Anchor Bolts Painting 1

[AymanS]

I am supervising a temporary site office (Porta-cabins) using structural steel materials. All steel members will be coated with epoxy before painting. my question is about anchor bolts shall be fitted in the concrete column nick, is it better to paint it with epoxy primer also before concrete pouring??

 

[hokie66]

You say you are supervising a temporary site office. Do you mean you are building them or erecting them? Or what?

What is a "column nick"?

 

[AymanS]

Supervising the erection.

column neck = column pedestal (sorry for wrong spelling)

 

[hokie66]

I've never heard of anchor bolts being coated with epoxy. They are normally black, or if in an aggressive environment, hot dipped galvanized. The part of the bolt within the pedestal will be protected by the concrete. As this is a temporary installation, I would just use black bolts, unless it is seaside. If subject to salt spray, then galvanize them.

 

[AymanS]

Thanks dear, but part of anchor bolts should be exposed out of the concrete pedestal for tightening. This exposed parts maight be rusted. Kindly advise

 

[MintJulep]

Paint it after you tighten the nut then.

 

[hokie66]

The anchor bolts will, or should, be oily. So since this is a temporary installation, why not just grease them? Or perhaps wrap with Denso tape.

And stop calling me "dear". Only my wife gets away with that.

 

[TXStructural]

You would NEVER field coat/paint anything structural that is threaded and that will have to accept a nut, since the coating will interfere with proper fastening. Hot dip galvanized anchor bolts should be used if corrosion is a concern. Do not have regular black anchor rods galvanized, since the clearances would not be correct.

As stated above, you can also coat the exposed portions with grease, paint, gooey-anti-corrosion-stuff, or whatever after fastening, but not before.

 

[HouseBoy]

"You would NEVER field coat/paint anything structural that is threaded and that will have to accept a nut, since the coating will interfere with proper fastening. Hot dip galvanized anchor bolts should be used if corrosion is a concern. "

If paint is capable of interfering with proper fastening, How would HDG NOT create a similar concern?

I don't know any better. It just SEEMS like HDG would be as problematic if not more so.

Can you speak to this?

Thanks,
Steve

 

[port125]

Modern steel construction magazine had a write up on this subject in June.
Below is the link to the archived article.

http://www.modernsteel.com/Uploads/Issues/June_2011/062011_June11_Bolting_web.pdf

To paraphrase the article. They make the bolts and nuts to be compatible by over tapping the threads prior to galvanizing.

 

[TXStructural]

Steve, a factory HDG bolt/nut combination is designed with this in mind. Threads are frequently "air wiped" or similar to avoid filling the threads. Galvanizing a bolt or nut can also lead to embrittlement, so this is considered when choosing metals and processes.

Another option is metallizing/thermal spray with sacrificial or corrosion-resistent alloy. These kinds of bolts and nuts are not widely available, but for long-term, critical applications, they might be an option.

 

[HouseBoy]

Great information. Now I have a "real" question:
I am designing a pedestrian bridge spanning 60 feet. (it will be made and shipped in 3 "pieces" - 15 ft sloping up at 1":12", 30 ft level and then 15 feet back "down" at 1":12")
The pieces will be bolted with end plate moment connections.
We are specifying hot dip galvanizing for the bridge steel.
The question -
Should we specify Hot Dip Galvanized A325 bolts for the moment connection?

 

[TXStructural]

You should use some kind of corrosion-resistant bolts, but plain steel bolts will be partially protected by the galvanizing on the remaining structure. This kind of unprotected component may rust due to local corrosion, but would be protected from macrocell corrosion by the sacrificial zinc elsewhere. It would function like any other sort of cathodic protection.

I would specify galvanized bolts, which may result in HDG or mechanical galvanized coating. I don't know whether performance would be different with the bolt. (With ordinary steel, HDG creates a zinc-iron intermetallic/alloy layer which adds to resistance)

 

[hokie66]

If the steel is hot dipped galvanized, the bolts should be HDG also. Don't just say galvanized if you can't trust the fabricator to know what you mean...you could get some type of zinc plating that is not nearly as good.