This is a common problem, and one that can be very difficult to remedy once the concrete is cured. As with most job-site fixes, the repair method depends on the nature of the problem and when in the construction process it is first noted. The repair method may be different if one bolt is out of place or if the entire anchor pattern has been misaligned. If the error is discovered before the column base plate has been fabricated, it might be possible to use a different pattern or even a different base plate.
If one or more rods in a pattern are out of alignment after the column has been fabricated, the easiest and most common repair is to slot the base plate, and use a plate washer to span the slot. If the entire bolt pattern is off uniformly, it might be possible to cut the base plate off and offset it on the column to accommodate the out of place bolts.
If the anchor rod or rods are more than a few inches out of position, the best solution may be to cut off the existing rods and install new drilled-in epoxy-type anchor rods. When using such rods, carefully follow the epoxy manufacturer’s installation recommendations, and provide inspection as required in the applicable building code. Take care to locate the holes to avoid any reinforcing steel in the concrete foundation. If any reinforcing steel is cut, a check of the effect on foundation strength should be made.
More detailed information can be found in section 2.11.1 of AISC Design Guide 1. It is also recommended that your project engineer should be consulted before any of these repairs are undertaken to make sure the best method for the specific application is chosen.
Dear Mr Dane, thanks for providing such information on this ” delicate” subject of anchor bolts misalignement! I have slightly different question, but still close to the subject! I have casted the concrete with the anchor bolts in place, I am worried that during concrete casting, the baseplates group in one line of a wall, might have moved and they are not in a perfect straight line, which may result in beam to column connection issue ( zigzag line rather than straight line between the baseplates groups if you can imagine!). I am talking about a maximum of 1 inch misalignement. Be advised that the H beams have been cut into sizes, so it’s the matter of errection schedule, where we might then discover that there is a problem! Thanks
@Nasser- I am not sure what your question is, but that does sound like a potential problem. Perhaps a tackweld or other device could be added to keep all the items in line.
Box columns for two story residence were installed on reinforced concrete plinths without any column anchor bolts. What kinds of remedies are appropriate for this situation?
@Hector- Because we do not have any engineers on staff, we cannot make any specific recommendations for your application. However, there are options like drilling and setting epoxy anchors, or wedge anchors that may be helpful. You would need to consult with the project engineer to evaluate the pros and cons of those types of options.
Hi Dane,
First of all, always good to cross paths with one of the clan! I am a MacKinnon from Lochaber in Scotland.
The query is regarding several sets of cast in bolts out that are slightly out of alignment, some 60mm some 25mm. The contractor wanted to use slotted holes I the baseplate to rectify, but this has been knocked back, so the proposal is to cut the cast in bolts and grout them in. We will then position the baseplate in the correct position and fix using resin anchors.
My concern is that the pilot hole for the resin anchors may be clipping the grout used to encase the cast in bolts, is this acceptable?
@Andrew- I read through the section of AISC Design Guide 1 that discusses foundation repair, and I did not see anything that addresses drilling into or close to the grout pocket, so I can’t really make any recommendations. Apologies.
HI
The anchor bolts are not properly fitting to base plate due to execution error. i am willing to cut my base plate bu using gas welding and keep set right of base plate. Is this method preferrable o? can you please suggest any other cutting method.
@Sai- I believe cutting the base plate either mechanically or with gas is acceptable but you should consult with the project engineer to make certain it will be acceptable in your application.
dear Mr. Dane,
very nice explanation while considering all issues
suppose we plan to replace one anchor bolt or more by make a concrete core around then put new anchor bolt and grouting
if during core cut some reinforced steel bars of foundation, what is suitable solution to repair? is epoxy grouting can help for this issue ? or other type of grouting?
@Emad- Apologies, but I am not sure how to repair cut rebar. You may need to contact an engineer with experience with that problem.