Grout repair and anchor bolt torque 1

[ahmadsalah]

Hello,

We are working on a project that was installed about a year ago. Column base plates are on shims and torqued, then afterwards the contractor did all grouting but did not follow correct procedure and all grout started to crack.

We are supposed to repair all grout for about 100 columns and we will need to remove all old grout, clean and start fresh, my question is should we release the anchor bolt torque say 20% before removing the old grout and then re-torque after pouring and curing the new grout? each base plate has 3/4 SS epoxy anchors.

Thanks

 

[dik]

Can you not loosen the anchor rods completely, each second one, staggered and then remove and replace the grout for the ones loosened?

Dik

 

[r13]

Do as dik suggested, one column at a time, or staggered. Check the plumb before operation, looks like you will have to jack up the column in the picture due to settlement.

 

[JLNJ]

Most base plate anchor rods are not required to be "torqued". Maybe it's much ado about nothing.

 

[dik]

from Iowa DOT:

Dik

 

[HTURKAK]

I understand column base plates leveled using shims and the anchor nuts tightened then afterwards the contractor did all grouting. In this case, essentially the grout is not loaded.

You did not describe the structure . The picture implies steel column base for a building type structure.
I will suggest you to repair the cracks with injectable epoxy repair compound.

 

[dik]

As the column is loaded beyond the installation, the grout will take some load. Epoxy injection, if possible or suitable is an excellent repair.

Dik

 

[ahmadsalah]

Thank you all for your replies. The structure is a pipe rack. The grout is poured in a wrong form that they didn't leave perimeter around the base plate and it is cracking from several locations each column, so we will end up jack hammering and removing the grout, the problem now is the procedure to do that without ruining the whole thing.

The structure is loaded below it's capacity for the time being. But still the problem of sequence, should we follow this sequence?
- un-torque anchors
- jack column
- remove grout
- re level base plate
- inject new grout
- torque anchors

 

[ldeem]

Why not knock out the loose pieces of grout and see what you have. I assume no columns have failed in the sense the grout pad has been crushed. If this is true knock out loose material then depending on what you have re-grout using something thin (like machine base epoxy) or crack injection as others have commented.

Loosening AB's, jacking columns, etc seems like a lot of work and potential to cause other issues like column plumb, frame squareness etc.

 

[STrctPono]

ahmadsalah,

One thing to note is that torquing post-installed adhesive anchors is not the same as torquing a cast-in place bolt. Each adhesive manufacturer gives very specific torque requirements based on their resin. My understanding is that they are quite a bit lower than the torque you would be in for a cast-in place bolt. I believe that dik provided a table for CIP anchor bolts so that would not be applicable to your project.

 

[dik]

correct...

Dik

 

[r13]

I suspect the shim is still there, which may have contributed to the crack of grout.

 

[JLNJ]

The whole process of “torquing” anchor rods yields unpredictable results. As such, don’t pretension bolts unless it’s really needed.

I would look into whether or not it’s necessary for this application. I’m guessing it’s not.

If it were a tall vessel or a special pieces of machinery, I’d be more careful. This looks like a normal column with simple anchorage.

If it were me, I’d look into just leaving it as is. That little crack doesn’t seem too bothersome.