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Concerns about stud rail punching shear reinforcement 6
- Thread starter hokie66
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rowingengineer
Structural
Goes to show changing a detail by a small amount can change the performance by a large amount.
How could you do anything so vicious? It was easy my dear, don't forget I spent two years as a building contractor. - Priscilla Presley & Ricardo Montalban
How could you do anything so vicious? It was easy my dear, don't forget I spent two years as a building contractor. - Priscilla Presley & Ricardo Montalban
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I think have never used such kind of reinforcement in shear. "Something" indicates it lacks integration enough with longitudinal rebar to form the required properly anchored ties for required strut and tie schemes. I find also interesting the research finding the strap holding the studs being flimsy, I also thought that when seeing the 3D representations in the literature. Whilst the matter is cleared, better keep clear of the detail.
Another interesting case in which following "the code" means not necessarily the sound and safe approach, and a reminder of the individual responsability of structural professionals to actively pursue structural safety.
Another interesting case in which following "the code" means not necessarily the sound and safe approach, and a reminder of the individual responsability of structural professionals to actively pursue structural safety.
rowingengineer
Structural
Concrete shear is based mostly on empirical equations making it hard for an engineer to assess the results and thus are left having to rely on manufacturers information.
How could you do anything so vicious? It was easy my dear, don't forget I spent two years as a building contractor. - Priscilla Presley & Ricardo Montalban
How could you do anything so vicious? It was easy my dear, don't forget I spent two years as a building contractor. - Priscilla Presley & Ricardo Montalban
msquared48
Structural
Another thing we didn't really know, but thought we did.
How many other things are there to discover in the "Practice" of engineering?
Thanks for posting this Hokie.
Mike McCann
MMC Engineering
How many other things are there to discover in the "Practice" of engineering?
Thanks for posting this Hokie.
Mike McCann
MMC Engineering
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- #8
The original research on shear studrails seems to have been done at the University of Calgary. I wonder how their tests compared to the Ann Arbor tests.
There are at least two types of studrails currently available: single headed studs welded to a rail which serves as the bottom anchorage, and double headed studs with a rail which just spaces the studs. I couldn't see where the report said which type was tested.
I haven't used studrail reinforcement, but have thought about doing so. This report has major ramifications, and will be a worry to lots of people.
There are at least two types of studrails currently available: single headed studs welded to a rail which serves as the bottom anchorage, and double headed studs with a rail which just spaces the studs. I couldn't see where the report said which type was tested.
I haven't used studrail reinforcement, but have thought about doing so. This report has major ramifications, and will be a worry to lots of people.
rowingengineer
Structural
I believe this is the first lot of testing that highlighted the issue.
Here is the results in graphic form from the article posted by hokie, also shows the studs they were using.
2008 presentation
How could you do anything so vicious? It was easy my dear, don't forget I spent two years as a building contractor. - Priscilla Presley & Ricardo Montalban
Here is the results in graphic form from the article posted by hokie, also shows the studs they were using.
2008 presentation
How could you do anything so vicious? It was easy my dear, don't forget I spent two years as a building contractor. - Priscilla Presley & Ricardo Montalban
This is likely just the beginning of what is going to be a very long and contentious discussion on the subject. The original punching tests run in Calgary that you speak of had some serious deficiencies. For one, Dilger and Ghali always used an overly conservative amount of flexural reinforcement to "force" a punching shear failure. For a while now tests with more realistic reinforcement ratios have reported lower capacities than from calgary. The current code equations don't take into account flexural steel at all, and if you ask me, this is the major downfall.
WillisV,
Good post as usual.
If anyone else had problems with the eng-tips download page, you can find this article at:
Good post as usual.
If anyone else had problems with the eng-tips download page, you can find this article at:
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rowingengineer
Structural
I do note int eh return of serve letter, that the decon rep states "Thus, it is not reasonable to expect an increased capacity by adding shear reinforcement, but not doing anything to increase the flexural strength."
This statement would support the theory that to much reinforcement has been used to justify the punching values. Punching shear is effected by the amount of reinforcement, this isn't stated in this particular code, but is covered in a few other codes, and punching shear articles.
"A safe structure will be the one whose weakest link is never overloaded by the greatest force to which the structure is subjected” Petroski 1992
This statement would support the theory that to much reinforcement has been used to justify the punching values. Punching shear is effected by the amount of reinforcement, this isn't stated in this particular code, but is covered in a few other codes, and punching shear articles.
"A safe structure will be the one whose weakest link is never overloaded by the greatest force to which the structure is subjected” Petroski 1992
slickdeals
Structural
The "other side" of the story in ENR
Slick - that article shows both sides fairly well.
On side says that:
1. Thousands of buildings have the ACI design integrated into the structure without any failures to date.
2. The tests that imply a problem were not designed with enough flexural reinforcement.
3. The code requires the stud rails to extend from column corners while the tests may have had rails not aligned with column corners.
4. The research doesn't directly show that there is a strength problem.
The other side says:
1. There may be lots of buildings with this implemented, but perhaps none have experienced a major seismic event where the problem would arise.
2. The code only shows rails from the corners in the commentary - the code itself does not require it.
Apparently a special committee has been established to look into the matter and advise ACI on how to proceed.
On side says that:
1. Thousands of buildings have the ACI design integrated into the structure without any failures to date.
2. The tests that imply a problem were not designed with enough flexural reinforcement.
3. The code requires the stud rails to extend from column corners while the tests may have had rails not aligned with column corners.
4. The research doesn't directly show that there is a strength problem.
The other side says:
1. There may be lots of buildings with this implemented, but perhaps none have experienced a major seismic event where the problem would arise.
2. The code only shows rails from the corners in the commentary - the code itself does not require it.
Apparently a special committee has been established to look into the matter and advise ACI on how to proceed.
The initial testing was done by calgary and also Leonhardt design group in Germany.
I saw some of the original German test results and discussed them with the Leonhardt suppervisor of the tests. They were baesd on a rail at the bottom and it was not a thin spacer. It was about 15-20mm deep. I am not sure of the actual layouts of studs that were tested but had alwaays understood that the concept of stud reinforcement was to be able to achieve a radial pattern. The early specifications I saw used this radial pattern. Obviously they have decided it is too hard to achieve on site so have gone to orthogonal patterns but that does not mean it is the best option!
They even did tests with continuous rails versus rails that stopped at the column edge. This had little effect on the basic punching shear strength but Collapse capacity increased by about a factor of 2 or more with continuous rails as they presumably acted as shear dowels. Interestingly the Canadian code now requires continuous bottom reinforcement through the column zone in the bottom of the slab in both directions, presumably as a response to this effect!
I saw some of the original German test results and discussed them with the Leonhardt suppervisor of the tests. They were baesd on a rail at the bottom and it was not a thin spacer. It was about 15-20mm deep. I am not sure of the actual layouts of studs that were tested but had alwaays understood that the concept of stud reinforcement was to be able to achieve a radial pattern. The early specifications I saw used this radial pattern. Obviously they have decided it is too hard to achieve on site so have gone to orthogonal patterns but that does not mean it is the best option!
They even did tests with continuous rails versus rails that stopped at the column edge. This had little effect on the basic punching shear strength but Collapse capacity increased by about a factor of 2 or more with continuous rails as they presumably acted as shear dowels. Interestingly the Canadian code now requires continuous bottom reinforcement through the column zone in the bottom of the slab in both directions, presumably as a response to this effect!
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