Extend Footer To Accommodate Anchor Bolt Edge Distance 4

[TVM90]

So things didn't go as planned on this project. Somehow the location of a large concrete footer was set incorrectly. Instead of moving the footer or re-pouring it the contractor and steel erector opted to cut the anchor bolts and epoxy in new ones. The columns eccentricity on the footer is 7" in the x direction and 5" in the y direction.

The problem I am running into is the anchor bolts that were epoxied in are coming up short on tension capacity. The reason they are insufficient is because I only have a 6" edge distance for a 1" dia threaded rod. Has anyone ever extended a footer to increase an anchor bolt edge distance? I was thinking that we could extend the footer by 12" with some Quikrete bonding adhesive and pinned reinforcing. I don't need to extend the footer for bearing capacity. The extension would be purely to increase my anchor bolt edge distance.

 

[thaidavid40]

Is your problem rupture strength at the side of the footing pedestal, and you have no rebar confinement along that edge? If that is your problem, then you are probably better off cost-wise to simply reinforce that edge. You can take a steel channel (or whatever) and anchor it to the side of the pedestal with epoxy anchor bolts, and it will provide external confinement and support for the free concrete edge.
Dave

Thaidavid

 

[KootK]

I'm down with external confinement in concept but it tends to fall apart in execution. How stiff and strong does the channel need to be to effectively confine? How tightly spaced does its fasteners need to be? Will the resulting arrangement get you back to something that sufficiently replicates the scenarios tested in the development of App D? Theses are tough questions to answer reliably. At least for me they are.

Just how big is this large footing?

Any chance you could design an eccentric base connection for which new post installed anchors would have sufficient edge distances?

Of the non-repour options available, extending the concrete is probably a good choice. Remember though, once you extend the footing, some of the bolt tension will then live out in that extension. That may mean that the extension will need to be anchored to bring that force back to the main body of the footing.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

If you go with external confinement, there may be something of value here: Link. For a rod with an anchored end, it suggests that lateral confinement to the tune of 1/4 the tensile capacity of the rod may be appropriate, installed close to the rod. I'd think that, for an un-headed rod, the demand would be less localized.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jike]

How about drilling and epoxying a horizontal U shaped bar centered on the anchor bolt? You will have to chip out a little concrete on the side of the footing and patch it back after the bar is installed.

This should help the breakout strength. Much simpler than adding concrete.

 

[Ron]

Whatever remedial method you choose, unless it has been tested by the anchor manufacturer, will not have quantitative approval, so you need to check with your code official for concurrence. Further, YOU will accept the liability for the fix and won't be able to point to the anchor manufacturer or anyone else....not even the "offending" contractor who screwed up the footing (not "footer"!!....pet peeve).

 

[KootK]

If your column is at the edge of a large footing and you've got large bolt tensions, is it correct to assume that this is an important moment connection between column and footing?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[hokie66]

If the contractor is not capable of locating a footing correctly, what makes you think he is capable of installing glued in anchors? Or extending an existing footing? Based on the limited information you have provided, I would want the footing recast. That would hopefully assure that it is done properly, and take the burden off you.

 

[TVM90]

Thanks for all of the responses.

The footing is 4'-0" x 8'-6" x 24" thick. I've been using Hilti's design tables so I am not sure what is controlling the design. My suspicion is concrete breakout capacity is insufficient due to the limited edge distance. I don't think the breakout cone is large enough with the limited edge distance. I'm going to run the calcs by hand later today to find out what's controlling. An eccentric base plate is a good idea however everything is installed already so the original anchor bolts have been cut.

It is an important moment connection. I think total replacement of the existing footing may be the way to go.

 

[Ron]

TVM90....adhesive anchors don't usually fail with a cone failure. Check your data. Also, agree with hokie66....not reasonable to assume your contractor could do a proper repair since he couldn't do the initial construction properly.