Base Plate no grout - method of failure

[WBUW]

Hi all,

Realize this has been discussed before, I reviewed the threads and can't seem to find a clear answer to this question.

In the case where one has a base plate supported by anchor bolts and leveling nuts lets say the assembly is sitting on an 18" thick footing. Anchor bolts are embedded, lets say 12" into the foundation. Smooth shank A307 bolts with 2 heavy hex. No grout is used.

The contractor is told to crank the leveling nuts to the top of foundation but cannot do so keeping everything level.

When under lateral load there is about 8 kips of compressive force on half the anchor group. Below the footing is a well compacted base.

Looking at the anchor bolts (smooth shank) it doesn't seem like there is going to be much of a bond between the bolt and the concrete. It seems like the axial force will make its way through the bolt shaft and into the head.

How does one get a handle on how much force the anchor bolt can take before it cracks the 6" of foundation left below the head of the bolt?

 

[engineertipsman]

I would think that you could do a concrete break out cone, just in reverse, use the same principles.

 

[bjcure]

I worked on a two story office building a number of years ago and the contractor poured the concrete (over steel deck) on the second floor before grouting under the column base plates. During the pour, the entire floor suddenly dropped about 1 to 1 1/2". The baseplate on one of the columns was sitting directly on the footing and had slightly shifted from where it was supposed to be; the four bolts had all buckled in the same direction.

Anyway, the break-out cone approach sounds reasonable to me.

 

[WBUW]

Agree, I think thats a reasonable conservative way to approach the situation. Thanks for the tip. Won't have much capacity that way but I can't think of a better way to approach it.

Leads me to wonder if it'd be possible to use some #6 bar, thread the top few inches and see if it can be developed so its not as dependant on bearing...seems to be hard to get reasonable size bar threaded at first glance though.