Carbon Steel plates fixed on concrete columns with chemical anchor bolt

[lganga]

I have some concern about this type of design. There are many misssing plates in the concrete pipe rack,the constructor wants to add plates, fixed with Hilti bolts, the original were embedded plates with bar connectors to the concrete and rebars. One of the problems I see with this design, besides the Hilti Bolts, is that there is a gap between the plate and the concrete, and that gap along the time,will be wetted all the time by rains and corrosion will appear(crevice corrosion) inside the plate and oxides will destroy in years the plate .In few mmonths, during construction, the concrete will be painted by the iron oxides.I have proposed to chip the concrete some thickness and put an expoxi concrete later fixing the steel plates with bolts, just to avoid any gap.
Let my know your opinion.

regards
Luis

 

[cvg]

nothing wrong with epoxy anchors, they may be better than expansion or wedge anchors. I would agree that grouting under the plates should be done in order to provide adequate bearing surface and reduce water intrusion. not sure that you need to chip concrete away first unless it is weathered.

 

[lganga]

Thanks cvg for your fast answer.
I have compared, the chemical bolt system with the original design, with welded connectors rods to the plate and tied to the rebar before pouring.
I hope this design will last enough time.
Thanks

 

[jrbaus]

Hi Luis,

I am not sure about your particular project and magnitude of the loads etc. however I think Hilti chemical anchors would be a robust solution if designed correctly. If the project involved fixing anchors horizontally into concrete, I would be tempted to use Hilti HVU capsules to facilitate easier placement otherwise HIT-RE 500 or HIT-HY 200 would likely work OK (speak to Hilti - I find them very helpful). As for the gap between the concrete and the anchor plate, I would specify a lite scabble of the existing concrete prior to bedding with an epoxy grout (grout selection will effect minimum bed thickness). Depending on the size of the anchor plates, some provision for egress holes might be appropriate to ensure correct application.

 

[KootK]

The only real corrosion issue here is the water trapped behind the plates. You'll use a stainless steel fasteners so that won't be much of a problem from a corrosion standpoint. And, so long as you don't mess with the column cover concrete, the column is in no corrosion danger either. For these reasons, I wouldn't chip or otherwise mess with the column cover concrete.

Depending on your loading situation, which you may want to share with us, here are some things that might help:

1) Use something akin to levelling nuts on the back of the plates. Omit grout and let there be a free draining air space behind the plate.

2) Galvanize your plates for extra protection.

3) Instead of grout, place a neoprene pad behind your plates. With some compression, the pads should effectively waterproof the space behind the plate. Exposure to sunlight might be a longevity issue.

4) If you use grout, specify a mix that has built in corrosion inhibitor. Also, try to get a mix that is not just non-shrink but, rather, slightly expansive. The expansion will compress the grout in service and improve water tightness. Sika 212 is expansive. It doesn't have corrosion inhibitor, however.

5) If you go with grout, perhaps you could carve a reglet around the perimeter and install an appropriate sealant. Again, you'll want to consider UV exposure.



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