Embedded HSS Sleeve to Timber Post Connection? 1

[Mostly Civil_CK]

In need of a peer check

I am designing a privacy screen that will be 12'-0" Tall by 12" Wide.
To limit the amount of steel + limit the moisture intrusion into the wood, I have decided to embed HSS post 2'-0" into a 5'-0 x 18" Dia pole footing. 3'-0" of the HSS post will extend vertical.

The timber post will extend 12'-0" from grade inside the HSS sleeve and transfer its overturning moment with (6) thru bolts.

LOADS
Mu = 11 kip-ft
V = 1.5 kip

QUESTIONS.
1. I am lacking a good solid check to see if 6 thru bolts is enough development to transfer load to the HSS, then the footing. Can someone provide me a good statics FBD / equ?
2. Is there any benefit to a different orientation of thru bolts or alternating pattern? I currently placed them parallel to the minor axis such that they are placed within the N.A of bending.


Please see image and let me know if I have missed something!
THANKS!

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1581612998/tips/Timber_Connection_IMG_uk83oy.pdf[/url]

 

[dauwerda]

I don't believe the bolts will transfer the load - the load will be transferred through bearing of the wood post on the steel HSS. The interaction will be similar to that of a drilled pier foundation (or direct buried post) in soil, only due to the stiffness of the steel the bearing pressure will be highest at the top and bottom of the the HSS.

 

[XR250]

I was noodling on this idea recently for free-standing carports. Seems an HSS6x6x1/4 would fit a 6x6 wood post (5 1/2x5 1/2) almost perfectly after knocking the corners off. I was thinking a few lags for uplift and counting on direct bearing to transfer the moment. Beats embedding the 6x6 in a lug of concrete. Could always shim if it got too sloppy.

 

[Mostly Civil_CK]

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1581617864/tips/Timber_Connection_2_IMG_p4icqq.pdf[/url]I was

trying to move away from the fact the timber column may "rock" with shrinkage over its life, and that enough snug thru bolts will mediate the minimal rotation at its base.
One bolt, not matter how tight, will still allow rotation, but what about 2 or 4 bolt in line.

In my mind, at some point with enough fasteners, I'll create a moment connection. I assume I'll have a "pile group analysis" of sorts.
See image...

Thoughts?

CK

 

[phamENG]

There was actually a thread on just this sort of connection recently. I think the consensus on the best choice was actually using an angle. That way you can draw it in tight to both legs of the angle. With HSS, you can never really tighten the connection all the way. The shrinkage will occur within the HSS, but the bolt can't get any tighter.

 

[wannabeSE]

How do you prevent water from filling the tube and rusting the HSS or rotting the post? There may be better options:

https://www.nfba.org/view/download....d-connections-between-wood-posts-and-concrete

https://www.midwestpermacolumn.com/...di-wall-plus-wet-set-concrete-anchor-brackets

 

[EdStainless]

Wood light pole base
thread507-462549

Look here, some good suggestions.


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P.E. Metallurgy

 

[Mostly Civil_CK]

@wannabeSE
I am going to paint / coat the Embeded HSS portion + bump up the size of the wall thickness to be sacrificial.
At the top of the exposed HSS to Timber I am putting on a SQ rubber flange that will cover the gap between timber and steel. Maybe add some caulking.

 

[EmilC]

Providing drainage holes below the bottom of timber, and spacing the timber up a bit from grade would both be good practice. AITC-104 Typical Details and Details to Avoid is a good resource for decay protection.

http://americaninstitutetimberconstruction.org/wp-content/uploads/Design_Standards/AITC-104-2003.pdf

Re: transferring moment with a line of bolts: I've been told that this doesn't work well with timber because it induces tension perpendicular to grain. In your case, you have the HSS to keep the whole thing from blowing apart, but I'd still be cautious. Are you aware of this Simpson product

https://www.strongtie.com/standoffpostbases_castinplacepostbases/mpb_base/p/mpbz

?