shearwall vertical reinforcing vs crossties ?

[boffintech]

I'm inspecting on a job right now, high rise CIP concrete, with lots of shearwalls.

One of the shearwall notes reads:

CROSS TIES ARE REQUIRED WHERE AREA OF SCHEDULED VERTICAL REINFORCEMENT
EXCEEDS 0.01 TIMES THE GROSS CONCRETE AREA OF THE WALL. IF CENTER TO
CENTER SPACING OF VERTICAL BARS IS 6" OR SMALLER, CROSS TIES SHALL BE
PLACED AT EVERY OTHER PAIR OF VERTICAL BARS; OTHERWISE, ALL VERTICAL BARS
SHALL BE CONFINED WITH CROSS TIES.

The plan view detail, of course, shows neatly placed #3 cross-ties confining #9 vertical bars; however, in real life there is a 66" lap splice and a #3 bent into a 135-degree hook is never going to wrap around #9's spliced side-by-side.

So I'm curious, out of all the CIP shearwalls I've seen over the years, I've never seen SW verts dog-legged similar to column vertical bars so that the bars can be spliced front-to-back instead of side-to-side.

Is there something in ACI-318 that disallows vertical bars in shearwalls from being dog-legged?

 

[JAE]

There's nothing in 318 that disallows "dog legs" in shear walls. In your case, with real world physical conditions, the vertical bars in the shear wall would have to be lapped on the front-to-back as you say to work with the hooks.

Othwersise, if side-to-side laps are preferred, then the cross ties would have to be altered to be a series of rectangular ties (like in a traditional column) and wrap around pairs of bar lines. Even with that, the corner of the tie may have to wrap on a dummy vertical bar or something. I've rarely had ties in shear walls so I may have to think about that.



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[TXStructural]

I am willing to bet the placer and fabricator are ahead of you on this. Discuss it with them.
There is seldom a need for an offset bend, but they can be used in congested walls. Also remember that lapped bars do not have to be in contact so the hook can go around one bar but not the other unless the design calls for ties around all bars.

 

[KootK]

@TXStructural: I almost gave the same answer regarding the nob-contact lap splices. I rejected it because the ties are invariably for the lap compression condition rather than the tension lap condition. Under compression, the one bar of the lap not engaged by the tie hook would be prone to buckling out of the wall.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[TXStructural]

Many things affect restraint, including whether it is the vertical or horizontal bar that is on the outer layer. In this case, some restraint is provided by cover and some by the horizontal bars. In pre-tied walls, it is unreasonable to expect every vertical bar to line up from one cage to the next, so a non-contact lap condition should be anticipated. If the laps are non-contact, the designer can specify if every bar in the lap requires a tie or how to handle the situation. If there is sufficient cover, tying the outer layer could be useful, but this would be unusual.

In the OP, the note says that bars spaced 6" or less, as would be the case with non-contact laps, require ties on every other bar. I would interpret this to mean that there will be ties on every other bar along the non-contact laps. The rebar detailer may or may not provide enough ties for this condition, so I would discuss it with the supplier or placer early in the project.