Steel Transfer Girder over Pool 2

[jike]

I am designing a 60 foot plate girder just below the 3rd floor of an 11 story hotel picking up a building column (supporting 8 floors and a roof) over a pool.

Any suggestions on how to provide corrosion protection on this very important structural member?

 

[Lutfi]

I would suggest:

It would be best to avoid the chlorides and vapors.

1. Hot Dip Galvanized
2. Inorganic zinc with three coats (prime, intermediate and finish) with each coat no less than 10 mills.
3. Cathodic protection (sacrificial anodes)

Regards,





Lutfi

http://www.cdeco.com

 

[JedClampett]

I agree with Lutfi. Hot dip galvanizing is the way to go. We design potable water reservoirs. The atmosphere above the water has a very strong chlorine odor, much higher than you'd accept for the public. We've been covering these reservoirs with hot dip galvanized framing for 40 years now. I've done surveillances of these existing reservoirs and the galvanized steel is never a problem. Sometimes we get mechanical wear of the galvanizing due to thermal movement of the metal roofs, but even that is unusual.

 

[jike]

At that length, there may need to be a field splice to get it into a dip tank. The bolted field splice will be a great place for corrosion to begin also. How do you protect the splice?

I will also need to fireproof this member. Is spray-on compatible with galvanizing?

 

[UcfSE]

What is Lutfi's #2, is that a paint-on protection of some sort?

 

[SlideRuleEra]

Agree with Lutfi & JedClampett on hot-dip galavanizing being the best. Here is a link that provides information on vendors and available kettle sizes - you can get an idea if your beam will fit

http://www.galvanizeit.org/resources/files/AGA_root/pdf_files/pubs/glsr.pdf

http://www.SlideRuleEra.net

 

[ghghghgh]

I would try to avoid the splice. If I recall correctly, plate girders can ship at more than double your length, so that shouldn't be a problem unless you have site specific access issues.

 

[JedClampett]

I know for a fact that in our area (with one 45 ft. kettle) that 60 ft. long members are not a problem.

 

[Lutfi]

I would contact local galvanizers and verify the longest piece that they can dip in the tank.

I have no issues with splicing. As a matter of fact, splicing may be required, as was mentioned by others, so that the steel can be maneuvered in the building. I would use bolted connections. One word of advice, account for the zinc coating for your holes. The standard AISC 1/16 larger than bolt does not apply unless you intend on hammering the bolts in!

UcfSE, the inorganic zinc is a nice coating that has been tested for the last 10 to 15 years here on the east coast of Florida. It requires steel to be blasted to near white metal according SSPC-SP10 which is expensive. The following link has more explanation of the cleaning specifications:

http://www.nace.org/nacestore/assets/freestandardsreports/NACE2.pdf#search='sspc 10'

When paint is sprayed, it has to be done under environmentally controlled conditions (certain Relative Humidity (RH and temperature).
It works great. Basically the paint has zinc in it and acts as a sacrificial anode (as in HDG) and the zinc are expended with time.

I specify it a lot on the east coast of Florida for exposed steel frames.

Regards,


Lutfi

http://www.cdeco.com

 

[d2TY]

What about the compatibility of spray on fireproofing? I would have thought that the humidity alone would not be good for the bond to steel, then compounded by galvanizing. This seems like a bigger problem to me.