Steel tube embedded in concrete moment and shear capacity.

[Torres_Structural]

I'm working on a open canopy with HSS 4x4x1/4 posts, the owner wants the posts to be placed embedded in the concrete and not a base plate with anchors. I can't seem to find a good reference for moment, shear and pull out capacity of the post embedded into concrete. I saw a few Eng-Tips threads that reference the PCI coupling beam embedment capacity for shear. I'm assuming the posts are only experiencing moment and shear from the wind loads. Any leads on where I can get more info would be well appreciated. Thanks!

 

[JedClampett]

This is the great unexplored problem. The other is design of through bolts.
I would add shear studs to the post and treat them as taking a couple to be resolved. It would likely work anyhow if you just embedded it in the concrete two feet, but it's not really easy to analyze.

 

[Lomarandil]

Agreed, it's not something that has been solved definitively.

For pull out, there are some rule of thumb figures about the bond of steel profiles embedded in concrete. No consensus, but if you run through a few threads here you'll get a sense of what magnitude is possible.

Something I've also done is specified a few holes in the post below grade, and have rebar dowels passed through the post to have a more positive connection for uplift.

For moment and shear, if the concrete is relatively shallow, your capacity will probably be limited by geotechnical parameters, not structural.

 

[SlideRuleEra]

I can't seem to find a good reference for moment, shear and pull out capacity of the post embedded into concrete.

Using first principles, calculating the upper bound of moment and shear of the post is straight forward:

1) Go to the "Beam Diagrams and Formulas" section of any edition of the AISC Manual of Steel Construction.

2) Assume the concrete is fixed and rigid. The post is cantilevered out of this concrete.

3) Select the loading you want to evaluate (four loadings are given for cantilever, others can be approximated from these four).

4) Do the calcs.

For example, here is the diagram/equations for "cantilever beam - concentrated load at free end" (that is, load applied at top of the post).

 

[phamENG]

It's probably conservative to just ignore the concrete for this check. You'll have your post embedment with some triangular distribution in the soil. You'll also have a load applied to the post. From that you can make a bending moment diagram and shear diagram by which to design your post. More than likely it'll end up close enough to SRE's suggestion that his would be just fine.

Jed - through bolts in HSS, or through bolts in masonry?

 

[JedClampett]

Jed - through bolts in HSS, or through bolts in masonry?

Yes.

 

[phamENG]

Through bolts in HSS are easy - they're functionally dowels, not bolts. Masonry is a bit murky, though.

 

[Tomfh]

What sort of support are we talking about? A pad footing? A suspended slab?

If you have an effectively an infinite mass of concrete (i.e. no free edges) then embedding that post a foot will see the post yield before the concrete. Two feet, happy days.

Drill a few holes and add some dowels if you want to anchor it down.

 

[HTURKAK]

My points are;

- If the question is the embedment length of the steel tube ( HSS 4x4x1/4 posts) in the concrete foundation, you may approach with embedment model ( similar to the pc pocket foundation etc ) and you may improve pull out capacity with adding some welded reinf. at the tip .


- If the question is the geotech design of the ftg, you may consider similar approach with foundation for lighting poles ..one of the past threads thread507-492495







I cannot give you the formula for success, but I can give you the formula for failure..It is: Try to please everybody.

 

[JedClampett]

Through bolts in HSS are easy - they're functionally dowels, not bolts. Masonry is a bit murky, though.

Sorry, I read HSS and thought concrete. I meant there's no code guidance for through bolts in concrete or CMU.
My sneaking suspicion is that no corporation makes any money in the through bolt or embedded post industry, so they're not paying grad students for researching it. That is opposed to the concrete microfiber business where there's a constant stream of research papers telling you they're not useless.