Most of finite element calculations are performed with an orthogonal mesh (Cartesian coordinate system). From this calculation, we get two values of required steel area per linear meter: $$Ax, Ay$$ ($$cm^2/m$$) for each direction. However, my slab is circular, so the steel reinforcement have to be put in orthoradial direction. How do I convert the reinforcement from orthogonal to orthoradial?

Thanks,

The fact that design of concrete slabs or beams uses straight reinforcing bars running orthogonally doesn't have much to do with the geometry of slab, beam or a deck, etc.

It has to do with the fact that straight bars can take large amount of tensile stress and with their counterpart compressive concrete take large moments, without any tendency to peel their way out of the embedding concrete.

Even if you have a round deck or slab, it's better and more efficient to design them with orthogonal strait bars.

In some projects architectural design specifies circular horizontal concrete beams for esthetic reasons. In those beams torque and twisting stresses and effects of lateral deflection make the design and construction complicated.

As pointed out above, it is fine to place rebars in orthogonal pattern, regardless of the geometric shape of the slab. However, sometimes we do need to follow the shape, but there is no published method on how to handle the conversion but engineering judgement.

In general, for a curved shape, the rebars in direction of the radius are usually the main reinforcement. It should be fanned out, with the inner most bars placed at a tight spacing. Intermittent bars are then added in between the full length bars to maintain the spacing. The important thing is at nowhere the spacing shall exceed the bar spacing suggested by the computer program.

The sketch below just to show the idea. It needs additional bars and modifications.