Concrete Corbels! Secondary Pour?

[JoelTXCive]

I have a question regarding concrete corbels similar to below........

Are Corbels like this generally cast with the wall, or are they cast in a secondary pour?

Background:

I have a pump station wall that is going to support some concrete beams. The wall geometry is tough, so I'm worried about the contractor being able to cast the wall with dowels in the correct place.

The floor below the wall slopes at about ~10%; and the top of wall slope will not be parallel. The line of supported beams will not be parallel to either the top of wall or the bottom of wall.

I'm thinking, I could leave some ~2ft x 2ft blockouts in the wall when it is cast. I would have the wall bars continuous across the blocked out opening.

Then, the contractor can weave in their bars for the corbels in exactly the correct spot; and a secondary pour may be made for the corbel?

I'm open to input.

Thank you!

 

[engineering_patrol]

I yesterday supervised an underpass in Ottawa with many similar corbels and all of them were casted together with the walls.

 

[MIStructE_IRE]

I often see pour 1 to underside of corbel. Pour 2 is the remainder of the wall and the corbel. Never wall - then corbel. It seems intuitively wrong.

 

[JoelTXCive]

My line of thinking was similar to repairs and wall modifications that we have done in the past.

We have broken-back existing concrete; and then weaved in new rebar. Then new concrete is cast.

The end result is a cold joint, but the since the rebar is continuous across the joint; it's basically the same thing as a construction joint.

 

[MIStructE_IRE]

I don’t like the idea of a vertical cold joint at the point of maximum shear. I wouldn’t joint an RC beam at the point of max shear and certainly not at a corbel/wall interface.

 

[STrctPono]

+1 for casting the corbel with the wall. I would never allow the cold joint at the faying surface of the corbel and wall. I have, however, done this only when we have added corbels to existing structures that are lightly loaded.

I yesterday supervised an underpass in Ottawa with many similar corbels and all of them were casted together with the walls.

Hard to imagine that you were able to "supervise an underpass in Ottawa" yesterday when you were so busy trolling Eng-Tips and insulting some of the more respected individuals on the site.

 

[JoelTXCive]

Alright...I'll put everyone down for not liking this idea.

I'll have to come up with a an alternate solution.

We are just kicking this project off, so I'm able to control the geometry to some extent.

 

[KootK]

I'll put everyone down for not liking this idea.

Not me. The majority of the precast wall corbels out there are done as two pour setups, similar to what you described. Is it as good as monolithic? Surely not. Is it good enough, particularly with the corbel keyed into the wall? Quite possibly in my book.

Good that you consider yourself the most respected individual on this site.

This site considers considers STrctPono to be one of the most respected members on this site, as do I. He's a little "recent" for my liking but prolific, knowledgeable, and cordial none the less.

 

[EZBuilding]

I have utilized a secondary pour for a corbel with Tilt-Up wall construction. Formsavers were placed within the tilt-up wall reinforcement to allow for development of the reinforcement.

 

[Settingsun]

Initially the title made me think of a construction joint on the face of the wall which didn't sound great, but a pocket for the full wall depth sounds fine.

 

[Enable]

I concur with others that a cold joint is not ideal at that location, and if it can be poured monolithically then I would tend to go that route. Whether or not it is economical to do so will largely depend on the form system your contractor intends to use. For example, panel forms might easily accommodate the monolithic pour sequence (I've personally formed such a corbel into a foundation wall with minimal aggravation) but an existing pre-fab Peri system would make such construction very uneconomical. Ask and see what they say. Might be surprised!

Also, for those suggesting that there is no way that the two-stage pour sequence should be done, I am with KootK in that it would not keep me up at night. In the concrete restoration industry we routinely replace full intermediate slabs where the new perimeter connection relies entirely on existing bars, shear dowels and a 1" chipped key (foundation walls & columns are typically kept in place and loaded during repair efforts). Such repairs have a long service history despite the concerns about a cold joint at / near the point of max shear. Sometimes nervous consultants add a steel angle underneath to extend the face of the shear support, but it is relatively uncommon.

 

[dik]

like most of us... there are over a dozen members in the structural group that have consistently shown they 'have it'. I've seen that type of form where the 2' wide corbel form mounts to the 2' wide wall form... The corbel, itself, may only be 1' wide... which looks like what was done...

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

-Dik

 

[STrctPono]

Thanks KootK.

 

[HTURKAK]

The answer is to both questions yes...they can be secondary pour depending on the conditions.. sometimes due to formwork requirements sometimes the the wall could be precast...

I have visited the Shanghai highway River Tunnel construction site in 2007 . The tunnel has 15m internal dia and constructed with TBM method . The tunnel composed of segmental precast units and the highway deck supported on cip corbels. The tunnel wall drilled and rebar planted with epoxy grout then CIP corbel poured.

If you want to prefer secondary pour , there are two options;

1- rebar cage is bended and placed with polystyrene board to make pocket, then the rebar re bended and the cage is completed then the second pour.

2- You may use threaded rebar coupler.. The coupler will be fixed to the interior surface of the formwork together with first embedded rebar and then second bar is installed after formwork removal.. The coupler will be similar to the following:

..and with chance i found the corbel sketch at the web;

Another example for the second phase corbell;