Railing Post embedment in concrete. 1

[atilashorse]

Hello!

I have been required to submit embedment calculations for a stair handrail with posts embedded in the concrete steps (pretty typical). The condition is not related to plates and anchors subject to axial loading, but to posts embedded directly in concrete, the posts being subject to lateral loading. I have found that like in the case of axially-loaded anchors, concrete is subject to shear. In the case of anchor tension, we have the famous pullout cone, but in this case, I am having difficulties finding the area of concrete subject to shear due to the moment the post imposes on the concrete embedment. Any ideas?

Tahnk you.

 

[ishvaaag]

I think you may calculate the thing as inserts or embedments in concrete of the kind of straight rods, thinking that concrete failure will control. Anyway some cuts and deformations and the ends may be done to help to forestall extraction. If resitance to shear against a close surface is a worry, use 90 deg hooks welded or not anchoring the outwards forces.

 

[cap4000]

I have never done this calculation before, but I would think you should try these 2 things. First, consider the grouted post as a fully fixed end and as such you would have a triangular distribution of the load above and below the centerline of slab thickness. Each triangle would go
opposite to each other. Second, calculate the force of the triangles which should equal one another and assume a 45 degree distribution out to the stair edge and use the typical pullout or in your case a "pushout" cone calculation. This problem should be verified in a Testing Lab. Good Luck.

 

[ERV]

ramcode,

I do not think that it would be possible to core a 2" dia. hole (or maybe larger, if accomodating a 2" pipe) within 2" of the slab edge and retain shear capacity or integrity in the concrete. Minimum edge distance for cored pipe embedment is somewhat different than for pipe cast in place. Typical shear is approximately 1/3 of compressive strength (fc), however, with all the tests that have been done, no reliable measure of shear is available. Even if there were, it would not apply to drilled holes close to the edge.

For balcony railing on the 20th floor of a building this can be critical (no way to predict failure point).

This may be the reason that your building official is asking for calculations to support drilling and setting posts close to the edge.