Appendix D Pryout for large members

[bpiermat]

So I have a post-installed anchor connection. All concrete is unreinforced, but members are large. My question is: Can I ignore Pry-out in Appendix D or can I modify the equation in Appendix D.

Here is my specific case: The Slab to Wall Connection, the Slab is 8' deep and the Wall is 3' Deep. If the dowel is post-installed in the wall at the center of the slab and then the slab is placed after the dowel is installed, should my pryout effective width be equal to 8' = 1.5 Hef? Or does this condition not even apply at all?

Thanks in advance!

 

[TehMightyEngineer]

Short answer; no you can not ignore it.

Longer answer; what kind of loading is on the anchor? Shear parallel to the edge?

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[KootK]

So this is an 8' thick elevated slab tying into the side of a 36" wall? If the bar can be developed into the wall, I'd be tempted to call it shear friction rather than app D. I'd also do this with dowels top and bottom and chipped in shear key(s). And maybe a new shotcrete wall under the slab edge.

 

[TehMightyEngineer]

How strong and how long is the embedment depth on the anchor?

I'd be tempted to call it shear friction rather than app D

Possibly, but aren't you the champion of the reinforcement needs to be developed on both sides of the joint?

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[KootK]

Possibly, but aren't you the champion of the reinforcement needs to be developed on both sides of the joint?

Indeed I am, even though I don't fully understand the need for that. Is there any reason that we wouldn't develop the dowels on both sides of the joint though? 36" seems like plenty of room develop some smaller bars with a little Hilti magic.

 

[KootK]

Speaking to OP's original concerns, it is pretty hard to see concrete prying out when there's substantial concrete on the other side of the joint to resist that very mode of failure.

 

[TehMightyEngineer]

If the bar can be developed into the wall

Oh, I missed that you mentioned this already in your post.

Speaking to OP's original concerns, it is pretty hard to see concrete prying out when there's substantial concrete on the other side of the joint to resist that very mode of failure.

Agreed.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[bpiermat]

Wow, thanks for the responses.
Yes the joint is under shear loading.

The 8' Slab is Slab on Grade, but that does not change much in my opinion.

The bars probably cannot be fully developed, since I will need to used #9 bars to resist shear. Kook, is correct, there is concrete on all sides of the joint. Therefore, prying should not be considered.

Thanks,

 

[KootK]

The bars probably cannot be fully developed, since I will need to used #9 bars to resist shear.

Any reason you can't just use a zillion #5 in eight layers or something? These things are more reliable when you spread it out a bit anyhow

 

[TehMightyEngineer]

If you're using #9 bars I imagine your loads are fairly large but the clamping from the large amounts of concrete involved does imply that the usual pryout equation should be taken with a dash of engineering judgement.

I'd say you can't exactly use the shear friction equations but taking the just dowel action of the anchors without prying per app. D seems reasonable.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[bpiermat]

KootK,

Yes, Still looking at this, but I will need #9@6, or 240 #9 in the wall (120 ft long connection). Going to #5 would mean 3.33 times this.
Not to make this more complicated, but the plan is to drill these about 20' under water with divers.

Thanks

 

[KootK]

May we know the shear demand per linear foot that you intend to transfer?

Not to make this more complicating, but the plan is to drill these about 20' under water with divers.

No sweat. When I first read the title of this thread, I just assumed that it was 8' thick concrete, under water, on the moon. Same old, same old.

 

[bpiermat]

46 kip/ft

 

[bpiermat]

Depending on how you do the calcs, i.e what phi you use, it maybe less dowels, trying to get it down to #6@12

 

[KootK]

I'll show you mine... #5 dowels in a 12" x 16" grid.

 

[bpiermat]

Wow, thanks.

 

[KootK]

Larger and fewer may still be better. You should be able to hilti anchor a pretty large bar for Fy into 36" of concrete.

 

[TehMightyEngineer]

One thing to consider when drilling and epoxying bars is larger and few is often not cheaper than smaller, but more bars.

Larger and longer coring bits or chisel drill bits get more expensive quick. In addition, drilling or coring deep into concrete takes more time the farther you get into the concrete, so many shorter holes is often cheaper.

For above-water work I've found that even though it's more time, the cost per square foot works out in favor of the smaller bars as they drill faster, use less epoxy per hole, and often have less cost. The extra redundancy and performance of the rebar across the joint also means you can sometimes reduce the amount of steel required as well making it even more favorable. All things equal, more bars at less spacing makes a better joint.

I of course have not run the economics of underwater anchoring; so it may change things drastically as my understanding is time underwater for a specialized diver per hour can make even the most expensive lawyer look cheap.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/