ACI-Appendix D Fig. RD.6.2.1.(b) 2

[0444]

I have had hard time to get the a proper bolt edge distance to satisfy the Ca1 for concrete break out strength of (two rows) anchors in shear. RD.6.2.2 has two deferent notes and assumptions of the distribution of forces. The first one is not necessary the bolt be welded to plate but the second note says, Only this assumption needs to be considered when anchors are rigidly connected to the attachment. The Question is both notes must be satisfy? Or if one assumption is o.k.to be satisfied.

 

[JAE]

The top note and detail is for the case where the bolts are NOT welded to the plate but work independently, each taking half of the load.

The bottom note and detail is for the case where the bolts are welded to the plate. In this case, the assumption is that the leading bolt would fail early (having a small ca1) and then the rear bolt, or rear row of bolts, would take 100% of the shear with a larger ca1 value.

 

[0444]

JAE,
But the issue is only first assumption is satisfy in my case not bottom one, the question is if one assumption satisfaction is o.k
Thank you so much.

 

[JAE]

Is your plate welded to the anchor bolts?

 

[0444]

no, Contractor doesn’t like that. I think I would stay by first assumption.
thanks.

 

[Lion06]

If your anchors are welded to the plate, you have to check the second assumption (with the back row of anchors taking the whole load).

If the anchors are not welded to the plate, you need to check both conditions (the leading row of anchors taking their share of the load (1/2 for two rows, 1/4 for 4 rows), AND with the back row taking all of the load. You have to use the lower of the two.

 

[JAE]

For non-welded situations, wouldn't the first assumption always control? i.e. with a very low ca1?

 

[Lion06]

Not always. The magnitude of the breakout value from the equations will almost always be lower, but if you have 3 rows of anchors you should be multiplying that breakout value for the leading row by 3 to get the total group capacity (since that row is only taking 1/3 of the load).

It can work out sometimes that he leading row (as a single row) gives greater capacity than the back row (as a group) if the side edge distances start getting small and the breakout is affected by 3 or more sides. The equations start doing funny things and giving un-intuitive results in some circumstances. ACI 318-08 partially addressed some of the issues, but not all.