ACI318-05, Appendix D: 3 edge influenced 1

[fbmok]

RD6.2.4 indicates that a group of anchor is influenced by 3 or more edges where any edge distance is less than 1.5*Ca1. My question is, when both Ca1 and Ca2 are huge, say Ca1 is 20 times of hef, however Ca2 in bothe sides are 10 times of hef, shall we strictly call this case as 3 edges influenced just because Ca2 <= 1.5*Ca1?

 

[Lion06]

I have to read the commentary there, but I don't think that's right.

 

[Lion06]

I'm sorry, I misread your post. Yes, you're correct. You do have to take the reduction (assuming that ha<1.5ca1, too. ACI318-08 has a new modification factor for this however, to account for just this situation, because the '05 equations give ridiculously small values.

 

[fbmok]

Thanks structuralEIT. What did ACI318-08 say? Sorry I don't have the copy. Thanks.

 

[Lion06]

It says the same as '05. After reading the commentary that you pointed out more closely, it does read a little funny. I think "any" should have been "every".

The '08 codes gives a new factor, which is ha<1.5ca1, of (1.5ca1/ha)^.5
This will give you a very good bump if ca1 is large and ha is small.

 

[fbmok]

Thanks a lot StructuralEIT. That means 3 edges only applies to the very small Ca1(corner or edge cases), where Ca1 is less than ha/1.5.

In the majority cases when the group of anchor is placed in the middle of slab, Ca1 is much larger than ha(say infinite), the capacity will increase a lot by the factor (1.5ca1/ha)^.5, so the concrete breakout failure is not a concern anymore even if Ca2 is very small?

 

[Lion06]

If ca2 is very small then you need to consider the shear force parallel to the slab edge. You just calc the capacity as though the shear force were perpendicular (ca2 becomes ca1 for calculation purposes) and double it.

The three edge typically applies for large ca1 values, not small ca1 values. When ca1 is very small, ca2 and ha are likely to be >1.5ca1. It's when ca1 gets to be larger that this is an issue.

 

[fbmok]

Thanks again for your input StructuralEIT. it applies for large Ca1, or else Ca2 or ha will be larger than 1.5Ca1, which is not the case.

Double the perpendicular case from D6.2.1(c) is quite good another way to get the value of parallel case. Which means basically we can get 2 sets of value, one is for 3 edge with Ca1, the other is for double of capacity of Ca2 becoming Ca1? Shall we use the smaller value? Thanks.