Confinement of serviceability compression reinforcement in beam

[aghaj]

compression reinforcement is sometimes provided in beams solely for the purpose of reducing time-delayed deformations due to creep and shrinkage of concrete. Does this reinforcement need be confined (with ties)?

What rules govern the termination points of such compression reinforcement?

 

[JAE]

aghaj,
I don't know if you are designing under the ACI 318 code or not. For ACI, they require that all compression reinforcing in beams be enclosed with ties or stirrups which satisfy Section 7.10.5. This section requires the following:

For longitudinal bars of #10 or smaller, the ties may be #3 bars. For longitudinal bars larger than #10, the ties must be #4 bars or larger.

The spacing of the ties cannot be greater than 16 longitudinal bar diameters, 48 tie bar diameters, or the least dimension of the member.

The compression ties must be provided throughout the distance wherever the compression longitudinal bars are required.

There's a bit more in section 7.11 that you should read. I

 

[ishvaaag]

But confinement able to cause 3D confinement is not required, as the answer JAE gives shows.

 

[aghaj]

Exactly, we have to confine the compression reinforcement and not the section. Besides, the compression reinforcement may be required only for critical segments of a span. For example, for simply-supported beams it may only be a limited length at midspan requiring compression reinforcement to reduce long-term deflection. How to deal with curtailment of this reinforcement

 

[ishvaaag]

If not counted on strength design using development length would be enough and even excess. I fail to find a formula somewhere to develop passive rebar to some serviceability stress level, that could be tantamount to what you are seeking.

 

[JAE]

aghaj, what do you mean by "curtailment"?