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Corrosion severed bars in slab that pass thru a column

Corrosion severed bars in slab that pass thru a column

Corrosion severed bars in slab that pass thru a column

(OP)
Would you agree with me that trying to install adhesive #5 (or 15M) adhesive bars into a column, to replace 8 (eight) #5 bars top in a waffle slab where the bars have corroded completely into two segments (i.e. a 15 foot long bar is now say a 7 foot long bar and an 8 foot long bar!) is not feasible? And the only way to fix this is to install new bars in the new repair concrete to each side of the column and check that the reaction can be transferred to the column by "interface shear" (as per CSA A23.3 interface shear expressions)? I will attach a sketch in a moment after sending this.

RE: Corrosion severed bars in slab that pass thru a column

Not sure about the CSA code, but those top bars through the column are required by other codes for negative moment capacity. But I have no idea how you could get them through the column now.

RE: Corrosion severed bars in slab that pass thru a column

I don't know what is being accomplished with the dowels and 5 5/8" adhesive embedment. In the sketch, it doesn't look like there will be enough lap to accomplish a splice. Can enough good bar be exposed to use mechanical splices (bar couplers)?

RE: Corrosion severed bars in slab that pass thru a column

I agree that the bars would need to go much deeper to form an effective lap. This article delves into what it might take to get the job done: Link.

While perhaps not in strict conformance with new construction CSA requirements, I believe that replacement bars to the sides of the column would be economical and could reasonably be expected to transfer negative moment as required. The only hiccup would be dealing with the shear lag between where the bars will be and where you would like them to be. I'd address that by:

1) Using a few more bars than you need. Maybe six each side rather than four.
2) Running the bars out a bit farther than you normally would, say four feet.
3) Keeping the new bars as close to the columns as possible. Maybe arrange them in three bundles of two 15M each side, spaced closely.

I don't believe that there's a need to summon the dark gods of shear friction to this particular fix. All of the stresses should be able to get where they need to go through conventional RC mechanisms.

My biggest concern with this would be the impact on punching shear. You'll be helped by the fact that most of the punching shear stresses develop over the corners of the columns, pretty close to where your new bars will be.

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.

RE: Corrosion severed bars in slab that pass thru a column

(OP)
ok thanks t all.

To Kootk: your suggestions correspond well with what I had been thinking. I did not know though that most of the punching shear stresses will develop near the corners of the column. Is there any reference paper that I could read up on that? It is because I was worried about the punching shear stress that I was going to check it be another mechanism, namely interface shear and I am not sure why you are so negative about it. The interface shear transfer equations were developed by Dr. Loov with whom I have worked and for whom I have high regard. I do agree though that shear friction equations (as opposed to the interface shear equations) are difficult to use because there is no accepted means of measuring the surface roughness. I am not sure though that interface shear is a substitute for satisfying the punching shear stress, so you may have a point there.

I suppose it would be possible to check it by strut and tie modeling.

As hokie66 noted, I am still of course going to have to satisfy the code requirement that not less than 33% of the total negative moment be resisted by bars placed within the column width plus 1.5 times the slab plus drop thickness each side (1.5 x 10" = 15" each side of the column). That my be a challenge, but I have not got that far yet.

I wonder if there would be some merit in placing some top bars in the slab within the 30" column width and hooked at the column, even if I do not count on them for anything?

Since the bars are totally corroded away at the column face I don't see how a coupler or welding could be used.

Thank you for your constructive suggestions. I will proceed along those lines.

RE: Corrosion severed bars in slab that pass thru a column

(OP)
Sorry, I made a mistake...interface shear transfer also requires a 5 mm full amplitude. I mistakenly said that it did not in my previous post.

RE: Corrosion severed bars in slab that pass thru a column

From Macgreggor's concrete text:

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.

RE: Corrosion severed bars in slab that pass thru a column

(OP)
Very good Kootk. We have that in the office and I will look it up Monday. Very much appreciated.

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