shear friction reinforcement

[joncle10]

Hello, I am checking the reinforcement at the construction joint of a retaining wall.
Regarding the dowels which will be verified versus the shear friction, is the reinforcement Avf the total steel section of the cross section or the one located at the tension face ?

 

[KootK]

The tension face. I believe that there's an ACI clause someplace indicating that bars in compression are not included.

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.

 

[joncle10]

I read all the clause of the shear friction and found nothing.
I would be grateful if u can post it. Thank u.

 

[KootK]

Did you read the commentaries?

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.

 

[joncle10]

Yes i read it. I didnt find anything clear stating the above. The only thing i found is the following:
If moment acts at the section, it is desirable to distribute the shear friction reinforcement at the tension face. Otherwise, distribute it uniformly.

 

[KootK]

I was thinking of the clause below. It came up here recently in the course of a bridge pier cap discussion. Upon re-reading it, however, it doesn't strictly apply to your situation.

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.

 

[joncle10]

Ok.
I asked this question because I had a doubt since shear friction will be resisted by the dowels crossing the shear plane.
Therefore, since the section is reinforced from both sides, both reinforced sides will be resisting.

 

[KootK]

I don't think that anything prevents you from using the dowels from both faces of the stem wall. That said, I usually find that the tension face bars, on their own, are adequate. And I like it that way.

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.

 

[JedClampett]

If you need the dowels on both sides to get your wall to work at the joint, how's it going to work say, 12 inches up?

 

[joncle10]

JedClampett, above the joint, the reinforcement located at the tension face will be able to handle the acting moment - (i didnt understand your interrogation).

 

[joncle10]

JedClampett, above the joint, the reinforcement located at the tension face will be able to handle the acting moment - (i didnt understand your interrogation).

 

[KootK]

Shear friction and diagonal tension shear (Vc) both need to be satisfied at all locations up the wall. That said, shear friction won't govern in monolithic concrete. As long as Vc works above the joint, you'll be fine.

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.

 

[JedClampett]

My interrogation is, that if you need two mats of steel to get the shear to work via shear friction (which only applies at the joint), how do you get the member to work adjacent to the joint?

 

[Teguci]

Calculate the shear friction using both layers of reinforcement. In order for the concrete to shear at the construction joint, it will need to separate and shift. Although compression zone stresses are not allowed to be considered (unless they come from tensioning strands) both layers of reinforcement, properly developed at the interface, will resist separation.

 

[hokie66]

This thread, among others, reinforces my opinion that shear friction is balderdash. I think that the most effective bars in resisting shear are on the compression side, but that is not because of any clamping action by the reinforcement. Even the supporters of the concept recognize that most of the capacity of these joints is due to dowel action. If you need dowels, they are best placed centrally.

 

[JedClampett]

Hokie66, that's kind of my point, too. Except for corbels, I've never seen the need for shear friction. It seems to be a theoretical solution in search for a practical application. No harm there. But I've had engineers tell me, when I asked if a tank walls works in shear, that they checked it for shear friction. So I had to make a wall for an identical tank immediately adjacent 4 inches thicker.

 

[hokie66]

Even with corbels, I don't buy it. Corbels are best designed by strut and tie theory (truss analogy). The main bars in corbels need to be anchored, rather than developed. There is a big difference. The shear friction provisions are based on testing, and the method is empirical. But I fail to see how development or yield strength of bars on the compression side affects their performance. It is really only the size that matters in dowel action.

 

[KootK]

Cannot. Resist. Urge to argue about shear friction...

But I've had engineers tell me, when I asked if a tank walls works in shear, that they checked it for shear friction.

Were those engineers suggesting that shear friction capacity could be used to justify a design where diagonal tension shear checks could not be satisfied? If so, they were horribly mistaken with regard to what shear friction is and is not.

t is really only the size that matters in dowel action.

It may be more nuanced than that. The only design guidance that I know of on dowel joints, separate from shear friction conceptually, is this: Link. It turns out that dowel capacities are rather heavily influenced by the anchorage condition of the dowels.


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.

 

[rapt]

The way I read the initial question is that this is a retaining wall with continuous reinforcement on both faces and the wall is poured in 2 sections with a temporary construction joint. The 2 faces of reinforcement are continuous through the joint.

If that is correct, where does shear friction come into it? What shear force are you trying to resist?

 

[hokie66]

rapt,
I thought he was talking about the joint between the footing and the wall. Thus the discussion of tension vs compression reinforcement contributing.