I was going to order the ridge beam in glulam for my greenhouse construction today. Then the glulam constructor remarked on my column for the ridge beam. He said I would need a column equivalent to 90x180, and what I have is 45x90.
I simply can't have such a thick column. It would look terrible. I learned from the constructor that it's specifically the 50-year winds (at 27m/s average) that cause lateral sway and then it breaks.
Now we're talking about the column on the far gable in the picture (which is 3m) and that there was not nearly as much problem there by the door since it stiffens and unloads, and the longest length there is about 1.5m.
I googled some wooden greenhouses (among others, the one at Leva Kungslador) and they seem to be dimensioned roughly like mine. What do you think? All suggestions are welcome!
Realize there are some things the designer didn't account for:
– 3m of the greenhouse is connected to the main house (braces).
– This is also at the end where the longest ridge post is (3000x90x45).
– In the other gable, there is a door, and there the ridge post is only 1400x90x45).
– A dormer will be built to prevent a snow pocket against the main house – there will also be a point that anchors the ridge beam.
I should add that the glulam I order is 90x405 but I actually wanted 66x305 to more closely resemble other wooden greenhouses.
Realize there are some things the constructor didn't take into account:
3m of the greenhouse is attached to the main house (supports).
This is also at the end where the longest ridge pole is (3000x90x45).
In the other gable, there is a door and the ridge pole is only 1400x90x45).
A dormer will be built to prevent a snow pocket against the main house where there will also be a point that anchors the ridge beam.
Should add the Glulam I order is 90x405 but actually wanted 66x305 to more closely resemble other wooden greenhouses.
We might be a bit different but don't you think it smells a bit off to lay a 90x405 glulam on a two-by-four? You say it will look really ugly with larger pillars, don't you see anything beautiful or harmonious in the balance between the parts?
don't you think there's something beautiful or harmonious in the balance between the parts?
Agree, I was so set on the glulam being 66x315 and then 45x90 feels completely reasonable. Then it grew. I agree that it purely looks nice with a thicker 90mm beam –*but in terms of the entire greenhouse's aesthetics, the 90-width is an "outlier". All the greenhouses I google don't have such pillars anywhere.
Pole structures such as a greenhouse are particularly sensitive. It is primarily the risk of buckling that you need to watch out for. Square cross-sections are always better in this case. Depending on where in "Västra Götaland" you live, the snow load can vary between 1.5 to 3 kN/sqm. If you calculate with a snow load of 2.5, the inner longer pole is certainly too weak. I suggest a glued laminated pole of 90x90. Alternatively, you can make one yourself by gluing together two 45x95 with a durable outdoor adhesive.
Could it be like this in the greenhouse above. That the glulam beam has a plank underneath it which ensures lateral rigidity? And thereby reduces the risk of buckling on the column? :
If you account for a snow load of 2.5, the inner longer post is certainly too weak.
The tools I find seem to only work on 90x90 glulam (Moelvens and byggbeskrivningar.se) and up. If I want to see what a 45x90 can handle –*how do I check that?
I searched for what 90x45 could withstand in kN straight down, but unclear what "Buckling length (m)" etc. means in these contexts. What I have is also slow-grown pine (very heavy) but maybe that's worse in buckling contexts?
The effective length is simply the part of a post that is free to move laterally without obstruction from noggins or other elements. For posts with rectangular cross-sections, one must differentiate between the x- and y-axis. An illustration in Träguiden clarifies which is which.
Snow load is always calculated in the horizontal plane. With a 30-degree roof incline, the snow load starts to decrease so that it is halved at 45 degrees and zero at 60 degrees. The total snow load on the roof is 32x2 = 64 kN. Half of this load is supported by the ridge beam and half by the sidewalls. The load on the ridge beam is then distributed to two end pillars, resulting in 16 kN per pillar.
Enter it into http://swelagerbalk.inadire.se/Lagerbalk.aspx and calculate there, but end up between 13-20kN post depending on the slope of the roof, unfortunately, I think like the others that 45x90 will be too weak but no extensive knowledge there...
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