I'm currently looking into the theoretical stiffness of steel sections
after they have been deformed into a circular shape.
The radius of curvature induces strains that are well beyond the
elastic region, though only just into the region of strain hardening
(around about 0.04, with a low carbon steel) - so I'll ignore the
effect of strain hardening for the time being.

The traditional stiffness equation relates E and I and the diameter. Determining I (the moment of inertia) is fine, using poisson's ratio to determine the change in section dimensional properties and hence also a change in the neutral axis depth. The elastic modulus is fine (for the elastic core of the steel section), however...

Do I use the secant modulus for the effective modulus for fibres at a given strain? Or am I completely off the mark?

Thanks in advance for any input.

Shaun

The traditional stiffness equation relates E and I and the diameter. Determining I (the moment of inertia) is fine, using poisson's ratio to determine the change in section dimensional properties and hence also a change in the neutral axis depth. The elastic modulus is fine (for the elastic core of the steel section), however...

Do I use the secant modulus for the effective modulus for fibres at a given strain? Or am I completely off the mark?

Thanks in advance for any input.

Shaun