stirrups ana ties diameter 1

[EYFS]

Hi all,
I have a questions about minimim ties and stirrups diamter. ACI 318 mention that the minimum diamter to be used is 10 mm. In my country, we always use 6 and 8. Because it's easier to be bent on site. But my question is do ACI 318 or any other code in old revisions accepts these small dimaeter of reinforcement ?

 

[manstrom]

ACI is pretty prescriptive when it comes to ties. #3 @ xx o.c. or #4 for bigger bars. Spacing is based on column dimension, tie and bar size.

I'm sure you could reasonably substitute an equal area of steel using smaller bars, but I don't see the point. These are normally prefabricated. They can bend anything in the shop.

Frankly, I've never seen bars smaller than a #3 on a construction site.

 

[jayrod12]

CSA A23.3 will let you use any diameter you want. as long as you meet the Avmin requirements. and a small list of other requirements to be counted as stirrups or ties.

 

[KootK]

For columns, ties help to confine the concrete. As such, there are concrete bearing stresses on the ties. I'd stick with #3 for that.

For beams, you could have no stirrups at all if you elected to do it that way. I've used WWF for stirrups in the past.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[fegenbush]

manstrom has the answer on this one, but I would like to add in a "why" component. How are the deformations to be made in a bar smaller than #3? If the concrete is not able to appropriately grip the reinforcement, how is the reinforcement going to be effective?

 

[KootK]

You can develop smooth bars. It just takes a little longer.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[TXStructural]

ACI does not recognize bars smaller than #3 (about 10 mm) because it is not produced in the US. The US market (and the ASTMs) once included #2 (1/4 inch, 6-7 mm) but hot rolling bar of this diameter is difficult. Most producers prefer to not produce #3, either. The rolling process becomes problematic when the red-hot bar is too small/flexible. Small bars also cool rapidly, which changes the mechanical properties of the finished bar.

When using wire (a cold worked equivalent), there is no reason you cannot simply use an equivalent A(sub)s, keeping in mind the reduced ductility of most wire. Some deformed wire is essentially a hot rolled steel rod with one drawing for size and one rolling for deformations, so the cold work can be minimal. And there is deformed wire used in welded wire reinforcement up to 5/8" diameter.

 

[hokie66]

The Australian Standard, at least the last time I checked, allowed the use of 6 mm ties in columns, for longitudinal bars up to 20 mm. But I don't think this is common in practice.

ACI318-63 did allow the use of 1/4" ties in columns. I am not sure when that was changed.

In Australia, bars 12 mm and greater are hot rolled, while smaller bars are typically cold rolled, both deformed and smooth. But I don't know how much of that is done, as much of our reinforcement now is imported.

Bending ties on site sounds strange, and difficult. Don't you have any bar bending facilities in your country?

 

[Ingenuity]

Bending ties on site sounds strange, and difficult. Don't you have any bar bending facilities in your country?

I worked in Guam (island territory of the USA) for a bunch of years from early 1990's until early 2000's and each and every general contractor (no sub contractors do rebar supply/bend/install) would set up a 'mobile' (2x4's with plywood roof) site bending facility for projects. All rebar (including column ties and beam stirrups) were cut and bent from stock length bar on site.

Given the seismic zone and typhoon belt, the buildings were well designed and constructed. With the exception of the Royal Palm Hotel where a 3rd floor column of a 20 story building popped out during the 8.0 EQ that caused the building to rotate and then had to be imploded in 1993. Experienced +200 mph winds too in 1997 too with typhoon Paka. We survived the high winds, but not having power and water for 3 weeks was the real killer.

Guam constructors also made there own 'adobe' concrete rebar support spacers - 8'x4' ply forms of varying thickness side forms (1", 1.5", 2" etc), tie wire loops inserted into each cut up slice - cut like you would cut a cake. First time I saw it I was gob smacked. But it worked...and still done that way too.