Is it beneficial/recommended to have longitudinal reinforcement placed at the corners of stirrups? 5

[Hydrostru]

For beams, is it beneficial/recommended from structural integrity standpoint to have longitudinal reinforcement placed at the corners of the stirrups or not really needed?

Thanks,

Ron

 

[AUCE98]

How would you support the stirrups otherwise?

 

[ALK2415]

1- A member subjected to given loading is treated as a space truss formed by a series of joined planar trusses.
2- The concrete member reinforced with longitudinal and transverse reinforcement resists shear/torsion by producing a circulatory shear flow at the outermost part of the beam cross-section. Thats why using steel rebars are preferred at circumferential surface of beam (with a nominal cover of 25-50mm.
3- Also the concept of concrete confinement is will suited/played if steel truss is distributed at circumferential surface of beam.

 

[Hydrostru]

There are quite a few rebar on the top and bottom of the beam so support is not a question.

So the question is about rebar placed at the corner or could be a few inches away?

I have been detailing the corner but just saw some plans other than that.

 

[ALK2415]

Confined and confined unconfined concrete terminology, benefits shown in attached curves.
Also using longitudinal reinforcement is needed in almost every concrete structure.

 

[ALK2415]

look at following paper, and also the concept of space truss [Mörsch's truss analogy model]
Link

 

[BridgeSmith]

It's easier to detail the bars in the corner, since dimensioning is unnecesary. It has a small advantage in confinement also.

The only reason I can think of to not detail the longitudinal bars in the corner of the tie/stirrup, is if the designer is concerned about the bars not being all the way to the bottom of the tie or stirrup, due to the bend radius of the ties/stirrups. I think if that's going to make the beam fail, the designer should just add or upsize the longitudinal reinforcing.

 

[Hydrostru]

Thanks to all of you.

 

[ALK2415]

@ BridgeSmith
"It has a small advantage in confinement also."
could you elaborate ?

my interpterion of confinement is similar to following

 

[BridgeSmith]

@ BridgeSmith
"It has a small advantage in confinement also."
could you elaborate ?

I was referring to confinement of the concrete - having the bars farther out puts a little more concrete inside the bars. The difference would be minimal, and the necessity probably non-existent, in most cases.

 

[cliff234]

Placing longitudinal bars in the corners of beam stirrups is an ACI 318 code requirement to ensure (near) instantaneous tension development of the stirrups. See ACI 318-08 Section 12.13.2. (I don't have my ACI 318-19 handy with me, but I don't think it's changed.)