Buried Column Bases and Corrosion 2

[rquerin]

In our typical structural steel design of commercial/industrial buildings (Toronto area), the column baseplates are normally placed some nominal distance below finished floor.
The columns and baseplates usually have a single shop coat of primer and are touched up on site. On one of our current projects the city building plans examiner has questioned us on tbe measures we've taken to prevent corrosion of the column below slab level. Of course I am not concerned with corrosion of the primed column or baseplate since we have uncovered countless existing columns from much older structures where everything is intact. This seems like a question from an inexperienced plans examiner however I would like to respond with some reference to the steel design code (S16.1) however I can't really find any clauses that would be directly applicable. I could just say the primer will prevent any significant amount of corrosion but I would like to back this assertion up with some reference. Any info on how I should respond would help.

 

[rmp319]

In our area (So. Calif.), the columns and base plates are not shop primed below slab. You may check UBC-97 Section 1906.3.6.2. This refers to pipe in concrete.

Also of interest is why reinforcement bars are not painted or coated to protect from corrosion.

 

[LPPE]

Good point on the rebar, rpoche.

 

[kayah]

This sounds like an interior (controlled) environment, so the concrete should be protection enough.

You may find S16.1 Cl.6.5 (Corrosion Protection) or Cl.29.1 (Cleaning, Surface Preparation & Priming - General Requirements) useful.

 

[Watermelon]

CSA S16.1, sections 29.1.2 & 3 say it all.

 

[AJUK]

In the UK, it is common practice to cast concrete to around all steelwork below ground floor level; the common thickness is 100mm. This is usually enough, in non aggressive environments, to provide protection throughout the lifespan of the building. Over here, the soils tend to be soft and wet!

Coating of reinforcement is not generally recommended as the bond between the two materials is affected making code design assumptions no longer applicable. In special circumstances, such as very aggressive corrosive conditions, epoxy coatings can be used for rebar with appropriate measures applied the design.