Double Reinforced T-Beam

[Nafa22]

I am trying to solve this problem but I am encountering an issue where my compression block depth is smaller than my d'. This is mainly due to my top steel's area being greater than my bottom steel. How can I tackle this question?

 

[BAretired]

It isn't really a problem. Disregard the top steel when considering positive moments; they aren't needed. Use them only for negative moments.

BA

 

[dik]

As BART notes, unless you have a high percentage of reinforcing, the top bars add little to the strength.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Celt83]

You are likely trying to apply the standard doubly reinforced formula for beam capacity that is not applicable here, the question is testing your ability to perform a complete strain compatibility analysis. You cannot ignore any of the reinforcing steel if you want to have the correct curvature.

 

[dik]

Unless you have a large percentage of rebar, by ignoring it, you are not 'taking much of a hit'.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[BridgeSmith]

To me, it seems that it depends on whether the answer needs to be exact, or what is typical engineering practice.

For the exact answer, strain compatibility must be considered. The top reinforcing that is below the neutral axis will have a small amount of tension strain, with a correspondingly small tensile force, with a short moment arm. It will change the flexural capacity very slightly, but it will change it.

For negative bending, the reinforcing in the bottom is likely in the compression zone, and would generally would not be included, and could not be included, unless it is properly confined. I see no indication of confinement for those bars, so I think bars in compression could be, and should be, ignored.

Rod Smith, P.E., The artist formerly known as HotRod10