Requirement of 2 in. Clear Cover from C.J. for Vertical Reinforcement

[CWEngineer]

In our structural details we have the vertical bar in the open face of the wall that goes down to the footing and then continous along the bottom of the heel. (Please see attached drawing - top drawing has continous reinforcement and bottom drawing has spliced reinforcement)

However the rebar will be spliced due to transporting issues. The rebar will be placed along the bottom of the heel and then hooked up to the required spliced length. The concrete will then be placed up to the Construction Joint. Then the vertical rebar will be placed 2 inches above the construction joint and spliced to the reinforcement that has already been set in the concrete.

I am trying to find why the 2" clearance between the bottom of the vertical splice and the Construction Joint is required.

Really appreciate if you guys can give an explanation or possibly provide reference where this is addressed.

Thanks

 

[Lion06]

I can only imagine that it is being conservatively assumed that it is exposed to weather and a #6 or larger, but I would still think that the 2" cover would not apply to the face of the existing pour.
Our typical detail doesn't show any such dimension and while there is probably no harm in it, I don't think it is necessary.

 

[jike]

I also believe that this is not necessary to say nothing of also being impractical. When you set the vertical bars, one normally sets them right on the poured concrete base.

 

[csd72]

The other bar is doing all the work at that point and it doesnt have 2 inch cover!

Just a note, but I noted you drew the bars on the compression side of the retaining wall.

 

[civilperson]

This is a mistake, no cover to a construction joint is required. Reinforcement is shown continuous through construction or cold joints. Aesthetics is the reason cold joints are prohibited, (not wanting a horizontal line to show after stripping the forms).

 

[CWEngineer]

The re-bar currently in question is the re-bar in the open face of the wall (compression side).

Per ACI 318-08, 12.5 Development of standard hooks in tension, 12.5.3, "For No. 11 bar and smaller hooks with side cover (normal to plane of hook) not less than 2-1/2 in., and for 90-degree hook with cover on bar extension beyond hook not less than 2 in. ...........0.7"

From this statement, if I calculated the development length of the hook in the re-bar in the earth face of the wall (tension) using the 0.7 factor, wouldn't it meant that a cover of the bar extension is to be 2 inches from the costruction joint?

Also, say you have construction joint in the invert of a channel. From what I have seen typically the horizontal re-bar from the concrete that has already been set is spliced with the horizontal re-bar in the slab section that is getting ready for concrete placement. The horizontal re-bar in the slab that is waiting for the concrete placement is not placed in direct conctact with the face of the other concrete section - it also has a clerance of 2 inches. Isn't the Construction Joint in the retaining wall similiar to the construction joint in the invert, with the exception that they are 90 degrees from each other? I would assume that the same reason for needing a 2 in. clear cover on the reinforcement in the inver construction joint would be the same for the one in the wall.

Hope I was not two confusing with my explanation. Please let me know if you need further clarification. Really appreciate your help.

Thanks

 

[Lion06]

That 2" that you are referencing would be from the hook to the bottom of the footing. The hook is at the bottom, not going up the wall. The bar going up the wall is what is being developed and the hook that is helping to develop it is along the bottom of the footing.

 

[DRC1]

I have never seen bars held off the bottom of a construction joint. Best I think you would get would be 1 1/2 inches, the height of a 2x4. Not sure i follow you channel invert analogy. What is that exactly?

 

[boffintech]

In the given diagram, shouldn't the horizontal CJ actually be at the top of the foundation? I've never seen a contractor erect a floating form along the top of a continuous wall footing in order to cast a curb monolithic with the footing. Isn't the bottom of the wall is normally placed at the top of the footing?

I think that maybe the vertical bar in the wall (not the vert leg of the hook but the second bar placed) is drawn with a gap between the top of footing and the bottom of the bar simply for clarity. There is not actual requirement for a gap.

The 2" limit arrows should be turned 90 to show the clearance from the vertical leg of the hook to the open-face of the wall. Wouldn't that make more sense?

 

[civilperson]

Cover to the face of the wall is required as per boffintech. The 2" dimension shown is from the location of the construction joint and there is no required distance for that dimension.

 

[kslee1000]

I guess the 2" clearance below the bars was intended to assure there is adequate fresh concrete below, and to avoid/minimize potential air gap/void below the bars to form a weak plane. Not bad idea, but difficult to image the contractor woulf follow it.

 

[CWEngineer]

Attached is a detail that shows my invert analogy. In this detail you need 50 mm (2 inches) of cover between the end of the horizontal bars and the face of the slab - you would not end the horizontal bar on the face of the slab. I believe the same reason you need these 2 inches of cover would be the same if you rotated this detail 90 degrees (retaining wall/footing).

Yes, In uderstand there is a clear cover from vertical reinforcement to the open face of the wall - but I am not showing that here.

Typically, flood control channels, at least in the southwest are constructed with a starter wall, in which the concrete for the footing/invert and the starter wall (first 3 inches of the stem of wall, up to construction jont) are placed monlithically.

Really appreciate your advice/guidance. THANKS.