Pocketed Handrail Base

[slickdeals]

thread507-287615
I recently had this submitted as part of shop drawing review. Has anyone come across the basis for these formulations? Any references/papers?

 

[MiketheEngineer]

Without spending an hour reviewing these calcs - a 4'' embedment just doesn't "feel" right - like in not good enough. But he might be right??

 

[RHTPE]

Do not like grout-anchored railing posts. In my area of the US they have a tendency to do one of 2 thing:

1. The grout expands and cracks the concrete substructures (all grout goes through a volume change as it cures - it's just a matter of how much), or

2. Over a few seasons the grout and post get pushed upward by the freeze-thaw cycles. I have seen as mush as 6" of upward movement.

My preference is an appropriate embed with a mechanical connection to the post or a UV resistant epoxy in a much smaller pocket (oversize pockets provide too much room for sloppy workmanship).

Ralph
Structures Consulting
Northeast USA

 

[slickdeals]

Luckily no freeze-thaw in Florida and it appears to be a very commonly used detail around here.

This is the first time I have seen a comprehensive set of calculations. However, I was not sure how some of the formulations were derived. I am hoping they have their basis in some testing or research.

 

[ron9876]

The diagram looks like a working stress analysis. Not sure what is happening in the calcs.

 

[ToadJones]

I like casting in a piece of PVC pipe or conduit about with an I.D. about 1" larger than the O.D. of the post.
Then you can grout the pipe into the sleeve

 

[slickdeals]

There is a formula to compute the distance to neutral axis ("a") and this results in a value that is greater than hef/2. Not sure how this formulation came about.

 

[racookpe1978]

By the (automated spreadsheet calc?) printout, the CL of the 1.9 x 1.9 post is 4 inches from the edge of the 4000 psi concrete.

Somehow, he is making a square cut (or assuming a pre-cast opening exists) in the 8 inch deep concrete 3.5 x 3.5 inches only 4 inches deep. (Should drill a deeper hole - it's easier and faster than a square opening.)

That means the edge of the hole is 2.25 inches from the side of the concrete. If he is assuming the grout is 10,000 psi strength, then the 3.5x3.5 x 4 inch deep "plug" of grout will be strong enough to hold the 42 high post -> but both the plug and the post will break out the then-walled concrete trying to hold the grouted assembly in place.

He needs to resist 200 lbs force at the top of the 42 inch guardrail, but only has 2 inches of concrete available to do that. (How will he verify 4000 psi concrete?)

 

[slickdeals]

Interestingly the same formulation is used here thread486-8797. Anyone tell me where it is referenced?

 

[StructuralEd]

I am a bit skeptical that it's appropriate to expect maximum concrete stress at the concrete surface as the diagram shows.
I would think a different force diagram would be expected with zero stress at the slab surface, more like a sheet piling or telephone pole analysis.