Shear and pullout for concrete inserts

[user 788]

I had a problem come up at work today and was wondering if someone could help me with it.

We always use 3/4" red head anchors on the jobsites and usually I get the allowable loads for a minimum embedment from the spec sheets. The shortest embedment listed on the spec sheet is 3-1/4". Now we have a hollow concrete pile with wall thickness of 3". How do I find the allowable load for shear and pullout for 3" embedment ?

What I did for now (since 3" is not so far off from 3-1/4") is interpolating the specified loads in the spec sheet and then applying a very generous safety factor. But next time I would like to back this up with some good calcs. Also I would think that the allowable loads probably don't decrease linearly. So how would you guys solve this problem ?

 

[kevo_55]

Tina,

Typically, I would use "ICC" reports on name brand fasteners besides using product literature. But are you sure that you're getting a 3/4" diameter Tru-Bolt with 3" embedment? The diameter seems a bit large.

But to fully answer your question, I'd go with ICC reports or possibly use Appx D of the concrete code for the design of these anchors.

 

[user 788]

kevo_55,

thanks for your reply. I looked at Appendix D and it seems to be exactly what I was looking for. Thanks.

 

[scottiesei]

I would be interested in the availability of a 3/4" red head that could net you a 3" embed. Usually the shortest embed., the 3-1/4" is based on a length of red-head which they supply. I have never worked on a hollow concrete pile but I NEVER let my masons use red heads on hollow block. I have seen many a red head blow out the block and the guys in the field just patched it to hide the failure. Is there not another connector that you could use? What are you fastening to the pile? What are the loads?

 

[user 788]

The load is very low, just about 1000 lbs. They're building a small pile cap on test piles and use overhang brackets to place the soffit. The whole thing is only 4ft tall. The 3/4" red head is overkill but that's what they want to use. They actually picked the piles with a crane and 5ea red heads when they set them.

 

[teda]

To get desired capacity, you must have sufficient concrete thickness in adition to embedment.

If pile is hollow, probably you won't get enough thickness. That will reduce your pullout/shear capacity a lot......

3/4''dia with 3'' emb in a hollow concrete unit is really not good practice.

In this case, the best way is using samll diameter epoxy bolts. Another option is using shot pins.

 

[scottiesei]

Good call with the shot pins