Concrete column repairs

[mfstructural]

I recently inspected a building for a client where the bases of the concrete columns were spalled and the exposed bars were corroded. I'm planning on providing details to shore up the existing structure above as required, then chip out the loose/debonded concrete to about an inch past the corroded bars. The spec will include mechanical cleaning of bars. Then providing bonding agents and forming to repour high strength concrete patch. I wanted to get opinions on whether its good practice to perform an analysis of the column vs loading. I don't know entirely how many bars there are as all the concrete is not spalled. I'm assuming it's at the 4 corners. I will also be adding a note to remove asphalt and repair concrete below surface of parking area as required. Will probably add a note for engineer to perform one inspection during repairs. Has anyone had experience with similar repairs?

 

[bugbus]

The starter bars being on the outside of the fitments is worrying

 

[mfstructural]

Yes. I was wondering how that even happened. It's significantly bent outward only at one column. All the others don't exhibit that condition.

 

[Retrograde]

Yes. I was wondering how that even happened

Probably the starter bar was cast into the footing in the wrong location.

 

[GeorgeTheCivilEngineer]

Structural carpet!

Think I'd be digging down to the foundation and enlarging the column to past where it's good.

 

[milkshakelake]

I'd only provide an analysis/design with loading if the client asks for it. They might not be happy to know that their columns are insufficient, if the design shows that. Ethically, I think it's okay to just inform them that there's a potential strength issue, and that you can investigate it further if needed (probably for $). You could potentially do a quick back-of-envelope axial load check to see if it warrants more attention.

I think your procedure makes sense for the most part. I don't know what you mean by "high strength concrete patch" but I'd look into repair mortar or repair concrete. These have specific procedures for wetting the concrete before applying, which would slightly affect your procedure. They will actually expand to fill in little voids and provide a better bond, rather than regular high strength concrete which would shrink. MasterEmaco S 440 is a good product, but there are similar ones.

 

[wrantler]

If they are asking for a repair I would give them a repair. So just reestablishing the capacity.
Of course if the column looks to be sig undersized then maybe go further.

 

[bridgebuster]

Design the shoring for the load in the column + contingency. Most DOT projects I work on require 25 to 50%. You may have to go more than an 1" behind the bars. 1 - 1 1/2" is standard practice to get concrete behind the bars but I can you from experience sometimes when you start chipping...well, goes a lot deeper than you thought.

 

[mfstructural]

Thanks for the input everyone. I am planning on providing loads to shore for in the drawing set and will keep the scope limited to removing the affected concrete, cleaning bars (calling to inform EOR if section loss exceeds 10% or if bars are cracked), and replacing concrete.

 

[SWComposites]

And just how are they supposed to determine the percent area loss?
I dislike percentage criteria without clear definition of what 100% exactly is (e.g., percent of what?)
Maybe a criteria based on bar diameter?

 

[mfstructural]

Based on the site inspection, existing exposed bars are #8, so I will include a note to say if bar diameter is less than 29/32" upon sandblasting notify work. I had initially only referred to #8 bar, but giving a measurable dimension might be a good idea.

 

[LittleWheels]

Be prepared for questions similar to " The bar diameter is measuring smaller than allowable in one direction but larger when measured perpendicularly. What do we do?" Section loss from localised corrosion can be a pain.