Concrete breakout cone area for group?
Concrete breakout cone area for group?
(OP)
Is anyone here familiar with AISC's Base Plate and Anchor Rod Design 2nd Edition? On Page 36, the concrete breakout cone area for group is written as [3(13) + (4)(3)(13) + 4 ] = 1849 in2. How did they get they this number? Is it a typo?
Can anyone provide the concrete breakout cone area for group and use it in a example for a base plate with four anchor rods? Thanks in advance.
Can anyone provide the concrete breakout cone area for group and use it in a example for a base plate with four anchor rods? Thanks in advance.






RE: Concrete breakout cone area for group?
Yes, it is a typo - It should say "[3(13)+4]*[3(13)+4]=1849 in2"
RE: Concrete breakout cone area for group?
Can you elaborate some on how the equation was derived, and what do the "3" and "4" refer to? Does the "3" refer to the edge distance, and "4" to the distance between the rods, for instance. Please clarify.
I have referred to my ACI-318-05 book on Page 391, and the formula I am getting for a 4-rod group is: A NC = (ca1 + s1 + 1.5hef)(ca2 + s2 + 1.5hef).
RE: Concrete breakout cone area for group?
2*1.5hef + 4 = the length of one side of the square for the projected area. If you square that you will get the projected area.
ca1 on page 391 will be replaced by 1.5hef in the AISC design guide example because they state that edge distance is not an issue. That ca1 represents a situation where you have less than 1.5hef to the edge of the footing.
The equation was derived based on a concrete breakout cone of about 35 degrees (I believe). ACI also says in the commentary that the surface area of the breakout cone will very closely match the area of the projected square/rectangle given by the equation with 1.5hef.
RE: Concrete breakout cone area for group?
I understand in the e.g. provided by AISC, edge distance was not a problem. That was why ca1 on Page 391 was replaced by 1.5hef. Now, what if edge distance is an issue? What if my base plate was near the edge of my foundation? I guess I would need to input the exact value for ca1, then, right? What value of ca1 would I use? Most likely, my concrete breakout cone area will be smaller which means concrete pullout strength would be less. Hope you can comment and add something to this.
RE: Concrete breakout cone area for group?
Yes, this will reduce your concrete breakout strength, but this may not be the controlling factor.
Also, be sure to note that if you are considering a column with a base moment, only use the (2) anchors that will be in tension, not all (4). Only use all (4) if there is a tensile reaction at the column base.
RE: Concrete breakout cone area for group?
My columns currently do not have a base moment,because they were designed not to take any moment, but will keep your comments in mind if I have any columns with base moments. BTW, how would I know, or how do I ensure that, "there is a tensile reaction at the column base"?
RE: Concrete breakout cone area for group?
If you don't have any shear in the column, then you won't need to consider shear breakout of the rods in the concrete, but if you do you will. It seems like you have covered the other criteria.
RE: Concrete breakout cone area for group?
I do have some shear at some columns, at the vertical bracing locations, but I am designing shear lugs to take care of those.
I hope I don't ruffle any feathers, but if I have six, or more bolts - instead of just four - do you know what I need to change in the ACI 318-02 formulas, or in the AISC example, to suit that condition?
RE: Concrete breakout cone area for group?
I doubt the (2) rods in the middle of the baseplate will add much (if anything) to the tensile breakout, but if you need it for the actual steel capacity, then you do.
RE: Concrete breakout cone area for group?
RE: Concrete breakout cone area for group?
RE: Concrete breakout cone area for group?
(ca1+s1+1.5hef)(ca2+s2+s3+1.5 hef), or (ca1+s1+s2+1.5 hef)(ca2+s3+1.5 hef). Is that right?
The concrete breakout cone area for a single anchor would remain unchanged as the 4-group.
BTW, what is a "sware"?
RE: Concrete breakout cone area for group?
You are correct. "sware" was meant to be "square", sorry for the typo.