Rebar Lap Question
Rebar Lap Question
(OP)
So, I was visiting a job today to take a look at rebar for a very large concrete beam carrying significant load (vertical, horizontal, and torsional). This is for an existing building, and the working space is minimal. The horizontal reinforcement is spliced at roughly the third points - there are hooked horizontal bars at the ends extending roughly 40% of the span at each end and then a straight bar in the middle lapped with each of the end bars.
The problem I noticed is that one of the corner longitudinal bars is not within the stirrups (only the straight bar over the middle 30% or so of the span). The two hooked end bars that are lapped with this particular straight bar are inside the cage, but the straight bar is outside the cage.
I raised this as a concern for a couple of reasons.
1) The bar has no confinement and is held in place only by ties to the stirrups (and bars that it's lapped with over the lap length.
2) Part of the reason that stirrups can develop Fy in such a short distance is because it's hooked over the top bar. If that isn't the case then that could have an impace on the effectiveness of the stirrups at this location.
The more senior engineer I was with didn't think it was a big deal because 1. the lap length was larger than it needed to be, and 2. There's a large amount of cover at this location > 6" so that the confinement issue really isn't a problem since that much concrete is not likely to spall off.
I'm still not convinced. Can I get some second opinions?
I see the point about so much cover being unlikely to spall off, but it still doesn't "feel" right when I look at it.
The problem I noticed is that one of the corner longitudinal bars is not within the stirrups (only the straight bar over the middle 30% or so of the span). The two hooked end bars that are lapped with this particular straight bar are inside the cage, but the straight bar is outside the cage.
I raised this as a concern for a couple of reasons.
1) The bar has no confinement and is held in place only by ties to the stirrups (and bars that it's lapped with over the lap length.
2) Part of the reason that stirrups can develop Fy in such a short distance is because it's hooked over the top bar. If that isn't the case then that could have an impace on the effectiveness of the stirrups at this location.
The more senior engineer I was with didn't think it was a big deal because 1. the lap length was larger than it needed to be, and 2. There's a large amount of cover at this location > 6" so that the confinement issue really isn't a problem since that much concrete is not likely to spall off.
I'm still not convinced. Can I get some second opinions?
I see the point about so much cover being unlikely to spall off, but it still doesn't "feel" right when I look at it.






RE: Rebar Lap Question
I have also seen something in the code about allowing extra concrete as lateral confinement, (not exact wording) but I can't find it now.
I don't know much about statistics, but I do know that if something has a 50-50 chance of going wrong, 9 times out of 10 it will.
RE: Rebar Lap Question
RE: Rebar Lap Question
As you can see, one of the lapped bars falls outside of the stirrups.
RE: Rebar Lap Question
RE: Rebar Lap Question
RE: Rebar Lap Question
RE: Rebar Lap Question
If the contractor says that it is too hard to relocate the outside bar, just provide a detail showing added extra cross-ties to confine the bar. One or the other has to be done. His mistake - His choice.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Rebar Lap Question
RE: Rebar Lap Question
RE: Rebar Lap Question
I would have thought that the stirrups would be 8" wider so that they enclose a larger rectangle for torsional loading.
BA
RE: Rebar Lap Question
But seriously, StructuralEIT, don't keep us in suspense. How did it work out?
RE: Rebar Lap Question
RE: Rebar Lap Question
Ultimately, the senior engineer said it's ok. When I'm put in that position and I'm making the call, I'm going to have him redo it. I don't like the way it looks and the "load path" (for lack of a better word here) looks incomplete to me.
Thanks for the input everyone.
RE: Rebar Lap Question
detail. Especially at beginning of a job. Otherwise they will keep pushing and get sloppier (rodbusters).
RE: Rebar Lap Question
RE: Rebar Lap Question
It is just minimum steel, but the beam is a critical member. It's supporting the entire 16" stone facade for a 4-story building, and supporting a large bay. The stone has a fairly large eccentricity to the beam.
The beam is seeing torsion, strong axis bending, and weak axis bending. There is no redundancy, either, if this beam fails, that whole side of the building will topple over (I'm not exaggerating).
RE: Rebar Lap Question
RE: Rebar Lap Question
Unless there is concentrate load or torque in mid-span, isn't shear & torsion critical near the supports? The end hooks are enclosed as mentioned in the OP.
I think there is nothing inconvenient to ask the contractor to correct it - a middle piece straight bar that can be inserted without much trouble. But, I wouldn't say it is necessary, as this bar was adequately confined by concrete mass on 3 sides, and there obviously has no cause for the bar to pop out/crack the top face (with std. covers only).
Again, this is my person opinion only. I will definitely try to talk the contractor into correction.
RE: Rebar Lap Question
True, it would be worse if the unanchored stirrups were in a high shear region.
RE: Rebar Lap Question
RE: Rebar Lap Question