repair of steel columns in natatorium 9chlorine0

huangyhg

repair of steel columns in natatorium (chlorine)
i have been hired to rapair steel built-up columns that are in a natatorium.  the chlorinated pool water soaked the bottom of the columns since the columns were not set up on piers.  
on a few of the columns, portions of the webs are rusted clear through.  the pool is closed and will be demolished at some time but there is an auditorium above the natatorium.  
how should we prepare the surface?  should we sandblast or is wire brushing good enough?  will sand blasting get rid of the chlorides?  i do not think so.
what about power washing the column webs and then drying them with a torch?  
am i worried about nothing?
i would research specs on marine structures to see what type of repairs they suggest.  the power washing sounds like the best technique to me.  has there been any damage to the base plate/anchor bolts?
there was a similar post a couple of months ago.  i would shore the columns, cut out the corroded section well above the damage and replace the section and baseplate.  
for one, all that heat added during welding to the columns might soften them up enough to deflect.  plus, instead of messing around with a bunch of little plates, you can just do the top weld.  and you've removed all the corrosion, instead of trying to clean it off.
i would chip the concrete around the column and verify the extent of corrosion below slab. i would also assess the % of steel loss by thickness. make the necessary structural calcs to prove to yourself that the remaining steel works or does not work. from there there are several options: 1) replace portion of column - expensive with shoring (epoxy coated, galvanized, or weathering steel) 2) weld plates at the base...and prep and coat surfaces (expoxy coating) 3) weld plates and provide cathodic protection (galvanized pucks).
for the rust, i would definately chip away all loss rust, and wire brush. i would specify a minimum steel thickness, before that portion needs to be cut out.
you will also need to deal with the cause of corrosion: water and chlorine. this could mean chipping all the concrete around the column and replacing it with a low permeability concrete and detailing it so water slopes away from the column. (because remember, your source of corrosion is still present). a more expensive solution is an extraction/muigration technique.
another question: is this column part of a lateral system? if so, then you will need to be careful about not leaving stress risers and notches....details!
now, if the column is corroding you may also want to explore with the client the option of verifying corrosion in the concrete slabs. take cores to verify extent of chlorine penetration. chip away to expose rebar and verify amount of steel area reduction.