Development Length of Reinforcement in Shear
Development Length of Reinforcement in Shear
(OP)
Are there any guidance on development length of reinforcement in shear? ACI defines requirements for tension and compression, but not for shear.
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Development Length of Reinforcement in Shear
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Development Length of Reinforcement in ShearDevelopment Length of Reinforcement in Shear(OP)
Are there any guidance on development length of reinforcement in shear? ACI defines requirements for tension and compression, but not for shear.
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RE: Development Length of Reinforcement in Shear
Also see 11.7.8 for shear-friction reinforcement.
RE: Development Length of Reinforcement in Shear
RE: Development Length of Reinforcement in Shear
Traditional practices used (maybe a bit less now) to fall short of the lengths required to properly anchor such stresses. Focusing at corners we would be able -more than once in a life- to see even cracked stirrups of the so sharp corners detailed. In much more cases, fully plastified regions at corners are present, then sometimes even welded, hopefully with welded rebar... and, er, with some times even visible sectionreduction of the main rebar!
It is for this surely that welded cages are not allowed in bridges, with the exception of non-critical meshes.
Some of these failures you can see as well in the detailing books.
So ample consideration by the code specifiers to these issues would be very welcome, from what my eyes have seen.
RE: Development Length of Reinforcement in Shear
Since I do not fulfill these development lengths on one or both sides of the shear plane, I will simply reduce the shear capacity of the bar. Is that common practice?
RE: Development Length of Reinforcement in Shear
ALL of the details that NCMA and others show across the U.S. usually indicates a bar grouted into the cells of the plank and then turned down into the masonry wall. The purpose of the rebar, of course, is to tie the floor/roof to the wall, taking lateral forces perpendicular to the wall as well as parallel to the wall.
The problem is that NONE OF THE DETAILS MEET CODE. (in our humble opinion)
The shear friction plane is located at the end of the plank and the bars generally extend out of the plank only about 2 to 4 inches before turning down into the wall. Therefore, the detail suggests that you are trying to develop a hook beyond the shear friction plane and your hook ldh is only 2-4 inches...which is obviously not the required amount for any bar.
I notified the NCMA on this issue and the response was that they would look into it at their next summit conference.
The way I read the code, you either meet the fy condition, or you have zero capacity in terms of shear friction. I don't see how you can reduce the capacity (this is what Asreq'd/As provided was doing...which is disallowed).
RE: Development Length of Reinforcement in Shear
If you grout (with epoxy) a Hilti anchor (using rebar) into concrete, you get a shear capacity, even though the embedded length is much less than the development length.
RE: Development Length of Reinforcement in Shear
RE: Development Length of Reinforcement in Shear
Joint design is still much to be worked out, so thes problems are likely to stay for some time, it is my view.
The RC buildings made the last decades are behaving well mainly on that they only have been facing vertical loads, if earthquake other thing might develop.
Development and slice lengths as per code stay 2 and more likely 2.t times those strictly required. With live loads usually present only in a percent of the capacity, the short as per the code embedments work well but for the real test in which the code requirement of limit strength becomes real.
Something of the same happens with excessive redistribution of negatives towards positives.
And respect masonry I had the experience of trying to support a 35 cm thick slab with I think about 7 m in the masonry wall and even without any wind loads it was not feasible to meet the code nor thick nor thin the wall would be (I think I discarded centering the load forcibly, don't exactly remember)... my conclusion was that the code is targeted to produce exclusively lightloaded shortspan structures (for masonry units), and make everybody look elsewhere even for normal spans.
RE: Development Length of Reinforcement in Shear
RE: Development Length of Reinforcement in Shear
The concept of shear friction is that the steel you install must cross the potential crack, keep the crack closed, and therefore engage the friction between the concrete surfaces. If you use a larger bar, and do not develop its full fy, then the potential exists for an overload condition that does not allow a gradual failure of the system.
You know that they do this throughout the code...for example, flexural capacity (phi Mn) uses a phi of 0.9 while for shear (which is abrupt) they use 0.85. For columns (even more non-redundant) we have phi = 0.7.
In this case, you want the potential crack to open wide at first, giving ample warning of a problem. With your #4 bar vs. #5 bar example, the #4 bar, if overstressed, would enter the yield zone and allow the crack to open. You'd be warned and you'd run out and hire a structural engineer to fix it.
With the #5 bar, your unanticipated overstress would at first stretch the bar, but the limit state is now the bar pulling out of the concrete....and it never gets a chance to yield. BOOM
The commentary in ACI 318 section 11.7 talks through shear friction pretty well...but it doesn't really address this rationale.
The above is my "guess" that seems to make sense to me. What do you think?
RE: Development Length of Reinforcement in Shear
RE: Development Length of Reinforcement in Shear