Undersized support beam for pergola?

[Jonobe]

I am planning to build a pergola with the design below, but I now realize that I've probably undersized the beams.

The pergola is intended to be of this design. The plan is around 3.6 m wide and 3 m deep. The posts will be 3 pieces, each 45x120mm. The beam is intended to be a 45x145mm.

However, the plan was for 6 pieces (2 on top or on the other side of the posts) rafters each at 45x145mm.

I realize now that the beam is probably too weak for that. What do you think? Any tips on how I can solve this with the existing timber I have at home? I have plenty of 45x120, 8 pieces of 45x145.

Reinforce the beam with a screw-laminated 45x120? Use 45x120 as rafters instead or split the rafters to about 45x95?

What will work?

 

[Gabbe1]

Do you really think that 45x145 will be too weak?
It's only the weight of the wood itself that needs to be supported, no load or snow, right?

 

[Jonobe]

Do you really think it will be too weak with 45x145?
It's supposed to only support the weight of the timber itself, no load or snow?

No idea. Tried using the Swedish timber dimensioning table but don't understand it at all and gave up on it. Do you think it will work? They weigh quite a bit.

 

[Gabbe1]

No idea. Tried using Swedish timber's dimension table but I don't get it and failed. Do you think it's possible? They weigh quite a lot.

Yes, I think it will be fine.

 

[Dublin]

I also find it hard to see that it wouldn't work. Now, I don't see how the attachments of the top rail are meant to be done, but you can avoid notching in the load-bearing beams to avoid weakening them.

 

[Jonobe]

I also find it hard to see why it wouldn't work. I can't see how the connections of the crossbeams are meant to be done, but you can avoid notching the support beams to prevent weakening them.

I was thinking of notching the crossbeams, not the support beam. Then probably using angle brackets on them. Unless someone has tips on how to do it hidden but stable?

Thanks for your responses

 

[Karrock]

I clicked on the dimensioning tool (not the table), it seems satisfied with exactly 45*120 as the lintel and 45*145 as the carrier beams. This in C14. C28, which is nicer to work with, holds up even better.

 

[Jonobe]

I clicked in the sizing tool (not table) it seems satisfied with exactly 45 * 120 as the top rail and 45 * 145 as the support beams. This in C14. C28, which is nicer to work with, holds even better.

I couldn't figure out whether it really calculated or not due to the error message for the posts.

But it sounds like a single support beam of 45x145 should work even with top rails of 45x145.

Thank you for your help now I don't have to worry about future guests getting a beam on their head.

 

[Swebfn]

My pergola is still standing a year later.
There is a little over 360 between the posts and the outer beam is 45x145. The "roof rafters" are 45x120 and then I have quite a bit of extra weight in the form of beveled 28x120 boards.