Timber portal frame

[Guy77]

Hi all,

I'm trying to design a portal frame out of timber instead of steel. Was originally thinking 203x133UB but can't use all steel due to foundation restrictions. Happy to use glitch beam or similar. Opening is 2400x2000 within a wall 4000x2400.

TIA

Guy

 

[ChorasDen]

What is your question?

By glitch beam, do you mean flitch?

Where is your project located? That may affect your design process for trying to justify a wood structural panel portal frame.

 

[Guy77]

Hi ChorasDen,

Thanks for your reply.

Question is is it possible?

Yes, I mean flitch (should check autocorrect before sending)

We're in Moray, Scotland.

Thanks

 

[dik]

It can be done... in the 'old days' it was done with timberframe construction... Portals can be constructed using steel connections to provide moment, as long as the portal isn't too large. There was an earlier thread on this site for that topic. I'll see if I can dig it up. Someone from Trada, in the UK may be able to help.

thread507-498439

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Guy77]

Thanks very much,

I'll also upload drawings tomorrow to make things clearer.

 

[dik]

I don't do much in wood products, but for the last few decades, timberframe has been my favourite. When I was in Ontario, I took photos of maybe 50 timberframed barns... showing connections and problems. Just a hobby, of sorts.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Guy77]

The drawing for the garage is attached below. The door is 2400w x 2000h and requires a timber portal frame to take a lateral load of 10kN (other diagram).

 

[dik]

Rafter framing, or trusses. If trusses, you can analyse it as a 'U' shaped building.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[ChorasDen]

Guy77, are you familiar with the portal frame provisions written for the U.S. and published by the APA? They include capacities for single and double pier portal frames. Not sure how you might convert or justify for local code, however.

Do you have Simpson StrongTie products in Scotland? Personally, I might consider using strong walls on either side of garage door, assuming your foundation can handle it.

 

[ChorasDen]

Also, a bit curious how you came to the conclusion that this portal frame needs to resist 10kN?
Are you assuming a flexible diaphragm? If so, why is it not 14.5kN to each wall?
Are you assuming rigid/semi-rigid diaphragm? If so, how have you determined the stiffness of a portal frame that you have not yet designed or detailed?

 

[dik]

likely based on the stiffness. The wall on the right would take more load because it is more stiff... in addition the top and bottom walls would be taking some load due to the torsion introduced by the non-symmetric stiffness.



So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[ChorasDen]

likely based on the stiffness

Hence my question: How have you determined the stiffness of a portal frame that you have not yet designed and detailed?

 

[dik]

First kick would be to see what forces are there if the portal frame was 1/3 the stiffness of the wall... and would take it from there, likely ending up with ignoring the portal frame and designing it as a 'U'... depends on the roof construction a lot... 10 seems a little high; I would have thought less than half the stiffness of the wall. Determined the portal to see if that 'flies'. The long walls can easily 'absorb' the effects of the torsion. Whatever the load, it would not be 14.5 to each wall...

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[ChorasDen]

likely ending up with ignoring the portal frame and designing it as a 'U'

Hmm, interesting idea, but if designed in U.S., we would run into issues with Section 4.2.4 of NDS, which limits diaphragm aspect ratios. Since this project is located in Scotland, diaphragm aspect ratios may or may not be an issue. We also have differential stiffness between the (2) long walls if the shear walls are designed as segmented due to the openings, which will shift the center of rigidity considerably away from the middle of the short wall.

All that to say, I don't think any of this is particularly unreasonable, and may be possible to even ignore the portal framed side as dik suggested, but I think it's up to the project engineer to configure, detail, and justify.