Minimum hook development length per CSA A23.3

[Baffled Engineer]

I'm trying to anchor a 6" reinforced concrete slab membrane into an existing 18" concrete slab underneath for remediation purposes.

There is a hydrophilic waterstop between the 6" slab membrane and the 18" slab which causes expansive pressures when wet, so I intend to tie both slabs together using post-installed 90 degree hooked dowels.

The problem is the Canadian code requires a 6" minimum development (embedment) for standard hook regardless of any reduction factors , which I can't accommodate with a 6" membrane slab. The most I can provide is a 4" embedment with a 2" clear cover in the 6" membrane slab. Does anyone know a way around this requirement?

Thank you.

 

[KootK]

1) I believe that what most engineers are doing in this situation is accepting that the hook embedment doesn't meet code and allowing that given that it's only a nominally "structural" application with limited safety implications.

2) I believe that you could use a 135 degree stirrup hook of size #5 or smaller wrapped around a longitudinal bar to technically meet the development requirement as we do with beam stirrups. I don't recommend that, however, given that:

a) that would be onerous to install and;

b) I don't feel that it would be effective anyhow. In my opinion, this isn't really a development problem but, rather, an anchorage problem. And you only really improve anchorage by engaging more concrete.

 

[r13]

Try this. If shear checks out.

 

[dik]

can you use a headed stud?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Celt83]

[ul]
[li]Install the dowels at an angle to increase the development length in the 6" slab[/li]
[li]If truly just for anchorage and not to try and develop composite action, use a threaded rod epoxied to the 18" slab and double nut+small washer plate in the 6" slab and perform the required anchorage checks[/li]
[li]Make the topping 8" thick to allow for standard hook + cover.[/li]
[/ul]

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https://github.com/open-struct-engineer

 

[r13]

Do you have information on the pressure exerted by the hydrophilic water stop when it expands? I suspect the concrete weight alone is able to keep it in check. For this case, you don't really need the full strength of the dowel.

 

[rowingengineer]

I agree with KK part one, in this case you are not looking for development length but anchorage.

 

[KootK]

I feel like the diagonal dowels, while a clever means of garnering more development, actually hurts you overall because it's an anchorage situation with the potential for spalling as shown below. Kinda depends on the bar diameter and the width of the gap I suppose.

 

[Tomfh]

Development and anchorage are the same thing.

 

[jayrod12]

Development and anchorage are the same thing.

Them's fighting words for Koot. Was it you and him that went at it the last time?

 

[rowingengineer]

Tomfh,
They are not defined as the same in Australia. If so all our hold down bolts would be stuffed.

 

[gharli]

An idea:

Hydrophilic seals typically ask for a minimum of 150 mm cover in unreinforced applications to avoid spalling.

Using this value, you could conservatively suggest that the expansion pressure is a maximum of 3.6 kPa (24 x 0.15). Based on your dowel spacing then work out the force per dowel and calculate how much anchorage you actually require. Obviously this is really conservative because you are ignoring the self weight of your new concrete. Including the self-weight would negate the requirement for any anchorage as suggested by r13.

I suspect the 6" minimum is not based on anything empirical and could be rationalized through calcs.

Post installed anchors are often embedded less than 6".

_________________
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[Tomfh]

They are not defined as the same in Australia.

Which definitions are you referring to?

 

[rowingengineer]

Anchorage vs development length are not defined the same, while they are Normally in combination, we define the hook or bend as the anchor and the remainder of the bar as the development length.

 

[Tomfh]

we define the hook or bend as the anchor and the remainder of the bar as the development length.,

Which definitions are you referring to? In my experience “Anchorage length” is often synonymous with “development length”.

I think kootk means something different by anchorage vs development anyway, as opposed to length of hook vs length of remainder. Kootk please clarify.

 

[KootK]

I think kootk means something different by anchorage vs development anyway, as opposed to length of hook vs length of remainder. Kootk pleaE clarify.

That's exactly right. It can be frustrating to discuss this stuff sometimes because of the ambiguity that you mentioned whereby, in many documents, anchorage really just means accelerated development. Things like hooks, bar end anchors (pucks), and weld plates. For me, the defining characteristic of this kind of anchorage is that the tensed bar has a concrete strut to react against in order to keep it from tearing out from the concrete mass.

The KootK / ACI App.D definition of anchorage describes a setup wherein the tensed bar relies primarily on concrete tension fields (breakout) to keep if from tearing out from the concrete mass. This kind of anchorage also requires some manner of bar development but the bar development on its own does not guarantee sufficiency (says me at least).

Post installed anchors are often embedded less than 6".

I'm leaning in that direction as well. Basically, treat both sides of the joint as you might a post installed anchor.

 

[r13]

I don't know if the code authorities share the view from dictionary

Definition of anchorage
1a: a place where vessels anchor : a place suitable for anchoring
1b: the act of anchoring : the condition of being anchored
2: a means of securing : a source of reassurance this anchorage of Christian hope — T. O. Wedel
3: something that provides a secure hold

Definition of development
1: the act, process, or result of developing
- the development of new ideas
- an interesting development in the case
2: the state of being developed
- a project in development
- a dowel/anchorage needs development (my words)