Pull out Strength of Anchor in Tension (ACI D.5.3) 2

[movasra]

Hi everybody,
I am woking on my spread sheet for group anchor bolts design and now I am just looking for equation D-14 but for group anchors. does anybody know if this section applies to group anchors at all. why everything in section D.5.3 is about single bolts. Can I simply multiply the equation by number of bolts?

 

[JAE]

Yes you can multiply the single anchor check by the number of bolts but I don't think it ever controls since the group load spread uniformly over all the anchors would mean a lessened load per anchor.

The critical conditions are:
1. The actual single anchor load (taking into account eccentricity of applied loads, etc.) vs. the single anchor capacity.

2. The actual group loading vs. the group capacity (some of the group capacities have eccentricity of load in the capacity equation).

 

[Lion06]

You can multiply by the number of anchors to get a total capacity, but the one caveat I would add with that is to account eccentricity. While you will get increased capacity (obviously) by using more than one anchor it is an individual anchor failure mechanism, unlike the concrete breakout. A group of anchors will break out as a group (not as single anchors, unless you have large spacings) and the eccentricity is accounted for explicitly in the equation. For pull-out, if a single anchor fails the connection has failed. If there is no eccentricity then they'll all fail at the same time and the point is moot, but if there is eccentricity then they won't all fail at the same time (in pull-out) and you have to account for it.