Deformed Wire Stirrups with "Standard Hooks"

[CARunderscore]

I have an unusual precast wall design that might need out-of-plane shear reinforcement. I might be able to use #3 bars, but I'm already in pencil-sharpening mode, and single-leg deformed wire stirrups look like they might be a hypothetically better option due to a need to keep congestion down within a constrained thickness of wall. I've never seen any such thing before, but neither have I encountered my current set of design constraints before.

Here are the code requirements as I understand them (ACI 318).
[ul]
[li]Shear stirrups are allowed to be single-leg.[/li]
[li]Deformed wire is a permissible stirrup type.[/li]
[li]Stirrups are a permissible type of shear reinforcement for one-way "slabs"... which this essentially is from an analytical perspective. ACI is silent about out-of-plane reinforcement for "walls".[/li]
[li]Acceptable anchorage for a deformed wire stirrup is a "standard hook" that encloses a longitudinal bar.[/li]
[/ul]

Questions:
1. Am I off-base on any bullet points above?
2. Are loose (not in a mat/mesh) deformed wires something that can be reasonably purchased? Not readily, just reasonably. Custom orders are acceptable.
3. What the heck is a "standard hook" for a deformed wire? ACI's tables only list bar sizes, though I see no technical reason that I can't assume that the "No. 3 through No. 5" case should just read "No. 5 and smaller bars/wires".

 

[KootK]

How thick is this wall?

 

[Lomarandil]

I share a frustration that ACI limits a lot of discussion to #3 and larger bars (for NA practice) despite regional or project circumstances that may guide a smaller bar solution. I've gone to the Australian code in the past to develop reasonable guidance for smaller bar sizes.

 

[CARunderscore]

How thick is this wall?

About 18 inches. I could add a couple inches if it helped, but it doesn't. Think heavy industrial.

It's primarily a flexural element, so there's a good bit of flexural steel on both faces (loading can come from either side). I hesitate to try something like stud rails because I want to tread lightly in terms of anchoring the ends of the shear reinforcement.

 

[KootK]

I hesitate to try something like stud rails because I want to tread lightly in terms of anchoring the ends of the shear reinforcement.

I would actually deem stud rails to be the best solution in terms of performance and congestion. The major drawback of them, in my opinion, being cost.

I've seen folks use z-bars, as shown below, to shear reinforce basement walls. It does tend to get pretty busy if you're having to reinforce large swaths of the wall however.

Think heavy industrial.

Got it. It might be worth mentioning that no reinforcement scheme will become active until after some icky shear cracks open up. This might factor into your decision making if your dealing with water retention etc. This is one of the reasons that I try to not use shear reinforcing for most wall applications. Obviously, you situation is exceptional.

 

[CARunderscore]

I don't think that z-bars will work, since they're directional. I just ran some calcs and, if I used stirrups, I'd be looking at either a #2 bar or a D5 wire. Probably not a worthwhile space savings over #3 bars, to be honest...

It should be able to retain water, but it doesn't need to be swimming pool tight. φVc is greater than the maximum unfactored shear, so theoretically the shear reinforcement is only there to provide a margin of safety and shouldn't actually need to engage. Theoretically. I've also been deliberately conservative in estimating the load effects in order to keep cracking down, but your comment has inspired me to look up some criteria for water-retaining structures to get a better handle on the expected level of cracking.

 

[KootK]

I don't think that z-bars will work, since they're directional.

That's easy enough to solve. Just make the bend angles 90 degrees. Or a 90/135 candycane if you prefer.

 

[KootK]

Or something like this viewed from the top if the bending would be feasible. This could just as easily be WWM if your prefer.