ACI Appendix D Clarification of section D.6.2.1

[JrStructuralUCSD]

Hello all,

This is my first time posting on eng-tips...this site has been a good source of information for me in times of need so thank you all who have contributed to my education as I begin my path as a professional SE.

I do need some clarification with appendix D of ACI 2011 (or 2008). It seems like this section of ACI is very unclear and impractical to many fellow engineers. Within section D.6.2.1 Concrete breakout strength of anchor in shear, there is a very confusing statement within the code that follows:

"Where anchors are located at varying distances from the edge and the anchors are welded to the attachment so as to distribute the force to all anchors, it shall be permitted to evaluate the strength based on the distance to the farthest row of anchors from the edge. In this case, it shall be permitted to use the value of ca1 on the distance from the edge to the axis of the farthest row that is selected as critical, and all of the shear shall be assumed to be carried by this critical anchor row alone."

So, in order to base the ca1 value from the farthest distance of anchor to edge of concrete, welding of the anchors needs to take place and the welds must be capable of transferring the shear force that is acting on the anchors accordingly amongst all the anchors. My first question is rather a statement clarification, the value of ca1 is only allowed to be the farthest distance from anchor to edge of concrete only of welding within the anchors transfer the force accordingly. Is this statement correct? This is more of a sanity check than anything!


Another question I do have is probably something that a Senior Engineer may laugh at. Please forgive me as I am new to this business, but from what I understood in my steel class welding of nuts is not permitted as this will hurt the integrity of the nut and cause a brittle failure. The proposed idea to fix our entire problem is to allow section D.6.2.1 to come into play and hence increase the projected concrete failure area which will therefore increase the capacity of the shear reinforcement for the anchors. By welding the nuts to the washers and the washers to the base plates we must use the right material (I think) in order to not hurt any nuts or washers by the heating process of welds. My question is, what nuts can be welding in order to apply section D.6.2.1 from ACI?

Any help would be greatly appreciated it. I thank you all once again for the valuable information in all these posts that I scour on a daily basis.

 

[JedClampett]

The code allows anchorages where the anchors act as a unit with the plate to be designed for shear using the farthest anchors from the edge. You're not insane.
As for the second part of the question, I don't think welding nuts to washers and washers to the base plate meets the intent of this section. It's meant for stud welding to plates. Besides your point regarding the brittleness of the material (which can be changed by using mild steel nuts and washers), the stiffness of those welds don't allow for the anchorage to act as a unit.

 

[JrStructuralUCSD]

Thank you very much Jed for your insightful response. You nailed my assumption spot on with the anchors acting as a unit, because this is how my system is acting like.

I do have a follow up question regarding your second answer. Like I said before, I am new to this game and I am not quite sure about welds in general. You said that "its meant for stud welding to plates". What exactly is this process? What is stud welding? I have googled this and came to a few different sites that do not paint a clear picture. Does stud welding require a certain type of material? Do you reccommend any manufactures that have the material needed for stud welding? Is stud welding permitted for my case, meaning where in any code does it talk about stud welding? You have already been a champion for your first response back and I am very grateful for that insightful response, if you can (or any one else here!) answer my follow up questions I would be greatly appreciative.



Thanks

 

[wannabeSE]

A stud welding gun is used to weld the studs. It is a quick process that takes only seconds to weld. Nelson Stud and Tru-Weld are two manufactures of the studs and welding equipment. Stud Welding is covered in AWS D1.1, Structural Welding Code - Steel. Sliderule Era's site has the Nelson Stud Design Manual from 1977 with some useful information

http://www.slideruleera.net/contributions.html