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Design of precast inverted tee beams for torsion

Design of precast inverted tee beams for torsion

Design of precast inverted tee beams for torsion

(OP)
Hi,

I am designing precast inverted tee beam with hollow core planks on either side (8" and 16"). 16" side is heavily loaded and I'm wondering if and when I should conciser torsion on IT beam. It seems design for torsion in this case is up to engineering judgement of a particular designer. Some people always consider torsion in IT beams, other say it doesn't really exist.
I have couple questions in case it exists:
1. I have 40" wide IT beam with 5" ledges. Should I assume my eccentricity is from the center of hollow-core plank bearing to the centroid of the section? Or is it too conservative?
2. What are some common methods in resolving torsion for precast IT beams? In my case, I can't resolve it in supports because IT beam is already over reinforced and torsional reinforcement simply won't fit. What are some details I can use in this case?

Any help on the matter would be great. Thank you

RE: Design of precast inverted tee beams for torsion

Quote (OP)

other say it doesn't really exist.

Those people are wrong unless unusual detailing has been provided to allow beam torsion to be converted into plank bending.

Quote (OP)

Should I assume my eccentricity is from the center of hollow-core plank bearing to the centroid of the section? Or is it too conservative?

It's probably a little non-conservative as your true bearing pressure is likely to be non-uniform and have its centre of pressure even further from the beam.

Quote (OP)

What are some common methods in resolving torsion for precast IT beams? In my case, I can't resolve it in supports because IT beam is already over reinforced and torsional reinforcement simply won't fit. What are some details I can use in this case?

If you have torsion in the beam that isn't being rectified by the plan, which is normally the case, then you have to resolve it in the supports.

I suppose that you could prestress (or increase prestress) the section to improve the concrete contribution to torsion and shear some.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

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