## Reinforcement Ratio

## Reinforcement Ratio

(OP)

Hi, first off I'm kind of a noob at this whole estimating concrete business. Well im looking at this project and I need some help interpreting what a line in our specifications means, and also how to apply it. The line refers to the structure were going to build regardless of what the structure is the line states

"structure...will be constructed of 4,000 psi reinforced concrete with a maximum reinforcement ratio of .25 pb."

Thats all it gives me. There are no details of any rebar called out on the drawings, nor any other info about reinforcement. I would like to understand what the pb means and how to incorporate it into our project. If anyone can help that would be great!

"structure...will be constructed of 4,000 psi reinforced concrete with a maximum reinforcement ratio of .25 pb."

Thats all it gives me. There are no details of any rebar called out on the drawings, nor any other info about reinforcement. I would like to understand what the pb means and how to incorporate it into our project. If anyone can help that would be great!

Geaux Tigers!

## RE: Reinforcement Ratio

_{b}which is a reinforcement ratio.The actual reinforcement ratio ρ = As / (bd)

where As is the area of tension steel reinforcing

b is the beam width

d is the depth from compression side of the beam to the centroid of the reinforcing.

ρ

_{b}is the balanced steel ratio.If you have a reinforced beam with As steel in it and you start applying greater and greater bending moment to it, at some point one of two failures can occur.

1. The compressed side of the beam will fail in concrete crushing.

2. The tension side of the beam will fail by the steel yielding.

So if you have too much rebar on the tension side, the concrete will crush first.

If you have too little reinforcing on the tension side the rebar will yield first.

The rebar yielding is what is desired as it offers advance warnings of overload while the concrete crushing is sudden and catastrophic.

The balanced ratio ρ

_{b}is when you have just the right amount of rebar so the concrete AND the steel fail at the same bending moment.So the codes (used to) limit the maximum amount of reinforcing to 75% of the balanced ratio to ensure that there would never be that catastrophic failure.

0.25ρ

_{b}doesn't make any sense to me other than to offer a suggested amount of rebar based upon a size of beam. If you know the b and the d of a beam, then you still need to determine ρ_{b}and I can't do that for you here in this forum.## RE: Reinforcement Ratio

## RE: Reinforcement Ratio

JAE: Excellent response.

## RE: Reinforcement Ratio

Is there any compression reinforcing? This can have an impact on your answer.

Dik

## RE: Reinforcement Ratio

Geaux Tigers!