Break away posts

[jplay2519]

I'm designing a wood post with concrete foundation for sign support. We need to design it as a breakaway post. The sign manufacturer is suggesting drilling large diameter holes into the base of the post. I'm not sure how to determine reduced capacity for a break away and I feel like just putting holes at the base will get us into failure during wind and not just impact.

 

[jayrod12]

How are you providing lateral stability? Generally with wood posts, they're either embedded in the ground, or some form of bracing is required.

Wouldn't your standard wood posts, even a 6x6 be it's own breakaway connection?

 

[JStructsteel]

Check DOT websites, they do this all the time. Dont need to re-invent the wheel

 

[JoelTXCive]

Spit-balling ideas here.....

I think several state highway departments have break away posts designs for steel round tubes (for stop signs etc.).

What if you took one of those designs, and then just welded a plate/bracket on top to receive your wood post?

ftp://ftp.dot.state.tx.us/pub/txdot-info/cmd/cserve/standard/traffic/smds1.pdf

TxDOT has a couple "Triangular Slip Base" designs on this page:

Link

https://www.dot.state.tx.us/insdtdot/orgchart/cmd/cserve/standard/toc.htm

 

[DETstru]

In the US, the Federal Highway Administration says that the largest un-weakened sign post is a 4x4.
6x6 posts require (2) 3"Ø holes drilled 4" and 18" above grade.

 

[jplay2519]

I'm providing the embedded post design. I'll try to look up that FHA document. I def don't want to reinvent the wheel! Thanks for your input everyone.

 

[Lomarandil]

Agreed about not re-inventing the wheel --

But if you had to for one reason or another, wouldn't it just be an exercise in finding the right amount of reduced section for your loads? (and with wood, accounting for the duration of load?)

It's hard for me to imagine wind loads being of similar magnitude to (vehicular?) impact. Unless your wind area is huge.

----
The name is a long story -- just call me Lo.