Concrete Breakout strength on an anchor in tension
Concrete Breakout strength on an anchor in tension
(OP)
The goal is to calculate the breakout strength of two embedded studs. This is applying to a plate embedded to a concrete wall with two studs attached anchoring horizontally into the concrete wall. This is to support a stairwell landing.
1.) I want to confirm the correct equaction to use, which I believe is Ncbg from D.5.2.1 in ACI 318-05.
2.) Within that equation is a Nb value, here I'm not sure what equation to use to calculate Nb. I see the conc. breakout strength for a single anchor in tension which is not my case. I also see Nb for cast-in headed studs and headed bolts with Hef between 11 and 25. I am using cast in studs however my Hef is not between 11 and 25, the embedment is only 4". Any ideas?
1.) I want to confirm the correct equaction to use, which I believe is Ncbg from D.5.2.1 in ACI 318-05.
2.) Within that equation is a Nb value, here I'm not sure what equation to use to calculate Nb. I see the conc. breakout strength for a single anchor in tension which is not my case. I also see Nb for cast-in headed studs and headed bolts with Hef between 11 and 25. I am using cast in studs however my Hef is not between 11 and 25, the embedment is only 4". Any ideas?






RE: Concrete Breakout strength on an anchor in tension
RE: Concrete Breakout strength on an anchor in tension
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Concrete Breakout strength on an anchor in tension
The Nelson "method" was never codified and was only used in the absense of a method provided by the UBC or IBC.
RE: Concrete Breakout strength on an anchor in tension
Can you post a sketch?
RE: Concrete Breakout strength on an anchor in tension
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Concrete Breakout strength on an anchor in tension
RE: Concrete Breakout strength on an anchor in tension
RE: Concrete Breakout strength on an anchor in tension
You shouldn't need to worry about shear breakout, but you'll still need to look at pryout and the shear strength of the steel.
RE: Concrete Breakout strength on an anchor in tension
RE: Concrete Breakout strength on an anchor in tension
RE: Concrete Breakout strength on an anchor in tension
Also, I agree that a moment will be produced putting the top stud in tension and bottom stud in compression(correct me if I'm wrong).Not sure how to calculate what exactly that moment would be in a continuous joint stair system.
Besides that, I plan to calculate the weld strength between the angle and the channel along with the weld strength between the channel and the plate.
StructuralEIT you also mentioned pryout. By this you mean the pryout strenght of the plate alone due to the tension at the top? Is this found in Appendix D also.
Thanks for the help.
RE: Concrete Breakout strength on an anchor in tension
You don't need to check the weld from the studs to the plate, these welds develop the stud so you only need to check the stud.
Pryout is a shear failure mechanism of headed studs embedded in concrete. It is in App. D (D6.3 in ACI 318-05), but as Ron notes, it likely will not be an issue. My guess is that the load would be less than (or pretty close to ) 20% of the capacity which allows you to ignore it for interaction purposes.
RE: Concrete Breakout strength on an anchor in tension
RE: Concrete Breakout strength on an anchor in tension
RE: Concrete Breakout strength on an anchor in tension
Since you said your embedment is only 4" I would check the concrete breakout strength of the stud in tension. Of course also check the pullout strength.
RE: Concrete Breakout strength on an anchor in tension
RE: Concrete Breakout strength on an anchor in tension
I haven't run through the numbers, because I don't have my ACI 318 in front of me, but the value seems unreasonably high. When I've gone through the calcs for this type of situation (admittedly, I've never done it for am 18" thick wall), the values are usually unreasonably low for a very large edge distance with a relatively thin member. The reason is that Avc/Avco gets extremely small very quickly.
For your case, I would look at the interaction of tension/shear using the worst case of Tension (for the steel strength, pull out, and concrete breakout (the concrete breakout will likely control)) and Shear (the steel strength and pryout).
RE: Concrete Breakout strength on an anchor in tension