corrosion of bolts in steel parking structure

huangyhg

corrosion of bolts in steel parking structure
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.
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you cannot use galvanized a325 bolts?
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).
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?


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.
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.
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:
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.  
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
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.
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: