Repairs to vertical CJ's between concrete columns and structural walls

[Ingenuity]

The general contractor to a 7-level concrete building consisting of 4 levels of residential and 3 levels of parking (all above ground) constructed the perimeter rectangular columns to the parking level using steel formwork, then after stripping the forms, constructed the concrete structural walls that are orthogonal to the long-axis of the column. 36"x12" columns with 8" walls that infill between the columns that are on 25' centers.

The contractor did not provide any horizontal reinforcement between the wall/column interface, nor was there any effort to roughen the off-form finish to the columns prior to constructing the walls.

The walls are part of the main lateral force-resisting system.

I have looked at more 'conventional' repair techniques like 1) drilling and dowelling in rebar and CIP concrete, and 2) horizontal steel through-bolts that pass though the columns 12" width and anchor to adjacent walls, with required fire protection.

I also looked at carbon FRP options to horizontally tie the adjacent walls through the columns, but without any mild steel rebar I am hesitant to rely upon a brittle materials like FRP, even if I downgrade the stress/strain levels.

Has anyone undertaken successful reinstatement of such a situation, and care to share their method/s?

Thank you.

 

[KootK]

You could go with two story struts to improve the angle. You'd still be stuck with some detailing issues at the ends of the struts as RHTPE alluded, particularly at the top.

If it's palatable to the design team, I'd definitely pitch the vertical steel angle solution. I'd expect the contractor to lap tha up like honey after being presented with the other, much more labour intensive, solutions.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

What's the foundation situation? Any chance the walls and columns share a nice, deep, monolithic pour of some sort?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Teguci]

Epoxy bars in something like this if you can map the existing rebar well. #8s are possible but #6 would probably be more practical. Don't want to go smaller due to the long length that needs to be drilled.

 

[Ingenuity]

Back from my travels, sorry for the delayed reply.


KootK: The walls are supported on 4' deep grade beams that span to 4' deep x 4'x9' pile caps, on 2 drilled piles. The wall/column interface aligns within the pile cap.

Teguci: Thank you for the sketch. The column rebar spacing may be problematic to make the drilling/grouting of dowels a viable option. I will see what the GC says.


I checked the 24' long walls for 1/3rd of the total moment and shear and they have ample capacity as stand-alone segmented walls.

I am going to look at transferring "some" vertical shear across the vertical interface, in an attempt to bring the situation back to the "as-designed" condition.

The GC and EoR are in some disagreement on what was portrayed on the "For Construction" documents. The drawings do not depict the actual column/wall rebar condition, and the GC is therefore trying to justify his position of the "as-built" condition.

 

[KootK]

1/3rd of the total moment and shear

If anything I'd expect demand to be less than that as you're softening the wall system relative to the other lateral elements in the building.

I am going to look at transferring "some" vertical shear across the vertical interface,

I'd go all or nothing as most of the remedial measures that have been discussed are likely to have brittle failure modes.

KootK: The walls are supported on 4' deep grade beams that span to 4' deep x 4'x9' pile caps, on 2 drilled piles. The wall/column interface aligns within the pile cap.

Sounds promising. On the compression side of your new segmented walls, I imagine that you'll be dumping the compression straight into the pile cap which is great. The tension side could be trickier:

1) If your segmented walls have zones at the edges, which seems unlikely, you'd need to make a go of anchorage into the pile cap there.

2) If your walls will be utilizing distributed vertical reinforcement, then your grade beam will collect a bunch of vertical rebar tension as an uplift load on the grade beam which would need to be checked for it's ability to resist that. Of particular importance would be the delivery of shear from the grade beam to the pile cap. If your grade beam continues right through the pile cap, you should be good to go. If not, you may need something akin to hanger steel at the interface. And, obviously, you've only got what you've got at this point.

More questions:

1) Is the top of grade beam at the same elevation as the top of the pile cap? Or does the grade beam run above the cap?

2) Is the pile cap centered on the columns with the 9' dimension parallel to the walls?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Ingenuity]

KootK,

Thanks for your input and comments.

The pile caps (4' thick) and grade beams (3' thick, not 4' as I previously stated) were cast monolithically, and the top of pile cap = top of grade beam. The 9' cap dimension is orthogonal to the wall long axis.

I agree with you wrt "everything" vs "nothing" as a remedial measure, along with brittle failure modes, and that the demand for segmented walls would be less than my assumed 1/3 distribution, but I conservatively assumed 1/3 for this exercise.

I checked the shear flow (VQ/I) assuming the three walls act compositely with columns, and it is less than 1.4 k/in at the internal column/wall interface so steel angles/plates with post-installed anchors are capable to transfer the full design actions. If the EoR accepts the concept, my guess is he shall want angles in the internal corners and plates on the flush 'exterior' wall to reduce any eccentricity of transfer, and if so the contractor may consider through-bolts connecting angles on the interior wall sides to the flat plates on the exterior wall sides (exterior still being enclosed by a parking structure ramp). They may bring up the issue of fire protection to the exposed steel.

I also checked the grade beam assuming the three walls act singularly, applying triangular equivalent loadings and the flexural capacity is okay, and shear is just okay, but interestingly, the conforming design does not meet ACI-318 for stirrup spacing limits of d/2, and only has 2 legs over a 36" wide grade beam. But it is what it is!

 

[KootK]

I checked the shear flow (VQ/I) assuming the three walls act compositely with columns, and it is less than 1.4 k/in at the internal column/wall interface

Based on the proportions of your wall, I feel that squat shear wall treatment is appropriate. As such, I'd look at it as shown below. Depending on how your went about your VQ/I (cracked, uncracked, etc), the difference may be slight.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.