Portal Frames (wood, non-prescriptive)

[RockyDiego07]

Hi all,

So I know the IRC and IBC has detailed portal frame criteria as long as the certain limitations are maintained. There’s even an APA documents which shows capacities (TT-100).
How does one engineer a portal frame outside the IBC/IRC limits?
Thank you.

 

[Lomarandil]

The primary challenge is developing (buildable) moment connections that don't have significant fastener slip. End-grain nails aren't going to cut it.

This isn't my area, but the others can probably point you toward some proprietary connectors (Simpson, etc) that solve that problem.

 

[dik]

Rigid frame design, engineered lumber, metal side plates and glulam rivets... I've only done a few of these.

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

-Dik

 

[XR250]

Honestly, I would never try to deviate from the prescriptive design. I doubt, in actual practice, that IRC moment frames perform as intended.
And, I imagine, their capacities are based on full-scale laboratory testing.
I would look at steel moment frames or Strongwalls if you need something outside of the prescriptive requirements.

 

[phamENG]

How does one engineer a portal frame outside the IBC/IRC limits?

This is a troubling question. How does one engineer anything?

1) Search for things that others have done (here, on Google, in your university library, etc.) and figure out how they went about it, what they got right, what they may have gotten wrong, and how you can either emulate it or (maybe) improve upon it.

2) Use first principals to figure something out and then take it to somebody with extensive knowledge in wood design to figure out why parts of it will work and why parts of it wont.

If you have the means to test it, so much the better.

I'm generally in agreement with XR on this. Wood + Moment = bad news. BUT...there is growing use/acceptance in some countries and applications. There was even a picture floating around here somewhere of what is essentially a PEMB using glulams rather than steel for the rigid frames. I believe they used circular fastener patterns with concealed steel plates to create the moment connections.

I'll do it for accessory structures, porches that are outside the building envelope, etc. The numbers can be made to "work" for strength, but I have doubts about long term resilience and ability to maintain serviceability limits.

I might make an exception for something like this adapted to the shape of the frame for light loads:

 

[XR250]

I might make an exception for something like this adapted to the shape of the frame for light loads:

LOL, I was the engineer on that job.
He is a customer of mine.

 

[phamENG]

I remembered you mentioning that you use it - didn't know you were the originator of the idea (at least in print). Very nice.