T beam reinforcement 1

[Mike1998]

Hello everybody,

I have a concrete T beam and I want to calculate the reinforcement. The flanged part of the beam is under compression and the height of the compression zone is less than the height of the flange. Apart from the bottom of the beam, where the reinforcement will be applied, do I also have to calculate reinforcement for the bottom of the flange (which is under tension)?

Thank you.

 

[BAretired]

No. Put the tension steel where it will do the most good, namely at the bottom of the beam.

BA

 

[Mike1998]

BAretired thank you for your response.

I would like to mention that my flange is not a slab. Actually, the height of my flange is 1,5 m and the total height of the cross section is 2,6 m. So I expect some tension at the bottom of the flange.

 

[BAretired]

With a "flange" of 1.5 m, I might provide temperature/shrinkage reinforcement, particularly if it extended well beyond the "web" of the beam. If it is a minor bump on the web, I likely would not provide reinforcement in that location. In the case of a rectangular beam, it is not necessary to provide tensile reinforcement in locations other than the bottom, simply because the concrete is in tension.

It is a question which requires engineering judgment depending on the cross section of the beam.

BA

 

[StrucPEng]

I would agree with BA. As long as the compression block is in the flange only you can usually design it the same as a rectangular section. The reinforcement in the bottom of the beam would do the most good seeing as how that is the extreme tension fiber. The web directly below the N.A. should see relatively small amounts of tension in comparison. With all that said BA is also right that there is some judgement to be applied given the actual cross section.

 

[BridgeSmith]

Given the thickness of the flange, and the fact it is well into tension zone, you should definitely put some reinforcement in the bottom of the flange (at least outside the web) to control cracking. With the reinforcing in the bottom of the flange somewhere near half the depth to the reinforcement at the bottom of the web, you can definitely count it as tension reinforcement. You can use the full yield strength of the bottom of flange reinforcing for ultimate strength, but for service loading conditions, I would limit it's resistance to the stress at first yield of the web reinforcement (strain compatibility).

The configuration seems very inefficient for bending resistance. Having a tee beam with a web less than the depth of the flangeb hardly seems worthwhile. Why not just dispense with the tee portion, and just have a rectangular beam? Alternately, if the flange doesn't need to be that thick, why have it that thick? Typically, the flange of a tee beam is sized so that most or all of it is in compression at the design loading.

 

[rapt]

Agree with BaR.

All required flexural reinforcement should be in the bottom of the beam.

The flange will experience significant shrinkage restraint due to differential shrinkage as well as the tension from flexure and should have minimum shrinkage reinforcement parallel to the beam. Probably based on a concrete depth of 200-300mm, not the full depth of the flange.

 

[Settingsun]

Most codes of practice require side face reinforcement in at least the tension half of such a deep beam, so you're probably required to have at least one bar in each corner of the flange. Then it's your/your client's tolerance to cracking. I would put in at least nominal reinforcing. Are you going to run a fitment across the flange/around the flange perimeter?

 

[hoshang]

As long as the compression block is in the flange only you can usually design it the same as a rectangular section.

As long as the compression block is in the flange only you can usually analyze it as a rectangular beam of width equal to the effective flange width b and depth d.