Basement Wall Corners: Horizontal Bar Development
Basement Wall Corners: Horizontal Bar Development
(OP)
It is common practice to analyze basement walls using tank-tables, which usually indicate high negative moments around corners and at counterforts. My question is how the bars around corners can be used for tension reinforcement in walls that are too thin to allow the minimum hooked-bar development length.
For example, how can the negative moments be resisted at the corners of an 8" or 9" basement wall when the horizontal reinforcing consists of #5 bars? (In the case where the backfilling and compacting would be performed prior to framing the floor)
I would appreciate any thoughts on how the corner conditions can be detailed in accordance with the ACI 318. Thanks!
For example, how can the negative moments be resisted at the corners of an 8" or 9" basement wall when the horizontal reinforcing consists of #5 bars? (In the case where the backfilling and compacting would be performed prior to framing the floor)
I would appreciate any thoughts on how the corner conditions can be detailed in accordance with the ACI 318. Thanks!






RE: Basement Wall Corners: Horizontal Bar Development
Mike McCann
MMC Engineering
RE: Basement Wall Corners: Horizontal Bar Development
RE: Basement Wall Corners: Horizontal Bar Development
RE: Basement Wall Corners: Horizontal Bar Development
With a good length of wall to work with why are you using a hook? - Not saying you shouldn't , just curious..
If you're not using std hook, just running h bars into each wall an appropriate distance, I dont see why 12.5.4 applies
RE: Basement Wall Corners: Horizontal Bar Development
DaveAtkins
RE: Basement Wall Corners: Horizontal Bar Development
RE: Basement Wall Corners: Horizontal Bar Development
VTEIT: the hook is not to develop the bar out in the wall, but rather to develop a tension-controlled section at the corner itself, which resists *negative* moment.
SplitRings: I've also added corner bars in between the horizontal reinf to tighten the spacing by 1/2, since it's what I leared from the beginning from other engineers, but I've also wondered how it was possible to develop the bars.
Dave: You've hit my concern. I am concerned about the discrepancy between "standard practice" and the code requirements. It seems there is a danger of the bars spalling out the inside corner of concrete.
RE: Basement Wall Corners: Horizontal Bar Development
RE: Basement Wall Corners: Horizontal Bar Development
RE: Basement Wall Corners: Horizontal Bar Development
But I'm still not seeing a problem. Lets say you have #5 H bars and have #5 crn bars extending 24" past each inside corner. Class b splice = 24" for that so it's good to go, correct? Why does it need confinement?
RE: Basement Wall Corners: Horizontal Bar Development
The problem is you can't extend the bar 24" past the inside corner if the wall is only 8" or 9" thick. You will only be able to extend it 6" or 7" to within 2" of the opposite face. The hook development length of a #5 bar is 8.4", so you cannot fully develop the bar.
DaveAtkins
RE: Basement Wall Corners: Horizontal Bar Development
Strictly speaking, the detail that I showed does not provide development according to any provision in ACI. However, the hairpin detail provides so much embedment, that I'm certain that it works.
RE: Basement Wall Corners: Horizontal Bar Development
RE: Basement Wall Corners: Horizontal Bar Development
Options are:
to reduce hook embedment by required by
As req'd / As provided
use smaller bars
provide thicker walls
increase corner thickness with triangular fillet
RE: Basement Wall Corners: Horizontal Bar Development
Attached is a detail I recently did for deep foundation (not actually a "deep" foundation but it has very high walls). Bars are not hooked - similar to hairpins in that they are just deeply embedded.
Are you saying that because they are not hooked @ corners that they are not developed there, and thus do not fully resist negative moments there?
RE: Basement Wall Corners: Horizontal Bar Development
RE: Basement Wall Corners: Horizontal Bar Development
RE: Basement Wall Corners: Horizontal Bar Development
RE: Basement Wall Corners: Horizontal Bar Development
DaveAtkins
RE: Basement Wall Corners: Horizontal Bar Development
First of all, it is generally not a good practice to backfill and compact prior to framing the floor. Better to avoid that by placing both floors before backfilling all the way to the top.
I do not see any problem in developing #5 bars on the exterior face of the wall at a corner. The problem in a rectangular tank occurs on the inside face with water pressure pushing outward, creating tension on the inside face at the corners. You don't have that situation so where is the problem?
BA
RE: Basement Wall Corners: Horizontal Bar Development
Sorry to post a question in another post, but i have been wondering about what you brought up.
When you reduce the spacing at the corners, is that total amount of steel provided at the corner the amount required by analysis for the moment at the corner and the reinforcing along the wall would be for the moment as it drops off? Or is the steel at half spacing in the corner in addition to what is required by analysis?
Thanks.
RE: Basement Wall Corners: Horizontal Bar Development
The additional steel in the corners is what is required by analysis. This addtional steel continues along each of the walls until the moment drops to a point where the wall reinforcing is sufficient.
RE: Basement Wall Corners: Horizontal Bar Development