Embedded guardrail post
Embedded guardrail post
(OP)
I sent this diagram to an architect to illustrate my concerns about a detail they proposed for an embedded guardrail post on the exposed rooftop amenity space of a concrete building I'm designing.
The diagram is somewhat to scale. Just wondering if anyone thinks my concerns are valid or if anyone has additional thoughts on it.
The diagram is somewhat to scale. Just wondering if anyone thinks my concerns are valid or if anyone has additional thoughts on it.
- I have concerns about water infiltration through the crack that will inevitably form at the embedded post.
- Getting this to pencil out structurally will be tough. I'll need DBA's or studs welded to the post to anchor it into the curb/stem wall. Then sufficient vertical dowels coming up from the concrete slab to anchor the curb into the slab. (I'm unsure how the development length of those dowels will even work since I'll have a moment directly at the top of the curb, where the dowels are not developed at all)
- And even if I do manage to make it work on paper, building this will be a nightmare. I can already hear my phone ringing with contractor complaints....






RE: Embedded guardrail post
Water-proofing. Yes, what you have proposed will not work. if this is what they want.... and it is ugly.... Then the roofing membrane needs to go over the curb, and at each post the roofer needs to wrap and seal the membrane to the rectangle penetration. You can see details of products if you look at Carlisle PVC or TPO details, but you are't getting paid for that. Ask the Arch.
I would also make the curb lower since it doesn't take the moment, or even don't use concrete. Stop it at the pavers, or bring it past and clad it to protect it.
RE: Embedded guardrail post
Dave
Thaidavid
RE: Embedded guardrail post
Further, as noted, the waterproofing will be compromised.
I agree with David....saddle it.
RE: Embedded guardrail post
It seems if it was a guard, it could be bolted to the outside of the curb.
RE: Embedded guardrail post
This shouldn't be a problem. With the connection strategy proposed, you wouldn't be delivering a concentrated moment at the top of the wall. Rather, you'd be delivering a concentrated shear which should be able to be calc'd out alright. Your moment turns into local shears, one at the anchor near the top and an opposing one lower down (presumably).
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.
RE: Embedded guardrail post
For the past 1.5 years I have been involved with a project near identical what you sketch.
Project built about 2 or 3 years ago - "green roof" situation with perimeter rails. At each and every post (4' c/c) there was a vertical crack. The crack formed before the facility opened. With such a close spacing of vertical posts and the narrow curb width there was inadequate reinforcement, especially when you consider that the roof was placed as a previous pour, providing significant restraint for longitudinal shrinkage, hence cracking.
Fast-forward to today, and the building owner (university) and the contractor and the A/E are all in court.
We were involved to look at repair/strengthening techniques. The re-work on the waterproofing was more costly than the curb/post strengthening.
Your concerns are warranted.
RE: Embedded guardrail post
It would be bad news if a car managed to get up there...
Koot, makes sense. I'm going to end up doing an embed plate at the top of the curb and weld the post to it. I'll probably use DBA's and lap them with the vertical dowels coming up from the slab.
Ingenuity, Sorry to hear that happened. It's exactly what I was afraid of and luckily the architect understood as well. We're changing the detail to an embed plate in the top of the curb, which should lessen the crack potential significantly.
Your comment about the slab below restraining the curb is good to keep in mind. I'll have to think about that to make sure the crack locations are controlled while maintaining waterproofing.