Base plate over misaligned anchor bolts
Base plate over misaligned anchor bolts
(OP)
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
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






RE: Base plate over misaligned anchor bolts
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.
RE: Base plate over misaligned anchor bolts
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.
RE: Base plate over misaligned anchor bolts
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).
RE: Base plate over misaligned anchor bolts
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.
RE: Base plate over misaligned anchor bolts
RE: Base plate over misaligned anchor bolts
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.
RE: Base plate over misaligned anchor bolts
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
RE: Base plate over misaligned anchor bolts
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.
RE: Base plate over misaligned anchor bolts
_____________________________________
I have been called "A storehouse of worthless information" many times.