Epoxy Anchor Issue

[XR250]

I am woking on a job where I specified Simpson SET epoxy for some shallow, 1/2" anchors (2 1/4" embedment due to embedded slab items). I used the Simpson tables which gave me an allowable pullout of of 1805 lbs (ASD) at 2 1/8" embedment in 2000 psi concrete. The contractor used Hilti RE100 instead. Their tables do not go below 2 3/4" embedment with no reductions allowed. The owner is asking for an appendix D calc. The epoxys are similar with the Simpson bond being 10% stronger (3300 psi versus 3000 psi). My demand is only 1400 lbs (ASD). I assume concrete breakout is the actual failure mode so the bond strength should not be an issue. Is it reasonable to assume that the Hilti product will perform similarly.

Thanks

 

[FSS]

Does the Hilti software for Appendix D calculations allow you to solve for your depth? I am not as familiar with their anchor software.

 

[XR250]

I am unable to run their software on my computer as I cannot get it to install (Simpson seems to install fine) They told me I could not use their software for depth's below 2 3/4"

 

[Shu Jiang PEng SE]

Concrete design breakout strength 0.75x17xsqrt(2000)x2.25^1.5/1000=1924lb (assume the bolt spacing is larger than 3x2.25=6.75" and edge distance us larger than 1.5x2.25=3.375", group reduction effect is not considered). The force, normally, is divided by 1.5 to get the resistance for the load derived per ASD load combinations, that is 1924/1.5=1283lbf. A little under design of the concrete breakout strength.

 

[XR250]

Interesting. I don't have a spacing or edge distance issue. Why is that so low in comparison to what Simpson calls out in their tables?
FWIW, the bolt is being used at the base of a moment clip to anchor some sill studs. I wonder if that will help as the the clip adds a compressive load to the top of the concrete under overturning (see attached)

 

[Shu Jiang PEng SE]

It seems there are two bolts in the connection and the bolts spacing should be less than 3 times of the bolt embedment length. Group reduction should be considered.
Please note the strength I am talking here is the concrete strength, see the picture for information about breakout failure and group reduction conception.

 

[XR250]

There is only one bolt in the connection.

 

[wannabeSE]

jiang,
I think the effectiveness factor, k[sub]c[/sub], for Simpson Set XP in uncracked concrete is 24 rather 17 used in your calculation. If that is not the case, Simpson may be increasing the capacity for uncracked concrete by using Ψ[sub]c,N[/sub] = 1.4. But if you are like me, you always assumed the concrete may become cracked.

 

[KootK]

There is a procedure for accounting for the benefit of the compression load. I posted details of it and a clipped diagram in that crazy long foundation wall thread of late. Your geometry here is such that I doubt it will be of much help however.

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.

 

[Shu Jiang PEng SE]

kc=24 is for cast in anchor bolt and 17 for post installed anchor. Also the embedment is only 2.25" the uncracked assumption may be not good idea
'

 

[XR250]

I have another issue on this job. Need some bolts to be installed in 4" concrete on metal deck (4" total thickness on 1 1/2" composite deck).
The bolts will be installed 2 3/4" clear from the slab edge. Shear due to wind toward and away from the slab edge is my only load. Due to the close edge distance, the capacity of a 3/8" epoxy anchor is quite low (about 450 lbs ASD). Do you think I can take into account confinement in the concrete due to the slab edge angle? I realize this would be an engineering judgement, but any thoughts?

Thanks

 

[jayrod12]

Can you not just connect to the slab edge angle then?

 

[XR250]

It is a metal stud job. That conceivably could be an option to explore but unconventional.
Thanks

 

[jayrod12]

What kind of load are we talking here? Wouldn't tapcon (or Titen HD) screws at a reasonable spacing provide enough capacity and be significantly more economical?

 

[XR250]

about 700 - 1000lbs.
They go in a light gage clip at the window jambs.
I am using those in other locations but they have spacing issues in this situation. I may look into adding them.
FWIW, I talked to some former colleagues and they feel the edge angle will prevent a shear blowout

 

[jayrod12]

I agree that intuitively, it would prevent edge blowout. But always try to find an easier way to make sure of the calcs.

 

[XR250]

Thanks for your help, Jayrod and everyone else!