Base plate over misaligned anchor bolts 1

[mehr27]

I have a set of anchor bolts that are not properly aligned at the top of a column. 8 - 1" x 3'-0" A307 bolts with triple nuts were used and almost all of them are out of plumb. There's no way to fit the base plate over the bolts. The column stands alone so there is plenty of room to maneuver.

I'm curious if there are any out of plumb tolerances for anchor bolts and what some remedial fixes might be. Many previous threads have address cutting, welding, and/or adding an additional plate. The anchor bolts are projecting 6 inches and the base plate is 1 1/4" thick with 2 inches of grout under the plate.

Thanks,
Glenn

 

[astructurale]

Can you enlarge the holes in the plate to fit it over the bolts and then weld smaller square/rectangular plates over each area to correct for the oversized holes? That might work if you have room and if the bolts are not at too severe an angle that the washer & nut does not bear on the plate fully.

Or assuming this is a steel column on a cip/precast column you could cut the bolts off flush, then epoxy a plate with DBA's on it into the column and weld the column directly to the plate. You'll need to be carefully when welding to keep as much welding as possible from heating the epoxy and you may want to go deeper than the standard embedment to offset it. If you field drill the holes and then attach the DBA (or re-bar if you want) to the plate you'll have a more fool proof fix.

I don't know of any plumb tolerances for bolts, but that does not mean they do not exist.
There are a lot of possible solutions depending on what you exact field conditions are.

 

[elpoblano]

Is the column erected already? Are the a. bolts at top of the column's foundation? Is this a concrete foundation?

Assuming that it is and that is larger than the base plate, you could calculate the pull-out resistance of the existing a. bolts and determine if they can be susbstituted with chemical anchor bolts (threaded rod and chemical cartridges). If it is possible, cut the existg. a. bolts flush with the concrete top surface. Redrill the base plate in the new a. bolts location, using a steel pl. template core drill them (to prevent damage to the foundation) let them set and you are ready to install your column.

To help you better, what is the spacing between bolts? What is the a. bolt pattern, square or circular? Is the grout cementitious or epoxy?

Do you know if the existing a. bolts have plastic sleeves?, they could be filled with grout. If they do your problem is practically solved, unless the grout is epoxy.

 

[mehr27]

Good suggestions and thanks. To be clearer, I have a rectangular concrete column already built and anchor bolts set at the top. The bolt pattern is square with spacing of 10 inches in one direction and 5 inches in the other direction. The bolts do not have plastic sleeves. A steel post/column will be anchored to the top of the concrete column and is not in place. The grout under the base plate will be cementitious.

astructurale, the base plate holes could be enlarged but the bolt angles are pretty severe and I am afraid of not achieving bearing with the washer and nut.

I’m waiting for the contractor to suggest bending the bars back in place but would definitely like to stay away from that. Sounds like my existing anchor bolts aren’t going to work out and I’m looking at a new connection, either adding new anchor bolts or an extra plate.

I did find some tolerances in the 1998 AISC LRFD manual, Volume 1, page 6-438. My bolts are well beyond the tolerance of 7.5.1.(a).

 

[transmissiontowers]

How about heating the A307 bolts up and bending them until straight, then do a proof load test to the rated strength of the bolt and see if the repair damaged the bolt due to cracking. It's been a long time since I thought about metallurgy, so excuse my ignorance if heating the A307 is a terrible idea.

Also, can you break out the bolts and repour the foundation with straight bolts? It sounds like the contractor did not use a template at the bottom of the bolts to hold them in place and the concrete pour moved them.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[astructurale]

mehr27 - thanks for posting that page number. I might need that someday. I'm marking my book for future reference.

 

[mehr27]

Perhaps heating and bending the bolts might work. I am concerned about cracking though and perhaps the test could check. Thanks for the ideas.

To go a step past cutting the bolts flush, I'm thinking of recommending the top portion of the column be removed six inches beyond the depth of the bolts (about 3'-6" total), then recast with fresh bolts. An easy fix from my end but I can understand the headaches that would cause. Ultimately we're leaving it up to the contractor and we'll review their fix.

Glad to return the favor, astructurale.

 

[14159]

You should download the updated AISC Design Guide 7 that's free at

http://www.aisc.org.

The authors have an updated section on fixing anchor rod problems.

One recommendation that I've heard a lot lately is to explicitely use the tolerances given in the AISC Code of Standard Practice instead of the ridiculous ones in the ACI (forgot the number -- 117?) document. Many engineers make the mistake of using the ACI document which allows a full inch of misalignment!

DBD

 

[elpoblano]

mehr27

Another proven solution (have done it many times with corroded or off-plumb anchor bolts) is, to completely cut off the existing a.bolts leaving enough projection to weld a new (and plumbed) section of the same type of rod. The welding shall be complete penetration groove weld and sized to take the same stresses than the original a. bolt.

There used to be a standard for welding rebar, but I can't find it. It was an old one, so anybody knows what is the new standard?

Ensure that your new a. bolts are plumb and will not deviate from it due to welding residual stresses. You can tread your new a. bolts after cooling. Install your column, plumb it and place your grout.

It sounds like a lot of work, it is not, and it is probably the cheapest solution too.

 

[transmissiontowers]

If the A307 bolts are weldable, then chip back down below top of concrete and weld on a new bolt top as elpoblano suggested, or if not weldable use the Cadweld technique to splice on a new thread. In either case do a proof load on each repaired bolt. We usually take a large sledge hammer to our 2.25 dia A615 bolts and persuade them back into place, but if our pole fails, people's electricity blinks off for a while.

_____________________________________
I have been called "A storehouse of worthless information" many times.