Appendix D: Anchor shear breakout
Appendix D: Anchor shear breakout
(OP)
The commentary for Section D.6.2.1 states that shear breakout will not control for anchors that are "far from the edge." I'm looking for guidance on how far an anchor should be from the edge in order to neglect shear breakout. For example, I'm calculating a shear breakout capacity of only 50 kips for an anchor in the middle of an 8'x8'x2'-thick footing. Judgement tells me this is rediculously conservative, but the numbers say otherwise. Has anyone else dealt with this?





RE: Appendix D: Anchor shear breakout
RE: Appendix D: Anchor shear breakout
RE: Appendix D: Anchor shear breakout
RE: Appendix D: Anchor shear breakout
Oops, you're right. I don't see a limiting distance in ACI or the PCA Notes on ACI318. Judging from the examples in PCA Notes, I believe that the research was done with small edge distances, less than 12 inches, and wouldn't apply to your case. Also, I should think you would engage the mat reinforcing, which would preclude Appendix D altogether.
RE: Appendix D: Anchor shear breakout
Here's an example that illustrates the problem I'm running into:
Code: ACI 318-05
Single 2"-dia anchor embedded 20", located at center of 8'x8'x2'-thick footing.
F'c = 3000 psi
Edge distance = 48" on all sides
Effective Ca1 = max(48"/1.5, 24"/1.5) = 32" (influenced by 3 edges, see D.6.2.4, changed from 318-02)
Running the numbers, I get:
Av = 2304 in^2
Avo = 4608 in^2
l/do = 8
Vb = 148.8 kips
TAOec,ed,c = 1.0
Vcbg = 74.4 kips
phi*Vn = 52.1 kips (phi = 0.7)
Here's the thing that gets me: If I increase the footing length in the direction of shear, I get the exact same answer, because my effective Ca1 is limited by the side edge distances. If my anchor is say 20 ft from the free edge in the direction of shear, I'm pretty sure it's not going to fail in breakout, even though the numbers say otherwise.
RE: Appendix D: Anchor shear breakout
RE: Appendix D: Anchor shear breakout
Generally for footings etc. jmiec his the nail on the head in that the breakout prism would cross the main footing reinforcing and therefore the shear breakout mechanism wouldn't really be valid - the strength of the main footing reinforcing in tension (provided it is properly developed on each side of the breakout prism line) would control.
RE: Appendix D: Anchor shear breakout
RE: Appendix D: Anchor shear breakout
RE: Appendix D: Anchor shear breakout
RE: Appendix D: Anchor shear breakout
RE: Appendix D: Anchor shear breakout
How do you account for the reinforcement like you mention in your post?
RE: Appendix D: Anchor shear breakout
RE: Appendix D: Anchor shear breakout
RE: Appendix D: Anchor shear breakout
RE: Appendix D: Anchor shear breakout
"For anchors exceeding the limitations of D.4.2.2, or for situations where geometric restrictions limit breakout capacity, or both, reinforcement oriented in the direction of load and proportioned to resist the total load within the breakout prism,and fully anchored on both sides of the breakout planes, may be provided instead of calculating breakout capacity.
RE: Appendix D: Anchor shear breakout
RE: Appendix D: Anchor shear breakout
RE: Appendix D: Anchor shear breakout
RE: Appendix D: Anchor shear breakout
However, I don't see anything in the code that would disallow using the bars to reinforce the breakout cone in the manner referred to (running 90deg thru the breakout prism). After all wouldn't that just be shear friction using the "monolithic" friction coefficient?
RE: Appendix D: Anchor shear breakout
RE: Appendix D: Anchor shear breakout
Anyway the bars won't be in pure shear. They will deform into an S bend and develop tension and bending; if they don't pull out themselves.
RE: Appendix D: Anchor shear breakout
The committee guy asked me to send him sketches with my questions. I haven't gotten around to it. That was a year and a half ago. Shame on me. Apparently there is one guy, yes 1 man, that is the expert on ACI Appendix D and could answer all of these questions. I didn't get his name from the committee guy. I have 75% of my sketches and questions done. If I ever get around to it, I'll post the answer I get.
Once again, kudos to the ACI committee members for not knowing what the #!@% is going on in their committe.
RE: Appendix D: Anchor shear breakout
RE: Appendix D: Anchor shear breakout