Question on ACI App D

[Lion06]

Page 369, Fig RD.6.2.1(b) has a note which says, "Note: Another assumption of the distribution of forces indicates that the total shear would be critical on the rear anchor and its projected area. Only this assumption needs to be considered when anchors are rigidly connected to the attachment."

The attachment is the embed/brg/base plate, correct?
Also, while it makes sense to me that this is realistic for the concrete failure area, it seems like this note is saying that the entire shear needs to be considered to act on the farthest anchor for the steel check as well. That doesn't make sense to me.

I can see that failure mode being checked for the concrete, but as far as the steel goes, I disagree and here is why. Even if you assume this embed plate is end loaded such that the first few anchors take the majority of the load, as the anchors yield the load will redistribute and at failure the load will be equally (or pretty darn close to it) shared. This is not unlike shear connectors for composite beams not being required where the shear is highest.

Does anyone have any comments? Am I way off base?

 

[ssweetland]

As I understand it, this figure is used in determining the term "Avc". "Avc" is only used in determining concrete strength. The strength of the steel anchors will be determine seperately and unrelated to "Avc".

So, if you have a group of anchors, say 2 x 2 pattern connected by a plate, you would use the anchors furthest from the edge to determine "Avc". When determining the shear strength of the steel anchors you would use all 4 anchors.

 

[COEngineeer]

It is just saying if it is not rigid, lets say you have 4 anchor bolts. Your holes are bigger than the bolts. So the worst condition is if the bolts closest to the edge is touching the steel plate and take all of the shear. If you have embed, that assumption is not valid anymore (too conservative).

Never, but never question engineer's judgement