Wire rebar in concrete forms or not?

Stan in Oly, WA

Well-known Member
Someone I consider knowledgeable on the subject of building concrete walls told me something I?d never heard before. We were talking about placing rebar in concrete forms. He said that where horizontal lengths of rebar overlap, it?s better if they aren?t wired together. He claimed that wiring rebar together in the forms is only to keep it from being moved out of position when the concrete is poured over it. In places where there is no danger of the rebar being moved by the concrete, the pour will be stronger when the pieces of rebar are not wired together than when they are. My first response was to reject this, but after giving it some thought I realized that I don?t actually know enough about it to have an educated opinion either way. I can?t honestly say that I have an educated reason for the way I pour concrete other than it?s the way I?ve always done it because it?s the way I?ve always seen it done. But I?m largely self-taught, and the small contractors I?ve worked with have also been largely self-taught, so maybe the only basis I have for the way I do it is habit. I wouldn?t mind being set straight, even though I hope I don?t have to pour much more concrete in this lifetime.

Stan
 
I agree, if the rebar is where it won't move it's unnecessary to wire it together. Having said that though rebar easily moves from the weight of concrete so I usually wire it all together. I'd rather spend the time wiring it together than have to watch it while making a pour and perhaps have to fight it back in place if it does move.
 
Well, wiring the rebar together certainly won't make the concrete any stronger; there's no way a few wraps of wire will be able transmit any tension force between two pieces of rebar. I don't think I'd go so far as to say it makes the structure significantly weaker, though.
 
I was an industrial construction carpenter for 5 years so I saw a lot of rebar, and it was always wired together, and there are specifications for for minimum overlap. The placement of the rebar is very important and if it's not wired together it may get pushed out of place by the pour. Rebar is supposed to be in the area of tension, it does very little good in a compression zone. Precast beams have to be handled very carefully as they are only deigned to be strong in one direction, I suspect the recent bridge collapse in FL was due to mis-handling.
 
Wiring is used to keep the bars in the proper position during concrete placement. Wiring itself adds very little to strength.
 
Stan, it's been a while since I've had the book open, but I can assure you that the Standard Specifications for Road and Bridge Construction specify that rebar splices WILL be wire tied - twice on each splice, if my memory serves me correctly. When you're loading wall forms with concrete, a loose bar can cause you much grief.

On your own work, you can do it as you please, of course.
 
I have always seen it tied, and would assume there is a standard for how much overlap on the rebar too.
 
Ever road construction job I've seen always has some workers bent over, hand tying rebar...

So it must be a necessity.

I can't imagine how a human body can take that day after day!
 
Just keeping the hard hat on is a pain. Gotta cinch it up tight.

Ironworkers are a tough bunch.
 
(quoted from post at 06:50:23 04/16/18) I have always seen it tied, and would assume there is a standard for how much overlap on the rebar too.

Like said, tying it just holds it from moving while poring the concrete. On the bigger re-bar we welded it. The rule we used for lapping was 30 X the diameter.
 
In recent years I have not saw anyone tie rebar when pouring a wall. They have all used cross ties (either plastic or metel) that the rebar snaps into.

When a company poured a long driveway around part of a apartment complex last year. The forming machine they used "injected" the rebar automatically as it poured, formed and finishsd the drive all in one pass.
 
Concrete specs generally call for rebar splices to be tied together so there is no gap between the pieces, and keeps the rebars from moving. Rebars may be not tied if there is sufficient distance between the rebars that it gets filled with concrete and no voids are created--the distance apart depends on the largest size aggregate in the mix.
 
many precast beams are subjected to negative moment in certain areas, so those beams are reinforced not only on the bottom but also on top. The designer will usually specify the pick up points and storage points to minimize the stresses.
 
the newer standards take many things into consideration when designing the length of a splice,
the grade of rebar
the stress level in the rebar
% of rebars spliced in any one cross section
strength of the concrete
location of splice (top or bottom of beam)

I have designed splices where I had to use up to 60 times the diameter.
 
> Concrete specs generally call for rebar splices to be tied together so there is no gap between the pieces, and keeps the rebars from moving.

Makes sense. Thanks.
 

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