D.6.2 Conc Breakout Strength in Shear for Embed Plate

[SteveGregory]

I have an 3/4" studs on an embed plate w/5" embedment cast into an 8" thick wall. Clip angles will be welded to the plate for a simple beam shear connection. I am assuming 3" of eccentricity to add some moment to the connection.

I am going through App D equations for ACI 318-05 without any problems except for the Concrete breakout strength in shear found in D.6.2. My loads are modest, 16.4k and another load a little bit higher.

I am new to App D. The only thing that I could imagine helping my situation would be introducing some sort of reinforcing in the wall that would allow me to skip the failure mode in D.6.2.

Does anyone know how to do that kind of reinforcing?

 

[ishvaaag]

You may forget the anchor scheme; sometimes thinking along ordinary lines is just a trap. I used to use RISA here in Spain almost when no one was using it; and saying that whenever they would use it I would be using another they neither are familiar with; this gives you some advantage, they don't know yor game.

The trick here may be hanging the plate from welded rebar, with anchored bars or clips at an angle. You simply will need to develop the reaction. You may add just for direct tension if any anchors as a complement.

 

[Lion06]

If you are loading a wall that goes down to a footing, you can't have a concrete shear breakout failure. I typically ignore it in these situations, since, like I said, it can't physically occur.

 

[SteveGregory]

StructuralEIT,

How about side edges?

 

[Lion06]

If you're close enough to a parallel edge I would probably check that. Can you post a sketch?

 

[SteveGregory]

S_EIT,
I agree with you that Shear Breakout shouldn't happen in a wall going down a "large enough" distance. Although, the ACI App D equations don't seem to acknowlege this. In my case, I have a large elevator door opening below some of these beams and I have beam reinforcing above the opening. In other cases, the wall keeps going.

From the beam centerline to the parallel edges, the distance varies from 4", 6", 16" to 3'-0".

 

[Lion06]

Steve-
Even if the embed plate is only 6" above the bottom of the wall, the shear breakout can't physically happen without a footing failure first. Here is how I rationalize it - the shear breakout failure is for an anchor that is being "held back" by a mass of concrete. That is not the case here. The anchor is being "held up" by the wall and footing. If the footing doesn't fail, the wall can't have a breakout failure in that direction.

You'll never get the App. D equations to work out for this. The equations start working against you when you have a large edge distance in the direction of the load and small side edge distances. If you have small side edge distances, your capacity will DECREASE as you increase the edge distance in the direction of the load. That is not intuitive, and ACI has tried to address it in the '08 version with a new provision for large edge distances in a thin member, but it still doesn't completely close the hole.

 

[LSPSCAT]

ACI needs to come out with a clear plain language statement on this to stop these concerns. It can be rationalized through engineering judgement when the shear breakout does not control, however, the equations can in the least be peicewise defined to clarify the matter. Mathematically the equations do not work and attempts to codify and spreadsheet that portion of the code leave many open holes to be filled with warnings to the user. Which is fine - but do not leave a code half completed with so many areas open to interpretation and then tell everyone they need to design to that code.

 

[bones206]

I have used 60 times the anchor diameter as a maximum free edge distance for calculating shear breakout. See this thread:

thread507-241415

 

[ishvaaag]

Just to remember that the PCI manual ((5th ed. at least) is full of tie details based in the same thing that I am above proposing: mere anchoring of forces at a welded plate.