Flexural Reinforcement Termination in Stem of Retaining Wall
Flexural Reinforcement Termination in Stem of Retaining Wall
(OP)
I am designing the tension reinforcement within the stem of a cantilever retaining wall. This wall, like most walls, is tall enough that it would be very inconvenient to require that the bars be placed full height at the time of the footing pour. I would like to provide a lap splice of the tension reinforcement within a reasonable distance of the top of the footing and so I think I must meet the provisions of ACI 12.10.5. Is this correct? Most designs I have seen for this scenario provide for the wall's moment and shear requirements, specify the general tension development length but do not address the fact that there is a termination in the tension zone.






RE: Flexural Reinforcement Termination in Stem of Retaining Wall
RE: Flexural Reinforcement Termination in Stem of Retaining Wall
Keep in mind that only ONE of the three requirements of 12.10.5 need to be met.
Section 12.10.3 must be met as well for the stem reinforcement.
RE: Flexural Reinforcement Termination in Stem of Retaining Wall
RE: Flexural Reinforcement Termination in Stem of Retaining Wall
In addition, for taller walls where the moment in the stem drops to 50% (or a portion thereof) of the maximum, the tension rebar can be terminated - like every other bar or so. Even CRSI has details for this.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Flexural Reinforcement Termination in Stem of Retaining Wall
But if the question is to just use lap splices on all the bars to avoid having long dangling vertical bars sticking out the footing - then nongamer12's comment does make sense and 12.10.5 would not apply.
RE: Flexural Reinforcement Termination in Stem of Retaining Wall
RE: Flexural Reinforcement Termination in Stem of Retaining Wall
Just to clarify, I intend to provide a lap splice at EVERY vertical bar along the entire length of the wall. I have attached a typical sketch of this type of configuration. One tension bar is cast and developed properly into the footing during the footing pour and then another bar lap spliced to that one for the wall pour. The back face of the entire wall, by virtue of its design as a cantilever, is in the tension zone. This will allow for the reinforcement cage to be constructed more readily, however I wanted to be sure that 12.10.5 applies. You can assume that I have provided the proper development length. There will not be any stirrups (12.10.5) so it would seem that I need to check for compliance with 12.10.5.1 or 12.10.5.3. Thank you all. Your posts have been very helpful. Thank You.
RE: Flexural Reinforcement Termination in Stem of Retaining Wall
So find the point up the wall where 18 mm bars work (Point A). At that point would the bottom of the 18 mm bars. The top of the 25 mm bars would be your lap splice length above point A.
RE: Flexural Reinforcement Termination in Stem of Retaining Wall
RE: Flexural Reinforcement Termination in Stem of Retaining Wall
I'm not sure about that. If you put the 18's as working fully at the top of the 25's, - if you go say 1/4 of the way down the splice, technically your 25's still have zero capacity as they aren't yet developed enough from their ends to really do anything.
So you'd have larger moment than the 18's can take, and the 25's aren't able to help any.
Not sure about your concrete code but in ACI, you must have a minimum length of development beyond the point where the bar begins to "do work".
RE: Flexural Reinforcement Termination in Stem of Retaining Wall
This old thread had a discussion about this issue, which was possibly inconclusive. I agree with what miecz said "If you have the required reinforcing developed at both ends of the splice, you'll have enough developed in between."
thread507-233274: Moment along a rebar lap splice
RE: Flexural Reinforcement Termination in Stem of Retaining Wall
As you show, Class B tension laps are acceptable. I would hook the footing-to-wall dowels to the bottom mat rather than sit them on top of it, to improve development and make placing more secure. Show the 18mm bars extending all the way to the top of footing or provide a dimension. Best practice also includes "D" diagonal bars across the footing to wall interface.
For crack width control in tall walls (over 10 ft) we recommend that only half of the flexural reinforcement be lap spliced at the base, the other half should be extended to mid height of the wall. Consider that the change in bar size and the large area of steel in the lap region create a discontinuity in stiffness, which this practice is intended to mitigate.