Development Length

[slickdeals]

Folks,
I have a question that may come across as retarded, but I gotta ask.

A standard hook for a #4 bar is 12 db = 12*0.5=6".

What happens for a #4 U bar or a #4 stirrup? Is the requirement that you need 2 * standard hook = 24 db to develop the bar?

 

[DaveAtkins]

Stirrups are treated differently--there are various ways to develop a stirrup bar. See ACI 318-08 Section 12.13. And remember a "standard stirrup hook" is different than a "standard hook."

DaveAtkins

 

[Lion06]

No, a 135 degree hook will develop the stirrup, see R12.13.2.2

 

[JAE]

And don't forget that the 12db is for the straight portion of the hook only - not the bend. The bend is in addition to the straight portion so for a #4 bar the total 90 degree hook size is 8".

See ACI 7.1.

 

[slickdeals]

Folks,
I guess I did not express myself correctly.

A quick sketch:

| |
| |
| |
|____|
?

What is the minimum length (based on db) of the horizontal leg of the U to develop this stirrup?

 

[JAE]

I think when it is looped around like a "U", you don't have to meet the standard hook distances/lengths....only the bend diameters. So for a #4 stirrup, using 2" for the bend diameter you'd have (out to out of bar):

2" + 2(1/2" bar dia) = 3" total width.

 

[slickdeals]

Interesting, i am surprised the codes don't address this in any more detail.

Another question I have is this:
How much concrete should you have around a reinforcing bar in order to adequately transfer the stresses from reinforcing bar into concrete?

Assuming that you have a #5 bar, what is the minimum cylindrical area around the bar needed so that it does not pull out (precluding tension failure in concrete).

 

[demayeng]

your last question depends on development length - you're allowed to not have full contact all the way around as long as you increase the length to compensate

The australian code requires an increase in the development length of around 25% when there is more than 300mm of concrete below a bar (to allow for a void formed under the bar due to the slumping and shrinkage away from the bar of the concrete mass under)

I would assume the minimum cylindrical area is the minimum development length required by your code multiplied by the circumference of your bar

 

[slickdeals]

Let me rephrase my question:
Assuming that you have a #5 bar, what is the minimum cylindrical area of concrete around the bar needed so that it does not pull out.

 

[rapt]

slickdeals

Read Chapter 12 of ACI. It explains the logic well.

The formula for development is based on the cover/spacing to the bar and the bar diameter. It is not expressed in terms of a cylinder of concrete required.