ACI 318 21.9.5.1 vertical rebar considered "effective" or can they be non-continuous betwe
ACI 318 21.9.5.1 vertical rebar considered "effective" or can they be non-continuous betwe
(OP)
When I read ACI 318-11 section 21.9.5.1, I read that all vertical reinforcement must be considered effective in the sense that the vertical bars shall be relied upon for shear in two directions. I also understand this to mean that all bars shall be considered effective for the purposes of yielding and to not over-estimate the moment capacity by putting all coupling bars at the wall edges. In effect, it's supposed to be detailed and designed consistently.
I'm responsible for the review of a retrofitted special reinforced concrete wall in an existing concrete building. It is spanning between T-beams of concrete whereby the wall effective thickness (12") matches the bottom tapered thickness of the t-beam web on each level. My problem is this: the shear reinforcement needs to be at least 0.0025 of the gross concrete area based on it being a special reinforced wall. Since all the bars are required to be considered effective, what would you detail for your tension between floors? The original engineer has rebar checked only for shear transfer (#5 at 12"oc) for the diaphragms at each level, but the code isn't explicitly clear to detail the tension bars (#6 at 8"oc e.w. both faces in this case) between floors, except in the above instance.
Thanks in advance for any helpful insites.
OUe
I'm responsible for the review of a retrofitted special reinforced concrete wall in an existing concrete building. It is spanning between T-beams of concrete whereby the wall effective thickness (12") matches the bottom tapered thickness of the t-beam web on each level. My problem is this: the shear reinforcement needs to be at least 0.0025 of the gross concrete area based on it being a special reinforced wall. Since all the bars are required to be considered effective, what would you detail for your tension between floors? The original engineer has rebar checked only for shear transfer (#5 at 12"oc) for the diaphragms at each level, but the code isn't explicitly clear to detail the tension bars (#6 at 8"oc e.w. both faces in this case) between floors, except in the above instance.
Thanks in advance for any helpful insites.
OUe






RE: ACI 318 21.9.5.1 vertical rebar considered "effective" or can they be non-continuous betwe
RE: ACI 318 21.9.5.1 vertical rebar considered "effective" or can they be non-continuous betwe
Based on what you've shared, the retrofit sounds like a pretty common design approach. That said, it is necessary that the boundary tension reinforcing be continuous vertically. Is that not the case? Are you able to post some sketches/details?
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.
RE: ACI 318 21.9.5.1 vertical rebar considered "effective" or can they be non-continuous betwe
RE: ACI 318 21.9.5.1 vertical rebar considered "effective" or can they be non-continuous betwe
Thanks for your comments!
RE: ACI 318 21.9.5.1 vertical rebar considered "effective" or can they be non-continuous betwe
Assuming the bars are effective does not by itself increase ductility. In fact, adding reinforcing beyond what is required by analysis will generally decrease ductility, especially if it is not accounted for when trying to ensure a flexural failure by capacity based design. This is what the SEAOC Seismic Design Manual is warning against in the quote below. What is important is making sure that your detailing matches your design assumptions so you don't underestimate the capacity of the wall. If the reinforcing is there and it's developed, it needs to be included in the analysis. This is different from requiring that all reinforcing be effective.
RE: ACI 318 21.9.5.1 vertical rebar considered "effective" or can they be non-continuous betwe
Cheers!