Corrosion of Bolts in Steel Parking Structure

[mrengineer]

I am designing a steel parking structure, and will likely be hot-dip galvanizing the steel frame. Since I have a moment frame, it looks like I need A490 bolts, which A.I.S.C. says you cannot galvanize. Others have suggested that I either use a Type 3 bolt, or use plain A490 bolts and paint them. Any comments or suggestions would be appreciated.

 

[haynewp]

You cannot use galvanized A325 bolts?

http://www.mcgonagall-online.org.uk/poems/pgdisaster.htm

 

[mrengineer]

We need A490 bolts to make our worst case moment connection work ("Eight Bolt Stiffened" connection as shown in A.I.S.C. Design Guide 4, Second Edition, Fig. 1.1(c).

 

[haynewp]

If you have the design guide for parking structures it gives info about painting vs galvanizing and what can be expected of each. If you have decided on galvanizing, I would try to get the bolts to be galvanized as well since somebody is paying for all the galvanizing of the frames anyway, it just seems like a shame to me not to get the bolts galvanized as well. If it's not a highly corrosive environment, maybe you can save some money and go with all painted frames anyway.

Have you tried to adjust the distances between the bolts at the connection to get A325's to work?

I would at least paint the A490's if you can't get A325's to work. I wouldn't use type 3 bolts in a corrosive or water leak prone environment. Is it even acceptable to have type 3 steel in contact with galvanized steel?

http://www.mcgonagall-online.org.uk/poems/pgdisaster.htm

 

[LPPE]

Do they make epoxy coated bolts? I have no idea if they exist, or if they'd even work if they did. But just a thought.

 

[haynewp]

If you look at Chapter 8 in the Parking Deck Design Guide, epoxy is part of the coating process in lieu of galvanizing. The chapter also says "weathering steel is not recommended in parking garages".

It looks like zinc is a constituent in the primer of the recommended coating systems. I don't know if it is ok to even paint A490's with that stuff. I would ask the AISC solutions center about your case and what kind of paint should be used or if just epoxy will be enough.

 

[HgTX]

There's no problem with painting the A 490s with zinc-rich primer. It's done on bridges all the time.

This looks like a good artice:

http://revobiz.dyndns.org/group/seaint/2002d/msg01039.html

(But don't take the "galvanic action" part to mean you can't put zinc-rich primer on them. You can.)

The AGA says that other countries galvanize ISO Grade 10.9 bolts, which are similar to A 490. I know nothing about this.

The problem with using the Type 3 bolts unpainted (other than they'd look funny) is that they might "eat" the galvanizing away from the girder around them.

I still find it hard to believe that there's no way to make the A 325s work.

Hg

 

[mrengineer]

HgTX:
1) Thanks for the link to article on galvanizing A490's.
2) We have a W27x194 beam with a 1,552 K-FT moment (service load). The fabricator would like to use a moment end plate connection.

 

[HgTX]

I don't have the AISC guide on hand. You can't up the bolt size and still meet bolt spacing requirements, and you can't fit more bolts into the connection?

Hg

 

[mrengineer]

Hg
We are using 1 1/2" diameter A490 bolts. A.I.S.C. does not have a design procedure for conditions with more than 8 bolts at the tension flange.

 

[haynewp]

I have been unable to find a manufacturer that supplies A490 bolts with a zinc paint coating.

I asked AISC about this and they didn't say you could use a zinc primer nor that you couldn't.

You may want to read through these papers:

http://www.boltcouncil.org/download/RCSC Specification 6-23-2000.pdf

http://www.boltcouncil.org/2nd Edition Guide.pdf

 

[HgTX]

You don't buy pre-painted bolts. Paint would never survive the installation process. You install the bolts first, and then paint them--after first providing the surface finish recommended by the coating manufacturer, of course; this would at least involve the removal of any lubricant from the surfaces to be painted.

Whether A 490 bolts can be coated with zinc-rich paint under ordinary structural service conditions is really not a matter of debate. One standard bridge construction method is to leave bolted splice areas unpainted until after the connections have been made, and then come back and paint with zinc-rich primer. This is done all the time and is in numerous state as well as nationwide specifications. If anyone knows of any specs that specifically bar the use of zinc-rich primer over A 490 bolts, I'd love to hear about it.

That does bring up a question I hadn't thought of before, though--I'd think A 490 bolts wouldn't be permitted in applications where the structure will be metallized in the field after connections are completed. Irrelevant to this thread, I think, but food for thought for me anyway.

Hg

 

[haynewp]

If just field painting these bolts is so effective against corrosion, then why do manufacturers even offer hot dip galvanized bolts?

If this parking deck is located on the beach, do you still say the corrosion protection from just field painting the A490's is going to be comparable to galvanized A325's? He is not asking about an insignificant connection here.

 

[HgTX]

Those who think that one can buy pre-painted bolts are in no position to get sarcastic.

Galvanizing offers better protection than painting, and typically longer-lasting. However, where galvanizing won't work or is cost-prohibitive, paint can be used. It's not an all-or-nothing situation.

My main point about the paint is that the concern about hot-dip galvanizing A 490 bolts does not apply to the zinc-rich paint. Painting the bolt will not hurt it. It won't provide quite the same level of protection (especially if not properly applied), but it won't embrittle the bolt either.

Things to take into consideration are the zinc loading of the paint, the surface prep of the bolts, and proper application of the paint. Don't just go to Home Depot and pick up a can of something (and yes, this happens on commercial jobs sometimes). Deal with a reputable industrial paint company who will provide technical support.

Or one can get creative about the connection (like hand-designing a connection with a different number of bolts from the "off-the-shelf" AISC 8-bolt connection) and figure out a way to use galvanized A 325 bolts. I woulda thunk that a different bolt arrangement with the same centroid would do the same job, but I ain't no designer.

Hg

 

[haynewp]

"Those who think that one can buy pre-painted bolts are in no position to get sarcastic."

I like that one.

 

[daniel2]

I would specify "zinc coated". That would include plating.

 

[HgTX]

What distinction do you make between galvanizing and plating?

Hg

 

[pba]

I've had this problem before.
Our thoughts went something along these lines:

We galvanise the steelwork because it is a relatively cheap method of achieving a very long life, or period to first maintenance.

We select the fastener with the best coating we can. If this is inferior to the steel work we need to assess the effect.

If we don't have galvanised fasteners in galvanised steelwork then galvanic action could occur to the detriment of the steel work NOT the fastener we thereforce need to do something to prevent the galvaninc action effecting the end plates.

The life of any applied coating is likly to be less than that of galvanised steelwork so we need to introduce a maintenence regime which includes periodic inspection of the steel connections.

If I recall correctly we specified a site applied epoxy zinc phosphate (this is generally better that zinc rich) for the connections and as a coating over the end plates and connections to the columns so that air would reasonably be excluded by the paint seal - A mordant wash is required to neutralise the galvanising and provide a suitable key. We specified inspections at five year intervals - which was not unrealistic for our structure.

I have heard of silicone being used to seal our moisture but suspect that this would not be appropriate in your circumstances.