Embedded Sleeve in Concrete to Support a Handrail Post.

[Jeg5393]

thread507-287615

I read through this post trying to figure out the best way to design the embedment depth for a sleeve placed in concrete to support a post. Towards the bottom "Ron" posts a sketch of the situation with a moment which is resolved by a couple in triangular distribution. In this sketch he solved for a stress area which I am having trouble understanding how he got this.

 

[KootK]

Deja vu. We're discussing this same issue, and with Ron's same sketch here: Link. I believe that the key to understanding Ron's stress area is that he's developed it as the maximum, triangular, elastic stress distribution that would not exceed the allowable concrete stress. This is similar in concept to the sketch that I posted at the bottom of the linked thread. The main difference being that sketch is based on a plastic stress distribution in the compression block.

Hopefully Ron will surface and 'splain it better.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Ron]

KootK is correct. It is an elastic stress distribution based on the concrete's capability. Further, it is primarily applicable to a square post cross section. Round isn't significantly different, just that you have to make assumptions on the contact stress distribution. If you use a square section, it is conservative. A round section will give a different stress distribution with an actual larger distribution area (you could integrate the hemisphere if you wanted to be technically accurate, but I don't see the need).

 

[BLSPAM]

I try and steer the architect away from sleeves. They let water, in and when it freezes, the slab cracks and, even if the reinf. is properly located, the railing gets loose. A base plate, with sealant below it, and post installed anchors will last allot longer. Never had one break out yet.

 

[Ron]

BLSPAM....be careful with top rail attachment if you use a baseplate for the posts. Baseplates and their anchors are usually too small to handle the moment when load is applied at the top of the post. The top rail has to be anchored at its ends so that you end up with only shear in the base plate and fasteners (and a small moment due to lateral deflection of the top rail).

 

[KootK]

. A base plate, with sealant below it

What kind of sealant do you use for this kind of thing?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Jeg5393]

Ok that makes a little more sense. I was reworking the sketch the Ron posted so that the triangles didn't overlap and I'm just going for a sanity check. Would someone mind letting me know if my thoughts through this sketch are correct? thanks for your time everyone

 

[SAIL3]

I stopped using round pipe as shear keys because of the concern of the peak contact stress along the centerline of the pipe....the pipe would have to "walk" to engage an equivalent square load capacity....may not be a major concern in the H/R post case...

 

[wannabeSE]

Jeg,
The sketch only includes the stress from the moment. Typically there will also be shear stress that is added to this (added on the top and subtracted from the bottom).