Glued laminated beam for pergola

[Hobby Bob]

Planning to build a pergola measuring 3x7 meters on 6 posts (115x115) but have now realized that it would be nicer to avoid the middle post on one long side.

I've looked at glulam beams of 8 or 9 meters (56x225x9000 or 56x270x8000).

There will be cross beams of 45x145 but otherwise, the load I'm planning is to hang a hanging swing or two, i.e., a weight of about 200 kg.

I've looked at building descriptions, but there's no pergola as an option there. Does anyone have knowledge if such a glulam would work?

 

[justusandersson]

Should the glulam beam's span be 7 meters?

 

[Hobby Bob]

Should the glulam beam's span be 7 meters?

Yes, exactly... That's the plan.

 

[Pappa1986]

If you decide on this, also run the transverse beams in the same as the glulam. It will look significantly nicer (at least I think so)

 

[justusandersson]

I would choose 56x270. Then the deflection from the dead weight would be only about 3 mm. The instantaneous deflection of two swings used simultaneously will be about 10 mm beyond that. Without swings, 56x225 is fine.

 

[Hobby Bob]

I would choose 56x270. Then the deflection from the self-weight will be only about 3 mm. The instantaneous deflection of two swings used simultaneously will be about 10 mm more. Without swings, 56x225 is fine.

Thanks for the answer, do you have any magic formula to calculate this or have you found the information somewhere? I would preferably use 56x225.

 

[justusandersson]

No, I just calculated that for you right now. You have to use a couple of different formulas in this case. Education in the field helps. 56x225 also holds. The swings won't be used all the time, will they?

 

[Hobby Bob]

No, I just calculated that for you now. You need to use a couple of different formulas in this case. Education in the field helps. 56x225 also holds. The swings won't be used all the time, right?

There you go, thank you kindly.

I'm thinking of two hanging chairs or alternatively a hammock, so no, it won't be used all the time, just occasionally for a short while.

Is it possible to say how much weight a 56x225 can temporarily support?

Since it's a pergola, the weights will only be temporary, like if someone sits in a swing for a while or decides to hang from the beam.

 

[gusvo085]

You don't break a beam like that with a few swings, it's the deflection that matters, so hang on 5 swings if you like

 

[justusandersson]

You are not near any cases of breakage. For pergolas, it is a matter of purely aesthetic judgments.

 

[Hobby Bob]

It will be a 56x225.

Thank you very much for answering my questions

 

[Hobby Bob]

Saw that the supplier (RAW) also has glulam 42x180 and 42x225. Would you say they are still sufficiently sized for the purpose?

 

[justusandersson]

With 42x180, two swings will bend down over 40 mm, with 42x225 over 20 mm. Deflection due to dead weight is 8 and 5 mm respectively.