Concrete Anchorage - Side Face Blowout vs. Splitting

[azcats]

Are side face blowout and splitting related or discrete failure mechanisms in concrete? I've seen a few places (some threads here & the Widianto pedestal reinforcing document) that reference the minimum edge distances in 318-14 17.7 (or 318-05/11 D.8) of 6*da to preclude side face blowout. It seems that the two mechanisms are being co-mingled.

1. Does meeting the 6*d_a of 17.7.2 allow one to ignore side face blowout? I think not.

2. Here I'm not suggesting that they're using them interchangeably, but they do reference D8.2. Has anyone reviewed how this 6*d_o was determined in the Widianto document? Ultimately they say, "Therefore, for simplicity and to prevent the side-face blowout failure, the minimum edge distance of 6do is recommended." Where did they get the h_ef,min of 12*d_o used to arrive at the 4.8*d_o? I ran some numbers based on the Furche and Elignehausen paper and came up with 8.4*d_o based upon my materials.


[URL unfurl="true"]https://www.eng-tips.com/viewthread.cfm?qid=419128[/url] OP here.

[URL unfurl="true"]https://www.eng-tips.com/viewthread.cfm?qid=439104[/url] Last post here.

[URL unfurl="true"]https://www.sefindia.org/forum/files/design_of_anchor_reinforcement_a_petrolium_project_papers_199.pdf[/url]

 

[azcats]

So I've continued thinking on this and come to the following conclusions:

1. 17.7.2 is unrelated to side face blowout.

2. I disagree with using 6 anchor diameters to conclude that side face blowout needn't be considered.

The Widianto paper makes a couple big leaps in the paragraph below.

3. They conclude that: the side-face blowout failure is independent of the embedment depth when the embedment depth is deeper than 12". I don't believe the 12" is supported in the data and that it is instead a function of the materials, edge distance, anchor diameter and bearing area.

4. I believe the h_eff,min of 12 times anchor diameter is from the anchor bolt design for petrochemical facilities manual. I also believe it's mis-applied here while attempting to define some sort of minimum edge distance to preclude side face blowout. The data on which Chapter 17/Appendix D (for side face blowout) is based indicate that side face blowout controls over breakout when the ratio of edge distance to embedment is between 0.2 and 0.4. The inverse of 0.4 is where ACI arrives that their 2.5*c_a1 in 17.4.4.1.

5. The use of a minimum edge distance to eliminate side face blowout doesn't consider group effects which is a problem.

6. IMO, the logic is somewhat faulty for the premise. The code embed to edge distance ratio is based upon test data which indicates the line where breakout will control over blowout in unreinforced concrete. IE- Not close to and edge or not highly loaded enough to be very deep. In pedestals, concrete breakout generally doesn't work so we're reinforcing for it anyway. While this makes the embed deeper than would be required (to develop the rebar) for just the bolts, it doesn't mean blowout isn't a concern. I contend that the code ratio isn't even applicable where breakout is being restrained by reinforcing and that blowout should be checked regardless.

I started digging into this when designing a foundation for a telecom pole with highly loaded headed anchors on a drilled pier. Pullout strength is close and breakout isn't working. Relatively close together based on their diameter and the designer assumed plastic behavior for the anchors which in this code precludes blowout as the governing failure. But I'm looking at dozens of designs by others where this isn't even considered so I'm not sure if I'm doing something wrong or not.

Now I'm just babbling into the ether - thanks for listening.