Shear stirrup requirements in reinforced concrete corbel design 2

[pmkPE]

I am reviewing a structure designed to the ACI-71 code which states shear stirrups are required for corbels. A.h of stirrups is to be no less than 50% of primary tension steel area, A.s. The designer decided that since the shear could be carried by the concrete that stirrups would not be required. (The corbel is actually a ledge that runs for the ful length of a wall that is approximately 20 feet long.) The design was made in the eary '80s. I am having difficulty locating papers discussing the development of the code requirements. I want to be able to justify the designers choice of not meeting the code requirements, and to do that I need to know the basis of the code requirements.

Does anyone have a good starting reference point; or other ideas of how I can determine the basis/history for the code requirements for corbels? (Yes, I have googled my eyes out, and researched several papers by Mattock, Alan H., but cannot find them; they were written in the early to mid '70s).

thanks in advance.

Paul

 

[dcarr82775]

I don't think a bearing ledge along a wall is a corbel. A grey area of the code, that is just my opinion. What bears on the ledge?

 

[msquared48]

Professor Mattock was one of my concrete professors in grad school at the UW in '71-'72, and I took a course from him specifically on corbel design. He had completed his work at that time I believe. I think I still have the course notes and data somewhere...

You might try contacting the Civil Engineering school at More Hall at the University of Washington and see if you can get what you need there. I will try to see what I have if I can find it.

Mike McCann
MMC Engineering

 

[pmkPE]

What are the dimensional limitations for a "bearing ledge" along a wall and a corbel? Where are these limitations stated? In what code/section?

 

[msquared48]

I did a quick check for the notes and they really must be buried. I think the UW is your best bet at tne moment.

Mike McCann
MMC Engineering

 

[pmkPE]

Thanks Mike, I appreciate the information.

Paul

 

[msquared48]

Oh, and if you do contact the University, the information, will most likely be found in the Engineering Library in Loew Hall, at least that's where it was back in the 70's. It may have moved. It will not be at the main library which is Suzallo.

Mike McCann
MMC Engineering

 

[msquared48]

Getting back to your original question though, the work he did was for a concrete projection from a concrete column, commonly referred to as a corbel, that sees both vertical and horizontal loads loads, and the shear/tensile reinforcing that was required.

This research did not address line loads, only point loads as from a beam sitting on the corbel. I do not know how your ledge projection is being loaded, but you may have to look at it differently than a corbel.

How is it loaded?

Mike McCann
MMC Engineering

 

[pmkPE]

Mike,

The "long" corbel is point loaded.

Thanks,
I did manage to find professor Mattock's research on the PCI Journal website. Initially I just searched under the quarter for which his articles were referenced. Surprisingly for the years that i searched (1975 and 1976) only two quarters for each year turned up - needless to say they were not the quarters that his research was referenced/published. Therefore I explicitly listed the titles of his research and found two of three.

I appreciate your help and comments.

Paul

 

[msquared48]

It might be possible to see how far the load could span laterally over the ledge and analyzt on that basis. Obviously you are not going to retrofit it with any corbel reinforcing, but you may be able to set a safe working load capacity.

Mike McCann
MMC Engineering

 

[Teguci]

PCI Handbook has a strut and tie model corbel design that shows no Ah reinforcement. Current ACI edition allows this.

Might be a starting point.

 

[pmkPE]

Thanks, I'll look into it.