Painted vs. Non-Painted Baseplates

[fabengr]

I am looking for some information about the affect of painting the bottom of a baseplate if you are counting on the contact between the steel and either grout or concrete for shear strenght. I am not going to be able to use any kind of shear key or welded washer to transfere the horzintal force. I beleive that the bottom of the baseplate must be unpainted to acheive a better bond but need some reference to support this position. Does anyone know a resource?

 

[ishvaaag]

http://www.jstage.jst.go.jp/article/jmmp/2/12/1528/_pdf

page 1529

http://www.iri.ku.edu/publications/SM58.PDF

Also, the ACI 318 code itself, asking for longer splice and embedment for epoxy coated reabar ... even with mechanical protrusions.

 

[hokie66]

I think you are splitting hairs in trying to compare painted or nonpainted conditions. Friction is not a reliable way of developing substantial horizontal forces of column bases.

 

[fabengr]

Thanks for the responces. The actual reason for my question is this. I am on a project that is using 3/4" A36 plate as deck plate. The top of the plate is covered with concrete, the bottom of the plate is exposed from underneath. The engineer I am dealing with does not want the steel to rust before the concrete is placed. I am trying to find any reasond I can to convince him that the project is better off if the steel deck is left uncoated.

 

[COEngineeer]

The bottom of baseplate is exposed?? I'm confused

Never, but never question engineer's judgment

 

[HgTX]

If you want to make friction arguments, you could tell him that light, tightly-adhering rust will enhance the friction coefficient.

Hg

Eng-Tips policies: faq731-376

 

[hokie66]

3/4" deck plate, then concrete? Why do you want the concrete and plate to bond? Is composite action intended?

 

[fabengr]

This in not a composite design. This application of the 3/4 deck plate is how this engineer wanted to carry the wet weight of the concrete. This deck plate is no top of a room in a nuclear structure where the 12" of concrete are used only as shielding. I have to use a paint that costs as much as $400 dollors a gallon. I want to give the engineer a structural reason not to paint the top of this plate. He wants it painted because his construction guys once complained about having rusting steel even when it was going to be covered with concrete.

 

[CTW]

I don't think you're going to find a structural reason not to paint this. Have you asked about using just a normal rust inhibitive primer on this side?

I'm not sure what type of paint was spec'd but I'm familiar with boron carbide paint which absorbs neutron radiation. I'm not sure why this, or another nuclear paint, would be needed on the surface in contact with concrete.

 

[dik]

If in contact with a cementitious material, the pH of the material will inhibit rust. If using an epoxy type of grout, this will provide a 'coating'. Not sure of the real reason; the cost differential in likely negligible.

Dik

 

[ToadJones]

So, what shear forces are you trying to transfer through friction?

 

[fabengr]

The actual design has not forces to be transfered. There is not even any shear studs on this steel plate deck. I simply don't want to have the expence of painting something that will be covered with concrete. The only reason the engineer has for wanting it painted is comments he has recived in the past from his field people. It is not design driven, it is not exposed, it is just an engineer who just does not want to hear the field complain. I want to give him something he can use back to the field that tells them that unpainted steel in contact with concrete is better than painted steel in contact with concrete.

 

[hokie66]

Sorry, that would be an overly broad and dubious statement. You will have to fight your case on a political rather than technical basis.

 

[fabengr]

The unfortunate world of a subcontractor means that you often find yourself in a position where because you have not authority even if you are right both technicaly and praticly you are dealing with decision makers who will not lessen to reason.

 

[CTW]

I'm assuming this item was missed in the bid, otherwise there shouldn't be any issue with painting it as the cost would have been included in the contract.