Reference Needed: Proper detailing of concrete wall
Reference Needed: Proper detailing of concrete wall
(OP)
I have always thought that proper detailing of a reinforced concrete wall with two layers of vertical reinforcing was for the hooked portion of the dowels in the footing to point towards one another.
However, I have seen this detailed the opposite more often than not and my supervisor and senior designers here show it as such.
Does anyone have a reference supporting the idea that detailing bars as shown in the attached sketch is indeed the proper way to do it? I think I may have seen this in ACI SP55 or the "Detailing Corner" section of their monthly publication, neither of which I have at my current company.
Thanks.
However, I have seen this detailed the opposite more often than not and my supervisor and senior designers here show it as such.
Does anyone have a reference supporting the idea that detailing bars as shown in the attached sketch is indeed the proper way to do it? I think I may have seen this in ACI SP55 or the "Detailing Corner" section of their monthly publication, neither of which I have at my current company.
Thanks.






RE: Reference Needed: Proper detailing of concrete wall
RE: Reference Needed: Proper detailing of concrete wall
Who details shear keys? I've never seen the need if you can prove that the bar takes the shear.
RE: Reference Needed: Proper detailing of concrete wall
Dik
RE: Reference Needed: Proper detailing of concrete wall
I sometimes use shear keys, if there is no slab or whatever to resist lateral loading... often happens with retaining walls, or the slab will be placed at a much later date, etc.
I split a 2x4 or whatever and cut it on a slope in the middle, I then rotate the members so that I have a key with sloped edges and a space in the middle to accommodate any dowels, or if doubly reinforced, trim off one edge (and cut down the middle) of a 2x? member to permit removal. The dowels are then placed at the outside edges of the 2x?.
I often use a bentonite rod in the keyway to prevent water passage.
Dik
RE: Reference Needed: Proper detailing of concrete wall
- For small strip footings under walls with 2-layers of rebar, the manual shows outward bound hooks (I typically read this as pin joints).
- For wall to mat connections, the manual shows the hooks towards each other (these details are usually for water retaining walls). In addition, the hooks continue and form the bottom layer of rebar in the mat (I've never done this).
I think either way is fine, just note the following:
1. Hooks towards each other will add to local congestion for tightly spaced wall rebar.
2. Outward bound hooks do not pass through the compression zone of the wall during overturning. Therefore, Ldh is critical.
Additionally, I like to detail a bar along the inside bend of a hooked bar.
RE: Reference Needed: Proper detailing of concrete wall
1) If you bend the bars towards each other, that provides for bettter "confinement". This is a real consideration for seismic design when that connection must take significant moment and have significant ductility.
2) The construction guys in the field will very much prefer that the bars be bent away from each other. It's just a lot easier to build.
Since my college professors were seismic guys, I started out detailing everything with the bends towards each other.... One of my first supervisors put a stop to that.
Josh
RE: Reference Needed: Proper detailing of concrete wall
Good points on this detail placing the hook in the compression area of the footing - that had not occurred to me.
This will probably get red-lined back to 'bars facing outward' but now I do have some justification here and for my piers which carry a substantial base moment. If anyone can find a document to support that would still be appreciated.
RE: Reference Needed: Proper detailing of concrete wall
I've started (couple of years ago) using these for corner bars...
Dik
RE: Reference Needed: Proper detailing of concrete wall
RE: Reference Needed: Proper detailing of concrete wall
RE: Reference Needed: Proper detailing of concrete wall
Typically, a wall-footing connection is designed as pin connected, since a strip footing is usually a gravity device (in cross section). If there is uplift, and the footing is designed properly, it shouldn't matter which way they turn.
For a wall where moment connection is required, you should treat it as a cantilever wall, placing bars at the bottom of the footing and turning them across the wall, developing them into the opposite end of the footing. Detailing should conform to the CRSI Design Handbook or ACI/CRSI 315 (they should show the same information.)
Continuous U-bars make placement difficult in taller walls, if the verticals are not spliced. Practice is often to form one side of the wall and then place the bars in layers as they move away from that form. Also, bending tolerances in u-bars may cause encroachment into cover (this can be alleviated by angling the U until the proper wall thickness is reached.)
I do not see this among our Detailing Corner articles or Tech Notes, which are available free on the crsi.org website.
RE: Reference Needed: Proper detailing of concrete wall
For smaller strip footings, the legs of these bars can serve as extra transverse reinforcing to the footing.
If bent out, for uplift, they can effectively serve to pick up more of the footing without additional steel.
Mike McCann
MMC Engineering
RE: Reference Needed: Proper detailing of concrete wall
If providing dwls on both sides, then U bars work fine and you may want to add the detail to your list. This is sometimes required for tunnel construction, etc. U bars have the same concrete cover spacing problems as a double line, except you only have to concern yourself once... not two lines to be off.
I often use a single layer of dwls in the middle and these are commonly spaced at twice the vertical wall reinforcing spacing.
Mike...
For small footings, I often don't use any reinforcing in the footing (even for commercial/industrial), just treat them as plain concrete. In most cases, as noted, there is not a moment to deal with. For larger footings, normally with large cantilever retaining walls, I wrap the dowels underneath the wall.
RE: Reference Needed: Proper detailing of concrete wall
As you mention, since the connection is essentially pinned at most footings, a single row of dowels should be sufficient.
RE: Reference Needed: Proper detailing of concrete wall
RE: Reference Needed: Proper detailing of concrete wall
RE: Reference Needed: Proper detailing of concrete wall