Concrete Corbel Damage and Repair 1

[JoeTXPE]

I have a client that has requested advice regarding a concrete column cap (corbel) that has cracks, spalls, and apparent prior repairs. The condition includes a concrete column with a cap that mushrooms out to support concrete beams from two directions in line with each other. One of the concrete beams is fixed to the top of the column and the other was apparently constructed in order to allow for lateral movement as part of an expansion/contraction joint that extends across the entire width of the building. To me, the part of the “column cap” that shows signs of damage is like a “corbel”, which is why I’ve structured my question this way. I’ve attached three photos of the current condition. I am open to conceptual recommendations on what other engineers would advise the client on this.

 

[bridgebuster]

Some thoughts...

Shore the girders, chop off the top of the column, and rebuild the mushroom cap.

One the left side, shore the girder, put a steel bracket on the column, repair the column spall, install a bolster between the bracket and the girder.

Is the left side girder notched? In the third picture, it looks like there's a joint at the edge of the "corbel"

A couple of years ago, I had a bridge rehab project where we mushroomed two 5-foot square columns to replace very large rocker bearings. This part of the bridge was over a railroad yard - a lot of logistical problems for shoring towers. The enlarged top gave us room for jacks and block to support the girder without shoring towers. At one column, we drilled and grouted 35 tie rods for the corbel. The bearing reaction was almost 1000k.

 

[JoeTXPE]

The idea of shoring both girders and replacing the top of the column is an idea I’ve had, and it’s not off the table.

The idea of reinforcing what’s there with structural steel in some form or fashion is also an idea; however, I don’t completely follow your idea of using a steel bracket and bolstering the girder. I would like to better understand that idea.

Another idea I’ve had is using FRP; however, I don’t believe the corbel has enough height. I’ve considered adding height to the “mushroom” all-around and then using FRP around the entire mushroom.

Another idea I’ve had is to just add a concrete “pilaster” onto the side of the existing column that extend from the foundation to the mushroom, which is only around 13 feet tall, and design the new “pilaster” to support the full load of the left girder.

If anyone has additional thoughts, it is greatly appreciated. I am going to have a meeting with the architect and contractor this week to discuss options and make sure there are no issues from a means and methods stand point. The good thing is I am really not limited by architecture.

By the way, that is pretty wild about the column with 1000k reactions!

 

[dik]

I think it's the easiest and most safe thing to do.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Brad805]

There is something odd about this corbel. If it were a typical corbel the depth of at the bearing point would be deeper. It appears you have a steel bracket in the region below. If it were a traditional corbel I expect it would be grossly under designed. I would investigate with a zoom boom if you cannot find dwgs.

 

[HTURKAK]

Apparently , the first picture shows that this is an expansion joint and the beam on the left side supported partially on the column and partially on the corbel with masonry plate while the beam on the right is monolitic with the column.

The first and third picture implies some repair work carried out but not succesfull ..

It is pity that a rubber pad is not provided on the bracket.

My opinion is,( similar with Bridge buster ) shoring the left beam and chipping the top of corbel and provide steel bracket with neoprene pad.

 

[JoeTXPE]

@hturkak you’re correct in that the “left” beam is intended to allow for lateral displacement relative to the column. I considered shoring just the left side and removing/repairing the corbel on that side; however, I have concerns over removing the load on the left and not the right and creating an eccentric load on the column that it may not have been designed for. So any recommendation to shore, in my opinion, should include shoring both sides to hopefully avoid that eccentric load condition. I really appreciate everyone’s feedback. This is my first thread on eng-tips.

 

[hokie66]

Another example of why two columns is a much better solution for a movement joint than a single column with or without corbels. I doubt that corbel can be successfully repaired, so would shore it all and build two new columns.

 

[Brad805]

My question is about the u shaped steel element. It appears there could be a rebar welded to the plate. The plate appears to span over the head of the column and and you can see thru bolts. Do you have a section of thru the head of the column in both directions? The depth at the face of the corbel appears to be something like 6"-12". If that is the case, and the load is 1000kip, I am not sure what load that element would have been designed for. I am not suggesting any of what we see is good, but if the corbel was intended to be the primary shear element I would have expected far more cracking.

I like hokie's 2 column idea. I would not be surprised if you are missing the appropriate development bars at the end of the beams.

Here is an example for a corbel for 1000kN. You have none of this and other than this piece that spalled, the assembly seems somewhat intact.

 

[JoeTXPE]

I noticed those bolts protruding from the sides of the beams and I am not sure what those are for.

I do not have any more information at this time besides what is in these photos. I do have some photos of another column within the same building that has an apparent repair by adding steel around the top (see photos attached to this reply).

The reaction on these beams is estimated to be roughly 30k. Also, it is not a pure corbel condition as the beam is sitting on top of half the column. I like the two column idea. That’s an idea that hadn’t crossed my mind yet.

 

[Tomfh]

I'd put a steel column next to each corbel, and run them to ground.

 

[hokie66]

For movement joints, double columns should always be the default design. Using corbels, slide bearings, etc. is fraught with risk. Now, there are some engineers who like that kind of connection because it generates work in retrofitting distressed structures.

 

[dik]

Hehehehe

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[XR250]

I don't do a whole lot of RC concrete design, but why is it that every corbel detail I see shows barely any cover over the rebar? Are they trying to save $1 worth of concrete? Seems like the worst place to skimp on anything.

 

[bridgebuster]

JoeTXPE - what I meant was to use the bolster to eliminate the concrete on the left side that was previously repaired.

 

[JoeTXPE]

Bridgebuster - I would likely need to see a sketch to understand what you’re saying. How would the bracket be attached? Where would the bolster be exactly? Nevertheless, you’ve certainly opened my mind to some ideas that may or may not align with what you’re talking about. Thank you for your input.

 

[MIStructE_IRE]

I’m all for simplicity. I’d go for a new steel column each side of the existing. Job done.

 

[robyengIT]

"I’m all for simplicity. I’d go for a new steel column each side of the existing. Job done." Agree : simple, easy, quick, safe, cheap

 

[BAretired]

I’m all for simplicity. I’d go for a new steel column each side of the existing. Job done.

Job done, provided the foundation supports both steel columns, but it's possible that the foundation is just large enough to support the existing column.

BA

 

[MIStructE_IRE]

Agreed BA. But that’s for him to figure out. I’m just a stranger on the internet