Another concrete corbel question 3

[Robbiee]

Hi everyone,
An Existing corbel is to support a new precast beam. The corbel doesn’t have the capacity to resist the reaction from the beam. Can we provide plates like the ones shown in the attached sketch welded to existing embedded plates in the column to reduce the load applied on the corbel? We thought we can do load distribution between the corbel and the new plates based on relative stiffness. How?
1- Apply a unit load on the corbel and the plate and calculate deflections due to bending, compression, and shear,
2- the load carried by the corbel/the load by plate = deflection in plate/deflection in corbel.
Is this correct?
If yes, what do you think can go wrong? BTW, we know that carrying all the load on the corbel is more certain approach, but the corbel, that is one of many, need be demolished and re-built, which we don't mind doing if other ways are not available.

 

[Robbiee]

Thank you everyone, you've been of a great help. The attached sketch shows two options essentially inferred from your suggestions. Please comment.

 

[kslee1000]

I select the lower option over the two. May consider to add L bars to the front face, and transverse bars. Do you have clue how to get concrete into place?

 

[Robbiee]

kslee1000,
Yes,form under the corbel and allow for an opening with a foot or so of concrete head and use high slump concrete (8" say), then breack the additional concrete after few hours from casting.

 

[kslee1000]

Good idea. Thinking carefully about effect of drying shrinkage, especiall with such high slump. How about adding superplasticer to make it workable? Or, maybe provide devices for grout after curing.

 

[Robbiee]

Yes. Super P will be used and a max. of W/C=0.4.

 

[kslee1000]

Ailmar:

looks like the design part is well set. Keep an eye on construction. Good luck.

 

[etabs2002]

Forget the connection with the plates. You can model how you want but reality is different story. The best is to use every connection for the function what is the originally designed. I will use option "2" on your sketch.

 

[BAretired]

I am not too confident in either option. I think the sloped bearing of the existing corbel will tend to push the new concrete away from the column in Option 2. Roughening the underside of corbel might help.

Also, I believe that through bolts with bearing plates front and back are better than epoxy anchored ties.


BA

 

[kslee1000]

When roughen the existing corbel, chip a few inches of the lower trainglar concrete may help. I would do that.

 

[BAretired]

Maybe the best thing to do is remove the existing corbel carefully, preserving the reinforcement, then roughen the column face to the bottom of the new corbel, add epoxy anchored ties and pour the whole corbel monolithically.


BA

 

[kslee1000]

BA:

It would be the best way among all.