Appendix D - Concrete Breakout in Shear

[Scud42]

Has anyone come up with a definitive answer for the concrete breakout in shear edge distance issue?

I am trying to write a program for concrete embed capacities and I am getting what I believe to be unreasonable results with the concrete breakout when the edge distance is large. I have found a number of old threads were other engineers have run into similar issues but none of the ones I read gave an answer to the problem.

I saw one thread were a comment was made to ignore the breakout if the "c distance is greater than 60*d." Where d is the anchor diameter. Does anyone know of a publication that identifies this guideline and if so does it consider the "c" distance the length from the edge to the closest stud or the furthest? Initially I assumed the furthest but that would not make sense for larger plates. For example, if I have a 36" plate with 1/2" studs and the plate is set at the edge of the concrete so that the furthest studs are 34" away.

I do not have the latest ACI 318-14 edition so I'm not sure if this was resolved/changed in that.

Thank you in advance for any comments.

 

[JedClampett]

When you say unreasonable, do you mean unreasonably high or low?

 

[dcarr82775]

You have to use your judgement. If you look at the shear breakout surface starting at the surface and extending outwards and downwards you need to get to an edge for that breakout to occur. If there is no edge, that mode goes away and you end up with prying being the limiting concrete 'shear' failure mode.

 

[Scud42]

JedClampett - Unreasonably low so that the concrete breakout seems to control in situations where I would assume the steel or pryout would.

dcarr82775 - Engineering judgement is what I was interpreting too. I am just surprised that there have not been guidelines set up for the engineers that do not do this on a daily basis and my not have a good "feel" on when it would control. From what I can tell this method has been the standard since around 2008 and I was hoping someone smarter than I came up with something.

Have you reviewed the new ACI 318-14 in regards to this topic? Is it still open ended or are the parameters more defined? Form what I've read, the new code reorganized information and "clarified" a few topics but most of the methods stayed the same. I'm wondering if this is a topic they "clarified."

 

[KootK]

When they finally got around to doing some full scale tests on shear loaded base plates, the results were predicted quite well by AppD CCD methodology (Link).

AppD remains largely unchanged for two reasons. First, it represents the state of the art in our understanding of anchorage mechanism. Second, it has the most predictive value of any method available, even if the results are frustrating to practitioners.

As for ways around shear breakout, Widianto's strut and tie method is the best that I know of for large scale stuff (Link). Unfortunately it's pretty labour intensive for a routine production tool.

I agree that edge distance for long embed plates should be based on the studs closest to the loaded edge. Axial strain in the plate will lead to the front studs taking the most load.

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.