1) If it's rectangular and not pre-stressed, it's probably not much different from solid section design.

2) Circular gets a bit messy and I'll leave that to somebody else. Lots of approximation I'd guess.

3) As far as examples go, I'd think that bridge box girders would be the place to look although most of those are bound to be prestressed.

You maybe able to find something from PCI. If this is to be a CIP beam, you can also use equations for reinforced concrete design. There is not much difference I can recall.

For bending about the major axis and shear design a hollow rectangular section is the same as a rectangular section if the neutral axis is in the top flange, or a T section if it is passing through the void, or an I section if it is in the bottom flange.

Different codes have different provisions for combined shear and torsion, so you need to refer to the applicable code if torsion is an issue.

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/

Thanks everyone. Actually the case that I was talking about is for cast in place hollow reinforced concrete section that is subjected to mainly flexure and shear (axial is small) similar to the attachment. IF anyone knows a reference or example for such case that would be appreciated. Thanks!

• https://files.engineering.com/getfile.aspx?folder=fd1c1042-95ca-4401-8c24-5

Is this an embedded pole type footing? If so, why not just have the pole do all of the bending resistance and the concrete is just there to widen the bearing area on the soil.

Yes it is. Good point! but what if the pole cannot resist the moment and I need the help of concrete? I still will need to design that hollow concrete section for flexure and shear.

it might be simpler to look at it as the front face of concrete the flag bears on spans horizontally to rectangular sections on either side of the pole to resist the bending.

Standard procedures for reinforced concrete bending and shear design are based on plane sections remaining plane and the tension reinforcement being fully developed. Neither of those assumptions are remotely near true for the footing as shown.

I assume there are established procedures for designing embedded pole footings, and you need to research those. Just applying simple bending capacity theory won't work.

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/