_Nordmark]

Which snow zone are you considering?

Assuming everything else is equal, they seem to be based on different loads: Even though I'm not quite sure if you can directly compare column load and support reaction (not sure of the difference, if there is any)?

Snow zone 2 as I wrote above.

Column load is what the beam actually presses downward on its support. Dim column load is the actual load plus some safety factors, i.e., the load you should design the column for.